The role of vector population variation and climate in Zika virus transmission patterns in Africa: a modelling study

Background

Zika virus (ZIKV) outbreaks have raised major global health concerns recently, yet reported outbreaks are rare in Africa, where ZIKV was first discovered. Recent studies on Aedes aegypti, the mosquito that transmits ZIKV, might explain this phenomenon. The Ae aegypti subspecies present in Africa shows lower preference for biting humans and reduced susceptibility to ZIKV infection compared with the subspecies distributed outside Africa. Alternatively, climate might strongly limit transmission as it affects multiple traits of ZIKV and the mosquito vector.

Methods

We used a modelling approach informed by empirical data to assess ZIKV transmission risk across Africa. We fitted the model using data from laboratory experiments, and validated the model by comparing predicted transmission suitability with seroprevalence surveys conducted across Africa. Additionally, we used mosquito genetic and climate-based projections to map future ZIKV outbreak risk at 59 urban centres in Africa.

Findings

The model predictions partially and significantly explain historical patterns of ZIKV circulation in Africa (accounting for 46% of the variation in seroprevalence surveys). Mosquito population genetics influence transmission more strongly than climate through two mechanisms: vector–host contact and vector competence. If climate and mosquito genetic population projections are accurate and there are no other changes to drivers of Zika virus transmission in Africa, we predict that approximately three-quarters of the most populous African cities will be suitable for ZIKV outbreaks by the end of the century.

Interpretation

Both population-level genomic variation in mosquitoes and climate contribute to the lack of ZIKV outbreaks in Africa. Given the importance of mosquito genetics in driving this pattern, local genomic surveillance of mosquito populations would help predict outbreaks in vulnerable communities. This will become increasingly important with population growth, urbanisation, and climate change.

Funding

Princeton University, French Government's Investissement d’Avenir and France 2030 programmes, MSDAVENIR, and US National Institutes of Health.