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Takken W, Charlwood D, Lindsay SW. The behaviour of adult Anopheles gambiae, sub-Saharan Africa's principal malaria vector, and its relevance to malaria control: a review. Malar J 2024; 23:161. [PMID: 38783348 PMCID: PMC11112813 DOI: 10.1186/s12936-024-04982-3] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/03/2023] [Accepted: 05/11/2024] [Indexed: 05/25/2024] Open
Abstract
BACKGROUND Mosquitoes of the Anopheles gambiae complex are one of the major vectors of malaria in sub-Saharan Africa. Their ability to transmit this disease of major public health importance is dependent on their abundance, biting behaviour, susceptibility and their ability to survive long enough to transmit malaria parasites. A deeper understanding of this behaviour can be exploited for improving vector surveillance and malaria control. FINDINGS Adult mosquitoes emerge from aquatic habitats at dusk. After a 24 h teneral period, in which the cuticle hardens and the adult matures, they may disperse at random and search upwind for a mate or to feed. Mating generally takes place at dusk in swarms that form over species-specific 'markers'. Well-nourished females may mate before blood-feeding, but the reverse is true for poorly-nourished insects. Females are monogamous and only mate once whilst males, that only feed on nectar, swarm nightly and can potentially mate up to four times. Females are able to locate hosts by following their carbon dioxide and odour gradients. When in close proximity to the host, visual cues, temperature and relative humidity are also used. Most blood-feeding occurs at night, indoors, with mosquitoes entering houses mainly through gaps between the roof and the walls. With the exception of the first feed, females are gonotrophically concordant and a blood meal gives rise to a complete egg batch. Egg development takes two or three days depending on temperature. Gravid females leave their resting sites at dusk. They are attracted by water gradients and volatile chemicals that provide a suitable aquatic habitat in which to lay their eggs. CONCLUSION Whilst traditional interventions, using insecticides, target mosquitoes indoors, additional protection can be achieved using spatial repellents outdoors, attractant traps or house modifications to prevent mosquito entry. Future research on the variability of species-specific behaviour, movement of mosquitoes across the landscape, the importance of light and vision, reproductive barriers to gene flow, male mosquito behaviour and evolutionary changes in mosquito behaviour could lead to an improvement in malaria surveillance and better methods of control reducing the current over-reliance on the indoor application of insecticides.
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Affiliation(s)
- Willem Takken
- Laboratory of Entomology, Wageningen University & Research, PO Box 16, 6700 AA, Wageningen, The Netherlands.
| | - Derek Charlwood
- Global Health and Tropical Medicine, Instituto de Hygiene e Medicina Tropical, Lisbon, Portugal
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Charlwood JD, Smith TA, Kampango A, Tomas EVE, Chitnis N. Time series analysis of survival and oviposition cycle duration of Anopheles funestus (Giles) in Mozambique. PeerJ 2023; 11:e15230. [PMID: 37273537 PMCID: PMC10234278 DOI: 10.7717/peerj.15230] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/30/2022] [Accepted: 03/24/2023] [Indexed: 06/06/2023] Open
Abstract
Background Survival and gonotrophic cycle duration are important determinants of the vectorial capacity of malaria vectors but there are a limited number of approaches to estimate these quantities from field data. Time-series of observations of mosquitoes at different stages in the life-cycle are under-used. Methods Anopheles funestus mosquitoes were caught using various methods over a 7.6-year period in Furvela, Mozambique. Survival and oviposition cycle duration were estimated using (i) an existing time-series approach for analysing dissections of mosquitoes caught in light-traps, extended to allow for variability in the duration of the cycle; (ii) an established approach for estimating cycle duration from resting collection data; (iii) a novel time-series approach fitted to numbers and categories of mosquitoes caught in exit-traps. Results Data were available from 7,396, 6,041 and 1,527 trap-nights for exit-traps, light-traps and resting collections respectively. Estimates of cycle duration varied considerably between the different methods. The estimated proportion of female mosquitoes surviving each day of 0.740 (95% credible interval [0.650-0.815]) derived from light-trap data was much lower than the estimated daily survival of male mosquitoes from the model fitted to exit-trap data (0.881, 95% credible interval [0.747-0.987]). There was no tendency for the oviposition cycle to become shorter at higher temperature while the odds of survival of females through the cycle was estimated to be multiplied by 1.021 for every degree of mean weekly temperature increase (95% credible interval [0.991-1.051]). There was negligible temperature dependence and little inter-annual variation in male survival. Discussion The time-series approach fitted to the exit-traps suggests that male An. funestus have higher survival than do females, and that male survival was temperature independent and unaffected by the introduction of long-lasting insecticidal nets (LLINs). The patterns of temperature dependence in females are at variance with results of laboratory studies. Time series approaches have the advantage for estimating survival that they do not depend on representative sampling of mosquitoes over the whole year. However, the estimates of oviposition cycle duration were associated with considerable uncertainty, which appears to be due to variability between insects in the duration of the resting period, and the estimates based on exit-trap data are sensitive to assumptions about relative trapping efficiencies.
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Affiliation(s)
- Jacques D. Charlwood
- DBL Centre for Health Research and Development, Department for Veterinary Pathobiology, Faculty of Life Sciences, University of Copenhagen, Copenhagen, Denmark
- Mozambican-Danish Rural Malaria Initiative (MOZDAN), Morrumbene, Inhambane Province, Mozambique
- Global Health and Tropical Medicine, Instituto de Higiene e Medicina Tropical, Lisbon, Portugal
| | - Thomas A. Smith
- Department of Epidemiology and Public Health, Swiss Tropical and Public Health Institute, Allschwil, Switzerland
- University of Basel, Basel, Switzerland
| | - Ayubo Kampango
- Mozambican-Danish Rural Malaria Initiative (MOZDAN), Morrumbene, Inhambane Province, Mozambique
- Sector de Estudo de Vectores, Instituto Nacional de Saúde, Vila de Marracuene, Província de Maputo, Mozambique
- Department of Zoology and Entomology, University of Pretoria, Hatfield, South Africa
| | - Erzelia V. E. Tomas
- Mozambican-Danish Rural Malaria Initiative (MOZDAN), Morrumbene, Inhambane Province, Mozambique
| | - Nakul Chitnis
- Department of Epidemiology and Public Health, Swiss Tropical and Public Health Institute, Allschwil, Switzerland
- University of Basel, Basel, Switzerland
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Ye Z, Liu F, Sun H, Ferguson ST, Baker A, Ochieng SA, Zwiebel LJ. Discrete roles of Ir76b ionotropic coreceptor impact olfaction, blood feeding, and mating in the malaria vector mosquito Anopheles coluzzii. Proc Natl Acad Sci U S A 2022; 119:e2112385119. [PMID: 35648836 PMCID: PMC9191353 DOI: 10.1073/pnas.2112385119] [Citation(s) in RCA: 8] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/05/2021] [Accepted: 04/13/2022] [Indexed: 11/18/2022] Open
Abstract
Anopheline mosquitoes rely on their highly sensitive chemosensory apparatus to detect diverse chemical stimuli that drive the host-seeking and blood-feeding behaviors required to vector pathogens for malaria and other diseases. This process incorporates a variety of chemosensory receptors and transduction pathways. We used advanced in vivo gene-editing and -labeling approaches to localize and functionally characterize the ionotropic coreceptor AcIr76b in the malaria mosquito Anopheles coluzzii, where it impacts both olfactory and gustatory systems. AcIr76b has a broad expression pattern in female adult antennal grooved pegs, coeloconic sensilla, and T1 and T2 sensilla on the labellum, stylets, and tarsi, as well as the larval sensory peg. AcIr76b is colocalized with the Orco odorant receptor (OR) coreceptor in a subset of cells across the female antennae and labella. In contrast to Orco and Ir8a, chemosensory coreceptors that appear essential for the activity of their respective sets of chemosensory neurons in mosquitoes, AcIr76b−/− mutants maintain wild-type peripheral responses to volatile amines on the adult palps, labellum, and larval sensory cone. Interestingly, AcIr76b−/− mutants display significantly increased responses to amines in antennal grooved peg sensilla, while coeloconic sensilla reveal significant deficits in responses to several acids and amines. Behaviorally, AcIr76b mutants manifest significantly female-specific insemination deficits, and although AcIr76b−/− mutant females can locate, alight on, and probe artificial blood hosts, they are incapable of blood feeding successfully. Taken together, our findings reveal a multidimensional functionality of Ir76b in anopheline olfactory and gustatory pathways that directly impacts the vectorial capacity of these mosquitoes.
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Affiliation(s)
- Zi Ye
- Department of Biological Sciences, Vanderbilt University, Nashville, TN 37235
| | - Feng Liu
- Department of Biological Sciences, Vanderbilt University, Nashville, TN 37235
| | - Huahua Sun
- Department of Biological Sciences, Vanderbilt University, Nashville, TN 37235
| | - Stephen T. Ferguson
- Department of Biological Sciences, Vanderbilt University, Nashville, TN 37235
| | - Adam Baker
- Department of Biological Sciences, Vanderbilt University, Nashville, TN 37235
| | - Samuel A. Ochieng
- Department of Biological Sciences, Vanderbilt University, Nashville, TN 37235
| | - Laurence J. Zwiebel
- Department of Biological Sciences, Vanderbilt University, Nashville, TN 37235
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4
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Charlwood JD, Andegiorgish AK, Asfaha YE, Tekle Weldu L, Petros F, Legese L, Afewerki R, Mihreteab S, LeClair C, Kampango A. Novel sampling methods for monitoring Anopheles arabiensis from Eritrea. PeerJ 2021; 9:e11497. [PMID: 34322315 PMCID: PMC8297471 DOI: 10.7717/peerj.11497] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/10/2020] [Accepted: 04/30/2021] [Indexed: 01/03/2023] Open
Abstract
Background Studies comparing novel collection methods for host seeking and resting mosquitoes A. arabiensis were undertaken in a village in Eritrea. Techniques included an odor baited trap, a novel tent-trap, human landing collection and three methods of resting collection. A technique for the collection of mosquitoes exiting vegetation is also described. Pre-gravid rates were determined by dissection of host seeking insects and post-prandial egg development among insects collected resting. Results Overall 5,382 host-seeking, 2,296 resting and 357 A. arabiensis exiting vegetation were collected. The Furvela tent-trap was the most efficient, risk-free method for the collection of outdoor host-seeking insects, whilst the Suna trap was the least effective method. Mechanical aspirators (the CDC backpack or the Prokopack aspirator) were superior to manual aspiration in a dark shelter but there was no advantage over manual aspiration in a well-lit one. An estimated two-thirds of newly-emerged mosquitoes went through a pre-gravid phase, feeding twice before producing eggs. Mosquitoes completed gonotrophic development in a dark shelter but left a well-lit shelter soon after feeding. One blood-fed female marked in the village was recaptured 2 days after release exiting vegetation close to the oviposition site and another, shortly after oviposition, attempting to feed on a human host 3 days after release. Exit rates of males from vegetation peaked 3 min after the initial male had left. Unfed and gravid females exited approximately 6 min after the first males. Conclusions Furvela tent-traps are suitable for the collection of outdoor biting A. arabiensis in Eritrea whilst the Prokopack sampler is the method of choice for the collection of resting insects. Constructing well-lit, rather than dark, animal shelters, may encourage otherwise endophilic mosquitoes to leave and so reduce their survival and hence their vectorial capacity.
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Affiliation(s)
- Jacques D Charlwood
- Epidemiology and Public Health, College of Health Sciences, Asmara, Eritrea.,Global Health and Tropical Medicine, Instituto de Higiene e Medicina Tropical, Lisbon, Portugal
| | - Amanuel Kidane Andegiorgish
- Epidemiology and Public Health, College of Health Sciences, Asmara, Eritrea.,Department of Epidemiology and Biostatistics, Xi'an Jiaotong University, Shaanxi, China
| | | | - Liya Tekle Weldu
- Epidemiology and Public Health, College of Health Sciences, Asmara, Eritrea
| | - Feven Petros
- Epidemiology and Public Health, College of Health Sciences, Asmara, Eritrea
| | - Lidia Legese
- Epidemiology and Public Health, College of Health Sciences, Asmara, Eritrea
| | - Robel Afewerki
- Epidemiology and Public Health, College of Health Sciences, Asmara, Eritrea
| | | | | | - Ayubo Kampango
- Instituto Nacional de Saude, Maputo, Mozambique.,Department of Zoology and Entomology, University of Pretoria, Pretoria, South Africa
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5
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Konopka JK, Task D, Afify A, Raji J, Deibel K, Maguire S, Lawrence R, Potter CJ. Olfaction in Anopheles mosquitoes. Chem Senses 2021; 46:6246230. [PMID: 33885760 DOI: 10.1093/chemse/bjab021] [Citation(s) in RCA: 21] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023] Open
Abstract
As vectors of disease, mosquitoes are a global threat to human health. The Anopheles mosquito is the deadliest mosquito species as the insect vector of the malaria-causing parasite, which kills hundreds of thousands every year. These mosquitoes are reliant on their sense of smell (olfaction) to guide most of their behaviors, and a better understanding of Anopheles olfaction identifies opportunities for reducing the spread of malaria. This review takes a detailed look at Anopheles olfaction. We explore a range of topics from chemosensory receptors, olfactory neurons, and sensory appendages to behaviors guided by olfaction (including host-seeking, foraging, oviposition, and mating), to vector management strategies that target mosquito olfaction. We identify many research areas that remain to be addressed.
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Affiliation(s)
- Joanna K Konopka
- The Solomon H. Snyder Department of Neuroscience, Johns Hopkins University School of Medicine, 855 North Wolfe Street, 434 Rangos Building, Baltimore, 21205 MD, USA
| | - Darya Task
- The Solomon H. Snyder Department of Neuroscience, Johns Hopkins University School of Medicine, 855 North Wolfe Street, 434 Rangos Building, Baltimore, 21205 MD, USA
| | - Ali Afify
- The Solomon H. Snyder Department of Neuroscience, Johns Hopkins University School of Medicine, 855 North Wolfe Street, 434 Rangos Building, Baltimore, 21205 MD, USA
| | - Joshua Raji
- The Solomon H. Snyder Department of Neuroscience, Johns Hopkins University School of Medicine, 855 North Wolfe Street, 434 Rangos Building, Baltimore, 21205 MD, USA
| | - Katelynn Deibel
- The Solomon H. Snyder Department of Neuroscience, Johns Hopkins University School of Medicine, 855 North Wolfe Street, 434 Rangos Building, Baltimore, 21205 MD, USA
| | - Sarah Maguire
- The Solomon H. Snyder Department of Neuroscience, Johns Hopkins University School of Medicine, 855 North Wolfe Street, 434 Rangos Building, Baltimore, 21205 MD, USA
| | - Randy Lawrence
- The Solomon H. Snyder Department of Neuroscience, Johns Hopkins University School of Medicine, 855 North Wolfe Street, 434 Rangos Building, Baltimore, 21205 MD, USA
| | - Christopher J Potter
- The Solomon H. Snyder Department of Neuroscience, Johns Hopkins University School of Medicine, 855 North Wolfe Street, 434 Rangos Building, Baltimore, 21205 MD, USA
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6
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Jansson S, Malmqvist E, Mlacha Y, Ignell R, Okumu F, Killeen G, Kirkeby C, Brydegaard M. Real-time dispersal of malaria vectors in rural Africa monitored with lidar. PLoS One 2021; 16:e0247803. [PMID: 33662005 PMCID: PMC7932069 DOI: 10.1371/journal.pone.0247803] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/27/2020] [Accepted: 02/12/2021] [Indexed: 11/18/2022] Open
Abstract
Lack of tools for detailed, real-time observation of mosquito behavior with high spatio-temporal resolution limits progress towards improved malaria vector control. We deployed a high-resolution entomological lidar to monitor a half-kilometer static transect positioned over rice fields outside a Tanzanian village. A quarter of a million in situ insect observations were classified, and several insect taxa were identified based on their modulation signatures. We observed distinct range distributions of male and female mosquitoes in relation to the village periphery, and spatio-temporal behavioral features, such as swarming. Furthermore, we observed that the spatial distributions of males and females change independently of each other during the day, and were able to estimate the daily dispersal of mosquitoes towards and away from the village. The findings of this study demonstrate how lidar-based monitoring could dramatically improve our understanding of malaria vector ecology and control options.
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Affiliation(s)
- Samuel Jansson
- Lund Laser Centre, Department of Physics, Lund University, Lund, Sweden
- Center for Animal Movement Research, Department of Biology, Lund University, Lund, Sweden
- * E-mail:
| | - Elin Malmqvist
- Lund Laser Centre, Department of Physics, Lund University, Lund, Sweden
- Center for Animal Movement Research, Department of Biology, Lund University, Lund, Sweden
| | - Yeromin Mlacha
- Environmental Health and Ecological Sciences Department, Ifakara Health Institute, Ifakara, Tanzania
- Swiss Tropical and Public Health Institute, Basel, Switzerland
- University of Basel, Basel, Switzerland
| | - Rickard Ignell
- Disease Vector Group, Department of Plant Protection Biology, Swedish University of Agricultural Sciences, Alnarp, Sweden
| | - Fredros Okumu
- Environmental Health and Ecological Sciences Department, Ifakara Health Institute, Ifakara, Tanzania
- School of Public Health, University of Witwatersrand, Johannesburg, South Africa
- Institute of Biodiversity, Animal Health and Comparative Medicine, University of Glasgow, Glasgow, United Kingdom
| | - Gerry Killeen
- Environmental Health and Ecological Sciences Department, Ifakara Health Institute, Ifakara, Tanzania
- Department of Vector Biology, Liverpool School of Tropical Medicine, Liverpool, United Kingdom
| | - Carsten Kirkeby
- Department of Veterinary and Animal Sciences, Faculty of Health and Medical Sciences, University of Copenhagen, Frederiksberg, Denmark
- FaunaPhotonics APS, Copenhagen N, Denmark
| | - Mikkel Brydegaard
- Lund Laser Centre, Department of Physics, Lund University, Lund, Sweden
- Center for Animal Movement Research, Department of Biology, Lund University, Lund, Sweden
- FaunaPhotonics APS, Copenhagen N, Denmark
- Norsk Elektro Optikk AS, Skedsmokorset, Norway
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7
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Malinga J, Maia M, Moore S, Ross A. Can trials of spatial repellents be used to estimate mosquito movement? Parasit Vectors 2019; 12:421. [PMID: 31477155 PMCID: PMC6720076 DOI: 10.1186/s13071-019-3662-x] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/30/2019] [Accepted: 08/09/2019] [Indexed: 11/16/2022] Open
Abstract
Background Knowledge of mosquito movement would aid the design of effective intervention strategies against malaria. However, data on mosquito movement through mark-recapture or genetics studies are challenging to collect, and so are not available for many sites. An additional source of information may come from secondary analyses of data from trials of repellents where household mosquito densities are collected. Using the study design of published trials, we developed a statistical model which can be used to estimate the movement between houses for mosquitoes displaced by a spatial repellent. The method uses information on the different distributions of mosquitoes between houses when no households are using spatial repellents compared to when there is incomplete coverage. The parameters to be estimated are the proportion of mosquitoes repelled, the proportion of those repelled that go to another house and the mean distance of movement between houses. Estimation is by maximum likelihood. Results We evaluated the method using simulation and found that data on the seasonal pattern of mosquito densities were required, which could be additionally collected during a trial. The method was able to provide accurate estimates from simulated data, except when the setting has few mosquitoes overall, few repelled, or the coverage with spatial repellent is low. The trial that motivated our analysis was found to have too few mosquitoes caught and repelled for our method to provide accurate results. Conclusions We propose that the method could be used as a secondary analysis of trial data to gain estimates of mosquito movement in the presence of repellents for trials with sufficient numbers of mosquitoes caught and repelled and with coverage levels which allow sufficient numbers of houses with and without repellent. Estimates from this method may supplement those from mark-release-recapture studies, and be used in designing effective malaria intervention strategies, parameterizing mathematical models and in designing trials of vector control interventions.
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Affiliation(s)
- Josephine Malinga
- Swiss Tropical and Public Health Institute, Basel, Switzerland.,University of Basel, Basel, Switzerland
| | - Marta Maia
- KEMRI Wellcome Trust Research Programme, Kilifi, Kenya.,Centre for Tropical Medicine and Global Health, University of Oxford, Oxford, UK
| | - Sarah Moore
- Swiss Tropical and Public Health Institute, Basel, Switzerland.,University of Basel, Basel, Switzerland.,Ifakara Health Institute, Ifakara, Tanzania
| | - Amanda Ross
- Swiss Tropical and Public Health Institute, Basel, Switzerland. .,University of Basel, Basel, Switzerland.
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Mashatola T, Ndo C, Koekemoer LL, Dandalo LC, Wood OR, Malakoane L, Poumachu Y, Lobb LN, Kaiser M, Bourtzis K, Munhenga G. A review on the progress of sex-separation techniques for sterile insect technique applications against Anopheles arabiensis. Parasit Vectors 2018; 11:646. [PMID: 30583746 PMCID: PMC6304763 DOI: 10.1186/s13071-018-3219-4] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022] Open
Abstract
The feasibility of the sterile insect technique (SIT) as a malaria vector control strategy against Anopheles arabiensis has been under investigation over the past decade. One of the critical steps required for the application of this technique to mosquito control is the availability of an efficient and effective sex-separation system. Sex-separation systems eliminate female mosquitoes from the production line prior to irradiation and field release of sterile males. This is necessary because female mosquitoes can transmit pathogens such as malaria and, therefore, their release must be prevented. Sex separation also increases the efficiency of an SIT programme. Various sex-separation strategies have been explored including the exploitation of developmental and behavioural differences between male and female mosquitoes, and genetic approaches. Most of these are however species-specific and are not indicated for the major African malaria vectors such as An. arabiensis. As there is currently no reliable sex-separation method for An. arabiensis, various strategies were explored in an attempt to develop a robust system that can be applied on a mass-rearing scale. The progress and challenges faced during the development of a sexing system for future pilot and/or large-scale SIT release programmes against An. arabiensis are reviewed here. Three methods of sex separation were examined. The first is the use of pupal size for gender prediction. The second is the elimination of blood-feeding adult females through the addition of an endectocide to a blood meal source. The third is the establishment of a genetic sexing strain (GSS) carrying an insecticide resistance selectable marker (dieldrin-resistance rdl gene and/or other GABA receptor antagonists that can be used as alternative insecticides to dieldrin) or a temperature-sensitive lethal marker.
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Affiliation(s)
- Thabo Mashatola
- Centre for Emerging Zoonotic and Parasitic Diseases, National Institute for Communicable Diseases of the National Health Laboratory Service, Johannesburg, South Africa
- Wits Research Institute for Malaria, MRC Collaborating Centre for Multi-Disciplinary Research on Malaria, School of Pathology, Faculty of Health Sciences, University of the Witwatersrand, Johannesburg, South Africa
- Insect Pest Control Laboratory, Joint FAO/IAEA Division of Nuclear Techniques in Food and Agriculture, Vienna, Austria
| | - Cyrille Ndo
- Organisation de Coordination pour la lutte Contre les Endémies en Afrique Centrale (OCEAC), Institut de recherche de Yaoundé (IRY), Yaoundé, Cameroon
- Department of Biological Sciences, Faculty of Medicine and Pharmaceutical Sciences, University of Douala, Douala, Cameroon
- Centre for Research in Infectious Disease (CRI), Yaoundé, Cameroon
| | - Lizette L. Koekemoer
- Centre for Emerging Zoonotic and Parasitic Diseases, National Institute for Communicable Diseases of the National Health Laboratory Service, Johannesburg, South Africa
- Wits Research Institute for Malaria, MRC Collaborating Centre for Multi-Disciplinary Research on Malaria, School of Pathology, Faculty of Health Sciences, University of the Witwatersrand, Johannesburg, South Africa
| | - Leonard C. Dandalo
- Centre for Emerging Zoonotic and Parasitic Diseases, National Institute for Communicable Diseases of the National Health Laboratory Service, Johannesburg, South Africa
- Wits Research Institute for Malaria, MRC Collaborating Centre for Multi-Disciplinary Research on Malaria, School of Pathology, Faculty of Health Sciences, University of the Witwatersrand, Johannesburg, South Africa
| | - Oliver R. Wood
- Centre for Emerging Zoonotic and Parasitic Diseases, National Institute for Communicable Diseases of the National Health Laboratory Service, Johannesburg, South Africa
- Wits Research Institute for Malaria, MRC Collaborating Centre for Multi-Disciplinary Research on Malaria, School of Pathology, Faculty of Health Sciences, University of the Witwatersrand, Johannesburg, South Africa
| | - Lerato Malakoane
- Centre for Emerging Zoonotic and Parasitic Diseases, National Institute for Communicable Diseases of the National Health Laboratory Service, Johannesburg, South Africa
- Wits Research Institute for Malaria, MRC Collaborating Centre for Multi-Disciplinary Research on Malaria, School of Pathology, Faculty of Health Sciences, University of the Witwatersrand, Johannesburg, South Africa
| | - Yacouba Poumachu
- Insect Pest Control Laboratory, Joint FAO/IAEA Division of Nuclear Techniques in Food and Agriculture, Vienna, Austria
- Organisation de Coordination pour la lutte Contre les Endémies en Afrique Centrale (OCEAC), Institut de recherche de Yaoundé (IRY), Yaoundé, Cameroon
- Vector Borne Disease Laboratory of the Applied Biology and Ecology Research Unit (VBDL-URBEA) Department of Animal Biology, Faculty of Sciences of the University of Dschang, Dschang, Cameroon
| | - Leanne N. Lobb
- Centre for Emerging Zoonotic and Parasitic Diseases, National Institute for Communicable Diseases of the National Health Laboratory Service, Johannesburg, South Africa
- Wits Research Institute for Malaria, MRC Collaborating Centre for Multi-Disciplinary Research on Malaria, School of Pathology, Faculty of Health Sciences, University of the Witwatersrand, Johannesburg, South Africa
| | - Maria Kaiser
- Centre for Emerging Zoonotic and Parasitic Diseases, National Institute for Communicable Diseases of the National Health Laboratory Service, Johannesburg, South Africa
- Wits Research Institute for Malaria, MRC Collaborating Centre for Multi-Disciplinary Research on Malaria, School of Pathology, Faculty of Health Sciences, University of the Witwatersrand, Johannesburg, South Africa
| | - Kostas Bourtzis
- Insect Pest Control Laboratory, Joint FAO/IAEA Division of Nuclear Techniques in Food and Agriculture, Vienna, Austria
| | - Givemore Munhenga
- Centre for Emerging Zoonotic and Parasitic Diseases, National Institute for Communicable Diseases of the National Health Laboratory Service, Johannesburg, South Africa
- Wits Research Institute for Malaria, MRC Collaborating Centre for Multi-Disciplinary Research on Malaria, School of Pathology, Faculty of Health Sciences, University of the Witwatersrand, Johannesburg, South Africa
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9
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Mulatier M, Porciani A, Nadalin L, Ahoua Alou LP, Chandre F, Pennetier C, Dormont L, Cohuet A. DEET Efficacy Increases With Age in the Vector Mosquitoes Anopheles gambiae s.s. and Aedes albopictus (Diptera: Culicidae). JOURNAL OF MEDICAL ENTOMOLOGY 2018; 55:1542-1548. [PMID: 30137424 PMCID: PMC6201824 DOI: 10.1093/jme/tjy134] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/09/2018] [Indexed: 05/04/2023]
Abstract
Old mosquitoes are the most likely to transmit pathogens due to the higher probability that they will be exposed to pathogens, and the time required before a mosquito becomes infectious, the extrinsic incubation period (EIP). However, old mosquitoes are rarely considered in the evaluation of control tools. This study evaluated the effect of mosquito aging on the repellent efficacy of N,N-diethyl-3-methylbenzamide (DEET) in two vector mosquitoes, Anopheles gambiae s.s. (Giles) (Diptera: Culicidae) and Aedes albopictus (Skuse) (Diptera: Culicidae), respective vectors of malaria parasites and arboviruses such as dengue, chikungunya, and Zika viruses. For both mosquito species, DEET-induced inhibition of blood-feeding was assessed in three age classes. Life-history traits related to mosquito fecundity and survival following DEET exposure were also measured. Results showed that, in both species, bloodmeal inhibition induced by DEET was significantly higher in old females (>18 d old) than in younger ones (<13 d old). Life history traits recording showed no combined effects of DEET and aging on mosquito blood engorgement, oviposition rate, number of eggs laid nor survival; however, age effects are reported for all these traits. These results highlight the need for taking into account mosquito age in the evaluation of integrated mosquito management tools. They also suggest that the control of vector-borne pathogens with a long EIP could be improved by targeting old mosquitoes and supports the efficacy of repellents in the fight against mosquito-borne diseases.
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Affiliation(s)
- Margaux Mulatier
- MIVEGEC, IRD, CNRS, Univ. Montpellier, BP, Montpellier Cedex, France
- CEFE, Univ. Paul Valéry Montpellier, CNRS, Univ. Montpellier, EPHE, IRD, Montpellier, France
| | | | - Louis Nadalin
- MIVEGEC, IRD, CNRS, Univ. Montpellier, BP, Montpellier Cedex, France
| | | | - Fabrice Chandre
- MIVEGEC, IRD, CNRS, Univ. Montpellier, BP, Montpellier Cedex, France
| | - Cédric Pennetier
- MIVEGEC, IRD, CNRS, Univ. Montpellier, BP, Montpellier Cedex, France
- Institut Pierre Richet, Bouaké, Côte d’Ivoire
| | - Laurent Dormont
- CEFE, Univ. Paul Valéry Montpellier, CNRS, Univ. Montpellier, EPHE, IRD, Montpellier, France
| | - Anna Cohuet
- MIVEGEC, IRD, CNRS, Univ. Montpellier, BP, Montpellier Cedex, France
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10
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Charlwood JD, Tomás EVE, Andegiorgish AK, Mihreteab S, LeClair C. 'We like it wet': a comparison between dissection techniques for the assessment of parity in Anopheles arabiensis and determination of sac stage in mosquitoes alive or dead on collection. PeerJ 2018; 6:e5155. [PMID: 30018854 PMCID: PMC6044268 DOI: 10.7717/peerj.5155] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/01/2018] [Accepted: 06/11/2018] [Indexed: 11/28/2022] Open
Abstract
Background The determination of parous rates in mosquitoes, despite numerous shortcomings, remains a tool to evaluate the effectiveness of control programs and to determine vectorial capacity in malaria vectors. Two dissection techniques are used for this. For one, the tracheoles of dried ovaries are examined with a compound microscope and in the other the follicular stalk of ovaries is examined, wet, with a stereomicroscope. The second method also enables the sac stage of parous insects (which provides information on the duration of the oviposition cycle) and the mated status of insects to be determined. Despite widespread use the two techniques have not previously been compared. Methods We compared the two dissection techniques using Anopheles arabiensis, collected with a tent-trap in Eritrea. The paired ovaries were removed in water and one was examined by each method. From a separate set of dissections from Tanzania, we also determined if the sac stages of Anopheles gambiae s.l. (83% of 183 identified by PCR being Anopheles arabiensis the remainder being A. gambiae) that were alive on collection were different to those that died on collection and what the implications for vectorial capacity estimation might be. Results Seven per cent of the dry ovaries could not be classified due to granulation (yolk) in the ovariole that obscured the tracheoles. The sensitivity of the dry dissection was 88.51% (CI [79.88–94.35%]) and the specificity was 93.55% (CI [87.68–97.17%]) among the 211 ovaries that could be classified by the dry technique and compared to the ovaries dissected wet. 1,823 live and 1,416 dead from Furvela tent-traps, CDC light-trap and window-trap collections were dissected ‘wet’ from Tanzania. In these collections parous insects were more likely to die compared to nulliparous ones. The proportion of parous mosquitoes with ‘a’ sacs (indicative of recent oviposition) was significantly greater in insects that were dead (0.36) on collection in the morning compared to those that were alive (0.12) (Chi square 138.93, p < 0.001). There was a preponderance of newly emerged virgin insects in the outdoor collection (Chi sq = 8.84, p = 0.003). Conclusions In anophelines the examination of mosquito ovaries using transmitted light in a ‘wet’ dissection is a more useful and informative technique than examination of dry ovaries. In order to correctly estimate the duration of the oviposition cycle mosquitoes should be dissected as soon as possible after collection. Younger insects were more likely to attempt to feed outdoors rather than indoors.
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Affiliation(s)
- Jacques D Charlwood
- Global Health and Tropical Medicine, Instituto de Higiene e Medicina Tropical, Universidade Nova de Lisboa, Lisbon, Portugal
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11
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Analysis of natural female post-mating responses of Anopheles gambiae and Anopheles coluzzii unravels similarities and differences in their reproductive ecology. Sci Rep 2018; 8:6594. [PMID: 29700344 PMCID: PMC5920108 DOI: 10.1038/s41598-018-24923-w] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/22/2017] [Accepted: 03/20/2018] [Indexed: 11/18/2022] Open
Abstract
Anopheles gambiae and An. coluzzii, the two most important malaria vectors in sub-Saharan Africa, are recently radiated sibling species that are reproductively isolated even in areas of sympatry. In females from these species, sexual transfer of male accessory gland products, including the steroid hormone 20-hydroxyecdysone (20E), induces vast behavioral, physiological, and transcriptional changes that profoundly shape their post-mating ecology, and that may have contributed to the insurgence of post-mating, prezygotic reproductive barriers. As these barriers can be detected by studying transcriptional changes induced by mating, we set out to analyze the post-mating response of An. gambiae and An. coluzzii females captured in natural mating swarms in Burkina Faso. While the molecular pathways shaping short- and long-term mating-induced changes are largely conserved in females from the two species, we unravel significant inter-specific differences that suggest divergent regulation of key reproductive processes such as egg development, processing of seminal secretion, and mating behavior, that may have played a role in reproductive isolation. Interestingly, a number of these changes occur in genes previously shown to be regulated by the sexual transfer of 20E and may be due to divergent utilization of this steroid hormone in the two species.
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12
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Krajacich BJ, Meyers JI, Alout H, Dabiré RK, Dowell FE, Foy BD. Analysis of near infrared spectra for age-grading of wild populations of Anopheles gambiae. Parasit Vectors 2017; 10:552. [PMID: 29116006 PMCID: PMC5678599 DOI: 10.1186/s13071-017-2501-1] [Citation(s) in RCA: 26] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/20/2017] [Accepted: 10/27/2017] [Indexed: 12/30/2022] Open
Abstract
BACKGROUND Understanding the age-structure of mosquito populations, especially malaria vectors such as Anopheles gambiae, is important for assessing the risk of infectious mosquitoes, and how vector control interventions may impact this risk. The use of near-infrared spectroscopy (NIRS) for age-grading has been demonstrated previously on laboratory and semi-field mosquitoes, but to date has not been utilized on wild-caught mosquitoes whose age is externally validated via parity status or parasite infection stage. In this study, we developed regression and classification models using NIRS on datasets of wild An. gambiae (s.l.) reared from larvae collected from the field in Burkina Faso, and two laboratory strains. We compared the accuracy of these models for predicting the ages of wild-caught mosquitoes that had been scored for their parity status as well as for positivity for Plasmodium sporozoites. RESULTS Regression models utilizing variable selection increased predictive accuracy over the more common full-spectrum partial least squares (PLS) approach for cross-validation of the datasets, validation, and independent test sets. Models produced from datasets that included the greatest range of mosquito samples (i.e. different sampling locations and times) had the highest predictive accuracy on independent testing sets, though overall accuracy on these samples was low. For classification, we found that intramodel accuracy ranged between 73.5-97.0% for grouping of mosquitoes into "early" and "late" age classes, with the highest prediction accuracy found in laboratory colonized mosquitoes. However, this accuracy was decreased on test sets, with the highest classification of an independent set of wild-caught larvae reared to set ages being 69.6%. CONCLUSIONS Variation in NIRS data, likely from dietary, genetic, and other factors limits the accuracy of this technique with wild-caught mosquitoes. Alternative algorithms may help improve prediction accuracy, but care should be taken to either maximize variety in models or minimize confounders.
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Affiliation(s)
- Benjamin J. Krajacich
- Arthropod-borne and Infectious Diseases Laboratory, Department of Microbiology, Immunology, and Pathology, Colorado State University, Fort Collins, CO USA
| | - Jacob I. Meyers
- Arthropod-borne and Infectious Diseases Laboratory, Department of Microbiology, Immunology, and Pathology, Colorado State University, Fort Collins, CO USA
| | - Haoues Alout
- Arthropod-borne and Infectious Diseases Laboratory, Department of Microbiology, Immunology, and Pathology, Colorado State University, Fort Collins, CO USA
| | - Roch K. Dabiré
- Direction Régionale de l’Ouest (DRO), Institut de Recherche en Sciences de la Santé (IRSS), Bobo Dioulasso, Burkina Faso
| | - Floyd E. Dowell
- Stored Product Insect and Engineering Research Unit, United States Department of Agriculture/Agricultural Research Services, Center for Grain and Animal Health Research, Manhattan, KS USA
| | - Brian D. Foy
- Arthropod-borne and Infectious Diseases Laboratory, Department of Microbiology, Immunology, and Pathology, Colorado State University, Fort Collins, CO USA
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13
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Sawadogo SP, Niang A, Bilgo E, Millogo A, Maïga H, Dabire RK, Tripet F, Diabaté A. Targeting male mosquito swarms to control malaria vector density. PLoS One 2017; 12:e0173273. [PMID: 28278212 PMCID: PMC5344402 DOI: 10.1371/journal.pone.0173273] [Citation(s) in RCA: 34] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/15/2016] [Accepted: 02/17/2017] [Indexed: 11/18/2022] Open
Abstract
Malaria control programs are being jeopardized by the spread of insecticide resistance in mosquito vector populations. It has been estimated that the spread of resistance could lead to an additional 120000 deaths per year, and interfere with the prospects for sustained control or the feasibility of achieving malaria elimination. Another complication for the development of resistance management strategies is that, in addition to insecticide resistance, mosquito behavior evolves in a manner that diminishes the impact of LLINs and IRS. Mosquitoes may circumvent LLIN and IRS control through preferential feeding and resting outside human houses and/or being active earlier in the evening before people go to sleep. Recent developments in our understanding of mosquito swarming suggest that new tools targeting mosquito swarms can be designed to cut down the high reproductive rate of malaria vectors. Targeting swarms of major malaria vectors may provide an effective control method to counteract behavioral resistance developed by mosquitoes. Here, we evaluated the impact of systematic spraying of swarms of Anopheles gambiae s.l. using a mixed carbamate and pyrethroid aerosol. The impact of this intervention on vector density, female insemination rates and the age structure of males was measured. We showed that the resulting mass killing of swarming males and some mate-seeking females resulted in a dramatic 80% decrease in population size compared to a control population. A significant decrease in female insemination rate and a significant shift in the age structure of the male population towards younger males incapable of mating were observed. This paradigm-shift study therefore demonstrates that targeting primarily males rather than females, can have a drastic impact on mosquito population.
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Affiliation(s)
- Simon Peguedwinde Sawadogo
- Department of Medical Biology and Public Health, Institut de Recherche en Science de la Santé (IRSS), Bobo-Dioulasso, Burkina Faso
- * E-mail:
| | - Abdoulaye Niang
- Department of Medical Biology and Public Health, Institut de Recherche en Science de la Santé (IRSS), Bobo-Dioulasso, Burkina Faso
| | - Etienne Bilgo
- Department of Medical Biology and Public Health, Institut de Recherche en Science de la Santé (IRSS), Bobo-Dioulasso, Burkina Faso
| | - Azize Millogo
- Deparment of Population Sciences, Institut des Sciences des Sociétés (INSS), Ouagadougou, Burkina Faso
| | - Hamidou Maïga
- Department of Medical Biology and Public Health, Institut de Recherche en Science de la Santé (IRSS), Bobo-Dioulasso, Burkina Faso
| | - Roch K. Dabire
- Department of Medical Biology and Public Health, Institut de Recherche en Science de la Santé (IRSS), Bobo-Dioulasso, Burkina Faso
| | - Frederic Tripet
- Centre for Applied Entomology and Parasitology, School of Life Sciences, Keele University, Staffordshire, United Kingdom
| | - Abdoulaye Diabaté
- Department of Medical Biology and Public Health, Institut de Recherche en Science de la Santé (IRSS), Bobo-Dioulasso, Burkina Faso
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14
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Disrupting Mosquito Reproduction and Parasite Development for Malaria Control. PLoS Pathog 2016; 12:e1006060. [PMID: 27977810 PMCID: PMC5158081 DOI: 10.1371/journal.ppat.1006060] [Citation(s) in RCA: 49] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/02/2016] [Accepted: 11/13/2016] [Indexed: 12/15/2022] Open
Abstract
The control of mosquito populations with insecticide treated bed nets and indoor residual sprays remains the cornerstone of malaria reduction and elimination programs. In light of widespread insecticide resistance in mosquitoes, however, alternative strategies for reducing transmission by the mosquito vector are urgently needed, including the identification of safe compounds that affect vectorial capacity via mechanisms that differ from fast-acting insecticides. Here, we show that compounds targeting steroid hormone signaling disrupt multiple biological processes that are key to the ability of mosquitoes to transmit malaria. When an agonist of the steroid hormone 20-hydroxyecdysone (20E) is applied to Anopheles gambiae females, which are the dominant malaria mosquito vector in Sub Saharan Africa, it substantially shortens lifespan, prevents insemination and egg production, and significantly blocks Plasmodium falciparum development, three components that are crucial to malaria transmission. Modeling the impact of these effects on Anopheles population dynamics and Plasmodium transmission predicts that disrupting steroid hormone signaling using 20E agonists would affect malaria transmission to a similar extent as insecticides. Manipulating 20E pathways therefore provides a powerful new approach to tackle malaria transmission by the mosquito vector, particularly in areas affected by the spread of insecticide resistance.
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15
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Shaw WR, Marcenac P, Childs LM, Buckee CO, Baldini F, Sawadogo SP, Dabiré RK, Diabaté A, Catteruccia F. Wolbachia infections in natural Anopheles populations affect egg laying and negatively correlate with Plasmodium development. Nat Commun 2016; 7:11772. [PMID: 27243367 PMCID: PMC4895022 DOI: 10.1038/ncomms11772] [Citation(s) in RCA: 91] [Impact Index Per Article: 11.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/16/2016] [Accepted: 04/27/2016] [Indexed: 11/21/2022] Open
Abstract
The maternally inherited alpha-proteobacterium Wolbachia has been proposed as a tool to block transmission of devastating mosquito-borne infectious diseases like dengue and malaria. Here we study the reproductive manipulations induced by a recently identified Wolbachia strain that stably infects natural mosquito populations of a major malaria vector, Anopheles coluzzii, in Burkina Faso. We determine that these infections significantly accelerate egg laying but do not induce cytoplasmic incompatibility or sex-ratio distortion, two parasitic reproductive phenotypes that facilitate the spread of other Wolbachia strains within insect hosts. Analysis of 221 blood-fed A. coluzzii females collected from houses shows a negative correlation between the presence of Plasmodium parasites and Wolbachia infection. A mathematical model incorporating these results predicts that infection with these endosymbionts may reduce malaria prevalence in human populations. These data suggest that Wolbachia may be an important player in malaria transmission dynamics in Sub-Saharan Africa. Wolbachia bacteria infect insects and could potentially be used to control populations of malaria-transmitting mosquitoes. Here, the authors provide evidence that natural Wolbachia infections affect the rate of egg laying and are associated with reduced presence of malaria parasites in Anopheles mosquitoes.
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Affiliation(s)
- W Robert Shaw
- Department of Immunology and Infectious Diseases, Harvard T.H. Chan School of Public Health, Boston, Massachusetts 02115, USA
| | - Perrine Marcenac
- Department of Immunology and Infectious Diseases, Harvard T.H. Chan School of Public Health, Boston, Massachusetts 02115, USA
| | - Lauren M Childs
- Center for Communicable Disease Dynamics, Harvard T.H. Chan School of Public Health, Boston, Massachusetts 02115, USA.,Department of Epidemiology, Harvard T.H. Chan School of Public Health, Boston, Massachusetts 02115, USA
| | - Caroline O Buckee
- Center for Communicable Disease Dynamics, Harvard T.H. Chan School of Public Health, Boston, Massachusetts 02115, USA.,Department of Epidemiology, Harvard T.H. Chan School of Public Health, Boston, Massachusetts 02115, USA
| | - Francesco Baldini
- Institute of Biodiversity, Animal Health and Comparative Medicine, University of Glasgow, Glasgow G12 8QQ, UK
| | - Simon P Sawadogo
- Institut de Recherche en Sciences de la Santé/Centre Muraz, O1 BP 390 Bobo-Dioulasso 01, Burkina Faso
| | - Roch K Dabiré
- Institut de Recherche en Sciences de la Santé/Centre Muraz, O1 BP 390 Bobo-Dioulasso 01, Burkina Faso
| | - Abdoulaye Diabaté
- Institut de Recherche en Sciences de la Santé/Centre Muraz, O1 BP 390 Bobo-Dioulasso 01, Burkina Faso
| | - Flaminia Catteruccia
- Department of Immunology and Infectious Diseases, Harvard T.H. Chan School of Public Health, Boston, Massachusetts 02115, USA
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16
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Zhu L, Marshall JM, Qualls WA, Schlein Y, McManus JW, Arheart KL, Hlaing WM, Traore SF, Doumbia S, Müller GC, Beier JC. Modelling optimum use of attractive toxic sugar bait stations for effective malaria vector control in Africa. Malar J 2015; 14:492. [PMID: 26643110 PMCID: PMC4672472 DOI: 10.1186/s12936-015-1012-9] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/09/2015] [Accepted: 11/24/2015] [Indexed: 11/10/2022] Open
Abstract
BACKGROUND The development of insecticide resistance and the increased outdoor-biting behaviour of malaria vectors reduce the efficiency of indoor vector control methods. Attractive toxic sugar baits (ATSBs), a method targeting the sugar-feeding behaviours of vectors both indoors and outdoors, is a promising supplement to indoor tools. The number and configuration of these ATSB stations needed for malaria control in a community needs to be determined. METHODS A hypothetical village, typical of those in sub-Saharan Africa, 600 × 600 m, consisting of houses, humans and essential resource requirements of Anopheles gambiae (sugar sources, outdoor resting sites, larval habitats) was simulated in a spatial individual-based model. Resource-rich and resource-poor environments were simulated separately. Eight types of configurations and different densities of ATSB stations were tested. Anopheles gambiae population size, human biting rate (HBR) and entomological inoculation rates (EIR) were compared between different ATSB configurations and densities. Each simulated scenario was run 50 times. RESULTS Compared to the outcomes not altered by ATSB treatment in the control scenario, in resource-rich and resource-poor environments, respectively, the optimum ATSB treatment reduced female abundance by 98.22 and 91.80 %, reduced HBR by 99.52 and 98.15 %, and reduced EIR by 99.99 and 100 %. In resource-rich environments, n × n grid design, stations at sugar sources, resting sites, larval habitats, and random locations worked better in reducing vector population and HBRs than other configurations (P < 0.0001). However, there was no significant difference of EIR reductions between all ATSB configurations (P > 0.05). In resource-poor environments, there was no significant difference of female abundances, HBRs and EIRs between all ATSB configurations (P > 0.05). The optimum number of ATSB stations was about 25 for resource-rich environments and nine for resource-poor environments. CONCLUSIONS ATSB treatment reduced An. gambiae population substantially and reduced EIR to near zero regardless of environmental resource availability. In resource-rich environments, dispersive configurations worked better in reducing vector population, and stations at or around houses worked better in preventing biting and parasite transmission. In resource-poor environments, all configurations worked similarly. Optimum numbers of bait stations should be adjusted according to seasonality when resource availability changes.
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Affiliation(s)
- Lin Zhu
- Department of Public Health Sciences, Miller School of Medicine, University of Miami, Miami, FL, USA.
| | - John M Marshall
- Divisions of Biostatistics and Epidemiology, School of Public Health, University of California, Berkeley, CA, USA.
| | - Whitney A Qualls
- Department of Public Health Sciences, Miller School of Medicine, University of Miami, Miami, FL, USA.
| | - Yosef Schlein
- Department of Microbiology and Molecular Genetics, Faculty of Medicine, IMRIC, Kuvin Centre for the Study of Infectious and Tropical Diseases, Hebrew University, Jerusalem, Israel.
| | - John W McManus
- Department of Marine Biology and Ecology, Rosenstiel School of Marine and Atmospheric Science, University of Miami, Miami, FL, USA.
| | - Kris L Arheart
- Department of Public Health Sciences, Miller School of Medicine, University of Miami, Miami, FL, USA.
| | - WayWay M Hlaing
- Department of Public Health Sciences, Miller School of Medicine, University of Miami, Miami, FL, USA.
| | - Sekou F Traore
- Malaria Research and Training Center, Faculty of Medicine, Pharmacy and Odonto-Stomatology, University of Bamako, BP 1805, Bamako, Mali.
| | - Seydou Doumbia
- Malaria Research and Training Center, Faculty of Medicine, Pharmacy and Odonto-Stomatology, University of Bamako, BP 1805, Bamako, Mali.
| | - Günter C Müller
- Department of Microbiology and Molecular Genetics, Faculty of Medicine, IMRIC, Kuvin Centre for the Study of Infectious and Tropical Diseases, Hebrew University, Jerusalem, Israel.
| | - John C Beier
- Department of Public Health Sciences, Miller School of Medicine, University of Miami, Miami, FL, USA.
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17
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Zhu L, Qualls WA, Marshall JM, Arheart KL, DeAngelis DL, McManus JW, Traore SF, Doumbia S, Schlein Y, Müller GC, Beier JC. A spatial individual-based model predicting a great impact of copious sugar sources and resting sites on survival of Anopheles gambiae and malaria parasite transmission. Malar J 2015; 14:59. [PMID: 25652678 PMCID: PMC4324791 DOI: 10.1186/s12936-015-0555-0] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/24/2014] [Accepted: 01/08/2015] [Indexed: 11/28/2022] Open
Abstract
Background Agent-based modelling (ABM) has been used to simulate mosquito life cycles and to evaluate vector control applications. However, most models lack sugar-feeding and resting behaviours or are based on mathematical equations lacking individual level randomness and spatial components of mosquito life. Here, a spatial individual-based model (IBM) incorporating sugar-feeding and resting behaviours of the malaria vector Anopheles gambiae was developed to estimate the impact of environmental sugar sources and resting sites on survival and biting behaviour. Methods A spatial IBM containing An. gambiae mosquitoes and humans, as well as the village environment of houses, sugar sources, resting sites and larval habitat sites was developed. Anopheles gambiae behaviour rules were attributed at each step of the IBM: resting, host seeking, sugar feeding and breeding. Each step represented one second of time, and each simulation was set to run for 60 days and repeated 50 times. Scenarios of different densities and spatial distributions of sugar sources and outdoor resting sites were simulated and compared. Results When the number of natural sugar sources was increased from 0 to 100 while the number of resting sites was held constant, mean daily survival rate increased from 2.5% to 85.1% for males and from 2.5% to 94.5% for females, mean human biting rate increased from 0 to 0.94 bites per human per day, and mean daily abundance increased from 1 to 477 for males and from 1 to 1,428 for females. When the number of outdoor resting sites was increased from 0 to 50 while the number of sugar sources was held constant, mean daily survival rate increased from 77.3% to 84.3% for males and from 86.7% to 93.9% for females, mean human biting rate increased from 0 to 0.52 bites per human per day, and mean daily abundance increased from 62 to 349 for males and from 257 to 1120 for females. All increases were significant (P < 0.01). Survival was greater when sugar sources were randomly distributed in the whole village compared to clustering around outdoor resting sites or houses. Conclusions Increases in densities of sugar sources or outdoor resting sites significantly increase the survival and human biting rates of An. gambiae mosquitoes. Survival of An. gambiae is more supported by random distribution of sugar sources than clustering of sugar sources around resting sites or houses. Density and spatial distribution of natural sugar sources and outdoor resting sites modulate vector populations and human biting rates, and thus malaria parasite transmission.
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Affiliation(s)
- Lin Zhu
- Department of Public Health Sciences, Miller School of Medicine, University of Miami, Miami, Florida, USA.
| | - Whitney A Qualls
- Department of Public Health Sciences, Miller School of Medicine, University of Miami, Miami, Florida, USA.
| | - John M Marshall
- Department of Infectious Disease Epidemiology, MRC Centre for Outbreak Analysis and Modelling, Imperial College London, London, UK.
| | - Kris L Arheart
- Department of Public Health Sciences, Miller School of Medicine, University of Miami, Miami, Florida, USA.
| | - Donald L DeAngelis
- USGS/Biological Resources Division and Department of Biology, University of Miami, Coral Gables, Florida, USA.
| | - John W McManus
- Department of Marine Biology and Ecology, University of Miami, Miami, Florida, USA.
| | - Sekou F Traore
- Malaria Research and Training Center, Faculty of Medicine, Pharmacy and Odonto-Stomatology, University of Bamako, BP 1805, Bamako, Mali.
| | - Seydou Doumbia
- Malaria Research and Training Center, Faculty of Medicine, Pharmacy and Odonto-Stomatology, University of Bamako, BP 1805, Bamako, Mali.
| | - Yosef Schlein
- Department of Microbiology and Molecular Genetics, IMRIC, Kuvin Centre for the Study of Infectious and Tropical Diseases, Faculty of Medicine, Hebrew University, Jerusalem, Israel.
| | - Günter C Müller
- Department of Microbiology and Molecular Genetics, IMRIC, Kuvin Centre for the Study of Infectious and Tropical Diseases, Faculty of Medicine, Hebrew University, Jerusalem, Israel.
| | - John C Beier
- Department of Public Health Sciences, Miller School of Medicine, University of Miami, Miami, Florida, USA.
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18
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Sangare I, Dabire R, Yameogo B, Da DF, Michalakis Y, Cohuet A. Stress dependent infection cost of the human malaria agent Plasmodium falciparum on its natural vector Anopheles coluzzii. INFECTION GENETICS AND EVOLUTION 2014; 25:57-65. [PMID: 24747607 DOI: 10.1016/j.meegid.2014.04.006] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/27/2014] [Revised: 04/01/2014] [Accepted: 04/08/2014] [Indexed: 01/25/2023]
Abstract
Unraveling selective forces that shape vector-parasite interactions has critical implications for malaria control. However, it remains unclear whether Plasmodium infection induces a fitness cost to their natural mosquito vectors. Moreover, environmental conditions are known to affect infection outcome and may impact the effect of infection on mosquito fitness. We investigated in the laboratory the effects of exposition to and infection by field isolates of Plasmodium falciparum on fecundity and survival of a major vector in the field, Anopheles coluzzii under different conditions of access to sugar resources after blood feeding. The results evidenced fitness costs induced by exposition and infection. When sugar was available after blood meal, infected and exposed mosquitoes had either reduced or equal to survival to unexposed mosquitoes while fecundity was either increased or decreased depending on the blood donor. Under strong nutritional stress, survival was reduced for exposed and infected mosquitoes in all assays. We therefore provide here evidence of an environmental-dependant reduced survival in mosquitoes exposed to infection in a natural and one of the most important parasite-mosquito species associations for human malaria transmission.
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Affiliation(s)
- I Sangare
- Institut de Recherche en Sciences de la Santé, Direction Régionale, 399 avenue de la liberté, 01 BP 545 Bobo Dioulasso 01, Burkina Faso; Institut de Recherche pour le Développement, unité MIVEGEC (UM1-UM2-CNRS 5290-IRD 224), 911 avenue Agropolis, 34394 Montpellier Cedex 5, France.
| | - R Dabire
- Institut de Recherche en Sciences de la Santé, Direction Régionale, 399 avenue de la liberté, 01 BP 545 Bobo Dioulasso 01, Burkina Faso.
| | - B Yameogo
- Institut de Recherche en Sciences de la Santé, Direction Régionale, 399 avenue de la liberté, 01 BP 545 Bobo Dioulasso 01, Burkina Faso.
| | - D F Da
- Institut de Recherche en Sciences de la Santé, Direction Régionale, 399 avenue de la liberté, 01 BP 545 Bobo Dioulasso 01, Burkina Faso; Institut de Recherche pour le Développement, unité MIVEGEC (UM1-UM2-CNRS 5290-IRD 224), 911 avenue Agropolis, 34394 Montpellier Cedex 5, France.
| | - Y Michalakis
- Institut de Recherche pour le Développement, unité MIVEGEC (UM1-UM2-CNRS 5290-IRD 224), 911 avenue Agropolis, 34394 Montpellier Cedex 5, France.
| | - A Cohuet
- Institut de Recherche en Sciences de la Santé, Direction Régionale, 399 avenue de la liberté, 01 BP 545 Bobo Dioulasso 01, Burkina Faso; Institut de Recherche pour le Développement, unité MIVEGEC (UM1-UM2-CNRS 5290-IRD 224), 911 avenue Agropolis, 34394 Montpellier Cedex 5, France.
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19
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Assogba BS, Djogbénou L, Saizonou J, Diabaté A, Dabiré RK, Moiroux N, Gilles JR, Makoutodé M, Baldet T. Characterization of swarming and mating behaviour between Anopheles coluzzii and Anopheles melas in a sympatry area of Benin. Acta Trop 2014; 132 Suppl:S53-63. [PMID: 24113221 DOI: 10.1016/j.actatropica.2013.09.006] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/11/2013] [Revised: 09/04/2013] [Accepted: 09/07/2013] [Indexed: 11/27/2022]
Abstract
The swarm structure of two sibling species, Anopheles gambiae coluzzii and Anopheles melas, was characterize to explore the ecological and environmental parameters associated with the formation of swarms and their spatial distribution. Swarms and breeding sites were searched and sampled between January and December 2010, and larval and adult samples were identified by PCR. During the dry season, 456 swarms of An. gambiae s.l. were sampled from 38 swarm sites yielding a total of 23,274 males and 76 females. Of these 38 swarming sites, 18 were composed exclusively of An. gambiae coluzzii and 20 exclusively of An. melas, presenting clear evidence of reproductive swarm segregation. The species makeup of couples sampled from swarms also demonstrated assortative mating. The swarm site localization was close to human dwellings in the case of the An. gambiae coluzzii and on salt production sites for An. melas. At the peak of the rainy season, swarms of An. melas were absent. These findings offer evidence that the ecological speciation of these two sibling species of mosquitoes is associated with spatial swarm segregation and assortative mating, providing strong support for the hypothesis that mate recognition is currently maintaining adaptive differentiation and promoting ecological speciation. Further studies on the swarming and mating systems of An. gambiae, with the prospect of producing a predictive model of swarm distribution, are needed to inform any future efforts to implement strategies based on the use of GMM or SIT.
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Baldini F, Gabrieli P, South A, Valim C, Mancini F, Catteruccia F. The interaction between a sexually transferred steroid hormone and a female protein regulates oogenesis in the malaria mosquito Anopheles gambiae. PLoS Biol 2013; 11:e1001695. [PMID: 24204210 PMCID: PMC3812110 DOI: 10.1371/journal.pbio.1001695] [Citation(s) in RCA: 76] [Impact Index Per Article: 6.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/07/2013] [Accepted: 09/05/2013] [Indexed: 11/18/2022] Open
Abstract
Molecular interactions between male and female factors during mating profoundly affect the reproductive behavior and physiology of female insects. In natural populations of the malaria mosquito Anopheles gambiae, blood-fed females direct nutritional resources towards oogenesis only when inseminated. Here we show that the mating-dependent pathway of egg development in these mosquitoes is regulated by the interaction between the steroid hormone 20-hydroxy-ecdysone (20E) transferred by males during copulation and a female Mating-Induced Stimulator of Oogenesis (MISO) protein. RNAi silencing of MISO abolishes the increase in oogenesis caused by mating in blood-fed females, causes a delay in oocyte development, and impairs the function of male-transferred 20E. Co-immunoprecipitation experiments show that MISO and 20E interact in the female reproductive tract. Moreover MISO expression after mating is induced by 20E via the Ecdysone Receptor, demonstrating a close cooperation between the two factors. Male-transferred 20E therefore acts as a mating signal that females translate into an increased investment in egg development via a MISO-dependent pathway. The identification of this male-female reproductive interaction offers novel opportunities for the control of mosquito populations that transmit malaria.
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Affiliation(s)
- Francesco Baldini
- Department of Immunology and Infectious Diseases, Harvard School of Public Health, Boston, Massachusetts, United States of America
- Dipartimento di Medicina Sperimentale e Scienze Biochimiche, Università degli Studi di Perugia, Terni, Italy
| | - Paolo Gabrieli
- Dipartimento di Medicina Sperimentale e Scienze Biochimiche, Università degli Studi di Perugia, Terni, Italy
| | - Adam South
- Department of Immunology and Infectious Diseases, Harvard School of Public Health, Boston, Massachusetts, United States of America
| | - Clarissa Valim
- Department of Immunology and Infectious Diseases, Harvard School of Public Health, Boston, Massachusetts, United States of America
| | - Francesca Mancini
- Dipartimento di Medicina Sperimentale e Scienze Biochimiche, Università degli Studi di Perugia, Terni, Italy
| | - Flaminia Catteruccia
- Department of Immunology and Infectious Diseases, Harvard School of Public Health, Boston, Massachusetts, United States of America
- Dipartimento di Medicina Sperimentale e Scienze Biochimiche, Università degli Studi di Perugia, Terni, Italy
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Yamada H, Soliban SM, Vreysen MJ, Chadee DD, Gilles JRL. Eliminating female Anopheles arabiensis by spiking blood meals with toxicants as a sex separation method in the context of the sterile insect technique. Parasit Vectors 2013; 6:197. [PMID: 23822117 PMCID: PMC3703270 DOI: 10.1186/1756-3305-6-197] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/15/2013] [Accepted: 06/26/2013] [Indexed: 11/10/2022] Open
Abstract
BACKGROUND Ivermectin has longevity reducing effects in several insect species, including disease transmitting mosquitoes after feeding on hosts that have received ivermectin treatment. This has important implications in mosquito population control and thus the reduction of disease transmission. In addition, ivermectin could play an enormous role in mosquito control operations by its use in the female elimination process during mass-rearing, enabling the release of only sterile males in the context of the sterile insect technique (SIT). METHODS Blood meals were spiked with various toxicants and were then offered to adult Anopheles arabiensis and killing effects were observed. Varying concentrations of the most effective substance were then tested in subsequent trials to obtain an optimal dose for quick and total female elimination. The remaining males were mated with untreated virgin females to assess whether their mating efficiency had been compromised. The most promising substance at the optimal concentration was further tested on a larger number of adults, after they had been irradiated and partially sterilised as pupae with 70 Gy to evaluate the feasibility of the method in a mass-rearing, and SIT context. The males resulting from the latter trial were also checked for mating efficiency post treatments. RESULTS Ivermectin (Virbamec®) at a concentration of 7.5 ppm was chosen from the toxicants tested as sufficiently effective in eliminating all female An. arabiensis in 4 days, the shortest time required for female elimination of all chemicals tested. Mating efficiency of the non-blood feeding male mosquitoes was not compromised significantly compared to controls even when they were kept for a total of 4 days (from emergence) before theoretical release. The irradiation treatment did not affect overall female feeding behaviour in this setting, nor were the sterile males less competitive for mating with virgin females after the treatments than virgin sterile males that had not been in the ivermectin treatment environment. CONCLUSIONS Spiking bloodmeals with ivermectin has shown potential as a viable treatment to eliminate female An. arabiensis from laboratory colonies although its practical use in a mass-rearing facility still needs to be tested.
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Lunde TM, Korecha D, Loha E, Sorteberg A, Lindtjørn B. A dynamic model of some malaria-transmitting anopheline mosquitoes of the Afrotropical region. I. Model description and sensitivity analysis. Malar J 2013; 12:28. [PMID: 23342980 PMCID: PMC3664083 DOI: 10.1186/1475-2875-12-28] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/21/2012] [Accepted: 01/07/2013] [Indexed: 11/10/2022] Open
Abstract
BACKGROUND Most of the current biophysical models designed to address the large-scale distribution of malaria assume that transmission of the disease is independent of the vector involved. Another common assumption in these type of model is that the mortality rate of mosquitoes is constant over their life span and that their dispersion is negligible. Mosquito models are important in the prediction of malaria and hence there is a need for a realistic representation of the vectors involved. RESULTS We construct a biophysical model including two competing species, Anopheles gambiae s.s. and Anopheles arabiensis. Sensitivity analysis highlight the importance of relative humidity and mosquito size, the initial conditions and dispersion, and a rarely used parameter, the probability of finding blood. We also show that the assumption of exponential mortality of adult mosquitoes does not match the observed data, and suggest that an age dimension can overcome this problem. CONCLUSIONS This study highlights some of the assumptions commonly used when constructing mosquito-malaria models and presents a realistic model of An. gambiae s.s. and An. arabiensis and their interaction. This new mosquito model, OMaWa, can improve our understanding of the dynamics of these vectors, which in turn can be used to understand the dynamics of malaria.
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Affiliation(s)
- Torleif Markussen Lunde
- Centre for International Health, University of Bergen, Bergen, Norway
- Bjerknes Centre for Climate Research, University of Bergen/Uni Research, Bergen, Norway
- Geophysical Institute, University of Bergen, Bergen, Norway
| | - Diriba Korecha
- National Meteorological Agency of Ethiopia, Addis Ababa, Ethiopia
- Geophysical Institute, University of Bergen, Bergen, Norway
| | | | - Asgeir Sorteberg
- Bjerknes Centre for Climate Research, University of Bergen/Uni Research, Bergen, Norway
- Geophysical Institute, University of Bergen, Bergen, Norway
| | - Bernt Lindtjørn
- Centre for International Health, University of Bergen, Bergen, Norway
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Sangare I, Michalakis Y, Yameogo B, Dabire R, Morlais I, Cohuet A. Studying fitness cost of Plasmodium falciparum infection in malaria vectors: validation of an appropriate negative control. Malar J 2013; 12:2. [PMID: 23282172 PMCID: PMC3543248 DOI: 10.1186/1475-2875-12-2] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/20/2012] [Accepted: 12/29/2012] [Indexed: 12/13/2022] Open
Abstract
Background The question whether Plasmodium falciparum infection affects the fitness of mosquito vectors remains open. A hurdle for resolving this question is the lack of appropriate control, non-infected mosquitoes that can be compared to the infected ones. It was shown recently that heating P. falciparum gametocyte-infected blood before feeding by malaria vectors inhibits the infection. Therefore, the same source of gametocyte-infected blood could be divided in two parts, one heated, serving as the control, the other unheated, allowing the comparison of infected and uninfected mosquitoes which fed on exactly the same blood otherwise. However, before using this method for characterizing the cost of infection to mosquitoes, it is necessary to establish whether feeding on previously heated blood affects the survival and fecundity of mosquito females. Methods Anopheles gambiae M molecular form females were exposed to heated versus non-heated, parasite-free human blood to mimic blood meal on non-infectious versus infectious gametocyte-containing blood. Life history traits of mosquito females fed on blood that was heat-treated or not were then compared. Results The results reveal that heat treatment of the blood did not affect the survival and fecundity of mosquito females. Consistently, blood heat treatment did not affect the quantity of blood ingested. Conclusions The study indicates that heat inactivation of gametocyte-infected blood will only inhibit mosquito infection and that this method is suitable for quantifying the fitness cost incurred by mosquitoes upon infection by P. falciparum.
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Affiliation(s)
- Ibrahim Sangare
- Institut de Recherche en Sciences de la Santé-Direction Régionale de l'Ouest, Bobo Dioulasso, Burkina Faso
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Yaro AS, Traoré AI, Huestis DL, Adamou A, Timbiné S, Kassogué Y, Diallo M, Dao A, Traoré SF, Lehmann T. Dry season reproductive depression of Anopheles gambiae in the Sahel. JOURNAL OF INSECT PHYSIOLOGY 2012; 58:1050-1059. [PMID: 22609421 PMCID: PMC4789105 DOI: 10.1016/j.jinsphys.2012.04.002] [Citation(s) in RCA: 47] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/21/2011] [Revised: 03/26/2012] [Accepted: 04/02/2012] [Indexed: 05/30/2023]
Abstract
The African malaria mosquito, Anopheles gambiae, is widespread south of the Sahara including in dry savannahs and semi-arid environments where no surface water exists for several months a year. Adults of the M form of An. gambiae persist through the long dry season, when no surface waters are available, by increasing their maximal survival from 4 weeks to 7 months. Dry season diapause (aestivation) presumably underlies this extended survival. Diapause in adult insects is intrinsically linked to depressed reproduction. To determine if reproduction of the Sahelian M form is depressed during the dry season, we assessed seasonal changes in oviposition, egg batch size, and egg development, as well as insemination rate and blood feeding in wild caught mosquitoes. Results from xeric Sahelian and riparian populations were compared. Oviposition response in the Sahelian M form dropped from 70% during the wet season to 20% during the dry season while the mean egg batch size among those that laid eggs fell from 173 to 101. Correspondingly, the fraction of females that exhibited gonotrophic dissociation increased over the dry season from 5% to 45%, while a similar fraction of the population retained developed eggs despite having access to water. This depression in reproduction the Sahelian M form was not caused by a reduced insemination rate. Seasonal variation in these reproductive parameters of the riparian M form population was less extreme and the duration of reproductive depression was shorter. Blood feeding responses did not change with the season in either population. Depressed reproduction during the dry season in the Sahelian M form of An. gambiae provides additional evidence for aestivation and illuminates the physiological processes involved. The differences between the Sahelian and riparian population suggest an adaptive cline in aestivation phenotypes between populations only 130 km apart.
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Affiliation(s)
- Alpha S Yaro
- Malaria Research and Training Center/Faculty of Medicine, Pharmacy and Odonto-Stomatology, Bamako, Mali.
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Scott TW, Takken W. Feeding strategies of anthropophilic mosquitoes result in increased risk of pathogen transmission. Trends Parasitol 2012; 28:114-21. [PMID: 22300806 DOI: 10.1016/j.pt.2012.01.001] [Citation(s) in RCA: 182] [Impact Index Per Article: 15.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/18/2009] [Revised: 01/02/2012] [Accepted: 01/03/2012] [Indexed: 10/14/2022]
Abstract
Vector-borne disease specialists have traditionally assumed that in each egg-laying cycle mosquitoes take a single bloodmeal that is used for egg development and feed on plant sugars for flight and production of energy reserves. Here we review research showing that for two of the most important vectors of human pathogens (Anopheles gambiae and Aedes aegypti) imbibing multiple bloodmeals during a gonotrophic cycle while foregoing sugar feeding is a common behaviour, not an exception. By feeding preferentially and frequently on human blood these species increase their fitness and exponentially boost the basic reproduction rate of pathogens they transmit. Although the epidemiological outcome is similar, there are important differences in processes underlying frequent human contact by these species that merit more detailed investigation.
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Affiliation(s)
- Thomas W Scott
- Department of Entomology, University of California, 1 Shields Avenue, Davis, CA 95616, USA.
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Stone C, Hamilton I, Foster W. A survival and reproduction trade-off is resolved in accordance with resource availability by virgin female mosquitoes. Anim Behav 2011; 81:765-774. [PMID: 21499504 PMCID: PMC3074587 DOI: 10.1016/j.anbehav.2011.01.008] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
Abstract
The first 2-4 days after an Anopheles gambiae female mosquito emerges are critical to her survival and reproductive success. Yet, the order of behavioural events (mating, sugar feeding, blood feeding) during this time has received little attention. We discovered that among female cohorts sampled from emergence, sugar feeding had a higher probability than blood feeding of occurring first, and mating rarely occurred before a meal was taken. The night after emergence, 48% of females fed on sugar in mesocosms, and 25% fed on human blood; in the absence of sugar, 49% of females fed on human blood. After 5 days, 39% of the sugar-supplied females had blood fed and mated, and were fructose negative, whereas only 8% of the sugar-denied females had both blood fed and mated by this time. The model that best explained the transitions suggests that females made use of two distinct behavioural pathways, the most common one being to sugar-feed, then mate, and then seek blood. Other females sought blood first, then mated, and forwent a sugar meal. Lipid levels were higher in females with access to sugar than in females without access to sugar, particularly for those in later gonotrophic stages, while glycogen levels in the sugar-supplied group were higher throughout. In single-night experiments with females having had access to sucrose since emergence, those given a blood meal 1 day before spending a night with males had higher insemination rates than those not receiving the blood meal. These results indicate that the trade-off between survival and immediate reproduction is resolved by young adult females in accordance with availability of resources and gonotrophic state.
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Affiliation(s)
- C.M. Stone
- Department of Entomology, The Ohio State University, 318 West 12th Avenue, Aronoff Laboratory, Columbus, OH 43210, U.S.A
| | - I.M. Hamilton
- Department of Evolution, Ecology and Organismal Biology, The Ohio State University, 318 West 12th Avenue, Aronoff Laboratory, Columbus, OH 43210, U.S.A
- Department of Mathematics, The Ohio State University, 231 West 18th Avenue, Math Tower, Columbus, OH 43210
| | - W.A. Foster
- Department of Evolution, Ecology and Organismal Biology, The Ohio State University, 318 West 12th Avenue, Aronoff Laboratory, Columbus, OH 43210, U.S.A
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Sylla M, Kobylinski KC, Gray M, Chapman PL, Sarr MD, Rasgon JL, Foy BD. Mass drug administration of ivermectin in south-eastern Senegal reduces the survivorship of wild-caught, blood fed malaria vectors. Malar J 2010; 9:365. [PMID: 21171970 PMCID: PMC3016374 DOI: 10.1186/1475-2875-9-365] [Citation(s) in RCA: 79] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/04/2010] [Accepted: 12/20/2010] [Indexed: 11/25/2022] Open
Abstract
Background In south-eastern Senegal, malaria and onchocerciasis are co-endemic. Onchocerciasis in this region has been controlled by once or twice yearly mass drug administration (MDA) with ivermectin (IVM) for over fifteen years. Since laboratory-raised Anopheles gambiae s.s. are susceptible to ivermectin at concentrations found in human blood post-ingestion of IVM, it is plausible that a similar effect could be quantified in the field, and that IVM might have benefits as a malaria control tool. Methods In 2008 and 2009, wild-caught blood fed An. gambiae s.l. mosquitoes were collected from huts of three pairs of Senegalese villages before and after IVM MDAs. Mosquitoes were held in an insectary to assess their survival rate, subsequently identified to species, and their blood meals were identified. Differences in mosquito survival were statistically analysed using a Glimmix model. Lastly, changes in the daily probability of mosquito survivorship surrounding IVM MDAs were calculated, and these data were inserted into a previously developed, mosquito age-structured model of malaria transmission. Results Anopheles gambiae s.s. (P < 0.0001) and Anopheles arabiensis (P = 0.0191) from the treated villages had significantly reduced survival compared to those from control villages. Furthermore, An gambiae s.s. caught 1-6 days after MDA in treated villages had significantly reduced survival compared to control village collections (P = 0.0003), as well as those caught pre-MDA (P < 0.0001) and >7 days post-MDA (P < 0.0001). The daily probability of mosquito survival dropped >10% for the six days following MDA. The mosquito age-structured model of malaria transmission demonstrated that a single IVM MDA would reduce malaria transmission (Ro) below baseline for at least eleven days, and that repeated IVM MDAs would result in a sustained reduction in malaria Ro. Conclusions Ivermectin MDA significantly reduced the survivorship of An. gambiae s.s. for six days past the date of the MDA, which is sufficient to temporarily reduce malaria transmission. Repeated IVM MDAs could be a novel and integrative malaria control tool in areas with seasonal transmission, and which would have simultaneous impacts on neglected tropical diseases in the same villages.
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Affiliation(s)
- Massamba Sylla
- Arthropod-borne and Infectious Diseases Laboratory, Department of Microbiology, Immunology & Pathology, Colorado State University, Fort Collins, Colorado, USA.
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Ng'habi KRN, Mwasheshi D, Knols BGJ, Ferguson HM. Establishment of a self-propagating population of the African malaria vector Anopheles arabiensis under semi-field conditions. Malar J 2010; 9:356. [PMID: 21143870 PMCID: PMC3017536 DOI: 10.1186/1475-2875-9-356] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/02/2010] [Accepted: 12/08/2010] [Indexed: 11/21/2022] Open
Abstract
Background The successful control of insect disease vectors relies on a thorough understanding of their ecology and behaviour. However, knowledge of the ecology of many human disease vectors lags behind that of agricultural pests. This is partially due to the paucity of experimental tools for investigating their ecology under natural conditions without risk of exposure to disease. Assessment of vector life-history and demographic traits under natural conditions has also been hindered by the inherent difficulty of sampling these seasonally and temporally varying populations with the limited range of currently available tools. Consequently much of our knowledge of vector biology comes from studies of laboratory colonies, which may not accurately represent the genetic and behavioural diversity of natural populations. Contained semi-field systems (SFS) have been proposed as more appropriate tools for the study of vector ecology. SFS are relatively large, netting-enclosed, mesocosms in which vectors can fly freely, feed on natural plant and vertebrate host sources, and access realistic resting and oviposition sites. Methods A self-replicating population of the malaria vector Anopheles arabiensis was established within a large field cage (21 × 9.1 × 7.1 m) at the Ifakara Health Institute, Tanzania that mimics the natural habitat features of the rural village environments where these vectors naturally occur. Offspring from wild females were used to establish this population whose life-history, behaviour and demography under semi-field conditions was monitored over 24 generations. Results This study reports the first successful establishment and maintenance of an African malaria vector population under SFS conditions for multiple generations (> 24). The host-seeking behaviour, time from blood feeding to oviposition, larval development, adult resting and swarming behaviour exhibited by An. arabiensis under SFS conditions were similar to those seen in nature. Conclusions This study presents proof-of-principle that populations of important African malaria vectors can be established within environmentally realistic, contained semi-field settings. Such SFS will be valuable tools for the experimental study of vector ecology and assessment of their short-term ecological and longer-term evolutionary responses to existing and new vector control interventions.
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Affiliation(s)
- Kija R N Ng'habi
- Biomedical and Environmental Thematic Group, Ifakara Health Institute, Box 53, Ifakara, Tanzania.
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Rogers DW, Baldini F, Battaglia F, Panico M, Dell A, Morris HR, Catteruccia F. Transglutaminase-mediated semen coagulation controls sperm storage in the malaria mosquito. PLoS Biol 2009; 7:e1000272. [PMID: 20027206 PMCID: PMC2785878 DOI: 10.1371/journal.pbio.1000272] [Citation(s) in RCA: 100] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/03/2009] [Accepted: 11/13/2009] [Indexed: 11/18/2022] Open
Abstract
The mating plug is a key regulator of mosquito fertility. Insect seminal fluid proteins are powerful modulators of many aspects of female physiology and behaviour including longevity, egg production, sperm storage, and remating. The crucial role of these proteins in reproduction makes them promising targets for developing tools aimed at reducing the population sizes of vectors of disease. In the malaria mosquito Anopheles gambiae, seminal secretions produced by the male accessory glands (MAGs) are transferred to females in the form of a coagulated mass called the mating plug. The potential of seminal fluid proteins as tools for mosquito control demands that we improve our limited understanding of the composition and function of the plug. Here, we show that the plug is a key determinant of An. gambiae reproductive success. We uncover the composition of the plug and demonstrate it is formed through the cross-linking of seminal proteins mediated by a MAG-specific transglutaminase (TGase), a mechanism remarkably similar to mammalian semen coagulation. Interfering with TGase expression in males inhibits plug formation and transfer, and prevents females from storing sperm with obvious consequences for fertility. Moreover, we show that the MAG-specific TGase is restricted to the anopheline lineage, where it functions to promote sperm storage rather than as a mechanical barrier to re-insemination. Taken together, these data represent a major advance in our understanding of the factors shaping Anopheles reproductive biology. Male seminal fluid proteins trigger a wide range of behavioural and physiological changes in females and can have important effects on reproductive success. In many animals, seminal fluid is transferred to females as a gelatinous mass termed a mating plug. Although many hypotheses have been put forward to explain the function of mating plugs, their precise role in most organisms remains unclear. We have studied the composition, mechanism of formation, and function of the mating plug in the mosquito Anopheles gambiae, the principal vector of human malaria. We show that the plug is formed through the action of a transglutaminase enzyme that links seminal fluid proteins together resulting in semen coagulation. This process is similar to the way seminal fluid is coagulated in mammals. Interfering with the production of this transglutaminase prevented plug formation. Females that did not receive a plug failed to store sperm correctly, with important consequences for fertility. Our data show that the mating plug is an important feature of An. gambiae reproduction, and reinforce the notion that a deeper understanding of mosquito reproductive biology can aid efforts to eradicate these disease vectors.
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Affiliation(s)
- David W. Rogers
- Division of Cell and Molecular Biology, Imperial College London, London, United Kingdom
| | - Francesco Baldini
- Università degli Studi di Perugia, Dipartimento di Medicina Sperimentale e Scienze Biochimiche, Terni, Italy
| | - Francesca Battaglia
- Division of Molecular Biosciences, Imperial College London, London, United Kingdom
| | - Maria Panico
- Division of Molecular Biosciences, Imperial College London, London, United Kingdom
| | - Anne Dell
- Division of Molecular Biosciences, Imperial College London, London, United Kingdom
| | - Howard R. Morris
- Division of Molecular Biosciences, Imperial College London, London, United Kingdom
| | - Flaminia Catteruccia
- Division of Cell and Molecular Biology, Imperial College London, London, United Kingdom
- Università degli Studi di Perugia, Dipartimento di Medicina Sperimentale e Scienze Biochimiche, Terni, Italy
- * E-mail:
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Combining fungal biopesticides and insecticide-treated bednets to enhance malaria control. PLoS Comput Biol 2009; 5:e1000525. [PMID: 19798436 PMCID: PMC2742557 DOI: 10.1371/journal.pcbi.1000525] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/15/2009] [Accepted: 08/31/2009] [Indexed: 11/19/2022] Open
Abstract
In developing strategies to control malaria vectors, there is increased interest in biological methods that do not cause instant vector mortality, but have sublethal and lethal effects at different ages and stages in the mosquito life cycle. These techniques, particularly if integrated with other vector control interventions, may produce substantial reductions in malaria transmission due to the total effect of alterations to multiple life history parameters at relevant points in the life-cycle and transmission-cycle of the vector. To quantify this effect, an analytically tractable gonotrophic cycle model of mosquito-malaria interactions is developed that unites existing continuous and discrete feeding cycle approaches. As a case study, the combined use of fungal biopesticides and insecticide treated bednets (ITNs) is considered. Low values of the equilibrium EIR and human prevalence were obtained when fungal biopesticides and ITNs were combined, even for scenarios where each intervention acting alone had relatively little impact. The effect of the combined interventions on the equilibrium EIR was at least as strong as the multiplicative effect of both interventions. For scenarios representing difficult conditions for malaria control, due to high transmission intensity and widespread insecticide resistance, the effect of the combined interventions on the equilibrium EIR was greater than the multiplicative effect, as a result of synergistic interactions between the interventions. Fungal biopesticide application was found to be most effective when ITN coverage was high, producing significant reductions in equilibrium prevalence for low levels of biopesticide coverage. By incorporating biological mechanisms relevant to vectorial capacity, continuous-time vector population models can increase their applicability to integrated vector management.
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Gu W, Novak RJ. Agent-based modelling of mosquito foraging behaviour for malaria control. Trans R Soc Trop Med Hyg 2009; 103:1105-12. [PMID: 19200566 DOI: 10.1016/j.trstmh.2009.01.006] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/03/2008] [Revised: 12/29/2008] [Accepted: 01/07/2009] [Indexed: 10/21/2022] Open
Abstract
Traditional environmental management programmes require extensive coverage of larval habitats to reduce drastically the emergence of adult mosquitoes. Recent studies have highlighted the impact of reduced availability of aquatic habitats on mosquito foraging for hosts and oviposition sites. In this study, we developed an agent-based model to track the status and movement of mosquitoes individually. Mosquito foraging was represented as a two-stage process: random flight when the resource was not within the mosquito's perception range and directional flight to the resource when it was detected. Three scenarios of targeted source reduction were devised to eliminate all aquatic habitats within certain distances of human habitations. For comparison, three non-targeted source reductions randomly eliminated the same numbers of aquatic habitats as their corresponding targeted scenarios. Our results show that the elimination of habitats within 100m, 200m and 300m of surrounding houses resulted in 13%, 91% and 94% reductions in malaria incidence, respectively; compared with -3%, 19% and 44%, respectively, for the corresponding conventional interventions. These findings indicate that source reduction might not require coverage of extensive areas, as previously thought, and that the distance to human habitations can be used for habitat targeting.
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Affiliation(s)
- Weidong Gu
- Division of Infectious Diseases, University of Alabama at Birmingham, Birmingham, AL 35294, USA.
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Moffett A, Shackelford N, Sarkar S. Malaria in Africa: vector species' niche models and relative risk maps. PLoS One 2007; 2:e824. [PMID: 17786196 PMCID: PMC1950570 DOI: 10.1371/journal.pone.0000824] [Citation(s) in RCA: 88] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/25/2007] [Accepted: 08/06/2007] [Indexed: 11/19/2022] Open
Abstract
A central theoretical goal of epidemiology is the construction of spatial models of disease prevalence and risk, including maps for the potential spread of infectious disease. We provide three continent-wide maps representing the relative risk of malaria in Africa based on ecological niche models of vector species and risk analysis at a spatial resolution of 1 arc-minute (9 185 275 cells of approximately 4 sq km). Using a maximum entropy method we construct niche models for 10 malaria vector species based on species occurrence records since 1980, 19 climatic variables, altitude, and land cover data (in 14 classes). For seven vectors (Anopheles coustani, A. funestus, A. melas, A. merus, A. moucheti, A. nili, and A. paludis) these are the first published niche models. We predict that Central Africa has poor habitat for both A. arabiensis and A. gambiae, and that A. quadriannulatus and A. arabiensis have restricted habitats in Southern Africa as claimed by field experts in criticism of previous models. The results of the niche models are incorporated into three relative risk models which assume different ecological interactions between vector species. The “additive” model assumes no interaction; the “minimax” model assumes maximum relative risk due to any vector in a cell; and the “competitive exclusion” model assumes the relative risk that arises from the most suitable vector for a cell. All models include variable anthrophilicity of vectors and spatial variation in human population density. Relative risk maps are produced from these models. All models predict that human population density is the critical factor determining malaria risk. Our method of constructing relative risk maps is equally general. We discuss the limits of the relative risk maps reported here, and the additional data that are required for their improvement. The protocol developed here can be used for any other vector-borne disease.
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Affiliation(s)
- Alexander Moffett
- Section of Integrative Biology, University of Texas at Austin, Austin, Texas, United States of America
| | - Nancy Shackelford
- Section of Integrative Biology, University of Texas at Austin, Austin, Texas, United States of America
| | - Sahotra Sarkar
- Section of Integrative Biology, University of Texas at Austin, Austin, Texas, United States of America
- * To whom correspondence should be addressed. E-mail:
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Voordouw MJ, Koella JC. Genetic variation of male reproductive success in a laboratory population of Anopheles gambiae. Malar J 2007; 6:99. [PMID: 17663767 PMCID: PMC1971063 DOI: 10.1186/1475-2875-6-99] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/14/2007] [Accepted: 07/30/2007] [Indexed: 12/16/2022] Open
Abstract
Background For Anopheline mosquitoes, the vectors of human malaria, genetic variation in male reproductive success can have important consequences for any control strategy based on the release of transgenic or sterile males. Methods A quantitative genetics approach was used to test whether there was a genetic component to variation in male reproductive success in a laboratory population of Anopheles gambiae. Swarms of full sibling brothers were mated with a fixed number of females and their reproductive success was measured as (1) proportion of ovipositing females, (2) proportion of ovipositing females that produced larvae, (3) proportion of females that produced larvae, (4) number of eggs laid per female, (5) number of larvae per ovipositing female and (6) number of larvae per female. Results The proportion of ovipositing females (trait 1) and the proportion of ovipositing females that produced larvae (trait 2) differed among full sib families, suggesting a genetic basis of mating success. In contrast, the other measures of male reproductive success showed little variation due to the full sib families, as their variation are probably mostly due to differences among females. While age at emergence and wing length of the males were also heritable, they were not associated with reproductive success. Larger females produced more eggs, but males did not prefer such partners. Conclusion The first study to quantify genetic variation for male reproductive success in A. gambiae found that while the initial stages of male reproduction (i.e. the proportion of ovipositing females and the proportion of ovipositing females that produced larvae) had a genetic basis, the overall reproductive success (i.e. the mean number of larvae per female) did not.
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Affiliation(s)
- Maarten J Voordouw
- Division of Biology, Imperial College of London, Silwood Park Campus, Buckhurst Road, Ascot, Berkshire, SL5 7PY, UK
- School of Life Sciences, Huxley Building, Keele University, Staffordshire, UK
| | - Jacob C Koella
- Division of Biology, Imperial College of London, Silwood Park Campus, Buckhurst Road, Ascot, Berkshire, SL5 7PY, UK
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Huho BJ, Ng'habi KR, Killeen GF, Nkwengulila G, Knols BGJ, Ferguson HM. A reliable morphological method to assess the age of male Anopheles gambiae. Malar J 2006; 5:62. [PMID: 16872516 PMCID: PMC1570359 DOI: 10.1186/1475-2875-5-62] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/20/2006] [Accepted: 07/27/2006] [Indexed: 11/10/2022] Open
Abstract
BACKGROUND Release of genetically-modified (GM) or sterile male mosquitoes for malaria control is hampered by inability to assess the age and mating history of free-living male Anopheles. METHODS Age and mating-related changes in the reproductive system of male Anopheles gambiae were quantified and used to fit predictive statistical models. These models, based on numbers of spermatocysts, relative size of sperm reservoir and presence/absence of a clear area around the accessory gland, were evaluated using an independent sample of mosquitoes whose status was blinded during the experiment. RESULTS The number of spermatocysts in male testes decreased with age, and the relative size of their sperm reservoir increased. The presence of a clear area around accessory glands was also linked to age and mating status. A quantitative model was able to categorize males from the blind trial into age groups of young (< or = 4 days) and old (> 4 days) with an overall efficiency of 89%. Using the parameters of this model, a simple table was compiled that can be used to predict male age. In contrast, mating history could not be reliably assessed as virgins could not be distinguished from mated males. CONCLUSION Simple assessment of a few morphological traits which are easily collected in the field allows accurate age-grading of male An. gambiae. This simple, yet robust, model enables evaluation of demographic patterns and mortality in wild and released males in populations targeted by GM or sterile male-based control programmes.
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Affiliation(s)
- Bernadette J Huho
- Ifakara Health Research and Development Centre, PO Box 53, Off Mlabani Passage, Ifakara, Tanzania
- Department of Zoology and Marine Biology, University of Dar es Salaam, PO Box 35064, Dar es Salaam, Tanzania
| | - Kija R Ng'habi
- Ifakara Health Research and Development Centre, PO Box 53, Off Mlabani Passage, Ifakara, Tanzania
- Department of Zoology and Marine Biology, University of Dar es Salaam, PO Box 35064, Dar es Salaam, Tanzania
| | - Gerry F Killeen
- Ifakara Health Research and Development Centre, PO Box 53, Off Mlabani Passage, Ifakara, Tanzania
- Department of Public Health and Epidemiology, Swiss Tropical Institute, Socinstrasse 57, Basel, C4-4002, Switzerland
- School of Biological and Biomedical Sciences, Durham University, Durham DH1 3LE, UK
| | - Gamba Nkwengulila
- Department of Zoology and Marine Biology, University of Dar es Salaam, PO Box 35064, Dar es Salaam, Tanzania
| | - Bart GJ Knols
- International Atomic Energy Agency (IAEA), Agency's Laboratories Seibersdorf, Seibersdorf A-2444, Austria
- Laboratory of Entomology, Wageningen University and Research Centre, PO Box 8031, 6700 EH Wageningen, The Netherlands
| | - Heather M Ferguson
- Ifakara Health Research and Development Centre, PO Box 53, Off Mlabani Passage, Ifakara, Tanzania
- Laboratory of Entomology, Wageningen University and Research Centre, PO Box 8031, 6700 EH Wageningen, The Netherlands
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della Torre A, Tu Z, Petrarca V. On the distribution and genetic differentiation of Anopheles gambiae s.s. molecular forms. INSECT BIOCHEMISTRY AND MOLECULAR BIOLOGY 2005; 35:755-69. [PMID: 15894192 DOI: 10.1016/j.ibmb.2005.02.006] [Citation(s) in RCA: 179] [Impact Index Per Article: 9.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Accepted: 02/11/2005] [Indexed: 05/02/2023]
Abstract
This paper summarises published and unpublished data on the spatial and temporal distribution, and on the genetic characterisation of molecular forms M and S of Anopheles gambiae s.s. The two forms are characterised by a high level of gene-flow restriction, by a largely overlapping geographical and temporal distribution, and by a low degree of genetic differentiation. Floating paracentric inversions on chromosome-2 are shown to be shared by the two forms, although with very different frequencies of alternative arrangements, confirming that these inversions are most probably involved in ecotypic adaptation, rather than in the building of reproductive barriers. Further studies and tools are needed to throw light on the genetic and biological differentiation of M and S to improve the knowledge of the real composition of the vector system, of its demography, population genetics and dynamics, also in view of the possible consequences on the transmission of human pathogens in sub-Saharan Africa. Preliminary results and perspectives of the use of transposable element insertion sites as markers of genetic differentiation and tools for population genetic studies are discussed.
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Affiliation(s)
- Alessandra della Torre
- Sezione di Parassitologia, Dipartimento di Scienze di Sanità Pubblica, Università di Roma La Sapienza, Piazzale Aldo Moro 5, 00185 Roma, Italy.
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Scholte EJ, Knols BGJ, Takken W. Autodissemination of the entomopathogenic fungus Metarhizium anisopliae amongst adults of the malaria vector Anopheles gambiae s.s. Malar J 2004; 3:45. [PMID: 15566626 PMCID: PMC535890 DOI: 10.1186/1475-2875-3-45] [Citation(s) in RCA: 47] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/25/2004] [Accepted: 11/28/2004] [Indexed: 01/13/2023] Open
Abstract
BACKGROUND The entomopathogenic fungus Metarhizium anisopliae is being considered as a biocontrol agent for adult African malaria vectors. In the laboratory, work was carried out to assess whether horizontal transmission of the pathogen can take place during copulation, as this would enhance the impact of the fungus on target populations when compared with insecticides. METHODS Virgin female Anopheles gambiae sensu stricto were exposed to conidia whilst resting on fungus-impregnated paper. These females were then placed together for one hour with uncontaminated males in proportions of either 1:1 or 1:10 shortly before the onset of mating activity. RESULTS Males that had acquired fungal infection after mating indicate that passive transfer of the pathogen from infected females does occur, with mean male infection rates between 10.7 +/- 3.2% and 33.3 +/- 3.8%. The infections caused by horizontal transmission did not result in overall differences in survival between males from test and control groups, but in one of the three experiments the infected males had significantly shorter life spans than uninfected males (P < 0.05). CONCLUSION This study shows that autodissemination of fungal inoculum between An. gambiae s.s. mosquitoes during mating activity is possible under laboratory conditions. Field studies are required next, to assess the extent to which this phenomenon may augment the primary contamination pathway (i.e. direct contact with fungus-impregnated targets) of vector populations in the field.
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Affiliation(s)
- Ernst-Jan Scholte
- Laboratory of Entomology, Wageningen University Research Centre, Binnenhaven 7, P.O. Box 8031, Wageningen, the Netherlands
| | - Bart GJ Knols
- Laboratory of Entomology, Wageningen University Research Centre, Binnenhaven 7, P.O. Box 8031, Wageningen, the Netherlands
- Entomology Unit, Agency's laboratories Seibersdorf, International Atomic Energy Agency, A-2444 Seibersdorf, Austria
| | - Willem Takken
- Laboratory of Entomology, Wageningen University Research Centre, Binnenhaven 7, P.O. Box 8031, Wageningen, the Netherlands
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Charlwood JD, Pinto J, Ferrara PR, Sousa CA, Ferreira C, Gil V, do Rosário VE. Raised houses reduce mosquito bites. Malar J 2003; 2:45. [PMID: 14667242 PMCID: PMC317347 DOI: 10.1186/1475-2875-2-45] [Citation(s) in RCA: 44] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/19/2003] [Accepted: 12/10/2003] [Indexed: 11/25/2022] Open
Abstract
Background In many parts of continental Africa house construction does not appear to impede entry of malaria vectors and, given their generally late biting cycle, the great majority of transmission takes place indoors. In contrast, many houses in São Tomé, 140 km off the coast of Gabon, are raised on stilts and built of wooden planks. Building on stilts is a time-honoured, but largely untested, way of avoiding mosquito bites. Exposure may also be affected by mosquito activity times and age composition of host-seeking females. A study was therefore undertaken on the island of São Tomé to determine if exposure to Anopheles gambiae, the only vector on the island, varied with house construction or time of the night. Methods A series of all-night landing collections were undertaken out of doors at ground level, inside houses at ground level, on the verandas of, and inside houses built on stilts. The gonotrophic age of an unselected sample of insects from the first three hours of landing collection (18:00–21:00) was determined by dissection. In addition, 1,149 miniature light-trap collections were obtained from 125 houses in the study area. Numbers collected were related to house construction. Results Biting of An. gambiae took place primarily outside at ground level. Less than one third of biting occurred inside houses. Houses built on stilts had half the number of An. gambiae in them compared to those built at ground level. Conversely houses with an eaves gap had more An. gambiae in them than houses without such a gap. Gonotrophic age did not affect house entry rates in An. gambiae. House construction affected Culex quinquefasciatus less than An. gambiae. Mean density per house, derived from a series of 1,490 randomly assigned light-trap collections, was over-dispersed with 18% of houses having 70% of the vectors. Conclusion House construction plays an important role in determining exposure to malaria vectors in São Tomé. Neighbours can have very different exposure levels. Recommendations for improvement in control are given.
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Affiliation(s)
- J Derek Charlwood
- Danish Bilharziasis Laboratories, Jaergersborg Allé 1-D, Charlottenlund, DK 2920, Denmark
| | - Joao Pinto
- Centro de Malária e Outras Doenças Tropicais, Instituto de Higiene e Medicina Tropical, Universidade Nova de Lisboa, Rua da Junqueira 96, 1349-008 Lisbon, Portugal
| | - Patrica R Ferrara
- SIMA Project, c/o Technoserve, Rua Bas N'Tchinga 509, Bairro da Coop, Maputo, Mozambique
| | - Carla A Sousa
- Unidade de Entomologia Médica Instituto de Higiene e Medicina Tropical, Universidade Nova de Lisboa, Rua da Junqueira 96, 1349-008 Lisbon, Portugal
| | - Conceicao Ferreira
- Centro Nacional de Endemias, Caixa Postal 218, São Tomé, Democratic Republic of São Tomé and Príncipe
| | - Vilfrido Gil
- Centro Nacional de Endemias, Caixa Postal 218, São Tomé, Democratic Republic of São Tomé and Príncipe
| | - Virgillo E do Rosário
- Centro de Malária e Outras Doenças Tropicais, Instituto de Higiene e Medicina Tropical, Universidade Nova de Lisboa, Rua da Junqueira 96, 1349-008 Lisbon, Portugal
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Hagmann R, Charlwood JD, Gil V, Ferreira C, do Rosário V, Smith TA. Malaria and its possible control on the island of Príncipe. Malar J 2003; 2:15. [PMID: 12875660 PMCID: PMC166171 DOI: 10.1186/1475-2875-2-15] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/07/2003] [Accepted: 06/18/2003] [Indexed: 11/25/2022] Open
Abstract
BACKGROUND Malaria can be eradicated from islands. To assess the prospects for eradication of malaria from the island of Príncipe in the Gulf of Guinea, we fitted a mathematical model to age-prevalence curves and thus obtained estimates of the vectorial capacity and of the basic reproductive number (R0) for malaria. METHODS A cross-sectional malariological survey was carried out, in mid-1999, in six communities, comprising circa 17% of the total 6,000 population of the island. All houses in these communities were registered and their mode of construction recorded. Thick and thin blood films were prepared from all consenting individuals. Each individual was asked whether they possessed a mosquito net, whether they had slept under a mosquito net the previous night, whether they were allergic to chloroquine, and whether they had visited the main island of São Tomé since the beginning of the year. Outpatient records from March 1999 until the end of December 2000 were also examined and the age and place of residence of diagnosed cases noted. RESULTS 203 (19.8%) of the 1,026 individuals examined were found to be infected with Plasmodium falciparum. By fitting the mathematical model of the Garki project to the age-prevalence curve we estimate that the basic reproductive number, R0, on the island is approximately 1.6. Over a period of one year, a total of 1,792 P. falciparum cases reported to an outpatient facility at the island's hospital. Overall, 54% of the people interviewed slept under mosquito nets and were at reduced risk of infection. Conversely, people living in houses with openings between the top of the wall and the roof had higher risk of infection. CONCLUSION This high incidence suggests that most of the malaria cases on the island attend the hospital and that treatment of these cases is an important factor reducing the effective rate of transmission. Providing that clinical cases are effectively treated, endemic malaria can probably be eliminated from the island mainly by reducing exposure to the vector with simple measures such as insecticide-treated nets and mosquito-proofing of dwellings. In contrast to traditional malaria eradication strategies, this would avoid the risk of malaria epidemics because the reduction in R0 should be sustainable.
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Affiliation(s)
- Reto Hagmann
- Swiss Tropical Institute, Socinstrasse 57, P.O. Box, CH-4002 Basel, Switzerland
- Current address: Swiss Federal Office of Public Health, Epidemiology and Infectious Diseases Division Section Vaccines, CH-3003 Bern, Switzerland
| | - J Derek Charlwood
- Danish Bilharziasis Laboratory, 1-D Jaegersborg Allé, Charlottenlund, DK-2920, Denmark
| | - Vilfrido Gil
- Centro Nacional de Endemias, C.P. 218, São Tomé, Democratic Republic of São Tomé and Príncipe
| | - Conceição Ferreira
- Centro Nacional de Endemias, C.P. 218, São Tomé, Democratic Republic of São Tomé and Príncipe
| | - Virgíllo do Rosário
- Centro de Malària e outras Doenças Tropicais, Rua da Junqueira 96, Lisbon 1349-008, Portugal
| | - Tom A Smith
- Swiss Tropical Institute, Socinstrasse 57, P.O. Box, CH-4002 Basel, Switzerland
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