Sex May Spread Zika Virus More Often Than Suspected, Researchers Find

Being bitten by a mosquito remains the easiest way to contract the Zika virus, but some researchers are beginning to worry more about the other known transmission route: sex, according to the New York Times.

While the evidence is still mounting, two reports now suggest that women in Latin America are much more likely to be infected through sex than men, although both are presumed to be equally exposed to mosquitoes.

The territory’s department of health on Wednesday reported three new cases of the Zika virus, bringing the islands’ total to 33 — 15 in St. Thomas, 17 in St. Croix and 1 case in St. John.

Dr. Anthony S. Fauci, the director of the National Institute of Allergy and Infectious Diseases, called the evidence “striking.” Like other scientists, he had doubts about aspects of the data, but thought the results justified a more rigorous study, probably in Puerto Rico, of the role of sex in transmitting the Zika virus, The Times wrote.

“I can’t say it’s not true that women are more at risk,” he said.

The Zika virus can persist for months in semen, even in men who have had very mild infections. That’s why women who are pregnant or trying to conceive are routinely warned not to have unprotected sex with men who have been in areas where the virus is spreading. According to D.O.H. statistics, only two women in the territory contracted Zika during their pregnancy.

Ten countries — Argentina, Canada, Chile, France, Germany, Italy, New Zealand, Peru, Portugal and the continental United States — have reported infections that were almost undoubtedly passed via sex. No case of female-to-male transmission has been documented, according to The Times.

In the U.S., however, the C.D.C. knows of just 13 sexually transmitted cases of Zika thus far. It does not try to count them in Puerto Rico because it cannot distinguish them from mosquito-borne cases. Because 80 percent of all infections are asymptomatic, the real number is probably higher.

To find out for sure how often sex spreads the virus, researchers would need to choose hundreds of men and women at random and quiz them about how often they were bitten by mosquitoes, how often and with whom they had sex, and how readily they sought medical care, among other factors. Then their blood would have to be tested for the infection.

It might not be possible to do that survey, Dr. Fauci said.

Not only has Congress been reluctant to authorize more spending on Zika prevention, but the most practical tests for such surveys — antibody tests — are the least accurate for Zika infections, because earlier infections with dengue or yellow fever create false positives.

Via NY Times.