Raphael Awah Abong1,2, Glory Ngongeh Amambo1,2, Ali Ahamat Hamid1,2, Belinda Agbor Enow1,2, Amuam Andrew Beng1,2, Franck Noel Nietcho1, Theobald Mue Nji2,3, Abdel Jelil Njouendou1,4, Manuel Ritter5, Mathias Eyong Esum1,2, Kebede Deribe6,7, Jerome Fru Cho1,2, Fanny Fri Fombad1,2, Peter Ivo Enyong1,2, Catherine Poole8, Kenneth Pfarr5,9, Achim Hoerauf5,9, Clotilde Carlow8, Samuel Wanji1,2. 1. Parasites and Vector Biology Research Unit (PAVBRU), Department of Microbiology and Parasitology, University of Buea, Buea, Cameroon. 2. Research Foundation in Tropical Diseases and Environment (REFOTDE), Buea, Cameroon. 3. Department of Sociology and Anthropology, University of Buea, Cameroon. 4. Department of Biomedical science, Faculty of Health Sciences, University of Buea, Buea, Cameroon. 5. Institute for Medical Microbiology, Immunology and Parasitology, University Hospital Bonn, Bonn, Germany. 6. Global Health and Infection Department, Brighton and Sussex Medical School, Brighton, United Kingdom. 7. School of Public Health, Addis Ababa University, Addis Ababa, Ethiopia. 8. New England Biolabs, Ipswich, Massachusetts, United States of America. 9. German Center for Infection Research (DZIF), partner site Bonn-Cologne, Bonn, Germany.
Abstract
BACKGROUND: The impact of large scale Mass Drug Adminstration (MDA) of ivermectin on active onchocerciasis transmission by Simulium damnosum, which transmits the parasite O. volvulus is of great importance for onchocerciasis control programmes. We investigated in the Mbam river system area, the impact of MDA of ivermectin on entomological indices and also verify if there are river system factors that could have favoured the transmission of onchocerciasis in this area and contribute to the persistence of disease. We compared three independent techniques to detect Onchocerca larvae in blackflies and also analyzed the river system within 9 months post-MDA of ivermectin. METHOD: Simulium flies were captured before and after 1, 3, 6 and 9months of ivermectin-MDA. The biting rate was determined and 41% of the flies dissected while the rest were grouped into pools of 100 flies for DNA extraction. The extracted DNA was then subjected to O-150 LAMP and real-time PCR for the detection of infection by Onchocerca species using pool screening. The river system was analysed and the water discharge compared between rainy and dry seasons. PRINCIPAL FINDINGS: We used human landing collection method (previously called human bait) to collect 22,274 adult female Simulium flies from Mbam River System. Of this number, 9,134 were dissected while 129 pools constituted for molecular screening. Overall biting and parous rates of 1113 flies/man/day and 24.7%, respectively, were observed. All diagnostic techniques detected similar rates of O. volvulus infection (P = 0.9252) and infectivity (P = 0.4825) at all monitoring time points. Onchocerca ochengi larvae were only detected in 2 of the 129 pools. Analysis of the river drainage revealed two hydroelectric dams constructed on the tributaries of the Mbam river were the key contributing factor to the high-water discharge during both rainy and dry seasons. CONCLUSION: Results from fly dissection (Microscopy), real-time PCR and LAMP revealed the same trends pre- and post-MDA. The infection rate with animal Onchocerca sp was exceptionally low. The dense river system generate important breeding sites that govern the abundance of Simulium during both dry and rainy seasons.
BACKGROUND: The impact of large scale Mass Drug Adminstration (MDA) of ivermectin on active onchocerciasis transmission by Simulium damnosum, which transmits the parasite O. volvulus is of great importance for onchocerciasis control programmes. We investigated in the Mbam river system area, the impact of MDA of ivermectin on entomological indices and also verify if there are river system factors that could have favoured the transmission of onchocerciasis in this area and contribute to the persistence of disease. We compared three independent techniques to detect Onchocerca larvae in blackflies and also analyzed the river system within 9 months post-MDA of ivermectin. METHOD: Simulium flies were captured before and after 1, 3, 6 and 9months of ivermectin-MDA. The biting rate was determined and 41% of the flies dissected while the rest were grouped into pools of 100 flies for DNA extraction. The extracted DNA was then subjected to O-150 LAMP and real-time PCR for the detection of infection by Onchocerca species using pool screening. The river system was analysed and the water discharge compared between rainy and dry seasons. PRINCIPAL FINDINGS: We used human landing collection method (previously called human bait) to collect 22,274 adult female Simulium flies from Mbam River System. Of this number, 9,134 were dissected while 129 pools constituted for molecular screening. Overall biting and parous rates of 1113 flies/man/day and 24.7%, respectively, were observed. All diagnostic techniques detected similar rates of O. volvulus infection (P = 0.9252) and infectivity (P = 0.4825) at all monitoring time points. Onchocerca ochengi larvae were only detected in 2 of the 129 pools. Analysis of the river drainage revealed two hydroelectric dams constructed on the tributaries of the Mbam river were the key contributing factor to the high-water discharge during both rainy and dry seasons. CONCLUSION: Results from fly dissection (Microscopy), real-time PCR and LAMP revealed the same trends pre- and post-MDA. The infection rate with animal Onchocerca sp was exceptionally low. The dense river system generate important breeding sites that govern the abundance of Simulium during both dry and rainy seasons.
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