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Ayisi F, Sedou N, Dieunang SK, Yaya F, Tchago EF, Ndellejong CE, Biholong B, Boakye DA. A cross-sectional study of Simulium damnosum sensu lato breeding sites and species distribution in Sudan savanna, mixed savanna-forest and rainforest regions in Cameroon. Parasit Vectors 2022; 15:382. [PMID: 36271434 PMCID: PMC9587638 DOI: 10.1186/s13071-022-05462-w] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/23/2022] [Accepted: 08/31/2022] [Indexed: 12/02/2022] Open
Abstract
Background The presence of breeding sites and distribution of species of Simulium damnosum sensu lato are critical in understanding the epidemiology of onchocerciasis and evaluating the impact of elimination interventions. Reports on breeding sites and species distribution of members of S. damnosum s.l. in Cameroon are scarce and the few ones available date back to more than three decades. The aim of this study is to provide information on S. damnosum breeding sites across the rainy (RS) and dry (DS) seasons and the species composition in three different regions in Cameroon: Southwest (SW), Northwest (NW) and North (N). Methods A cross-sectional two-season study was carried out in three regions with different ecological characteristics (SW—rainforest; NW—mixed forest–Guinea savanna; N—Sudan savanna). Pre-control onchocerciasis endemicity, relief maps and historical entomological information were used to identify potential rivers for purposive sampling. Sampled larvae were fixed in Carnoy’s solution and sorted, and S. damnosum s.l. larvae were stored until identification by cytotaxonomy. Geographical coordinates of potential breeding sites were recorded to produce maps using ArcGIS, while Chi-square tests in SPSS were used to test for any differences between black fly seasonal breeding rates. Results A total of 237 potential breeding sites were sampled (RS = 81; DS = 156) and 72 were found positive for S. damnosum s.l. The SW had the most positive sites [67 (RS = 24; DS = 43)], with a significant difference in the rate of breeding between the seasons (P < 0.05). Among 68 sites visited in both seasons, 16 (23.5%) were positive in one of the two seasons with more sites positive in DS(11) than RS(05), 14 (20.6%) and 38 (55.9%) respectively positive and negative in both seasons. Simulium damnosum sensu stricto and S. sirbanum were the main species in the N, while S. squamosum and S. mengense were the predominant species in the NW and SW. Simulium soubrense and S. yahense were uniquely recorded in the SW. Conclusions A comprehensive mapping of breeding sites requires rainy and dry seasons sampling. This study demonstrates that a breeding site survey of S. damnosum s.l. is achievable in forest as well as savanna zones. Not all potential breeding sites are actual breeding sites. Observation of S. soubrense in the SW indicates changes in species composition over time and could affect onchocerciasis epidemiology in this area. Graphical abstract ![]()
Supplementary Information The online version contains supplementary material available at 10.1186/s13071-022-05462-w.
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Affiliation(s)
- Franklin Ayisi
- National Onchocerciasis Control Programme, Ministry of Public Health, Yaoundé, Cameroon.,African Regional Postgraduate Programme in Insect Science (ARPPIS), University of Ghana, Legon-Accra, Ghana
| | | | | | - Florent Yaya
- National Onchocerciasis Control Programme, Ministry of Public Health, Yaoundé, Cameroon
| | | | | | - Benjamin Biholong
- National Onchocerciasis Control Programme, Ministry of Public Health, Yaoundé, Cameroon
| | - Daniel Adjei Boakye
- Noguchi Memorial Institute for Medical Research (NMIMR), University of Ghana, Legon-Accra, Ghana. .,The End Fund, New York, NY, USA.
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Hendy A, Krit M, Pfarr K, Laemmer C, De Witte J, Nwane P, Kamgno J, Nana-Djeunga HC, Boussinesq M, Dujardin JC, Post R, Colebunders R, O'Neill S, Enyong P, Njamnshi AK. Onchocerca volvulus transmission in the Mbam valley of Cameroon following 16 years of annual community-directed treatment with ivermectin, and the description of a new cytotype of Simulium squamosum. Parasit Vectors 2021; 14:563. [PMID: 34727965 PMCID: PMC8561987 DOI: 10.1186/s13071-021-05072-y] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/27/2021] [Accepted: 10/16/2021] [Indexed: 11/10/2022] Open
Abstract
BACKGROUND The onchocerciasis focus surrounding the lower Mbam and Sanaga rivers, where Onchocerca volvulus is transmitted by Simulium damnosum s.l. (Diptera: Simuliidae), was historically the largest in the southern regions of Cameroon. Annual community-directed treatment with ivermectin (CDTI) has been taking place since 2000, but recent studies have shown that new infections are occurring in children. We aimed to investigate blackfly biting and O. volvulus transmission rates along the lower Mbam river 16 years after the formal onset of annual CDTI. METHODS Black flies were collected for three consecutive days each month between July 2016 and June 2017 at two riverside villages and two inland sites situated 4.9 km and 7.9 km from the riverside. Specimens collected at each site were dissected on one of the three collection days each month to estimate parity rates and O. volvulus infection rates, while the remaining samples were preserved for pool screening. RESULTS In total, 93,573 S. damnosum s.l. black flies were recorded biting humans and 9281 were dissected. Annual biting rates of up to 606,370 were estimated at the riverside, decreasing to 20,540 at 7.9 km, while, based on dissections, annual transmission potentials of up to 4488 were estimated at the riverside, decreasing to 102 and 0 at 4.9 km and 7.9 km, respectively. However, pool screening showed evidence of infection in black flies at the furthest distance from the river. Results of both methods demonstrated the percentage of infective flies to be relatively low (0.10-0.36%), but above the WHO threshold for interruption of transmission. In addition, a small number of larvae collected during the dry season revealed the presence of Simulium squamosum E. This is the first time S. squamosum E has been found east of Lake Volta in Ghana, but our material was chromosomally distinctive, and we call it S. squamosum E2. CONCLUSIONS Relatively low O. volvulus infection rates appear to be offset by extremely high densities of biting black flies which are sustaining transmission along the banks of the lower Mbam river.
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Affiliation(s)
- Adam Hendy
- Department of Biomedical Sciences, Institute of Tropical Medicine, Antwerp, Belgium. .,Department of Pathology, University of Texas Medical Branch, Galveston, TX, USA.
| | - Meryam Krit
- Department of Biomedical Sciences, Institute of Tropical Medicine, Antwerp, Belgium
| | - Kenneth Pfarr
- Institute for Medical Microbiology, Immunology and Parasitology, University Hospital Bonn, Bonn, Germany.,German Center for Infection Research, Partner Site Bonn-Cologne, Cologne, Germany
| | - Christine Laemmer
- Institute for Medical Microbiology, Immunology and Parasitology, University Hospital Bonn, Bonn, Germany.,German Center for Infection Research, Partner Site Bonn-Cologne, Cologne, Germany
| | - Jacobus De Witte
- Department of Biomedical Sciences, Institute of Tropical Medicine, Antwerp, Belgium
| | - Philippe Nwane
- Centre for Research on Filariasis and Other Tropical Diseases (CRFilMT), Yaoundé, Cameroon
| | - Joseph Kamgno
- Centre for Research on Filariasis and Other Tropical Diseases (CRFilMT), Yaoundé, Cameroon.,Department of Public Health, Faculty of Medicine and Biomedical Sciences, The University of Yaoundé I, Yaoundé, Cameroon
| | - Hugues C Nana-Djeunga
- Centre for Research on Filariasis and Other Tropical Diseases (CRFilMT), Yaoundé, Cameroon
| | - Michel Boussinesq
- Institut de Recherche pour le Développement (IRD), Montpellier, France
| | - Jean-Claude Dujardin
- Department of Biomedical Sciences, Institute of Tropical Medicine, Antwerp, Belgium
| | - Rory Post
- Department of Disease Control, London School of Hygiene and Tropical Medicine, London, UK.,School of Natural Sciences and Psychology, Liverpool John Moores University, Liverpool, UK
| | | | - Sarah O'Neill
- Department of Public Health, Institute of Tropical Medicine, Antwerp, Belgium.,CR 5, Ecole de Santé Publique, Université Libre de Bruxelles, Brussels, Belgium
| | - Peter Enyong
- Research Foundation in Tropical Diseases and Environment, Buea, Cameroon
| | - Alfred K Njamnshi
- Neuroscience Lab, Faculty of Medicine and Biomedical Sciences, The University of Yaoundé I, Yaoundé, Cameroon.,Brain Research Africa Initiative (BRAIN), Yaoundé, Cameroon.,Brain Research Africa Initiative (BRAIN), Geneva, Switzerland.,Neurology Department, Central Hospital Yaoundé, Yaoundé, Cameroon
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Cheke RA, Little KE, Young S, Walker M, Basáñez MG. Taking the strain out of onchocerciasis? A reanalysis of blindness and transmission data does not support the existence of a savannah blinding strain of onchocerciasis in West Africa. ADVANCES IN PARASITOLOGY 2021; 112:1-50. [PMID: 34024357 DOI: 10.1016/bs.apar.2021.01.002] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/22/2022]
Abstract
Onchocerciasis (also known as 'river blindness'), is a neglected tropical disease (NTD) caused by the (Simulium-transmitted) filarial nematode Onchocerca volvulus. The occurrence of 'blinding' (savannah) and non-blinding (forest) parasite strains and the existence of corresponding, locally adapted Onchocerca-Simulium complexes were postulated to explain greater blindness prevalence in savannah than in forest foci. As a result, the World Health Organization (WHO) Onchocerciasis Control Programme in West Africa (OCP) focused anti-vectorial and anti-parasitic interventions in savannah endemic areas. In this paper, village-level data on blindness prevalence, microfilarial prevalence, and transmission intensity (measured by the annual transmission potential, the number of infective, L3, larvae per person per year) were extracted from 16 West-Central Africa-based publications, and analysed according to habitat (forest, forest-savannah mosaic, savannah) to test the dichotomous strain hypothesis in relation to blindness. When adjusting for sample size, there were no statistically significant differences in blindness prevalence between the habitats (one-way ANOVA, P=0.68, mean prevalence for forest=1.76±0.37 (SE); mosaic=1.49±0.38; savannah=1.89±0.26). The well-known relationship between blindness prevalence and annual transmission potential for savannah habitats was confirmed and shown to hold for (but not to be statistically different from) forest foci (excluding data from southern Côte d'Ivoire, in which blindness prevalence was significantly lower than in other West African forest communities, but which had been the focus of studies leading to the strain-blindness hypothesis that was accepted by OCP planners). We conclude that the evidence for a savannah blinding onchocerciasis strain in simple contrast with a non-blinding forest strain is equivocal. A re-appraisal of the strain hypothesis to explain patterns of ocular disease is needed to improve understanding of onchocerciasis epidemiology and disease burden estimates in the light of the WHO 2030 goals for onchocerciasis.
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Affiliation(s)
- Robert A Cheke
- Natural Resources Institute, Department of Agriculture, Health & Environment, University of Greenwich at Medway, Kent, United Kingdom; London Centre for Neglected Tropical Disease Research (LCNTDR), Department of Infectious Disease Epidemiology, Faculty of Medicine, School of Public Health, Imperial College London, London, United Kingdom
| | | | - Stephen Young
- Natural Resources Institute, Department of Agriculture, Health & Environment, University of Greenwich at Medway, Kent, United Kingdom
| | - Martin Walker
- London Centre for Neglected Tropical Disease Research, Department of Pathobiology and Populations Sciences, Royal Veterinary College, Hatfield, United Kingdom
| | - Maria-Gloria Basáñez
- London Centre for Neglected Tropical Disease Research (LCNTDR), Department of Infectious Disease Epidemiology, Faculty of Medicine, School of Public Health, Imperial College London, London, United Kingdom; MRC Centre for Global Infectious Disease Analysis, Department of Infectious Disease Epidemiology, Faculty of Medicine, School of Public Health, Imperial College London, London, United Kingdom.
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Adeleke MA, Mafiana CF, Sam-Wobo SO, Akinwale OP, Olatunde GO, Sanfo SM, Adjami A, Toè L. Molecular characterisation of theSimulium damnosumcomplex (Diptera: Simuliidae) found along the Osun River system, in south–western Nigeria. ANNALS OF TROPICAL MEDICINE AND PARASITOLOGY 2013; 104:679-83. [DOI: 10.1179/136485910x12851868780225] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
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Post RJ, Onyenwe E, Somiari SAE, Mafuyai HB, Crainey JL, Ubachukwu PO. A guide to the Simulium damnosum complex (Diptera: Simuliidae) in Nigeria, with a cytotaxonomic key for the identification of the sibling species. ANNALS OF TROPICAL MEDICINE AND PARASITOLOGY 2011; 105:277-97. [PMID: 21871165 DOI: 10.1179/136485911x12987676649700] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/31/2022]
Abstract
Although approximately 40% of all the people blinded by Onchocerca volvulus are Nigerians, almost nothing was known about the various cytospecies of the blackfly vectors present in Nigeria until 1981. The activation of the Nigerian National Onchocerciasis Control Programme in 1986 (and that programme's initiation of mass distributions of ivermectin in 1991) provided a significant stimulus to understand the biology of the Nigerian vectors but the exploration of any possible differences between the cytospecies has been hampered by a lack of accessible taxonomic information. This review attempts to satisfy that need. There are nine different cytoforms reliably recorded from Nigeria (Simulium damnosum s.s. Nile form, S. damnosum s.s. Volta form, S. sirbanum Sirba form, S. sirbanum Sudanense form, S. soubrense Beffa form, S. squamosum A, S. squamosum B, S. squamosum C and S. yahense typical form), and three more are known from surrounding countries and might be reasonably expected to occur in Nigeria. All of these cytospecies are presumed to be vectors, although there have been almost no identifications of the vectors of O. volvulus in Nigeria. The biogeographical distribution of the cytoforms is broadly similar to that known in other parts of West Africa (although many of the cytoforms remain insufficiently studied). The physico-chemical hydrology of the Nigerian breeding sites of the cytospecies does not, however, correspond to that seen elsewhere in West Africa, and it is not clear whether this might be related to differences in the cytoforms. An illustrated cytotaxonomic key is presented to facilitate and encourage future studies.
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Affiliation(s)
- R J Post
- Department of Infectious and Tropical Diseases, London School of Hygiene and Tropical Medicine, U.K.
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Post RJ, Mustapha M, Krueger A. Taxonomy and inventory of the cytospecies and cytotypes of the Simulium damnosum complex (Diptera: Simuliidae) in relation to onchocerciasis. Trop Med Int Health 2008; 12:1342-53. [PMID: 18045261 DOI: 10.1111/j.1365-3156.2007.01921.x] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
We provide an inventory of all named cytoforms of the Simulium damnosum complex (including those which are now considered invalid), along with all inversions that have been recorded (including synonyms and homonyms). There are 55 valid and distinct cytoforms known from the S. damnosum complex making it the largest sibling species complex of any vectors, and probably of any insect or other animal. All cytoforms are listed along with their fixed and diagnostic inversions and country distribution. There are 183 inversions known from the complex as a whole, of which 49% are fixed and/or diagnostic between cytoforms, and the fixed/diagnostic inversions seem to occur disproportionately on chromosome arm 2L.
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Affiliation(s)
- R J Post
- The Natural History Museum London and London School of Hygiene & Tropical Medicine, UK.
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Mansiangi P, Kiyombo G, Mulumba P, Josens G, Krueger A. Molecular systematics of Simulium squamosum, the vector in the Kinsuka onchocerciasis focus (Kinshasa, Democratic Republic of Congo). ANNALS OF TROPICAL MEDICINE AND PARASITOLOGY 2007; 101:275-9. [PMID: 17362602 DOI: 10.1179/136485907x157013] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Affiliation(s)
- P Mansiangi
- Ecole de Santé Publique/Faculté de Médecine, Université de Kinshasa, Kinshasa, Democratic Republic of the Congo
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