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

Parasites & Vectors

Hugues C. Nana-Djeunga¹  Philippe Nwane¹  Joseph Kamgno²  Jacobus De Witte³  Meryam Krit³  Jean-Claude Dujardin³  Adam Hendy⁴  Rory Post⁵  Sarah O’Neill⁶  Robert Colebunders⁷  Michel Boussinesq⁸  Kenneth Pfarr⁹  Christine Laemmer⁹  Alfred K. Njamnshi^1,10  Peter Enyong^1,11 

[1] Centre for Research on Filariasis and Other Tropical Diseases (CRFilMT), Yaoundé, Cameroon;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;Department of Biomedical Sciences, Institute of Tropical Medicine, Antwerp, Belgium;Department of Biomedical Sciences, Institute of Tropical Medicine, Antwerp, Belgium;Department of Pathology, University of Texas Medical Branch, Galveston, TX, USA;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;Department of Public Health, Institute of Tropical Medicine, Antwerp, Belgium;CR 5, Ecole de Santé Publique, Université Libre de Bruxelles, Brussels, Belgium;Global Health Institute, University of Antwerp, Antwerp, Belgium;Institut de Recherche pour le Développement (IRD), Montpellier, France;Institute for Medical Microbiology, Immunology and Parasitology, University Hospital Bonn, Bonn, Germany;German Center for Infection Research, Partner Site Bonn-Cologne, Cologne, Germany;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;Research Foundation in Tropical Diseases and Environment, Buea, Cameroon;

关键词: Onchocerciasis;    Elimination;    Ivermectin;    Onchocerca volvulus;    Simulium damnosum;    Simulium squamosum;    Mbam;    Cameroon;   

DOI  :  10.1186/s13071-021-05072-y

来源: Springer

【 摘 要 】

BackgroundThe 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.MethodsBlack 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.ResultsIn 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.ConclusionsRelatively 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

【 授权许可】

CC BY