When a mosquito transmits a pathogen it does not simply act as a flying syringe. Instead most mosquito-borne pathogens, after being consumed with the bloodmeal, must invade the mosquito gut, leave the mosquito gut and enter the body cavity, and finally find its way across the salivary gland and into the mosquito’s saliva. Only at this point can the pathogen be transmitted to another person when the saliva is injected along with the bite. For example, the incubation period in the mosquito for the malaria parasite is typically 10-14 days, while for the dengue virus it is typically 8-10 days. Since most mosquitoes in the field perish within 14 days, it is only the oldest mosquitoes that transmit most of the pathogens to people. Furthermore, this incubation is temperature dependent, with higher temperatures resulting in shorter incubation periods. Unfortunately, little is known about the incubation period of Zika virus in the mosquito. So for this work examined the incubation period of Zika in its primary mosquito vector, the Yellow Fever mosquito Aedes aegypti, at three different temperatures; 27?C, 30?C or 33?C. Most surprisingly, the Zika virus appears to have a very short incubation period relative to other mosquito borne pathogens with nearly 9% of mosquitoes fed a Zika infectious bloodmeal having detectable virus in the saliva after only three days. There was a trend towards enhanced movement from the gut to the body of the mosquito as the temperature increased, however we did not detect increases in the in the number of mosquitoes with virus in the saliva as the temperature rises. In fact, at our highest temperature mosquito mortality was quite high and fewer mosquitoes with virus in the saliva were observed.

In addition to the rate at which the virus travels through the mosquito, we were also interested to see if Zika virus could be directly transmitted from the female mosquito to her offspring. Direct transmission to offspring would eliminate the need for the mosquito to first acquire an infectious bloodmeal, allowing the mosquito to transmit the virus during her first bloodfeeding event. To test this we first infected female mosquitoes with the Zika virus and examined the larvae that were produced by the infected female. The only way Zika virus could be detected in larval mosquitoes is if they acquired the virus from the mother. To our surprise 90% of the pools of larval mosquitoes (10-15 individual larvae per pool) were positive for Zika virus. Looking more closely at individual mosquitoes we found that over 8% of the adult offspring tested positive for Zika virus, with nearly half of those with Zika virus in the saliva. This indicates that not only can the virus be passed to a female mosquito’s offspring, but that the virus can persist to adulthood where it can be transmitted back to a person.      

In summary, the incubation period for Zika virus is quite short in Ae. aegypti mosquitoes relative to other mosquito transmitted viruses. Further, it is possible for female mosquitoes to transmit the virus directly to their offspring. Taken together, these results suggest that Zika virus transmission can occur quite rapidly and that the virus can persist in the environment even without transmission to the vertebrate host. These data will allow us to generate better models for determining the spread of Zika virus and potential Zika outbreaks.

Last Modified: 08/28/2017
Modified by: Michael A Riehle