Field studies of Culex mosquitoes in Tanzania and Kenya: A systematic review motivated by changing Rift Valley fever virus transmission patterns

Culex mosquitoes are assumed to be secondary vectors of Rift Valley fever virus (RVFV), with Aedes being the most important for initiating outbreaks. However, environmental change may be affecting the role Culex species play in transmission. We aimed to curate a collection of published studies from Tanzania and Kenya, identify gaps in research concerning Culex communities and establish whether sufficient spatio-temporal published data may be available for future meta-analysis. This presents a first step in leveraging published data to better understand the role of Culex in maintaining RVFV transmission. We carried out a systematic search of the published literature using Web of Science for studies that sampled Culex in Tanzania or Kenya, up until the 28th April 2023. We determined motivations for studies, their duration and the geographic coverage in relation to an RVFV risk map. We then assessed species identification methods and how these may have impacted results. Of 275 studies, 17 explicitly stated the motivation for the study was RVFV. Despite most studies being motivated by other topics, there was good coverage of studies reporting mosquito sampling in areas associated with the risk of RVFV outbreaks. Fifty studies were at least 12 months in duration. In terms of species identification, studies were c. 14 times more likely to have identified more species than just the Culex pipiens complex if they stated that they used a Culex specific key. Although the majority of published studies sampling Culex in Kenya and/or Tanzania did not state RVFV explicitly as a key motivation for research, we propose that drawing on the data contained within these wider studies may still be of value for understanding how RVFV transmission is maintained. Our work here presents a first step to this end.