Scientists discover that mosquitoes can transmit Zika to their offspring

Freya Preimesberger

A survival mechanism may keep Zika alive across generations of mosquitoes.

Researchers at the UT Medical Branch in Galveston have found that female mosquitoes are capable of passing the Zika virus onto their offspring. This helps the virus survive in difficult conditions and changes recommendations for preventative measures against Zika. On Aug. 29, the researchers published their findings in the American Journal of Tropical Medicine and Hygiene.

The Zika virus, a type of flavivirus, is spread primarily by mosquitoes of the genus Aedes. Although infected adults usually display mild symptoms, if any, women infected while pregnant may give birth to children with birth defects. The Center for Disease Control has issued alerts to pregnant women traveling to Zika-affected areas.

Other mosquito-borne flaviviruses, including the West Nile and yellow fever viruses, can be transmitted directly from female mosquitoes to their offspring through a process called vertical transmission. Scientists at UT Medical Branch conducted a study to see if the Zika virus uses the same mechanism.

Researchers injected the virus into female mosquitoes from two species, Aedes aegypti and Aedes albopictus. They found that in one in 290 cases involving the Aedes aegypti species, which is found in Austin, the Zika virus was passed from mother to offspring. None of the Aedes albopictus offspring were infected, according to the study. 

“Vertical transmission is a probable survival mechanism of Zika virus during adverse climatic conditions,” said Saravanan Thangamani, associate professor of pathology at UT Medical Branch and first author of the study.

Vertical transmission of Zika doesn’t mean there will be many new cases, but rather that the virus will not completely disappear, said Robert Tesh, pathology professor at UT Medical Branch and co-author of the study. Tesh said this makes it harder to eliminate Zika in mosquito populations.

Mosquitoes typically breed by laying their eggs in water. Adult mosquitoes die during cooler weather, but their eggs can survive until rain and warm weather return.

“If a few of those eggs are infected, then those mosquitoes, when they emerge, will be infected,” Tesh said. “That’s enough to get the cycle started again, and they can feed on a person and infect them. Once you have people with the virus getting bitten, they infect more mosquitoes and get the cycle going again.” 

The study recommends that efforts also be taken to kill mosquito larvae. People in Florida have put larvicide in water in the wake of a recent Zika outbreak near Miami this month.

“The current vector control is primarily targeted to adult mosquitoes,” Thangamani said. “Both adulticides and larvicides must be used to eliminate Zika virus-infected mosquitoes.”

Mosquito larvae and eggs are resistant to some common insecticide chemicals, making eradication of the virus difficult.

“The best way to get rid of the eggs is to get rid of the containers in which they’re laid,” Tesh said. ”You need to get rid of those eggs by getting rid of those containers, old tires, junk in people’s yard collecting water that allow for breeding of mosquitoes.”