Mosquito Species Abundance, Diversity and Arbovirus Prevalence across Different Land-use in The Gambia

Abstract

Mosquito-borne arboviruses represent an escalating public health threat across sub-Saharan Africa, yet surveillance remains limited in many countries, including The Gambia. This study investigates mosquito species abundance and diversity, as well as the arbovirus prevalence across human, agricultural, and sylvatic habitats in The Gambia, accounting for ecological and seasonal variation. Adult mosquito samples were collected using a BG-Pro and CDC light traps. Larval and egg collections were made using dippers and oviposition cups, respectively. Sampling was conducted across three regions and several periods of seasonality (dry season, early and late rainy season) from December 2021 to October 2022. Mosquitoes were morphologically identified to species, or the lowest resolvable taxonomic level. Over 40,000 mosquitoes representing 51 species across 12 genera were collected. Mansonia uniformis was the overall predominant species, particularly dominating collections from sylvatic and agricultural habitats, while Culex quinquefasciatus was the most abundant species in human inhabitated areas. The sylvatic and agricultural sites exhibited the highest species richness, with 45 identifiable species, whereas human habitation sites yielded 36 identifiable species. Mosquito abundance, species richness and Shannon diversity were significantly influenced by seasonality, with all peaking at the end of the rainy season, but showed no significant effects of habitat type or trap type. Mosquito pools were screened for arboviruses using isolation techniques on Vero cell culture; then isolates identified via reverse transcription polymerase chain reaction (RT-PCR) and Sanger sequencing. Five pools have been confirmed to be Ngari virus (two pools), Bunyamwera virus (one pool) and Sindbis virus (two pools), representing the first confirmed detection of these arboviruses in field-collected mosquitoes from The Gambia. Interestingly, all five pools were identified during the late rainy season across inland sylvatic, agricultural, and human-inhabited landscapes, highlighting the possible role of ecological context in shaping arbovirus transmission risk. This study provides the first systematic, habitat-inclusive assessment of mosquito biodiversity and arbovirus circulation in The Gambia. Findings highlight the presence of competent vector species and potential silent virus circulation in understudied regions, reinforcing the need for integrated entomological and virological surveillance.