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

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 (...

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Autores principales:	Adam Hendy, Meryam Krit, Kenneth Pfarr, Christine Laemmer, Jacobus De Witte, Philippe Nwane, Joseph Kamgno, Hugues C. Nana-Djeunga, Michel Boussinesq, Jean-Claude Dujardin, Rory Post, Robert Colebunders, Sarah O’Neill, Peter Enyong, Alfred K. Njamnshi
Formato:	article
Lenguaje:	EN
Publicado:	BMC 2021
Materias:	Onchocerciasis Elimination Ivermectin Onchocerca volvulus Simulium damnosum Simulium squamosum Infectious and parasitic diseases RC109-216
Acceso en línea:	https://doaj.org/article/3ec07af81cf74bad9316eeaba190b09c
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spelling	oai:doaj.org-article:3ec07af81cf74bad9316eeaba190b09c2021-11-08T10:57:16ZOnchocerca 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 squamosum10.1186/s13071-021-05072-y1756-3305https://doaj.org/article/3ec07af81cf74bad9316eeaba190b09c2021-11-01T00:00:00Zhttps://doi.org/10.1186/s13071-021-05072-yhttps://doaj.org/toc/1756-3305Abstract 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. Graphical AbstractAdam HendyMeryam KritKenneth PfarrChristine LaemmerJacobus De WittePhilippe NwaneJoseph KamgnoHugues C. Nana-DjeungaMichel BoussinesqJean-Claude DujardinRory PostRobert ColebundersSarah O’NeillPeter EnyongAlfred K. NjamnshiBMCarticleOnchocerciasisEliminationIvermectinOnchocerca volvulusSimulium damnosumSimulium squamosumInfectious and parasitic diseasesRC109-216ENParasites & Vectors, Vol 14, Iss 1, Pp 1-14 (2021)
institution	DOAJ
collection	DOAJ
language	EN
topic	Onchocerciasis Elimination Ivermectin Onchocerca volvulus Simulium damnosum Simulium squamosum Infectious and parasitic diseases RC109-216
spellingShingle	Onchocerciasis Elimination Ivermectin Onchocerca volvulus Simulium damnosum Simulium squamosum Infectious and parasitic diseases RC109-216 Adam Hendy Meryam Krit Kenneth Pfarr Christine Laemmer Jacobus De Witte Philippe Nwane Joseph Kamgno Hugues C. Nana-Djeunga Michel Boussinesq Jean-Claude Dujardin Rory Post Robert Colebunders Sarah O’Neill Peter Enyong Alfred K. Njamnshi 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
description	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. Graphical Abstract
format	article
author	Adam Hendy Meryam Krit Kenneth Pfarr Christine Laemmer Jacobus De Witte Philippe Nwane Joseph Kamgno Hugues C. Nana-Djeunga Michel Boussinesq Jean-Claude Dujardin Rory Post Robert Colebunders Sarah O’Neill Peter Enyong Alfred K. Njamnshi
author_facet	Adam Hendy Meryam Krit Kenneth Pfarr Christine Laemmer Jacobus De Witte Philippe Nwane Joseph Kamgno Hugues C. Nana-Djeunga Michel Boussinesq Jean-Claude Dujardin Rory Post Robert Colebunders Sarah O’Neill Peter Enyong Alfred K. Njamnshi
author_sort	Adam Hendy
title	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
title_short	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
title_full	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
title_fullStr	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
title_full_unstemmed	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
title_sort	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
publisher	BMC
publishDate	2021
url	https://doaj.org/article/3ec07af81cf74bad9316eeaba190b09c
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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

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