Vertically infected Aedes aegypti excrete infectious arboviruses in saliva

Epidemics of dengue (DENV), chikungunya (CHIKV), and Zika (ZIKV) viruses are primarily driven by transmission to humans via Aedes aegypti mosquitoes. In addition to this horizontal route, Ae. aegypti can also transmit these viruses to their offspring through vertical transmission. In this study, using a field-derived Ae. aegypti population, we assessed vertical transmission of the three viruses, and we assessed whether female mosquitoes maternally infected can excrete infectious virus in their saliva-a key requirement for subsequent transmission to humans.

We detected infectious CHIKV and ZIKV in the saliva of 15% and 11% of daughters obtained from infected mothers, respectively. In the case of DENV-1, 14% of female offspring had infectious virus in their heads, although saliva samples were negative, meriting further investigation. Moreover, pooled male progeny was found positive for CHIKV and ZIKV.

These findings suggest that vertical transmission may be an underestimated mechanism which provides a potential route by which Ae. aegypti can become infective independently of biting a viremic host, thereby contributing to arbovirus persistence and spread. The presence of infected male progeny also demonstrates that vertically transmitted viruses can persist in mosquito populations even in individuals that do not blood-feed.