Vertical transmission of Zika virus from orally infected Aedes aegypti produces infectious adult progeny.

Abstract

Vertical transmission, or pathogen transfer from mother to offspring, can facilitate persistence of emerging arboviruses, such as Zika virus (ZIKV), in mosquito populations. Understanding vertical transmission and the different environmental and temporal conditions that affect it is important to assess whether new outbreaks could occur without reintroduction of the virus. To determine the rate of vertical transmission for ZIKV, Aedes aegypti females were fed on ZIKV infected blood, maintained under three temperature conditions (27{degrees}C, 30{degrees}C, and 33{degrees}C), and allowed to oviposit three times. Progeny were tested for virus presence at 3, 7, and 14 days after adult emergence. The overall vertical transmission rate was 6.5% (3.9 - 9.9). Vertical transmission was observed across all maternal temperature conditions and was detected in adult progeny as young as 3 days and as late as 14 days post-emergence. In total, 3.4% (1.6 - 6.2) of adult progeny produced saliva with detectable ZIKV, indicating their capacity to transmit ZIKV to humans. To our knowledge, this is the first evidence that vertical transmission occurs from orally-infected female Aedes aegypti to their adult progeny at a range of temperatures, and proof that Zika virus can persist in the saliva of those progeny throughout their lifetimes. These results suggest that the virus may be maintained in Ae. aegypti populations without a vertebrate host, allowing for human infections to occur without consistent re-introductions of ZIKV.\n\nAuthor SummaryIn 2015, Zika virus spread to over 50 countries. However, it is not known whether the virus persisted in the outbreak areas or became locally extinct. One way mosquito-borne viruses, like Zika, could become established is by transferring directly between mosquito generations rather than circulating between mosquitoes and humans. This is known as vertical transmission, and happens when the virus infects the developing eggs of infected maternal mosquitoes. As with other mosquito-borne diseases, like dengue, in order to infect humans the virus must be present in the saliva of infected mosquito progeny during blood feeding. We found vertical transmission occurred throughout the infected mothers reproductive lifetime and across a range of temperature conditions. Vertically infected progeny had Zika virus in their saliva as early as three days after adult emergence, implying that they could infect a person even during their first bloodmeal. Importantly, this work indicates that Zika virus could establish itself in the mosquito population even when human to mosquito transmission is not actively occurring.