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Ondeto BM, Wang X, Atieli H, Orondo PW, Ochwedo KO, Omondi CJ, Otambo WO, Zhong D, Zhou G, Lee MC, Muriu SM, Odongo DO, Ochanda H, Kazura J, Githeko AK, Yan G. Malaria vector bionomics and transmission in irrigated and non-irrigated sites in western Kenya. Parasitol Res 2022; 121:3529-3545. [PMID: 36203064 DOI: 10.1007/s00436-022-07678-2] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/26/2022] [Accepted: 09/20/2022] [Indexed: 10/10/2022]
Abstract
Irrigation not only helps to improve food security but also creates numerous water bodies for mosquito production. This study assessed the effect of irrigation on malaria vector bionomics and transmission in a semi-arid site with ongoing malaria vector control program. The effectiveness of CDC light traps in the surveillance of malaria vectors was also evaluated relative to the human landing catches (HLCs) method. Adult mosquitoes were sampled in two study sites representing irrigated and non-irrigated agroecosystems in western Kenya using a variety of trapping methods. The mosquito samples were identified to species and assayed for host blood meal source and Plasmodium spp. sporozoite infection using polymerase chain reaction. Anopheles arabiensis was the dominant malaria vector in the two study sites and occurred in significantly higher densities in irrigated study site compared to the non-irrigated study site. The difference in indoor resting density of An. arabiensis during the dry and wet seasons was not significant. Other species, including An. funestus, An. coustani, and An. pharoensis, were collected. The An. funestus indoor resting density was 0.23 in irrigated study site while almost none of this species was collected in the non-irrigated study site. The human blood index (HBI) for An. arabiensis in the irrigated study site was 3.44% and significantly higher than 0.00% for the non-irrigated study site. In the irrigated study site, the HBI of An. arabiensis was 3.90% and 5.20% indoor and outdoor, respectively. The HBI of An. funestus was 49.43% and significantly higher compared to 3.44% for An. arabiensis in the irrigated study site. The annual entomologic inoculation rate for An. arabiensis in the irrigated study site was 0.41 and 0.30 infective bites/person/year indoor and outdoor, respectively, whereas no transmission was observed in the non-irrigated study site. The CDC light trap performed consistently with HLC in terms of vector density. These findings demonstrate that irrigated agriculture may increase the risk of malaria transmission in irrigated areas compared to the non-irrigated areas and highlight the need to complement the existing malaria vector interventions with novel tools targeting the larvae and both indoor and outdoor biting vector populations.
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Affiliation(s)
- Benyl M Ondeto
- Department of Biology, University of Nairobi, Nairobi, 00100, Kenya. .,Sub-Saharan Africa International Center of Excellence for Malaria Research, Tom Mboya University, Homa Bay, 40300, Kenya.
| | - Xiaoming Wang
- Program in Public Health, College of Health Sciences, University of California at Irvine, Irvine, CA, 92697, USA
| | - Harrysone Atieli
- Sub-Saharan Africa International Center of Excellence for Malaria Research, Tom Mboya University, Homa Bay, 40300, Kenya
| | - Pauline Winnie Orondo
- Sub-Saharan Africa International Center of Excellence for Malaria Research, Tom Mboya University, Homa Bay, 40300, Kenya.,Department of Biochemistry, Jomo Kenyatta University of Agriculture and Technology, Nairobi, 00200, Kenya
| | - Kevin O Ochwedo
- Department of Biology, University of Nairobi, Nairobi, 00100, Kenya.,Sub-Saharan Africa International Center of Excellence for Malaria Research, Tom Mboya University, Homa Bay, 40300, Kenya
| | - Collince J Omondi
- Department of Biology, University of Nairobi, Nairobi, 00100, Kenya.,Sub-Saharan Africa International Center of Excellence for Malaria Research, Tom Mboya University, Homa Bay, 40300, Kenya
| | - Wilfred O Otambo
- Sub-Saharan Africa International Center of Excellence for Malaria Research, Tom Mboya University, Homa Bay, 40300, Kenya.,Department of Zoology, Maseno University, Maseno, Kenya
| | - Daibin Zhong
- Program in Public Health, College of Health Sciences, University of California at Irvine, Irvine, CA, 92697, USA
| | - Guofa Zhou
- Program in Public Health, College of Health Sciences, University of California at Irvine, Irvine, CA, 92697, USA
| | - Ming-Chieh Lee
- Program in Public Health, College of Health Sciences, University of California at Irvine, Irvine, CA, 92697, USA
| | - Simon M Muriu
- Department of Biological Sciences, Pwani University, Kilifi, 80108, Kenya
| | - David O Odongo
- Department of Biology, University of Nairobi, Nairobi, 00100, Kenya
| | - Horace Ochanda
- Department of Biology, University of Nairobi, Nairobi, 00100, Kenya
| | - James Kazura
- Center for Global Health and Disease, Case Western Reserve University, Cleveland, OH, 44106, USA
| | - Andrew K Githeko
- Sub-Saharan Africa International Center of Excellence for Malaria Research, Tom Mboya University, Homa Bay, 40300, Kenya.,Centre for Global Health Research, Kenya Medical Research Institute, Kisumu, 40100, Kenya
| | - Guiyun Yan
- Program in Public Health, College of Health Sciences, University of California at Irvine, Irvine, CA, 92697, USA.
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2
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Baeshen R. Swarming Behavior in Anopheles gambiae (sensu lato): Current Knowledge and Future Outlook. JOURNAL OF MEDICAL ENTOMOLOGY 2022; 59:56-66. [PMID: 34617121 PMCID: PMC8755986 DOI: 10.1093/jme/tjab157] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 02/10/2021] [Indexed: 06/13/2023]
Abstract
Effective management of insect disease vectors requires a detailed understanding of their ecology and behavior. In Anopheles gambiae sensu lato (s.l.) (Diptera: Culicidae) mating occurs during swarming, but knowledge of their mating behavior under natural conditions is limited. Mosquitoes mate in flight over specific landmarks, known as swarm markers, at particular locations. Swarms consist of males; the females usually approach the swarm and depart following copulation. The number of mating pairs per swarm is closely associated with swarm size. The shape and height of swarm markers vary and may depend on the environmental conditions at the swarm's location. Male-male interactions in mosquito swarms with similar levels of attractive flight activity can offer a mating advantage to some individuals. Flight tone is used by mosquitoes to recognize the other sex and choose a desirable mate. Clarifying these and other aspects of mosquito reproductive behavior can facilitate the development of population control measures that target swarming sites. This review describes what is currently known about swarming behavior in Anopheles gambiae s.l., including swarm characteristics; mating within and outside of swarms, insemination in females, and factors affecting and stimulating swarming.
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Affiliation(s)
- Rowida Baeshen
- Faculty of Sciences, Biology Department, University of Tabuk, Tabuk, Kingdom of Saudi Arabia
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Ndawula C. From Bench to Field: A Guide to Formulating and Evaluating Anti-Tick Vaccines Delving beyond Efficacy to Effectiveness. Vaccines (Basel) 2021; 9:vaccines9101185. [PMID: 34696291 PMCID: PMC8539545 DOI: 10.3390/vaccines9101185] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/06/2021] [Revised: 08/25/2021] [Accepted: 08/26/2021] [Indexed: 01/04/2023] Open
Abstract
Ticks are ubiquitous blood-sucking ectoparasites capable of transmitting a wide range of pathogens such as bacteria, viruses, protozoa, and fungi to animals and humans. Although the use of chemicals (acaricides) is the predominant method of tick-control, there are increasing incidents of acaricide tick resistance. Furthermore, there are concerns over accumulation of acaricide residues in meat, milk and in the environment. Therefore, alternative methods of tick-control have been proposed, of which anti-tick cattle vaccination is regarded as sustainable and user-friendly. Over the years, tremendous progress has been made in identifying and evaluating novel candidate tick vaccines, yet none of them have reached the global market. Until now, Bm86-based vaccines (Gavac™ in Cuba and TickGARDPLUS™ Australia-ceased in 2010) are still the only globally commercialized anti-tick vaccines. In contrast to Bm86, often, the novel candidate anti-tick vaccines show a lower protection efficacy. Why is this so? In response, herein, the potential bottlenecks to formulating efficacious anti-tick vaccines are examined. Aside from Bm86, the effectiveness of other anti-tick vaccines is rarely assessed. So, how can the researchers assess anti-tick vaccine effectiveness before field application? The approaches that are currently used to determine anti-tick vaccine efficacy are re-examined in this review. In addition, a model is proposed to aid in assessing anti-tick vaccine effectiveness. Finally, based on the principles for the development of general veterinary vaccines, a pipeline is proposed to guide in the development of anti-tick vaccines.
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Affiliation(s)
- Charles Ndawula
- National Agricultural Research Organization, P.O. Box 295, Entebbe, Wakiso 256, Uganda;
- National Livestock Resources Research Institute, Vaccinology Research Programme, P.O. Box 5704, Nakyesasa, Wakiso 256, Uganda
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4
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Ngowo HS, Hape EE, Matthiopoulos J, Ferguson HM, Okumu FO. Fitness characteristics of the malaria vector Anopheles funestus during an attempted laboratory colonization. Malar J 2021; 20:148. [PMID: 33712003 PMCID: PMC7955623 DOI: 10.1186/s12936-021-03677-3] [Citation(s) in RCA: 9] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/05/2020] [Accepted: 03/01/2021] [Indexed: 01/05/2023] Open
Abstract
BACKGROUND The malaria vector Anopheles funestus is increasingly recognized as a dominant vector of residual transmission in many African settings. Efforts to better understand its biology and control are significantly impeded by the difficulties of colonizing it under laboratory conditions. To identify key bottlenecks in colonization, this study compared the development and fitness characteristics of wild An. funestus from Tanzania (FUTAZ) and their F1 offspring during colonization attempts. The demography and reproductive success of wild FUTAZ offspring were compared to that of individuals from one of the only An. funestus strains that has been successfully colonized (FUMOZ, from Mozambique) under similar laboratory conditions. METHODS Wild An. funestus (FUTAZ) were collected from three Tanzanian villages and maintained inside an insectary at 70-85% RH, 25-27 °C and 12 h:12 h photoperiod. Eggs from these females were used to establish three replicate F1 laboratory generations. Larval development, survival, fecundity, mating success, percentage pupation and wing length were measured in the F1 -FUTAZ offspring and compared with wild FUTAZ and FUMOZ mosquitoes. RESULTS Wild FUTAZ laid fewer eggs (64.1; 95% CI [63.2, 65.0]) than FUMOZ females (76.1; 95% CI [73.3, 79.1]). Survival of F1-FUTAZ larvae under laboratory conditions was low, with an egg-to-pupae conversion rate of only 5.9% compared to 27.4% in FUMOZ. The median lifespan of F1-FUTAZ females (32 days) and males (33 days) was lower than FUMOZ (52 and 49 for females and males respectively). The proportion of female F1-FUTAZ inseminated under laboratory conditions (9%) was considerably lower than either FUMOZ (72%) or wild-caught FUTAZ females (92%). This resulted in nearly zero viable F2-FUTAZ eggs produced. Wild FUTAZ wings appear to be larger compared to the lab reared F1-FUTAZ and FUMOZ. CONCLUSIONS This study indicates that poor larval survival, mating success, low fecundity and shorter survival under laboratory conditions all contribute to difficulties in colonizing of An. funestus. Future studies should focus on enhancing these aspects of An. funestus fitness in the laboratory, with the biggest barrier likely to be poor mating.
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Affiliation(s)
- Halfan S Ngowo
- Department of Environmental Health and Ecological Sciences, Ifakara Health Institute, P.O. Box 53, Ifakara, Tanzania. .,Institute of Biodiversity, Animal Health and Comparative Medicine, University of Glasgow, Glasgow, G12, 8QQ, UK.
| | - Emmanuel E Hape
- Department of Environmental Health and Ecological Sciences, Ifakara Health Institute, P.O. Box 53, Ifakara, Tanzania.,Institute of Biodiversity, Animal Health and Comparative Medicine, University of Glasgow, Glasgow, G12, 8QQ, UK
| | - Jason Matthiopoulos
- Institute of Biodiversity, Animal Health and Comparative Medicine, University of Glasgow, Glasgow, G12, 8QQ, UK
| | - Heather M Ferguson
- Department of Environmental Health and Ecological Sciences, Ifakara Health Institute, P.O. Box 53, Ifakara, Tanzania.,Institute of Biodiversity, Animal Health and Comparative Medicine, University of Glasgow, Glasgow, G12, 8QQ, UK
| | - Fredros O Okumu
- Department of Environmental Health and Ecological Sciences, Ifakara Health Institute, P.O. Box 53, Ifakara, Tanzania.,Institute of Biodiversity, Animal Health and Comparative Medicine, University of Glasgow, Glasgow, G12, 8QQ, UK.,School of Public Health, University of the Witwatersrand, 1 Smuts Avenue, Braamfontein, 2000, Republic of South Africa.,School of Life Science and Bioengineering, Nelson Mandela African Institution of Science and Technology, P.O. Box 447, Arusha, Tanzania
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Sangoro OP, Gavana T, Finda M, Mponzi W, Hape E, Limwagu A, Govella NJ, Chaki P, Okumu FO. Evaluation of personal protection afforded by repellent-treated sandals against mosquito bites in south-eastern Tanzania. Malar J 2020; 19:148. [PMID: 32268907 PMCID: PMC7140554 DOI: 10.1186/s12936-020-03215-7] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/21/2020] [Accepted: 03/30/2020] [Indexed: 11/19/2022] Open
Abstract
Background Outdoor and early evening mosquito biting needs to be addressed if malaria elimination is to be achieved. While indoor-targeted interventions, such as insecticide-treated nets and indoor residual spraying, remain essential, complementary approaches that tackle persisting outdoor transmission are urgently required to maximize the impact. Major malaria vectors principally bite human hosts around the feet and ankles. Consequently, this study investigated whether sandals treated with efficacious spatial repellents can protect against outdoor biting mosquitoes. Methodology Sandals affixed with hessian bands measuring 48 cm2 treated with 0.06 g, 0.10 g and 0.15 g of transfluthrin were tested in large cage semi-field and full field experiments. Sandals affixed with hessian bands measuring 240 cm2 and treated with 0.10 g and 0.15 g of transfluthrin were also tested semi field experiments. Human landing catches (HLC) were used to assess reduction in biting exposure by comparing proportions of mosquitoes landing on volunteers wearing treated and untreated sandals. Sandals were tested against insectary reared Anopheles arabiensis mosquitoes in semi-field experiments and against wild mosquito species in rural Tanzania. Results In semi-field tests, sandals fitted with hessian bands measuring 48 cm2 and treated with 0.15 g, 0.10 g and 0.06 g transfluthrin reduced mosquito landings by 45.9%, (95% confidence interval (C.I.) 28–59%), 61.1% (48–71%), and 25.9% (9–40%), respectively compared to untreated sandals. Sandals fitted with hessian bands measuring 240 cm2 and treated with 0.15 g and 0.10 g transfluthrin reduced mosquito landings by 59% (43–71%) and 64% (48–74%), respectively. In field experiments, sandals fitted with hessian bands measuring 48 cm2 and treated with 0.15 g transfluthrin reduced mosquito landings by 70% (60–76%) against Anopheles gambiae sensu lato, and 66.0% (59–71%) against all mosquito species combined. Conclusion Transfluthrin-treated sandals conferred significant protection against mosquito bites in semi-field and field settings. Further evaluation is recommended for this tool as a potential complementary intervention against malaria. This intervention could be particularly useful for protecting against outdoor exposure to mosquito bites. Additional studies are necessary to optimize treatment techniques and substrates, establish safety profiles and determine epidemiological impact in different settings.
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Affiliation(s)
- Onyango P Sangoro
- Environmental Health and Ecological Sciences, Ifakara Health Institute, Ifakara, Tanzania. .,International Centre for Insect Physiology and Ecology, Nairobi, Kenya.
| | - Tegemeo Gavana
- Environmental Health and Ecological Sciences, Ifakara Health Institute, Ifakara, Tanzania
| | - Marceline Finda
- Environmental Health and Ecological Sciences, Ifakara Health Institute, Ifakara, Tanzania.,School of Public Health, Faculty of Health Sciences, University of the Witwatersrand, Johannesburg, South Africa
| | - Winfrida Mponzi
- Environmental Health and Ecological Sciences, Ifakara Health Institute, Ifakara, Tanzania
| | - Emmanuel Hape
- Environmental Health and Ecological Sciences, Ifakara Health Institute, Ifakara, Tanzania
| | - Alex Limwagu
- Environmental Health and Ecological Sciences, Ifakara Health Institute, Ifakara, Tanzania
| | - Nicodem J Govella
- Environmental Health and Ecological Sciences, Ifakara Health Institute, Ifakara, Tanzania.,Institute of Biodiversity, Animal Health and Comparative Medicine, University of Glasgow, Glasgow, UK.,School of Life Sciences and Bio Engineering, The Nelson Mandela, African Institution of Science and Technology, Tengeru, Arusha, United Republic of Tanzania
| | - Prosper Chaki
- Environmental Health and Ecological Sciences, Ifakara Health Institute, Ifakara, Tanzania.,Pan African Mosquito Control Association, Nairobi, Kenya
| | - Fredros O Okumu
- Environmental Health and Ecological Sciences, Ifakara Health Institute, Ifakara, Tanzania.,Institute of Biodiversity, Animal Health and Comparative Medicine, University of Glasgow, Glasgow, UK.,School of Public Health, Faculty of Health Sciences, University of the Witwatersrand, Johannesburg, South Africa.,School of Life Sciences and Bio Engineering, The Nelson Mandela, African Institution of Science and Technology, Tengeru, Arusha, United Republic of Tanzania
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6
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Autodissemination of pyriproxyfen suppresses stable populations of Anopheles arabiensis under semi-controlled settings. Malar J 2019; 18:166. [PMID: 31072359 PMCID: PMC6507228 DOI: 10.1186/s12936-019-2803-1] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/09/2019] [Accepted: 05/06/2019] [Indexed: 11/10/2022] Open
Abstract
BACKGROUND Autodissemination of pyriproxyfen (PPF), i.e. co-opting adult female mosquitoes to transfer the insect growth regulator, pyriproxyfen (PPF) to their aquatic habitats has been demonstrated for Aedes and Anopheles mosquitoes. This approach, could potentially enable high coverage of aquatic mosquito habitats, including those hard to locate or reach via conventional larviciding. This study demonstrated impacts of autodissemination in crashing a stable and self-sustaining population of the malaria vector, Anopheles arabiensis under semi-field conditions in Tanzania. METHODS Self-propagating populations of An. arabiensis were established inside large semi-field cages. Larvae fed on naturally occurring food in 20 aquatic habitats in two study chambers (9.6 × 9.6 m each), while emerging adults fed on tethered cattle. The mosquito population was monitored using emergence traps and human landing catches, each time returning captured adults into the chambers. Once the population was stable (after 23 filial generations), PPF dissemination devices (i.e. four clay pots each treated with 0.2-0.3 g PPF) were introduced into one of the chambers (treatment) and their impact monitored in parallel with untreated chamber (control). RESULTS Daily adult emergence was similar between control and treatment chambers, with average (± SE) of 14.22 ± 0.70 and 12.62 ± 0.74 mosquitoes/trap, respectively, before treatment. Three months post-treatment, mean number of adult An. arabiensis emerging from the habitats was 5.22 ± 0.42 in control and 0.14 ± 0.04 in treatment chambers. This was equivalent to > 97% suppression in treatment chamber without re-treatment of the clay pots. Similarly, the number of mosquitoes attempting to bite volunteers inside the treatment chamber decreased to zero, 6 months post-exposure (i.e. 100% suppression). In contrast, biting rates in control rose to 53.75 ± 3.07 per volunteer over the same period. CONCLUSION These findings demonstrate effective suppression of stable populations of malaria vectors using a small number of simple autodissemination devices, from which adult mosquitoes propagated pyriproxyfen to contaminate aquatic habitats in the system. This is the first proof that autodissemination can amplify treatment coverage and deplete malaria vector populations. Field trials are necessary to validate these results, and assess impact of autodissemination as a complementary malaria intervention.
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Stevenson JC, Simubali L, Mudenda T, Cardol E, Bernier UR, Vazquez AA, Thuma PE, Norris DE, Perry M, Kline DL, Cohnstaedt LW, Gurman P, D'hers S, Elman NM. Controlled release spatial repellent devices (CRDs) as novel tools against malaria transmission: a semi-field study in Macha, Zambia. Malar J 2018; 17:437. [PMID: 30477502 PMCID: PMC6258499 DOI: 10.1186/s12936-018-2558-0] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/11/2018] [Accepted: 10/30/2018] [Indexed: 11/10/2022] Open
Abstract
BACKGROUND The emergence of mosquitoes that can avoid indoor-deployed interventions, such as treated bed nets and indoor residual spraying, threatens the mainstay of malaria control in Zambia. Furthermore, the requirement for high coverage of these tools poses operational challenges. Spatial repellents are being assessed to supplement these vector control tools, but limitations exist in the residual effect of the repellent and the need for external power or heat for diffusion of the volatiles. METHODS A semi-field evaluation of a novel controlled release spatial repellent device (CRD) was conducted in Macha, Zambia. These devices emanate metofluthrin with no need for external power. Devices were deployed in huts within the semi-field system (SFS). Female Anopheles gambiae sensu stricto released within the SFS were trapped overnight by light traps and collected by aspiration the next morning inside and outside of huts to determine the extent of mosquito repellency and the impact on host-seeking and survival. Experiments studied the impact of number of devices as well as the presence of hut occupants. The study was complemented with numerical methods based on computational fluid dynamics to simulate spatial distribution of metofluthrin. RESULTS Presence of CRDs was associated with significant reductions in indoor counts of mosquitoes, regardless of whether huts were occupied or not. Repellency ranged from 15 to 60% compared to huts with no devices. Reducing the number of devices from 16 to 4 had little impact on repellency. When huts were occupied, indoor mosquito host-seeking was higher in the presence of CRDs, whilst survival was significantly reduced. CONCLUSIONS This study demonstrated that deployment of as few as four CRDs within a hut was associated with reduced indoor mosquito densities. As would be expected, presence of occupants within huts, resulted in greater indoor catches (both with and without devices). The increased indoor mosquito host-seeking and mortality in huts when devices were present may be explained by the excito-repellency activity of metofluthrin. These semi-field experiments provide preliminary data on the utility of CRD spatial repellents to reduce indoor densities of An. gambiae mosquitoes. Studies will further investigate the impact of CRDs on mosquito behaviour as well as epidemiological protective efficacy.
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Affiliation(s)
- Jennifer C Stevenson
- Macha Research Trust, P.O. Box 630166, Choma, Zambia. .,The W. Harry Feinstone Department of Molecular Microbiology and Immunology, The Johns Hopkins Malaria Research Institute, Johns Hopkins Bloomberg School of Public Health, 615 North Wolfe Street, Baltimore, MD, 21205, USA.
| | | | - Twig Mudenda
- Macha Research Trust, P.O. Box 630166, Choma, Zambia
| | - Esther Cardol
- Radboud University Nijmegen, Comeniuslaan 4, 6525 HP, Nijmegen, Netherlands
| | - Ulrich R Bernier
- United States Department of Agriculture-Agricultural Research Service, Center for Medical, Agricultural, and Veterinary Entomology, 1600 SW 23rd Drive, Gainesville, FL, 32608, USA
| | - Agustin Abad Vazquez
- Instituto Tecnológico de Buenos Aires (ITBA), Av. Madero 399, Ciudad Autónoma de Buenos Aires, Buenos Aires, Argentina
| | - Philip E Thuma
- Macha Research Trust, P.O. Box 630166, Choma, Zambia.,The W. Harry Feinstone Department of Molecular Microbiology and Immunology, The Johns Hopkins Malaria Research Institute, Johns Hopkins Bloomberg School of Public Health, 615 North Wolfe Street, Baltimore, MD, 21205, USA
| | - Douglas E Norris
- The W. Harry Feinstone Department of Molecular Microbiology and Immunology, The Johns Hopkins Malaria Research Institute, Johns Hopkins Bloomberg School of Public Health, 615 North Wolfe Street, Baltimore, MD, 21205, USA
| | - Melynda Perry
- Textile Materials Evaluation Team, The US Army Natick Soldier Research and Development Engineering Center (NSRDEC), Natick, MA, USA
| | - Daniel L Kline
- United States Department of Agriculture-Agricultural Research Service, Center for Medical, Agricultural, and Veterinary Entomology, 1600 SW 23rd Drive, Gainesville, FL, 32608, USA
| | - Lee W Cohnstaedt
- United States Department of Agriculture-Agricultural Research Service, The Arthropod-Borne, Animal Diseases Research Unit (ABADRU), Manhattan, KS, USA
| | - Pablo Gurman
- GearJump Technologies, LLC, P.O. Box 1600, Boston, MA, 02446, USA
| | - Sebastian D'hers
- Instituto Tecnológico de Buenos Aires (ITBA), Av. Madero 399, Ciudad Autónoma de Buenos Aires, Buenos Aires, Argentina
| | - Noel M Elman
- GearJump Technologies, LLC, P.O. Box 1600, Boston, MA, 02446, USA.
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Ng'habi K, Viana M, Matthiopoulos J, Lyimo I, Killeen G, Ferguson HM. Mesocosm experiments reveal the impact of mosquito control measures on malaria vector life history and population dynamics. Sci Rep 2018; 8:13949. [PMID: 30224714 PMCID: PMC6141522 DOI: 10.1038/s41598-018-31805-8] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/20/2018] [Accepted: 08/24/2018] [Indexed: 11/29/2022] Open
Abstract
The impact of control measures on mosquito vector fitness and demography is usually estimated from bioassays or indirect variables in the field. Whilst indicative, neither approach is sufficient to quantify the potentially complex response of mosquito populations to combined interventions. Here, large replicated mesocosms were used to measure the population-level response of the malaria vector Anopheles arabiensis to long-lasting insecticidal nets (LLINs) when used in isolation, or combined with insecticidal eave louvers (EL), or treatment of cattle with the endectocide Ivermectin (IM). State-space models (SSM) were fit to these experimental data, revealing that LLIN introduction reduced adult mosquito survival by 91% but allowed population persistence. ELs provided no additional benefit, but IM reduced mosquito fecundity by 59% and nearly eliminated all populations when combined with LLINs. This highlights the value of IM for integrated vector control, and mesocosm population experiments combined with SSM for identifying optimal combinations for vector population elimination.
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Affiliation(s)
- Kija Ng'habi
- Ifakara Health Institute, Environmental Health and Ecological Sciences, Ifakara, United Republic of Tanzania
- School of Health Sciences, University of Dar es Salaam, Dar es Salaam, Tanzania
| | - Mafalda Viana
- Institute of Biodiversity, Animal Health and Comparative Medicine, College of Medical, Veterinary and Life Sciences, University of Glasgow, Glasgow, G12 8QQ, United Kingdom
| | - Jason Matthiopoulos
- Institute of Biodiversity, Animal Health and Comparative Medicine, College of Medical, Veterinary and Life Sciences, University of Glasgow, Glasgow, G12 8QQ, United Kingdom
| | - Issa Lyimo
- Ifakara Health Institute, Environmental Health and Ecological Sciences, Ifakara, United Republic of Tanzania
| | - Gerry Killeen
- Ifakara Health Institute, Environmental Health and Ecological Sciences, Ifakara, United Republic of Tanzania
- Liverpool School of Tropical Medicine, Department of Vector Biology, Liverpool, United Kingdom
| | - Heather M Ferguson
- Institute of Biodiversity, Animal Health and Comparative Medicine, College of Medical, Veterinary and Life Sciences, University of Glasgow, Glasgow, G12 8QQ, United Kingdom.
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9
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Milali MP, Sikulu-Lord MT, Kiware SS, Dowell FE, Povinelli RJ, Corliss GF. Do NIR spectra collected from laboratory-reared mosquitoes differ from those collected from wild mosquitoes? PLoS One 2018; 13:e0198245. [PMID: 29851994 PMCID: PMC5978888 DOI: 10.1371/journal.pone.0198245] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/22/2017] [Accepted: 05/16/2018] [Indexed: 11/18/2022] Open
Abstract
BACKGROUND Near infrared spectroscopy (NIRS) is a high throughput technique that measures absorbance of specific wavelengths of light by biological samples and uses this information to classify the age of lab-reared mosquitoes as younger or older than seven days with an average accuracy greater than 80%. For NIRS to estimate ages of wild mosquitoes, a sample of wild mosquitoes with known age in days would be required to train and test the model. Mark-release-recapture is the most reliable method to produce wild-caught mosquitoes of known age in days. However, it is logistically demanding, time inefficient, subject to low recapture rates, and raises ethical issues due to the release of mosquitoes. Using labels from Detinova dissection results in a mathematical model with poor accuracy. Alternatively, a model trained on spectra from laboratory-reared mosquitoes where age in days is known can be applied to estimate the age of wild mosquitoes, but this would be appropriate only if spectra collected from laboratory-reared and wild mosquitoes are similar. METHODS AND FINDINGS We performed k-means (k = 2) cluster analysis on a mixture of spectra collected from lab-reared and wild Anopheles arabiensis to determine if there is any significant difference between these two groups. While controlling the numbers of mosquitoes included in the model at each age, we found two clusters with no significant difference in distribution of spectra collected from lab-reared and wild mosquitoes (p = 0.25). We repeated the analysis using hierarchical clustering, and similarly, no significant difference was observed (p = 0.13). CONCLUSION We find no difference between spectra collected from laboratory-reared and wild mosquitoes of the same age and species. The results strengthen and support the on-going practice of applying the model trained on spectra collected from laboratory-reared mosquitoes, especially first-generation laboratory-reared mosquitoes.
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Affiliation(s)
- Masabho P. Milali
- Department of Mathematics, Statistics and Computer Science, Marquette University, Wisconsin, United States of America
- Ifakara Health Institute, Environmental Health and Ecological Sciences Thematic Group, Ifakara, Tanzania
| | - Maggy T. Sikulu-Lord
- Queensland Alliance of Agriculture and Food Innovation, The University of Queensland, Brisbane, Australia
| | - Samson S. Kiware
- Department of Mathematics, Statistics and Computer Science, Marquette University, Wisconsin, United States of America
- Ifakara Health Institute, Environmental Health and Ecological Sciences Thematic Group, Ifakara, Tanzania
| | - Floyd E. Dowell
- USDA, Agricultural Research Service, Center for Grain and Animal Health Research, Manhattan, KS, United States of America
| | - Richard J. Povinelli
- Department of Electrical and Computer Engineering, Marquette University, Wisconsin, United States of America
| | - George F. Corliss
- Department of Electrical and Computer Engineering, Marquette University, Wisconsin, United States of America
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Lyimo IN, Kessy ST, Mbina KF, Daraja AA, Mnyone LL. Ivermectin-treated cattle reduces blood digestion, egg production and survival of a free-living population of Anopheles arabiensis under semi-field condition in south-eastern Tanzania. Malar J 2017; 16:239. [PMID: 28587669 PMCID: PMC5461717 DOI: 10.1186/s12936-017-1885-x] [Citation(s) in RCA: 40] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/27/2016] [Accepted: 05/30/2017] [Indexed: 01/26/2023] Open
Abstract
Background Anopheles arabiensis feed on cattle and contributes to residual transmission of malaria in areas with high coverage of long-lasting insecticide-treated nets and indoor residual spraying in East Africa. This study aimed to evaluate the effects of ivermectin-treated cattle as a complementary vector control tool against population of An. arabiensis under the semi-field conditions in south-eastern Tanzania. Methods The free-living population of An. arabiensis was allowed to forage on untreated or ivermectin-treated cattle in alternating nights within the semi-field system in south-eastern Tanzania. Fresh blood fed mosquitoes were collected in the morning using mouth aspirators and assessed for their blood meal digestion, egg production, and survivorship. The residual activity of ivermectin-treated cattle was also determined by exposing mosquitoes to the same treatments after every 2 days until day 21 post-treatments. These experiments were replicated 3 times using different individual cattle. Results Overall, the ivermectin-treated cattle reduced blood meal digestion in the stomach of An. arabiensis, and their subsequent egg production and survival over time. The ivermectin-treated cattle halved blood meal digestion in mosquitoes, but reduced their egg production for up to 15 days. The ivermectin-treated cattle reduced the survival, and median survival times (1–3 days) of An. arabiensis than control cattle. The daily mortality rates of mosquitoes fed on ivermectin-treated cattle increased by five-fold relative to controls in the first week, and it gradually declined up to 21 days after treatment. Conclusion This study demonstrates that long-lasting effects of ivermectin-treated cattle on egg production and survival of An. arabiensis may sustainably suppress their vector density, and reduce residual transmission of malaria. This study suggests that ivermectin-treated non-lactating cattle (i.e. calves, heifers and bulls) could be suitable option for large-scale malaria vector control without limiting consumption of milk and meat by communities in rural settings. Furthermore, simulation models are underway to predict the impact of ivermectin-treated cattle alone, or in combination with LLIN/IRS, the frequency of treatment, and their coverage required to significantly suppress population of An. arabiensis and reduce residual transmission of malaria.
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Affiliation(s)
- Issa N Lyimo
- Environmental Health and Ecological Sciences Department, Ifakara Health Institute, Off Mlabani Passage, P.O.BOX 53, Ifakara, Morogoro, United Republic of Tanzania.
| | - Stella T Kessy
- Environmental Health and Ecological Sciences Department, Ifakara Health Institute, Off Mlabani Passage, P.O.BOX 53, Ifakara, Morogoro, United Republic of Tanzania
| | - Kasian F Mbina
- Environmental Health and Ecological Sciences Department, Ifakara Health Institute, Off Mlabani Passage, P.O.BOX 53, Ifakara, Morogoro, United Republic of Tanzania
| | - Ally A Daraja
- Environmental Health and Ecological Sciences Department, Ifakara Health Institute, Off Mlabani Passage, P.O.BOX 53, Ifakara, Morogoro, United Republic of Tanzania
| | - Ladslaus L Mnyone
- Environmental Health and Ecological Sciences Department, Ifakara Health Institute, Off Mlabani Passage, P.O.BOX 53, Ifakara, Morogoro, United Republic of Tanzania.,Pest Management Centre, Sokoine University of Agriculture, Morogoro, Tanzania.,School of Public Health, University of the Witwatersrand, Parktown, Republic of South Africa
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11
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Milali MP, Sikulu-Lord MT, Govella NJ. Bites before and after bedtime can carry a high risk of human malaria infection. Malar J 2017; 16:91. [PMID: 28241888 PMCID: PMC5329919 DOI: 10.1186/s12936-017-1740-0] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/15/2016] [Accepted: 02/20/2017] [Indexed: 11/10/2022] Open
Abstract
BACKGROUND Understanding biting distribution of potentially infectious (parous) mosquitoes at various hours of the night would be useful in establishing the likely impact of bed nets on malaria transmission. Bed nets are highly effective at preventing biting by older malaria vectors, which occurs when most people are in bed. However, this behaviour is likely to vary across ecological settings and among mosquito populations. METHODS Field experiments were conducted in Minepa village within Kilombero Valley. Two outdoor catching stations located approximately 50 m from each other were established for mosquito collection. On each experimental night, mosquitoes were collected using human landing catch (HLC) by a single adult male at each station from 18:00 to 07:00 h. To compare the distribution of mosquito biting and the composition of their age structure, mosquitoes were sorted and recorded according to the hour they were collected. A sub-sample of Anopheles arabiensis was dissected to determine their parity status. Insectary-reared An. arabiensis within the semi-field system (SFS) with known age were also released in the SFS (10 m × 20 m) and recaptured hourly using HLC to determine the effect of parity on biting distribution. RESULTS Overall, there was no statistical association between the parity status and the biting time of An. arabiensis either in the field or in the SFS (P ≥ 0.05). The wild and insectary-reared An. arabiensis were observed to exhibit different hourly biting patterns. CONCLUSION The study has shown that mosquito biting time phenotype is not influenced by their parity status. These findings imply that the risk of human exposure to potentially infectious bites is equally distributed throughout the night, thus supplementary measures to protect people against bites in evening and morning are desirable.
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Affiliation(s)
- Masabho P Milali
- Ifakara Health Institute, Environmental Health and Ecological Sciences Thematic Group, Coordination Office, PO Box 78373, Kiko Avenue, Mikocheni, Dar es Salaam, United Republic of Tanzania.,Marquette University, Department of Mathematics, Statistics and Computer Sciences, Milwaukee, WI, USA
| | - Maggy T Sikulu-Lord
- Ifakara Health Institute, Environmental Health and Ecological Sciences Thematic Group, Coordination Office, PO Box 78373, Kiko Avenue, Mikocheni, Dar es Salaam, United Republic of Tanzania.,QIMR Berghofer Medical Research Institute, Herston, QLD, 4006, Australia
| | - Nicodem J Govella
- Ifakara Health Institute, Environmental Health and Ecological Sciences Thematic Group, Coordination Office, PO Box 78373, Kiko Avenue, Mikocheni, Dar es Salaam, United Republic of Tanzania.
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12
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Swai JK, Finda MF, Madumla EP, Lingamba GF, Moshi IR, Rafiq MY, Majambere S, Okumu FO. Studies on mosquito biting risk among migratory rice farmers in rural south-eastern Tanzania and development of a portable mosquito-proof hut. Malar J 2016; 15:564. [PMID: 27876050 PMCID: PMC5120485 DOI: 10.1186/s12936-016-1616-8] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/17/2016] [Accepted: 11/15/2016] [Indexed: 11/19/2022] Open
Abstract
Background Subsistence rice farmers in south-eastern Tanzania are often migratory, spending weeks or months tending to crops in distant fields along the river valleys and living in improvised structures known as Shamba huts, not fully protected from mosquitoes. These farmers also experience poor access to organized preventive and curative services due to long distances. Mosquito biting exposure in these rice fields, relative to main village residences was assessed, then a portable mosquito-proof hut was developed and tested for protecting these migratory farmers. Methods Pair-wise mosquito surveys were conducted in four villages in Ulanga district, south-eastern Tanzania in 20 randomly-selected Shamba huts located in the distant rice fields and in 20 matched houses within the main villages, to assess biting densities and Plasmodium infection rates. A portable mosquito-proof hut was designed and tested in semi-field and field settings against Shamba hut replicas, and actual Shamba huts. Also, semi-structured interviews were conducted, timed-participant observations, and focus-group discussions to assess experiences and behaviours of the farmers regarding mosquito-bites and the mosquito-proof huts. Results There were equal numbers of mosquitoes in Shamba huts and main houses [RR (95% CI) 27 (25.1–31.2), and RR (95% CI) 30 (27.5–33.4)], respectively (P > 0.05). Huts having >1 occupant had more mosquitoes than those with just one occupant, regardless of site [RR (95% CI) 1.57 (1.30–1.9), P < 0.05]. Open eaves [RR (95% CI) 1.15 (1.08–1.23), P < 0.05] and absence of window shutters [RR (95% CI) 2.10 (1.91–2.31), P < 0.05] increased catches of malaria vectors. All Anopheles mosquitoes caught were negative for Plasmodium. Common night-time outdoor activities in the fields included cooking, eating, fetching water or firewood, washing dishes, bathing, and storytelling, mostly between 6 and 11 p.m., when mosquitoes were also biting most. The prototype hut provided 100% protection in semi-field and field settings, while blood-fed mosquitoes were recaptured in Shamba huts, even when occupants used permethrin-impregnated bed nets. Conclusion Though equal numbers of mosquitoes were caught between main houses and normal Shamba huts, the higher proportions of blood-fed mosquitoes, reduced access to organized healthcare and reduced effectiveness of LLINs, may increase vulnerability of the itinerant farmers. The portable mosquito-proof hut offered sufficient protection against disease-transmitting mosquitoes. Such huts could be improved to expand protection for migratory farmers and possibly other disenfranchised communities.
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Affiliation(s)
- Johnson K Swai
- Environmental Health and Ecological Sciences Thematic Group, Ifakara Health Institute, Ifkara, Tanzania.
| | - Marceline F Finda
- Environmental Health and Ecological Sciences Thematic Group, Ifakara Health Institute, Ifkara, Tanzania
| | - Edith P Madumla
- Environmental Health and Ecological Sciences Thematic Group, Ifakara Health Institute, Ifkara, Tanzania
| | - Godfrey F Lingamba
- Environmental Health and Ecological Sciences Thematic Group, Ifakara Health Institute, Ifkara, Tanzania
| | - Irene R Moshi
- Environmental Health and Ecological Sciences Thematic Group, Ifakara Health Institute, Ifkara, Tanzania.,School of Public Health, University of the Witwatersrand, Parktown, Johannesburg, Republic of South Africa
| | - Mohamed Y Rafiq
- Environmental Health and Ecological Sciences Thematic Group, Ifakara Health Institute, Ifkara, Tanzania
| | - Silas Majambere
- Environmental Health and Ecological Sciences Thematic Group, Ifakara Health Institute, Ifkara, Tanzania.,Innovative Vector Control Consortium, Liverpool, UK
| | - Fredros O Okumu
- Environmental Health and Ecological Sciences Thematic Group, Ifakara Health Institute, Ifkara, Tanzania.,School of Public Health, University of the Witwatersrand, Parktown, Johannesburg, Republic of South Africa
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13
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Sternberg ED, Ng'habi KR, Lyimo IN, Kessy ST, Farenhorst M, Thomas MB, Knols BGJ, Mnyone LL. Eave tubes for malaria control in Africa: initial development and semi-field evaluations in Tanzania. Malar J 2016; 15:447. [PMID: 27586055 PMCID: PMC5009540 DOI: 10.1186/s12936-016-1499-8] [Citation(s) in RCA: 46] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/18/2016] [Accepted: 08/18/2016] [Indexed: 11/17/2022] Open
Abstract
Background Presented here are a series of preliminary experiments evaluating “eave tubes”—a technology that combines house screening with a novel method of delivering insecticides for control of malaria mosquitoes. Methods Eave tubes were first evaluated with overnight release and recapture of mosquitoes in a screened compartment containing a hut and human sleeper. Recapture numbers were used as a proxy for overnight survival. These trials tested physical characteristics of the eave tubes (height, diameter, angle), and different active ingredients (bendiocarb, LLIN material, fungus). Eave tubes in a hut with closed eaves were also compared to an LLIN protecting a sleeper in a hut with open eaves. Eave tubes were then evaluated in a larger compartment containing a self-replicating mosquito population, vegetation, and multiple houses and cattle sheds. In this “model village”, LLINs were introduced first, followed by eave tubes and associated house modifications. Results Initial testing suggested that tubes placed horizontally and at eave height had the biggest impact on mosquito recapture relative to respective controls. Comparison of active ingredients suggested roughly equivalent effects from bendiocarb, LLIN material, and fungal spores (although speed of kill was slower for fungus). The impact of treated netting on recapture rates ranged from 50 to 70 % reduction relative to controls. In subsequent experiments comparing bendiocarb-treated netting in eave tubes against a standard LLIN, the effect size was smaller but the eave tubes with closed eaves performed at least as well as the LLIN with open eaves. In the model village, introducing LLINs led to an approximate 60 % reduction in larval densities and 85 % reduction in indoor catches of host-seeking mosquitoes relative to pre-intervention values. Installing eave tubes and screening further reduced larval density (93 % relative to pre intervention values) and virtually eliminated indoor host-seeking mosquitoes. When the eave tubes and screening were removed, larval and adult catches recovered to pre-eave tube levels. Conclusions These trials suggest that the “eave tube” package can impact overnight survival of host-seeking mosquitoes and can suppress mosquito populations, even in a complex environment. Further testing is now required to evaluate the robustness of these findings and demonstrate impact under field conditions.
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Affiliation(s)
- Eleanore D Sternberg
- Department of Entomology, Center for Infectious Disease Dynamics, the Pennsylvania State University, University Park, USA.
| | - Kija R Ng'habi
- Environmental Health and Ecological Sciences Thematic Group, Ifakara Health Institute, P.O.BOX 53, Off Mlabani, Ifakara, Tanzania
| | - Issa N Lyimo
- Environmental Health and Ecological Sciences Thematic Group, Ifakara Health Institute, P.O.BOX 53, Off Mlabani, Ifakara, Tanzania
| | - Stella T Kessy
- Environmental Health and Ecological Sciences Thematic Group, Ifakara Health Institute, P.O.BOX 53, Off Mlabani, Ifakara, Tanzania
| | | | - Matthew B Thomas
- Department of Entomology, Center for Infectious Disease Dynamics, the Pennsylvania State University, University Park, USA
| | - Bart G J Knols
- In2Care BV, Marijkeweg 22, 6709 PG, Wageningen, The Netherlands
| | - Ladslaus L Mnyone
- Environmental Health and Ecological Sciences Thematic Group, Ifakara Health Institute, P.O.BOX 53, Off Mlabani, Ifakara, Tanzania
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14
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Achee NL, Youngblood L, Bangs MJ, Lavery JV, James S. Considerations for the use of human participants in vector biology research: a tool for investigators and regulators. Vector Borne Zoonotic Dis 2016; 15:89-102. [PMID: 25700039 PMCID: PMC4340630 DOI: 10.1089/vbz.2014.1628] [Citation(s) in RCA: 38] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/25/2022] Open
Abstract
A thorough search of the existing literature has revealed that there are currently no published recommendations or guidelines for the interpretation of US regulations on the use of human participants in vector biology research (VBR). An informal survey of vector biologists has indicated that issues related to human participation in vector research have been largely debated by academic, national, and local Institutional Review Boards (IRBs) in the countries where the research is being conducted, and that interpretations and subsequent requirements made by these IRBs have varied widely. This document is intended to provide investigators and corresponding scientific and ethical review committee members an introduction to VBR methods involving human participation and the legal and ethical framework in which such studies are conducted with a focus on US Federal Regulations. It is also intended to provide a common perspective for guiding researchers, IRB members, and other interested parties (i.e., public health officials conducting routine entomological surveillance) in the interpretation of human subjects regulations pertaining to VBR.
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Affiliation(s)
- Nicole L Achee
- 1 Department of Biological Sciences, Eck Institute for Global Health , University of Notre Dame, Notre Dame, Indiana
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15
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Achinko D, Thailayil J, Paton D, Mireji PO, Talesa V, Masiga D, Catteruccia F. Swarming and mating activity of Anopheles gambiae mosquitoes in semi-field enclosures. MEDICAL AND VETERINARY ENTOMOLOGY 2016; 30:14-20. [PMID: 26508420 DOI: 10.1111/mve.12143] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/23/2015] [Revised: 06/18/2015] [Accepted: 07/23/2015] [Indexed: 06/05/2023]
Abstract
Anopheles gambiae Giles sensu stricto (Diptera: Culicidae) is the major Afro-tropical vector of malaria. Novel strategies proposed for the elimination and eradication of this mosquito vector are based on the use of genetic approaches, such as the sterile insect technique (SIT). These approaches rely on the ability of released males to mate with wild females, and depend on the application of effective protocols to assess the swarming and mating behaviours of laboratory-reared insects prior to their release. The present study evaluated whether large semi-field enclosures can be utilized to study the ability of males from a laboratory colony to respond to natural environmental stimuli and initiate normal mating behaviour. Laboratory-reared males exhibited spatiotemporally consistent swarming behaviour within the study enclosures. Swarm initiation, peak and termination time closely tracked sunset. Comparable insemination rates were observed in females captured in copula in the semi-field cages relative to females in small laboratory cages. Oviposition rates after blood feeding were also similar to those observed in laboratory settings. The data suggest that outdoor enclosures are suitable for studying swarming and mating in laboratory-bred males in field-like settings, providing an important reference for future studies aimed at assessing the comparative mating ability of strains for SIT and other vector control strategies.
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Affiliation(s)
- D Achinko
- Molecular Biology and Bioinformatics Unit, International Centre of Insect Physiology and Ecology, Nairobi, Kenya
- Department of Biochemistry and Molecular Biology, Egerton University, Njoro, Kenya
| | - J Thailayil
- Department of Life Sciences, Imperial College London, London, U.K
| | - D Paton
- Dipartimento di Medicina Sperimentale e Scienze Biochimiche, Universita degli Studi di Perugia, Perugia, Italy
| | - P O Mireji
- Biotechnology Research Institute, Kenya Agricultural and Livestock Research Organization, Kikuyu, Kenya
- Division of Epidemiology of Microbial Diseases, Yale School of Public Health, New Haven, CT, U.S.A
| | - V Talesa
- Dipartimento di Medicina Sperimentale e Scienze Biochimiche, Universita degli Studi di Perugia, Perugia, Italy
| | - D Masiga
- Molecular Biology and Bioinformatics Unit, International Centre of Insect Physiology and Ecology, Nairobi, Kenya
| | - F Catteruccia
- Department of Life Sciences, Imperial College London, London, U.K
- Dipartimento di Medicina Sperimentale e Scienze Biochimiche, Universita degli Studi di Perugia, Perugia, Italy
- Department of Immunology and Infectious Diseases, Harvard School of Public Health, Boston, MA, U.S.A
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16
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Matowo NS, Koekemoer LL, Moore SJ, Mmbando AS, Mapua SA, Coetzee M, Okumu FO. Combining Synthetic Human Odours and Low-Cost Electrocuting Grids to Attract and Kill Outdoor-Biting Mosquitoes: Field and Semi-Field Evaluation of an Improved Mosquito Landing Box. PLoS One 2016; 11:e0145653. [PMID: 26789733 PMCID: PMC4720432 DOI: 10.1371/journal.pone.0145653] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/26/2015] [Accepted: 12/07/2015] [Indexed: 11/19/2022] Open
Abstract
BACKGROUND On-going malaria transmission is increasingly mediated by outdoor-biting vectors, especially where indoor insecticidal interventions such as long-lasting insecticide treated nets (LLINs) are widespread. Often, the vectors are also physiologically resistant to insecticides, presenting major obstacles for elimination. We tested a combination of electrocuting grids with synthetic odours as an alternative killing mechanism against outdoor-biting mosquitoes. METHODS An odour-baited device, the Mosquito Landing Box (MLB), was improved by fitting it with low-cost electrocuting grids to instantly kill mosquitoes attracted to the odour lure, and automated photo switch to activate attractant-dispensing and mosquito-killing systems between dusk and dawn. MLBs fitted with one, two or three electrocuting grids were compared outdoors in a malaria endemic village in Tanzania, where vectors had lost susceptibility to pyrethroids. MLBs with three grids were also tested in a large semi-field cage (9.6 × 9.6 × 4.5m), to assess effects on biting-densities of laboratory-reared Anopheles arabiensis on volunteers sitting near MLBs. RESULTS Significantly more mosquitoes were killed when MLBs had two or three grids, than one grid in wet and dry seasons (P<0.05). The MLBs were highly efficient against Mansonia species and malaria vector, An. arabiensis. Of all mosquitoes, 99% were non-blood fed, suggesting host-seeking status. In the semi-field, the MLBs reduced mean number of malaria mosquitoes attempting to bite humans fourfold. CONCLUSION The improved odour-baited MLBs effectively kill outdoor-biting malaria vector mosquitoes that are behaviourally and physiologically resistant to insecticidal interventions e.g. LLINs. The MLBs reduce human-biting vector densities even when used close to humans, and are insecticide-free, hence potentially antiresistance. The devices could either be used as surveillance tools or complementary mosquito control interventions to accelerate malaria elimination where outdoor transmission is significant.
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Affiliation(s)
- Nancy S. Matowo
- Environmental and Ecological Sciences Thematic Group, Ifakara Health Institute, Dar es Salaam, Tanzania
- Wits Research Institute for Malaria, School of Pathology, Faculty of Health Sciences, University of the Witwatersrand, Johannesburg, South Africa
| | - Lizette L. Koekemoer
- Wits Research Institute for Malaria, School of Pathology, Faculty of Health Sciences, University of the Witwatersrand, Johannesburg, South Africa
- Centre for Opportunistic, Tropical and Hospital Infections, National Institute for Communicable Diseases, Johannesburg, South Africa
| | - Sarah J. Moore
- Environmental and Ecological Sciences Thematic Group, Ifakara Health Institute, Dar es Salaam, Tanzania
- Swiss Tropical and Public Health Institute, Basel, Switzerland
- University of Basel, Basel, Switzerland
| | - Arnold S. Mmbando
- Environmental and Ecological Sciences Thematic Group, Ifakara Health Institute, Dar es Salaam, Tanzania
| | - Salum A. Mapua
- Environmental and Ecological Sciences Thematic Group, Ifakara Health Institute, Dar es Salaam, Tanzania
| | - Maureen Coetzee
- Wits Research Institute for Malaria, School of Pathology, Faculty of Health Sciences, University of the Witwatersrand, Johannesburg, South Africa
- Centre for Opportunistic, Tropical and Hospital Infections, National Institute for Communicable Diseases, Johannesburg, South Africa
| | - Fredros O. Okumu
- Environmental and Ecological Sciences Thematic Group, Ifakara Health Institute, Dar es Salaam, Tanzania
- School of Public Health, Faculty of Health Sciences, University of the Witwatersrand, Johannesburg, South Africa
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Otienoburu PE, Nikbakhtzadeh MR, Foster WA. Orientation of Anopheles gambiae (Diptera: Culicidae) to Plant-Host Volatiles in a Novel Diffusion-Cage Olfactometer. JOURNAL OF MEDICAL ENTOMOLOGY 2016; 53:237-240. [PMID: 26502752 PMCID: PMC5007598 DOI: 10.1093/jme/tjv162] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/04/2015] [Accepted: 09/28/2015] [Indexed: 06/05/2023]
Abstract
A novel diffusion-cage olfactometer tested the responses of Anopheles gambiae Giles to plant volatiles. Green-leaf volatiles are often released from cut or injured plant tissue and may alter the headspace of plants used in olfactometer assays. The diffusion-cage olfactometer is designed for use with whole, intact plants, hence giving a more realistic behavioral assay. Its simple plastic construction, ease of assembly, and accommodation to whole plants makes it a useful tool for measuring mosquito orientation to plant volatiles within large enclosures. We compared its performance to that of the more commonly used T-tube wind-tunnel olfactometer, by testing the orientation of mosquitoes to volatiles of a few prevalent plants of eastern Africa reportedly utilized by An. gambiae for sugar: Parthenium hysterophorus (Asteraceae), Ricinus communis (Euphorbiaceae), Lantana camara (Verbenaceae), and Senna occidentalis (Fabaceae). Results indicate that the diffusion-cage olfactometer is an effective alternative to conventional wind-tunnel olfactometers, to test mosquito orientation to plant volatiles under seminatural conditions.
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Affiliation(s)
- Philip E Otienoburu
- The Ohio State University, 318W 12th Ave., Columbus, Ohio 43210 (; ; ), Johnson C. Smith University, 100 Beatties Ford Rd., Charlotte, NC 28216, and
| | - Mahmood R Nikbakhtzadeh
- The Ohio State University, 318W 12th Ave., Columbus, Ohio 43210 (; ; ), Department of Molecular & Cellular Biology, University of California Davis, 1 Shields Ave., Davis, CA 95616
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Mamai W, Simard F, Couret D, Ouedraogo GA, Renault D, Dabiré KR, Mouline K. Monitoring Dry Season Persistence of Anopheles gambiae s.l. Populations in a Contained Semi-Field System in Southwestern Burkina Faso, West Africa. JOURNAL OF MEDICAL ENTOMOLOGY 2016; 53:130-138. [PMID: 26576935 DOI: 10.1093/jme/tjv174] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/05/2023]
Abstract
To gain insight into the dry season survival strategies of Anopheles gambiae s.l., a new contained semi-field system was developed and used for the first time in Burkina Faso, West Africa. The system consisted of a screened greenhouse within which the local environment was reproduced, including all ecological requirements for mosquito development cycle completion. The system was seeded with the progenies of female Anopheles gambiae, Anopheles coluzzii, and Anopheles arabiensis collected in the vicinity of the greenhouse during the rainy season. After successful establishment in the semi-field system, mosquito populations were monitored over a 1-yr period by regular surveys of larval and adult specimens. We provided evidence for the persistence of adult mosquitoes throughout the dry season, in the absence of any suitable larval development site. During the hot and dry periods, adult insects were observed in artificial shelters (clay pots, building blocks, and dark corners). The mosquito population rapidly built up with the return of the rainy season in the area, when artificial breeding sites were refilled in the enclosure. However, only An. coluzzii and, later, An. arabiensis were detected in the subsequent rainy season, whereas no An. gambiae specimen was found. Our findings suggest that An. coluzzii and An. arabiensis may be able to aestivate throughout the dry season in Southwestern Burkina Faso, whereas An. gambiae might adopt a different dry-season survival strategy, such as long-distance re-colonization from distant locations. These results may have important implications for malaria control through targeted vector control interventions.
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Mmbando AS, Okumu FO, Mgando JP, Sumaye RD, Matowo NS, Madumla E, Kaindoa E, Kiware SS, Lwetoijera DW. Effects of a new outdoor mosquito control device, the mosquito landing box, on densities and survival of the malaria vector, Anopheles arabiensis, inside controlled semi-field settings. Malar J 2015; 14:494. [PMID: 26645085 PMCID: PMC4673850 DOI: 10.1186/s12936-015-1013-8] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/29/2015] [Accepted: 11/24/2015] [Indexed: 11/10/2022] Open
Abstract
BACKGROUND The significance of malaria transmission occurring outdoors has risen even in areas where indoor interventions such as long-lasting insecticidal nets and indoor residual spraying are common. The actual contamination rates and effectiveness of recently developed outdoor mosquito control device, the mosquito landing box (MLB), on densities and daily survival of host-seeking laboratory Anopheles arabiensis, which readily bites humans outdoors was demonstrated. METHODS Experiments were conducted in large semi-field systems (SFS) with human volunteers inside, to mimic natural ecosystems, and using MLBs baited with natural or synthetic human odours and carbon dioxide. The MLBs were dusted with 10% pyriproxyfen (PPF) or entomopathogenic fungi (Metarhizium anisopliae) spores to mark mosquitoes physically contacting the devices. Each night, 400 laboratory-reared An. arabiensis females were released in one SFS chamber with two MLBs, and another chamber without MLBs (control). Mosquitoes were individually recaptured while attempting to bite volunteers inside SFS or by aspiration from SFS walls. Mosquitoes from chambers with PPF-treated MLBs and respective controls were individually dipped in water-filled cups containing ten conspecific third-instar larvae, whose subsequent development was monitored. Mosquitoes recaptured from chambers with fungi-treated MLBs were observed for fungal hyphal growth on their cadavers. Separately, effects on daily survival were determined by exposing An. arabiensis in chambers having MLBs treated with 5% pirimiphos methyl compared to chambers without MLBs (control), after which the mosquitoes were recaptured and monitored individually until they died. RESULTS Up to 63% (152/240) and 43% (92/210) of mosquitoes recaptured inside treatment chambers were contaminated with pyriproxyfen and M. anisopliae, respectively, compared to 8% (19/240) and 0% (0/164) in controls. The mean number of larvae emerging from cups in which adults from chambers with PPF-treated MLBs were dipped was significantly lower [0.75 (0.50-1.01)], than in controls [28.79 (28.32-29.26)], P < 0.001). Daily survival of mosquitoes exposed to 5% pirimiphos methyl was nearly two-fold lower than controls [hazard ratio (HR) = 1.748 (1.551-1.920), P < 0.001]. CONCLUSION High contamination rates in exposed mosquitoes even in presence of humans, demonstrates potential of MLBs for controlling outdoor-biting malaria vectors, either by reducing their survival or directly killing host-seeking mosquitoes. The MLBs also have potential for dispensing filial infanticides, such as PPF, which mosquitoes can transmit to their aquatic habitats for mosquito population control.
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Affiliation(s)
- Arnold S Mmbando
- Environmental Health and Ecological Sciences Thematic Group, Ifakara Health Institute, PO Box 53, Ifakara, Tanzania.
| | - Fredros O Okumu
- Environmental Health and Ecological Sciences Thematic Group, Ifakara Health Institute, PO Box 53, Ifakara, Tanzania.
- Faculty of Health Sciences, School of Public Health, University of the Witwatersrand, Johannesburg, South Africa.
| | - Joseph P Mgando
- Environmental Health and Ecological Sciences Thematic Group, Ifakara Health Institute, PO Box 53, Ifakara, Tanzania.
| | - Robert D Sumaye
- Environmental Health and Ecological Sciences Thematic Group, Ifakara Health Institute, PO Box 53, Ifakara, Tanzania.
| | - Nancy S Matowo
- Environmental Health and Ecological Sciences Thematic Group, Ifakara Health Institute, PO Box 53, Ifakara, Tanzania.
- Faculty of Health Sciences, School of Pathology, University of the Witwatersrand, Johannesburg, South Africa.
| | - Edith Madumla
- Environmental Health and Ecological Sciences Thematic Group, Ifakara Health Institute, PO Box 53, Ifakara, Tanzania.
| | - Emmanuel Kaindoa
- Environmental Health and Ecological Sciences Thematic Group, Ifakara Health Institute, PO Box 53, Ifakara, Tanzania.
| | - Samson S Kiware
- Environmental Health and Ecological Sciences Thematic Group, Ifakara Health Institute, PO Box 53, Ifakara, Tanzania.
- Department of Mathematics, Statistics and Computer Science, Marquette University, Milwaukee, WI, USA.
| | - Dickson W Lwetoijera
- Environmental Health and Ecological Sciences Thematic Group, Ifakara Health Institute, PO Box 53, Ifakara, Tanzania.
- Vector Biology Department, Liverpool School of Tropical Medicine, Pembroke Place, Liverpool, L3 5QA, UK.
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Ng'habi KR, Lee Y, Knols BGJ, Mwasheshi D, Lanzaro GC, Ferguson HM. Colonization of malaria vectors under semi-field conditions as a strategy for maintaining genetic and phenotypic similarity with wild populations. Malar J 2015; 14:10. [PMID: 25604997 PMCID: PMC4340333 DOI: 10.1186/s12936-014-0523-0] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/29/2014] [Accepted: 12/20/2014] [Indexed: 11/12/2022] Open
Abstract
Background Malaria still accounts for an estimated 207 million cases and 627,000 deaths worldwide each year. One proposed approach to complement existing malaria control methods is the release of genetically-modified (GM) and/or sterile male mosquitoes. As opposed to laboratory colonization, this requires realistic semi field systems to produce males that can compete for females in nature. This study investigated whether the establishment of a colony of the vector Anopheles arabiensis under more natural semi-field conditions can maintain higher levels of genetic diversity than achieved by laboratory colonization using traditional methods. Methods Wild females of the African malaria vector An. arabiensis were collected from a village in southern Tanzania and used to establish new colonies under different conditions at the Ifakara Health Institute. Levels of genetic diversity and inbreeding were monitored in colonies of An. arabiensis that were simultaneously established in small cage colonies in the SFS and in a large semi-field (SFS) cage and compared with that observed in the original founder population. Phenotypic traits that determine their fitness (body size and energetic reserves) were measured at 10th generation and compared to founder wild population. Results In contrast to small cage colonies, the SFS population of An. arabiensis exhibited a higher degree of similarity to the founding field population through time in several ways: (i) the SFS colony maintained a significantly higher level of genetic variation than small cage colonies, (ii) the SFS colony had a lower degree of inbreeding than small cage colonies, and (iii) the mean and range of mosquito body size in the SFS colony was closer to that of the founding wild population than that of small cage colonies. Small cage colonies had significantly lower lipids and higher glycogen abundances than SFS and wild population. Conclusions Colonization of An. arabiensis under semi-field conditions was associated with the retention of a higher degree of genetic diversity, reduced inbreeding and greater phenotypic similarity to the founding wild population than observed in small cage colonies. Thus, mosquitoes from such semi-field populations are expected to provide more realistic representation of mosquito ecology and physiology than those from small cage colonies.
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Affiliation(s)
- Kija R Ng'habi
- Ifakara Health Institute, Environmental Health and Ecological Sciences Thematic Group, Ifakara, Kilombero, Morogoro, United Republic of Tanzania.
| | - Yoosook Lee
- Vector Genetics Laboratory, Department of Pathology, Microbiology and Immunology, School of Veterinary Medicine, University of Calfornia, Davis, USA.
| | - Bart G J Knols
- In2Care BV, Costerweg 5, 6702 AA, Wageningen, The Netherlands.
| | - Dickson Mwasheshi
- Ifakara Health Institute, Environmental Health and Ecological Sciences Thematic Group, Ifakara, Kilombero, Morogoro, United Republic of Tanzania.
| | - Gregory C Lanzaro
- Vector Genetics Laboratory, Department of Pathology, Microbiology and Immunology, School of Veterinary Medicine, University of Calfornia, Davis, USA.
| | - Heather M Ferguson
- Institute of Biodiversity, Animal Health & Comparative Medicine, College of Medical, Veterinary & Life Sciences, University of Glasgow, Glasgow, G12 8QQ, UK.
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Lwetoijera D, Harris C, Kiware S, Dongus S, Devine GJ, McCall PJ, Majambere S. Effective autodissemination of pyriproxyfen to breeding sites by the exophilic malaria vector Anopheles arabiensis in semi-field settings in Tanzania. Malar J 2014; 13:161. [PMID: 24779515 PMCID: PMC4012545 DOI: 10.1186/1475-2875-13-161] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/03/2014] [Accepted: 04/25/2014] [Indexed: 11/10/2022] Open
Abstract
Background Malaria vector control strategies that target adult female mosquitoes are challenged by the emergence of insecticide resistance and behavioural resilience. Conventional larviciding is restricted by high operational costs and inadequate knowledge of mosquito-breeding habitats in rural settings that might be overcome by the juvenile hormone analogue, Pyriproxyfen (PPF). This study assessed the potential for Anopheles arabiensis to pick up and transfer lethal doses of PPF from contamination sites to their breeding habitats (i.e. autodissemination of PPF). Methods A semi-field system (SFS) with four identical separate chambers was used to evaluate PPF-treated clay pots for delivering PPF to resting adult female mosquitoes for subsequent autodissemination to artificial breeding habitats within the chambers. In each chamber, a tethered cow provided blood meals to laboratory-reared, unfed female An. arabiensis released in the SFS. In PPF-treated chambers, clay pot linings were dusted with 0.2 – 0.3 g AI PPF per pot. Pupae were removed from the artificial habitats daily, and emergence rates calculated. Impact of PPF on emergence was determined by comparing treatment with an appropriate control group. Results Mean (95% CI) adult emergence rates were (0.21 ± 0.299) and (0.95 ± 0.39) from PPF-treated and controls respectively (p < 0.0001). Laboratory bioassay of water samples from artificial habitats in these experiments resulted in significantly lower emergence rates in treated chambers (0.16 ± 0.23) compared to controls 0.97 ± 0.05) (p < 0.0001). In experiments where no mosquitoes introduced, there were no significant differences between control and treatment, indicating that transfer of PPF to breeding sites only occurred when mosquitoes were present; i.e. that autodissemination had occurred. Treatment of a single clay pot reduced adult emergence in six habitats to (0.34 ± 0.13) compared to (0.98 ± 0.02) in the controls (p < 0.0001), showing a high level of habitats coverage amplification of the autodissemination event. Conclusion The study provides proof of principle for the autodissemination of PPF to breeding habitats by malaria vectors. These findings highlight the potential for this technique for outdoor control of malaria vectors and call for the testing of this technique in field trials.
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Affiliation(s)
- Dickson Lwetoijera
- Environmental Health and Ecological Sciences Thematic Group, Ifakara Health Institute, P,O, Box 53, Ifakara, Tanzania.
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Okumu FO, Kiware SS, Moore SJ, Killeen GF. Mathematical evaluation of community level impact of combining bed nets and indoor residual spraying upon malaria transmission in areas where the main vectors are Anopheles arabiensis mosquitoes. Parasit Vectors 2013; 6:17. [PMID: 23324456 PMCID: PMC3564902 DOI: 10.1186/1756-3305-6-17] [Citation(s) in RCA: 53] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/15/2012] [Accepted: 01/11/2013] [Indexed: 01/08/2023] Open
Abstract
Background Indoor residual insecticide spraying (IRS) and long-lasting insecticide treated nets (LLINs) are commonly used together even though evidence that such combinations confer greater protection against malaria than either method alone is inconsistent. Methods A deterministic model of mosquito life cycle processes was adapted to allow parameterization with results from experimental hut trials of various combinations of untreated nets or LLINs (Olyset®, PermaNet 2.0®, Icon Life® nets) with IRS (pirimiphos methyl, lambda cyhalothrin, DDT), in a setting where vector populations are dominated by Anopheles arabiensis, so that community level impact upon malaria transmission at high coverage could be predicted. Results Intact untreated nets alone provide equivalent personal protection to all three LLINs. Relative to IRS plus untreated nets, community level protection is slightly higher when Olyset® or PermaNet 2.0® nets are added onto IRS with pirimiphos methyl or lambda cyhalothrin but not DDT, and when Icon Life® nets supplement any of the IRS insecticides. Adding IRS onto any net modestly enhances communal protection when pirimiphos methyl is sprayed, while spraying lambda cyhalothrin enhances protection for untreated nets but not LLINs. Addition of DDT reduces communal protection when added to LLINs. Conclusions Where transmission is mediated primarily by An. arabiensis, adding IRS to high LLIN coverage provides only modest incremental benefit (e.g. when an organophosphate like pirimiphos methyl is used), but can be redundant (e.g. when a pyrethroid like lambda cyhalothin is used) or even regressive (e.g. when DDT is used for the IRS). Relative to IRS plus untreated nets, supplementing IRS with LLINs will only modestly improve community protection. Beyond the physical protection that intact nets provide, additional protection against transmission by An. arabiensis conferred by insecticides will be remarkably small, regardless of whether they are delivered as LLINs or IRS. The insecticidal action of LLINs and IRS probably already approaches their absolute limit of potential impact upon this persistent vector so personal protection of nets should be enhanced by improving the physical integrity and durability. Combining LLINs and non-pyrethroid IRS in residual transmission systems may nevertheless be justified as a means to manage insecticide resistance and prevent potential rebound of not only An. arabiensis, but also more potent, vulnerable and historically important species such as Anopheles gambiae and Anopheles funestus.
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Affiliation(s)
- Fredros O Okumu
- Environmental Health and Ecological Sciences Thematic Group, Ifakara Health Institute, Ifakara, Tanzania.
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Ferguson HM, Maire N, Takken W, Lyimo IN, Briët O, Lindsay SW, Smith TA. Selection of mosquito life-histories: a hidden weapon against malaria? Malar J 2012; 11:106. [PMID: 22471997 PMCID: PMC3364143 DOI: 10.1186/1475-2875-11-106] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/19/2012] [Accepted: 04/03/2012] [Indexed: 11/10/2022] Open
Abstract
Background There has recently been a substantial decline in malaria incidence in much of Africa. While the decline can clearly be linked to increasing coverage of mosquito vector control interventions and effective drug treatment in most settings, the ubiquity of reduction raises the possibility that additional ecological and associated evolutionary changes may be reinforcing the effectiveness of current vector control strategies in previously unanticipated ways. Presentation of hypothesis Here it is hypothesized that the increasing coverage of insecticide-treated bed nets and other vector control methods may be driving selection for a shift in mosquito life history that reduces their ability to transmit malaria parasites. Specifically it is hypothesized that by substantially increasing the extrinsic rate of mortality experienced in vector populations, these interventions are creating a fitness incentive for mosquitoes to re-allocate their resources towards greater short-term reproduction at the expense of longer-term survival. As malaria transmission is fundamentally dependent on mosquito survival, a life history shift in this direction would greatly benefit control. Testing the hypothesis At present, direct evaluation of this hypothesis within natural vector populations presents several logistical and methodological challenges. In the meantime, many insights can be gained from research previously conducted on wild Drosophila populations. Long-term selection experiments on these organisms suggest that increasing extrinsic mortality by a magnitude similar to that anticipated from the up-scaling of vector control measures generated an increase in their intrinsic mortality rate. Although this increase was small, a change of similar magnitude in Anopheles vector populations would be predicted to reduce malaria transmission by 80%. Implications of hypothesis The hypothesis presented here provides a reminder that evolutionary processes induced by interventions against disease vectors may not always act to neutralize intervention effectiveness. In the search for new intervention strategies, consideration should be given to both the potential disadvantages and advantages of evolutionary processes resulting from their implementation, and attempts made to exploit those with greatest potential to enhance control.
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Affiliation(s)
- Heather M Ferguson
- Boyd Orr Centre for Population and Ecosystem Health, University of Glasgow, Glasgow, UK.
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