Mosquito-borne viruses, like dengue and chikungunya, tend to come in seasonal waves, flaring up in the summer or wet seasons, and fading in the winter or dry seasons. Zika is expected to behave similarly, though hopefully future flare-ups will be less intense than the current epidemic as people in affected populations develop immunity.
One way these diseases can survive the winter, even as mosquito populations dip, is in eggs. There is evidence that dengue, West Nile, and chikungunya can be vertically transmitted—that is, mosquitoes can sometimes pass the viruses along to their offspring. A new study published in the American Journal of Tropical Medicine and Hygiene has found evidence that Zika can also be vertically transmitted.
Researchers from the University of Texas Medical Branch infected populations of Aedes aegypti, the main vector for Zika, and Aedes albopictus, which can also spread the virus, but is less likely to bite humans. They collected the infected females’ eggs, raised them, and then tested the adult offspring for Zika. In the Aedes aegypti, some of the offspring tested positive, at a rate of 1 Zika-infected mosquito per 290 offspring. (None of the Aedes albopictus offspring had Zika, but the researchers tested fewer of them, and it’s possible they have a small enough vertical transmission rate that the study just didn’t pick it up.)