The Centers for Disease Control and Prevention (CDC) have confirmed that Zika is already a sexually transmitted disease. Public health experts now know that Zika can be passed in bodily fluids. So far, in the continental United States, 15 cases of Zika are confirmed to have been transmitted by sexual contact. This has been reported in ten other countries, and in the United States, the first known case of sexual transmission was in 2008. Until the giant South American outbreak began, Zika was under-researched, and that was true for sexual transmission of the disease as well.
It seems clear that Zika virus can persist in some bodily fluids longer than it does in the bloodstream, which is where mosquitoes pick it up. Some small studies have shown viral persistence in urine and saliva up to 21 days, and a recent study found the virus in cervical mucus as well. The biggest risk appears to be semen: Studies have shown molecular traces of the virus, though not necessarily infectiousness, for as long as 93 days. But the research that could determine how long that transmission risk lasts, and whether it is the same for people with no symptoms, has not yet been done.
The CDC’s updated advice now is: “Men and women who want to reduce the risk for sexual transmission of Zika virus should use barrier methods against infection consistently and correctly during sex or abstain from sex when one sex partner has traveled to or lives in an area with active Zika virus transmission.”
The point of the new advice is twofold: to protect pregnant women, or ones about to become pregnant, from risking a devastating birth defect; and also to slow down the transmission of Zika from infected travelers into the rest of the population. But it emphasizes the tricky nature of detecting and preventing the advance of Zika, since four out of five people infected show no symptoms.