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Atekem K, Nwane P, Nditanchou R, Jeyam A, Wilhelm A, Selby R, Hamill L, Schmidt E, Dixon R, Boakye D. Comparison of standard and modified human landing catching techniques for blackfly collection. Int Health 2024; 16:351-356. [PMID: 37624092 PMCID: PMC11062189 DOI: 10.1093/inthealth/ihad066] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/05/2023] [Revised: 06/18/2023] [Accepted: 07/26/2023] [Indexed: 08/26/2023] Open
Abstract
BACKGROUND Human landing catches (HLCs) are required to collect blackflies for entomological evaluation to verify onchocerciasis elimination. However, there are ethical concerns regarding exposure of vector collectors to infectious blackflies and safer alternative methods are needed. This study evaluated a modified HLC technique where collectors wore coloured trousers (blue, black or blue-black), protecting them from bites during fly collection, and their performance was compared with the standard. METHODS The study was conducted in Makouopsap, Cameroon, in the Massangam health district for 4 months. Four collector pairs-one 'standard' (bare-legged) and three modified-were placed 50 m apart along known breeding sites on the Mbam and Nja Rivers. Collections were performed from 07:00 to 17:00 h, 4 d/month. Hourly rates of flies caught were analysed using a negative binomial generalised linear model to explore associations between flies caught and collection techniques and seasons. RESULTS Overall, 17 246 blackflies were caught. There was no significant statistical difference in the number of blackflies and parous flies caught between black trousers and the standard. Thus there is a strong indication that wearing black trousers is a viable non-inferior alternative to the standard HLC. CONCLUSIONS Further studies are needed to confirm generalisability in different ecozones and transmission environments and among different blackfly species.
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Affiliation(s)
- Kareen Atekem
- Department of Entomology, Center for Infectious Disease Dynamics, Pennsylvania State University, University Park, PA, USA
- Sightsavers – Yaoundé, Cameroon; Haywards Heath, UK
| | - Philippe Nwane
- Centre for Research on Filariasis and Other Tropical Diseases, Yaoundé, Cameroon
- University of Yaoundé I, Cameroon
| | | | - Anita Jeyam
- Sightsavers – Yaoundé, Cameroon; Haywards Heath, UK
| | - Aude Wilhelm
- Sightsavers – Yaoundé, Cameroon; Haywards Heath, UK
| | | | | | | | - Ruth Dixon
- Sightsavers – Yaoundé, Cameroon; Haywards Heath, UK
| | - Daniel Boakye
- Parasitology Department, Noguchi Memorial Institute for Medical Research, University of Ghana, Legon, Accra
- End Fund, New York, NY, USA
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Valkiūnas G, Iezhova TA. Insights into the Biology of Leucocytozoon Species (Haemosporida, Leucocytozoidae): Why Is There Slow Research Progress on Agents of Leucocytozoonosis? Microorganisms 2023; 11:1251. [PMID: 37317225 DOI: 10.3390/microorganisms11051251] [Citation(s) in RCA: 7] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/21/2023] [Revised: 05/04/2023] [Accepted: 05/05/2023] [Indexed: 06/16/2023] Open
Abstract
Blood parasites of the genus Leucocytozoon (Leucocytozoidae) only inhabit birds and represent a readily distinct evolutionary branch of the haemosporidians (Haemosporida, Apicomplexa). Some species cause pathology and even severe leucocytozoonosis in avian hosts, including poultry. The diversity of Leucocytozoon pathogens is remarkable, with over 1400 genetic lineages detected, most of which, however, have not been identified to the species level. At most, approximately 45 morphologically distinct species of Leucocytozoon have been described, but only a few have associated molecular data. This is unfortunate because basic information about named and morphologically recognized Leucocytozoon species is essential for a better understanding of phylogenetically closely related leucocytozoids that are known only by DNA sequence. Despite much research on haemosporidian parasites during the past 30 years, there has not been much progress in taxonomy, vectors, patterns of transmission, pathogenicity, and other aspects of the biology of these cosmopolitan bird pathogens. This study reviewed the available basic information on avian Leucocytozoon species, with particular attention to some obstacles that prevent progress to better understanding the biology of leucocytozoids. Major gaps in current Leucocytozoon species research are discussed, and possible approaches are suggested to resolve some issues that have limited practical parasitological studies of these pathogens.
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Koala L, Tirados I, Nikiema AS, Thomsen E, McCall PJ, Dabire RK. Prospects for developing efficient targets for the xenomonitoring and control of Simulium damnosum s.l., the major vectors of onchocerciasis in Africa. MEDICAL AND VETERINARY ENTOMOLOGY 2022; 36:235-246. [PMID: 35866620 PMCID: PMC9543835 DOI: 10.1111/mve.12598] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 02/28/2022] [Accepted: 06/27/2022] [Indexed: 06/15/2023]
Abstract
Despite the ethical issues concerning the continued use of Human Landing Catches (HLC) to monitor the Simulium damnosum complex for epidemiological monitoring of onchocericasis, few attempts to develop alternatives have been reported. In studies on a wild population of S. damnosum in Burkina Faso, we tested visual targets (different sizes and shapes) and olfactory stimuli (CO2 , and POCA and BG-lure® odour blends) for their ability to attract and collect host seeking blackflies. At each trap, blackflies were caught with appropriately sized electrocuting grids and results from Latin square design tests were compared. Throughout, HLCs captured more blackflies than the targets. Of the traps tested, small targets (0.0625 and 0.5 m2 ) were the most efficient visual lure in terms of the number of S. damnosum captured per unit area 1.7-5× more than larger targets. Overall, results suggested that sticky black targets of horizontal rectangular shape (0.125-0.5 m2 ) and baited with a POCA and/or CO2 mixture could provide a cheap practical field alternative to HLC for onchocerciasis xenomonitoring, subject to confirmation that the design has no inherent bias for certain members of the S. damnosum species complex.
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Affiliation(s)
- Lassane Koala
- Departement Biomédicale et Santé PubliqueCentre National de Recherche Scientifique et Technologique (CNRST)/Institut de Recherche en Sciences de la Santé (IRSS)/Direction Régionale de l'OuestBobo DioulassoBurkina Faso
| | - Inaki Tirados
- Vector Biology DepartmentLiverpool School of Tropical MedicineLiverpoolUK
| | - Achille S. Nikiema
- Departement Biomédicale et Santé PubliqueCentre National de Recherche Scientifique et Technologique (CNRST)/Institut de Recherche en Sciences de la Santé (IRSS)/Direction Régionale de l'OuestBobo DioulassoBurkina Faso
| | - Edward Thomsen
- Vector Biology DepartmentLiverpool School of Tropical MedicineLiverpoolUK
| | - Philip J. McCall
- Vector Biology DepartmentLiverpool School of Tropical MedicineLiverpoolUK
| | - Roch K. Dabire
- Departement Biomédicale et Santé PubliqueCentre National de Recherche Scientifique et Technologique (CNRST)/Institut de Recherche en Sciences de la Santé (IRSS)/Direction Régionale de l'OuestBobo DioulassoBurkina Faso
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Willen L, Milton P, Hamley JID, Walker M, Osei-Atweneboana MY, Volf P, Basáñez MG, Courtenay O. Demographic patterns of human antibody levels to Simulium damnosum s.l. saliva in onchocerciasis-endemic areas: An indicator of exposure to vector bites. PLoS Negl Trop Dis 2022; 16:e0010108. [PMID: 35020729 PMCID: PMC8789114 DOI: 10.1371/journal.pntd.0010108] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/30/2021] [Revised: 01/25/2022] [Accepted: 12/17/2021] [Indexed: 11/18/2022] Open
Abstract
BACKGROUND In onchocerciasis endemic areas in Africa, heterogenous biting rates by blackfly vectors on humans are assumed to partially explain age- and sex-dependent infection patterns with Onchocerca volvulus. To underpin these assumptions and further improve predictions made by onchocerciasis transmission models, demographic patterns in antibody responses to salivary antigens of Simulium damnosum s.l. are evaluated as a measure of blackfly exposure. METHODOLOGY/PRINCIPAL FINDINGS Recently developed IgG and IgM anti-saliva immunoassays for S. damnosum s.l. were applied to blood samples collected from residents in four onchocerciasis endemic villages in Ghana. Demographic patterns in antibody levels according to village, sex and age were explored by fitting generalized linear models. Antibody levels varied between villages but showed consistent patterns with age and sex. Both IgG and IgM responses declined with increasing age. IgG responses were generally lower in males than in females and exhibited a steeper decline in adult males than in adult females. No sex-specific difference was observed in IgM responses. CONCLUSIONS/SIGNIFICANCE The decline in age-specific antibody patterns suggested development of immunotolerance or desensitization to blackfly saliva antigen in response to persistent exposure. The variation between sexes, and between adults and youngsters may reflect differences in behaviour influencing cumulative exposure. These measures of antibody acquisition and decay could be incorporated into onchocerciasis transmission models towards informing onchocerciasis control, elimination, and surveillance.
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Affiliation(s)
- Laura Willen
- Department of Parasitology, Faculty of Science, Charles University, Prague, Czech Republic
- Centre for the Evaluation of Vaccinations, Vaccine and Infectious Disease Institute, University of Antwerp, Wilrijk, Belgium
- * E-mail: (LW); (OC)
| | - Philip Milton
- MRC Centre for Global Infectious Disease Analysis and London Centre for Neglected Tropical Disease Research, Department of Infectious Disease Epidemiology, School of Public Health, Imperial College London, London, United Kingdom
| | - Jonathan I. D. Hamley
- MRC Centre for Global Infectious Disease Analysis and London Centre for Neglected Tropical Disease Research, Department of Infectious Disease Epidemiology, School of Public Health, Imperial College London, London, United Kingdom
| | - Martin Walker
- London Centre for Neglected Tropical Disease Research and Department of Pathobiology and Population Sciences, Royal Veterinary College, Hatfield, United Kingdom
| | | | - Petr Volf
- Department of Parasitology, Faculty of Science, Charles University, Prague, Czech Republic
| | - Maria-Gloria Basáñez
- MRC Centre for Global Infectious Disease Analysis and London Centre for Neglected Tropical Disease Research, Department of Infectious Disease Epidemiology, School of Public Health, Imperial College London, London, United Kingdom
| | - Orin Courtenay
- Zeeman Institute for Systems Biology & Infectious Disease Epidemiology Research and School of Life Sciences, University of Warwick, Coventry, United Kingdom
- * E-mail: (LW); (OC)
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Evaluating the diagnostic test accuracy of molecular xenomonitoring methods for characterising the community burden of Onchocerciasis. PLoS Negl Trop Dis 2021; 15:e0009812. [PMID: 34637436 PMCID: PMC8509893 DOI: 10.1371/journal.pntd.0009812] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/05/2021] [Accepted: 09/13/2021] [Indexed: 11/19/2022] Open
Abstract
Background Molecular xenomonitoring (MX), the detection of parasite nucleic acid in the vector population, is recommended for onchocerciasis surveillance in elimination settings. However, the sensitivity of MX for detecting onchocerciasis-positive communities has not previously been evaluated. MX may have additional applications for control programmes but its utility is restricted by a limited understanding of the relationship between MX results and human prevalence. Methods We conducted a systematic review of studies reporting the prevalence of Onchocerca volvulus DNA in wild-caught Simulium spp. flies (MX rate) and corresponding prevalence of microfilaria (mf) in humans. We evaluated the sensitivity of MX for detecting onchocerciasis-positive communities and describe the characteristics of studies with reduced sensitivity. We conducted a linear regression to evaluate the relationship between mf prevalence and MX rate. Results We identified 15 relevant studies, with 13 studies comprising 34 study communities included in the quantitative analyses. Most communities were at advanced stages towards elimination and had no or extremely low human prevalence. MX detected positive flies in every study area with >1% mf prevalence, with the exception of one study conducted in the Venezuelan Amazonian focus. We identified a significant relationship between the two measurements, with mf prevalence accounting for half of the variation in MX rate (R2 0.50, p<0.001). Conclusion MX is sensitive to communities with ongoing onchocerciasis transmission. It has potential to predict human mf prevalence, but further data is required to understand this relationship, particularly from MX surveys conducted earlier in control programmes before transmission has been interrupted. Traditional surveillance of onchocerciasis relies on the detection of Onchocerca volvulus microfilaria or antibodies in human skin or blood samples. Molecular xenomonitoring, the detection of parasite nucleic acid in vector insects, provides a non-invasive alternative. The sensitivity of molecular xenomonitoring to areas where infected people are found has not previously been evaluated and the extent to which xenomonitoring can be used to predict human prevalence is unknown. We searched for previous studies that reported the infection rates in humans and detection rates in black flies, finding 15 studies comprising 34 study communities that contributed to our analyses. Studies were conducted across Africa and the Americas, mostly in areas of very low prevalence. The findings show molecular xenomonitoring was sensitive to areas with greater than 1% microfilaria prevalence in the human population, indicating that molecular xenomonitoring is effective at detecting ongoing transmission. We further found evidence that infection rates in humans and detection rates in flies were related, providing scope for the use of xenomonitoring to predict human prevalence. With further research to better understand this relationship, control programmes may be able to use xenomonitoring for other purposes such as identifying areas that require intervention and monitoring the impact of treatments.
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Taylor ME, Auten CR, Foster T, Ebbs E, Hofkin BV. Canine ocular onchocerciasis in New Mexico: Risk factors for disease. Vet Ophthalmol 2021; 24:288-294. [PMID: 33834584 DOI: 10.1111/vop.12889] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/29/2020] [Revised: 02/23/2021] [Accepted: 03/28/2021] [Indexed: 11/26/2022]
Abstract
OBJECTIVE To determine whether dogs are at variable risk of developing canine ocular onchocerciasis based on coat color or size, factors that may influence feeding behavior of the putative vectors of Onchocerca lupi¸ the filarial nematode parasite causing this disease. ANIMALS STUDIED One hundred twenty-five client-owned dogs diagnosed with confirmed or suspected onchocerciasis. 1255 dogs without signs of this disease were utilized for comparison. PROCEDURES Dogs lacking signs of canine onchocerciasis were assessed for coat color and weight. Proportions of dogs with these characteristics were used to predict signalment in a group of dogs with this disease, if the investigated characteristics were unrelated to disease risk. Predicted values were compared statistically with observed values in the diseased dog population. Black fly color preference was assessed utilizing black, brown, and white traps and statistically assessing any differences in trapping based on trap color. RESULTS Results suggest that large, black dogs are more likely to develop canine ocular onchocerciasis than was predicted by chance alone (p = 0.012). Results for smaller dogs with other coat colors were not significant. An increased risk for black dogs was supported by trapping data, as black flies were trapped significantly more often in black traps (p < 0.001). CONCLUSION While factors other than size and color probably also influence the likelihood of O. lupi infection and disease development, our results may assist clinicians in their diagnosis of canine ocular onchocerciasis and provide them with a tool to help educate their clients as to their dogs' risk of developing this disease.
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Affiliation(s)
- Melise E Taylor
- Environmental Health Department, City of Albuquerque, Albuquerque, NM, USA
| | | | - Tania Foster
- VCA Veterinary Care Animal Hospital and Referral Center, Albuquerque, NM, USA
| | - Erika Ebbs
- The Department of Biology, Purchase College, The State University of New York, Purchase, NY, USA
| | - Bruce V Hofkin
- Department of Biology, University of New Mexico, Albuquerque, NM, USA
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Romão Ribeiro da Silva T, Crainey JL, Costa Pessoa FA, Vinícius Serra dos Santos Y, Pereira-Silva JW, Ferreira de Oliveira Leles L, Vicente AC, Bessa Luz SL. Blackflies in the ointment: O. volvulus vector biting can be significantly reduced by the skin-application of mineral oil during human landing catches. PLoS Negl Trop Dis 2019; 13:e0007234. [PMID: 30933979 PMCID: PMC6459560 DOI: 10.1371/journal.pntd.0007234] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/01/2018] [Revised: 04/11/2019] [Accepted: 02/11/2019] [Indexed: 12/02/2022] Open
Abstract
Background Standard human landing catches (sHLCs) have historically been a key component of Onchocerca volvulus transmission monitoring, but expose health-workers to potentially hazardous vector bites. Novel human-bait-free trapping methods have been developed, but do not always work where they are needed and may not generate O. volvulus surveillance data that is directly comparable with historic data. Methodology Simuliid sHLCs and mineral-oil protected HLCs (mopHLCs) were performed in a rural village of Amazonas state, Brazil. A four-hour direct comparisons of sHLCs and mopHLCs was carried-out using six vector collectors, each of whom used one leg for a sHLC and one for a mopHLC. Two-person collection teams then exclusively performed either mopHLCs or sHLCs for a further set of 12 four-hour collections. Following the completion of all collections, simuliid-bite mark estimates were made from legs used exclusively in sHLCs and legs used exclusively in mopHLCs. Principal findings All of the 1669 captured simuliids were identified as the O. volvulus vector Simulium oyapockense. Overall, mopHLC simuliids captured per hour (S/H) rates were lower than those obtained with sHLC trapping (15.5 S/H versus 20 S/H). Direct comparisons of simuliid capture rates found that vector-collectors captured simuliids significantly more efficiently ( x¯: 20.5 S/H) with mopHLC trapping than with sHLC trapping ( x¯: 16.4 S/H): P-value = 0.002. MopHLCs performed in isolation were, however, observed to capture vectors less efficiently ( x¯: 13.4 S/H) than sHLCs performed under similar conditions ( x¯: 19.98 S/H). All six vector collectors had significantly higher simuliid capture per counted bite mark (SC/CBM) rates using mopHLCs than they were observe to have using sHLCs ( x¯: 21 SC/CBM versus x¯: 1 SC/CBM; p-value = 0.03125). Conclusions Vector collectors captured significantly more simuliids per counted bite mark with mopHLCs than with sHLCs. Further investigations into the utility of mopHLCs for onchocerciasis xenomonitoring and beyond are merited. Standard human landing catches (sHLCs) have historically been used to obtain key Onchocerca volvulus transmission data that has helped with the design and monitoring of the WHO´s onchocerciasis control programmes. To avoid the health risks associated with sHLCs, alternative human-bait-free blackfly trapping methods, most of which immobilize and suffocate blackflies with a viscous liquid substance, have been developed. Questions, however, have be raised as to whether these human-bait-free trapping methods generate O. volvulus transmission data that is directly comparable with historic sHLC data. In this study, we have combined sHLCs with mineral oil vector capture and shown that the skin application of mineral oil can significantly reduce (and possibly eliminate) simuliid biting during HLCs. In direct comparisons, we have shown that mineral oil protected human landing catches (mopHLCs) were more efficient at capturing the O. volvulus vector Simulium oyapockense than sHLCs. We have also shown that mopHLCs, performed in isolation of vector collectors using exposed skin for their trapping, are less efficient than HLCs, but still function well. We believe that mopHLCs represent a promising alternative to sHLCs that merit further testing for their utility in the epidemiological monitoring of onchocerciasis and, indeed, other vector borne diseases as well.
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Affiliation(s)
- Túllio Romão Ribeiro da Silva
- Instituto Leônidas e Maria Deane/ILMD/FIOCRUZ, Laboratório de Ecologia de Doenças Transmissíveis na Amazônia, 476 Rua Teresina, Adrianópolis, Manaus, Amazonas, Brazil
- Programa de Pós-graduação Stricto sensu em Biologia Parasitária do Instituto Oswaldo Cruz (IOC/Fiocruz), Rio de Janeiro, Brazil
| | - James Lee Crainey
- Instituto Leônidas e Maria Deane/ILMD/FIOCRUZ, Laboratório de Ecologia de Doenças Transmissíveis na Amazônia, 476 Rua Teresina, Adrianópolis, Manaus, Amazonas, Brazil
- * E-mail:
| | - Felipe Arley Costa Pessoa
- Instituto Leônidas e Maria Deane/ILMD/FIOCRUZ, Laboratório de Ecologia de Doenças Transmissíveis na Amazônia, 476 Rua Teresina, Adrianópolis, Manaus, Amazonas, Brazil
| | - Yago Vinícius Serra dos Santos
- Instituto Leônidas e Maria Deane/ILMD/FIOCRUZ, Laboratório de Ecologia de Doenças Transmissíveis na Amazônia, 476 Rua Teresina, Adrianópolis, Manaus, Amazonas, Brazil
- Programa de Pós-Graduação em Biologia da Interação Patógeno Hospedeiro (PPGBIO-Interação), Manaus, Amazonas, Brazil
| | - Jordam William Pereira-Silva
- Instituto Leônidas e Maria Deane/ILMD/FIOCRUZ, Laboratório de Ecologia de Doenças Transmissíveis na Amazônia, 476 Rua Teresina, Adrianópolis, Manaus, Amazonas, Brazil
- Programa de Pós-Graduação Stricto Sensu em Condições de Vida e Situações de Saúde na Amazônia (PPGVIDA), Manaus, Amazonas, Brazil
| | - Lorena Ferreira de Oliveira Leles
- Instituto Leônidas e Maria Deane/ILMD/FIOCRUZ, Laboratório de Ecologia de Doenças Transmissíveis na Amazônia, 476 Rua Teresina, Adrianópolis, Manaus, Amazonas, Brazil
- Programa de Pós-Graduação em Biologia da Interação Patógeno Hospedeiro (PPGBIO-Interação), Manaus, Amazonas, Brazil
| | - Ana Carolina Vicente
- Instituto Oswaldo Cruz/IOC/FIOCRUZ, Laboratório de Genética Molecular de Microrganismos, Rio de Janeiro, RJ, Brazil
| | - Sérgio Luiz Bessa Luz
- Instituto Leônidas e Maria Deane/ILMD/FIOCRUZ, Laboratório de Ecologia de Doenças Transmissíveis na Amazônia, 476 Rua Teresina, Adrianópolis, Manaus, Amazonas, Brazil
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