Rebound in prevalence and intensity of Onchocerca volvulus infection five years after cessation of alternative treatment strategies in the Massangam Health District, West Region, Cameroon: need for coordinated and sustained efforts

BACKGROUND: The control of onchocerciasis currently relies on yearly distribution of ivermectin to at-risk populations. To tackle onchocerciasis in areas of high transmission (so-called hotspots) and achieve elimination of transmission, several complementary/alternative strategies (biannual ivermectin, doxycycline-based test-and-treat and vector control) were implemented in Massangam Health District (HD) in Cameroon, following World Health Organization (WHO) guidelines. A short-term impact evaluation revealed significant reductions in the endemicity levels in three focal hotspot communities (Makouopsap, Mankakoun, and Njinja-Njingouet). This study aimed to assess the situation of onchocerciasis in the focal hotspot communities five years after the cessation of the short pilot implementation of Alternative Treatment Strategies (ATS). METHODOLOGY: A quantitative cross-sectional survey was conducted in December 2023 in three focal hotspot communities of the Massangam Health District. Participants underwent a comprehensive assessment including parasitological examination (skin snipping) to establish Onchocerca volvulus microfilaridermia. PRINCIPAL FINDINGS: The overall prevalence of O. volvulus infection in the three focal communities was 18.7% (95% confidence interval CI: 14.1-24.3), significantly higher in the Mankakoun (30.8%) and Makouopsap (24.0%) communities compared to the Njinja-Njingouet community (7.0%) (p = 0.001). The intensity of infection was 3.136 (standard deviation, SD: 19.3099) mf/ss, ranging from 5.218 mf/ss (Mankakoun community) to 2.840 mf/ss (Njinja-Njingouet community). Parasitological indicators significantly increased five years after the cessation of ATS in all three focal communities (p = 0.0409). CONCLUSION/SIGNIFICANCE: These findings indicate a rebound in onchocerciasis transmission and underscore the need for coordinated and sustained efforts, implemented at the scale of a transmission zone per WHO recommendations, to achieve elimination goals.