Human exposure to zoonotic malaria vectors in village, farm and forest habitats in Sabah, Malaysian Borneo

The zoonotic malaria parasite,Plasmodium knowlesi, is now a substantial public health problem in Malaysian Borneo. Current understanding ofP.knowlesivector bionomics and ecology in Sabah comes from a few studies near the epicentre of human cases in one district, Kudat. These have incriminatedAnopheles balabacensisas the primary vector, and suggest that human exposure to vector biting is peri-domestic as well as in forest environments. To address the limited understanding of vector ecology and human exposure risk outside of Kudat, we performed wider scale surveillance across four districts in Sabah with confirmed transmission to investigate spatial heterogeneity in vector abundance, diversity and infection rate. Entomological surveillance was carried out six months after a cross-sectional survey ofP.knowlesiprevalence in humans throughout the study area; providing an opportunity to investigate associations between entomological indicators and infection. Human-landing catches were performed in peri-domestic, farm and forest sites in 11 villages (3-4 per district) and paired with estimates of humanP.knowlesiexposure based on sero-prevalence.Anopheles balabacensiswas present in all districts but only 6/11 villages. The mean density ofAn.balabacensiswas relatively low, but significantly higher in farm (0.094/night) and forest (0.082/night) than peri-domestic areas (0.007/night). Only oneAn.balabacensis(n = 32) was infected withP.knowlesi.Plasmodium knowlesisero-positivity in people was not associated withAn.balabacensisdensity at the village-level however post hoc analyses indicated the study had limited power to detect a statistical association due low vector density. Wider scale sampling revealed substantial heterogeneity in vector density and distribution between villages and districts. Vector-habitat associations predicted from this larger-scale surveillance differed from those inferred from smaller-scale studies in Kudat; highlighting the importance of local ecological context. Findings highlight potential trade-offs between maximizing temporal versus spatial breadth when designing entomological surveillance; and provide baseline entomological and epidemiological data to inform future studies of entomological risk factors for humanP.knowlesiinfection.