Although the Zika virus is most often transmitted by the Aedes aegypti mosquito, it's important to remember that it can also be sexually transmitted from infected male partners. Unfortunately, at this time scientists don't know for sure how long semen can carry Zika, but it definitely lasts a lot longer than it does in the blood.

According to PBS, a British man contracted Zika in the South Pacific in 2014 (that's the same strain of Zika that's currently making its way throughout the Americas). The man was studied by Public Health England (the country's equivalent to the United States' Centers for Disease Control), and blood, urine, and semen samples were taken from the patient at regular intervals after his recovery. Traces were still detectable in his semen 62 days after he became ill, long after the virus disappeared from his blood and urine. Public Health England did not grow live samples from the traces, so it's unknown whether 62-day-old Zika still has the potential to infect a partner, but it's really not something one should gamble on. According to The Lancet, Ebola virus has been detected in semen as long as nine months after onset, so it's quite possible that Zika could last just as long.

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RECIFE, BRAZIL - JANUARY 26: Biologist Danielle Varjal demonstrates her research with Aedes aegypti mosquitos in a lab at the Fiocruz institute on January 26, 2016 in Recife, Pernambuco state, Brazil. The Aedes aegypti mosquito transmits the Zika virus and is being studied at the institute. In the last four months, authorities have recorded close to 4,000 cases in Brazil in which the mosquito-borne Zika virus may have led to microcephaly in infants. The ailment results in an abnormally small head in newborns and is associated with various disorders including decreased brain development. According to the World Health Organization (WHO), the Zika virus outbreak is likely to spread throughout nearly all the Americas. At least twelve cases in the United States have now been confirmed by the CDC. (Photo by Mario Tama/Getty Images)

Unfortunately, this is just one of many unanswered questions regarding the sexual transmission of Zika; scientists still don't know if infected men without symptoms can spread Zika, if women can spread Zika, or if it can be spread through oral sex (although the prevailing hypothesis is that it probably can be). To that end, the CDC has issued some very cautious guidelines for safe sex in the time of Zika:

  • Asymptomatic men in Zika-affected areas should use condoms or abstain from sex while in the area
  • Men who have visited Zika-affected areas but are asymptomatic should use condoms or abstain from sex for eight weeks following their return
  • Men who have been diagnosed with Zika or had symptoms of Zika should use condoms or abstain from sex for at least six months after symptoms began

Bummer, I know. But it's preferable to risking Zika, which can cause a whole host of birth defects, not the least of which is microcephaly. And it's not just pregnant women who need to worry; Zika may also lead to Guillain-Barré syndrome or acute disseminated encephalomyelitis in adults. This is bad news, but it could be worse. There could be half a million people planning on traveling to Zika virus ground zero this summer for a sporting event (the Olympics)... Oh, that's right, there are.