Zika vector competence data reveals risks of outbreaks: the contribution of the European ZIKAlliance project

Abstract

First identified in 1947, Zika virus took roughly 70 years to cause a pandemic unusually associated with virus-induced brain damage in newborns. Zika virus is transmitted by mosquitoes, mainly Aedes aegypti, and secondarily, Aedes albopictus, both colonizing a large strip encompassing tropical and temperate regions. As part of the international project ZIKAlliance initiated in 2016, 50 mosquito populations from six species collected in 12 countries were experimentally infected with different Zika viruses. Here, we show that Ae. aegypti is mainly responsible for Zika virus transmission having the highest susceptibility to viral infections. Other species play a secondary role in transmission while Culex mosquitoes are largely non-susceptible. Zika strain is expected to significantly modulate transmission efficiency with African strains being more likely to cause an outbreak. As the distribution of Ae. aegypti will doubtless expand with climate change and without new marketed vaccines, all the ingredients are in place to relive a new pandemic of Zika.

Fig. 1. Infection rate, dissemination and transmission efficiencies of ZIKV strains (Africa, America, Asia) according to time since infection in three Aedes mosquito species.

Panels show the rates achieved by averaging over all sampled mosquitoes, i.e., by pooling together mosquitoes from all countries used in the study. Error bars are exact 95% binomial confidence intervals centered on the observed means of IR, DE and TE. (n = 30 biologically independent mosquitoes for each combination of species, country, mosquito population, days post-infection and ZIKV strain were studied, unless stated otherwise. See Supplementary Table 1 for complete break-down of sample sizes). Colors correspond to the studied outcome (IR, DE, TE).

Fig. 2. Model-predicted transmission efficiency of Aedes mosquitoes according to time since infection, split by country of mosquito sampling.

TE predicted for (A) Ae. aegypti and (B) Ae. albopictus. Countries are ordered to reflect geographic proximity. Error bars show asymptotic 95% confidence interval from the mixed regression models centered on the average predictions of IR, DE and TE. (n = 30 biologically independent mosquitoes for each combination of species, country, mosquito population, days post-infection and ZIKV strain were studied, unless stated otherwise. See Supplementary Table 1 for complete break-down of sample sizes). Colors correspond to continent-aggregated ZIKV strains.

Fig. 3. Transmission efficiencies of ZIKV strains at the regional level for Ae. aegypti and Ae. albopictus mosquitoes sampled at one or more locations in every studied country, at 21 dpi.

ZIKV strains were pooled in a geographical clustering that reflected their phylogeny. Vertical bars help identify different countries, shown on the x-axis with individual colors. Empty cells represent absence of data. Color gradients correspond to TE values (ranging 0–100%).

Fig. 4. Distribution of mosquito species experimentally infected with Zika viruses.

The color code used represents the different mosquito species and numbers refer to the number of mosquito populations tested. In green, are the countries sampled. Colors correspond to mosquito species. The map was built using the open source map site https://cmap.comersis.com/cartes-Monde-WORLD.html.