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Zika-infected mosquitoes lay Zika-infected eggs

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This is the first experimental proof that mosquitoes can transmit Zika to their own offspring

Mosquito moms can transmit zika virus to their offspring — at least in the lab, a new study shows. If this also happens in nature, the virus might be able to survive in tough mosquito eggs even when cold weather, dry spells, and pesticides kill off the infectious adults.

Mosquitoes can transmit viruses in the same family as Zika, such as yellow fever and dengue, to their offspring — but it wasn’t clear whether this was also true for Zika. So scientists led by Robert Tesh, an epidemiologist at the University of Texas Medical Branch, injected Zika virus into approximately 200 females from two different species of mosquitoes: Aedes aegypti, and Aedes albopictus. None of the A. albopictus offspring tested positive for the virus, but about one in every 290 A. aegypti offspring were infected. They published these results today in the American Journal of Tropical Medicine and Hygiene.

"It’s a nice strategy for the virus to hide."

In the last year, 67 countries and territories have reported transmission of Zika virus by mosquitoes. That means mosquito control is crucial for curbing the disease. The FDA has already approved field trials with genetically modified male mosquitoes that pass a gene to their offspring that kills the young mosquitoes before they reach adulthood. Targeting the eggs and preventing mosquitoes from successfully reproducing looks to be an especially critical strategy in light of today’s findings.

Aedes mosquitoes lay tough little eggs that can lie dormant for months during dry periods, but still manage to hatch when it rains. So even a few infected eggs could be enough to keep Zika circulating in mosquito populations when the nearby people have developed immunity, or during cold snaps and dry spells when the adult mosquitoes die. "It’s a nice strategy for the virus to hide," says Phil Lounibos, a medical entomologist with the University of Florida who was not involved in the research.

Lounibos and Tesh point out that it’s too early to say whether mosquito moms transmit Zika to their offspring at similar rates in the wild. And both scientists note that the mosquitoes in this study were infected by an injection of the virus rather than by slurping up infected blood. The more natural route also produces more variable results, Tesh says. But Lounibos says this study sets the stage for future research that mimics the conditions in nature.

Tesh adds that studying how viruses behave in the mosquitoes that transmit them will be critical as we continue to fight mosquito-borne diseases like malaria, yellow fever, dengue, chikungunya, and Zika.