Entomological Indices and Community Knowledge of Onchocerciasis Transmission in the Menchum Valley Health District, An Endemic Area of Northwestern Cameroon

Abstract

Background: Recent successes in several foci in Venezuela, Mexico, and Nigeria underscore the importance of understanding local transmission conditions and mapping all high-risk areas to achieve the human onchocerciasis transmission-interruption targets of the 2021–2030 Neglected Tropical Diseases roadmap. Therefore, this study aimed to determine the transmission indices of the Simulium damnosum complex and assess community knowledge of onchocerciasis transmission in Menchum Valley Subdivision, North West Region, Cameroon. Methods: The human-bait sampling method was used to collect adult flies from November 2022 to April 2023 on two consecutive days each month, from 07:00 to 18:00. Members of the Simulium damnosum complex were caught and dissected, and transmission indices, including biting density, monthly biting rate (MBR), monthly transmission potential (MTP), and monthly parous biting rate (MPBR), were calculated using standard methods. A household-based survey using a structured questionnaire assessed community knowledge of blackfly biting activity and bioecology. Results: A total of 1,932 adult S. damnosum s.l. were caught at Menchum Falls and Mawong River; 1,766 (91.4%) were dissected, 1,416 (73.3%) were parous, and 15 were infected with Onchocerca species larvae. The monthly biting rate (3,681 vs 1,224.5 bites/person/month) and monthly transmission potential (71.3 vs 38.7) were highest in January in both communities. The monthly parous biting rates (MPBRs) were 2,960.5 vs 922.3 flies/person/month, whereas the infectivity rates were 21 vs 42 per 1,000 parous flies. Of the 170 respondents, 98.2% reported knowing about onchocerciasis. However, 66.5% stated that onchocerciasis is transmitted by mosquito bites, and 37.1% reported that blackflies primarily originate from tree holes. Conclusions: These results indicated that, despite more than two decades of ongoing intervention, transmission of Onchocerca species remained active in Menchum Valley Subdivision. The study also revealed limited knowledge of onchocerciasis transmission and blackfly bioecology among inhabitants of the study area. Robust community-awareness and vector-control interventions scheduled for January and February could accelerate onchocerciasis elimination.