There's still a lot that we don't know about the Zika virus, a mosquito-transmitted illness that World Health Organization director general Margaret Chan says has been "spreading explosively" in the Americas.
We do know that the spread of Zika in Brazil (where the current outbreak in the Americas really took off) has been linked to an alarming increase in the number of babies born with microcephaly, a much smaller head and brain than normal.
While there's not yet definitive proof that Zika in pregnant mothers causes microcephaly in their babies, "lab tests at the CDC strongly suggest a link," Centers for Disease Control and Prevention principal deputy director Dr. Anne Schuchat said on a press call on January 28.
One of the other mysteries about the currently untreatable Zika has to do with its transmission. While it's primarily a mosquito-transmitted virus, there are reasons to believe that Zika might be sexually transmitted as well.
To be clear: This is not something to panic about. Most people living in the US (as opposed to many Central and South American countries) have almost no chance of catching Zika, unless they travel to a place where the virus is being transmitted. Even in those places, mosquitoes are far and away the main route for Zika infections, which is why efforts to slow the virus's spread are currently focused on mosquito control.
But from the perspective of trying to understand the virus and how it spreads, it is interesting that several cases indicate that Zika can spread through sex.
Schuchat explained that there are two cases that indicate the biological plausibility of sexual transmission.
The first occurred in 2008, when two US researchers were infected with Zika in Senegal. In a report of the incident that was published in the journal Emerging Infectious Diseases, the authors report that after returning to Colorado, one researcher and his wife observed "red–brown fluid in his ejaculate." That same day, the researcher's wife developed malaise, chills, severe headache, extreme sensitivity to light, and muscle pain — all symptoms of a Zika infection. Blood test results show that she too was infected.
In this case, the researchers assume that Zika was transmitted sexually, since the researcher's wife hadn't traveled and there were no mosquitoes in the area that are known to be able to transmit the virus. Plus, none of the four children in the house were infected, and there's no indication at all that Zika can spread like a cold or flu.
The other bit of evidence for possible sexual transmission comes from Tahiti in 2013, in the midst of a Zika outbreak. A 44-year-old man sought treatment after noticing blood in his semen (he had Zika symptoms twice a few weeks before but hadn't sought medical care, since those symptoms are usually mild). Researchers were able to isolate the virus in semen and urine samples, though not in his blood.
These are only two cases, so it's possible that this is very unusual. But the ability of a virus to persist somehow in a person's body even after they are "cured" is not unheard of. Disturbingly, the Ebola virus seems to do the same thing in some cases, something that was only learned during the recent epidemic.
CDC officials did say that most people don't have much to fear from Zika from what we know right now, as symptoms are usually mild (if they appear at all). The exception is pregnant women or women who plan on becoming pregnant.
For those women only, Schuchat says the CDC recommends postponing travel to affected regions. If you have to go, she said to take all possible precautions to avoid mosquitoes, including using insect repellent with DEET, which she says is safe to use during pregnancy.
