Lyle Petersen, MD, MPH: What Do We Now Know About Zika Virus?

Lyle Petersen, MD, MPH, Director of Vector-Borne Diseases, Centers for Disease Control and Prevention: I think there's a couple things we found out last year that we know a lot more of. First of all we have a better idea about the effect on the fetus when the mother has been infected. So now we know that once a mother becomes infected during her pregnancy about 5—10% of the fetuses will be affected. So we have pretty good data at that, and we also know that the primary risk is for a woman who's gotten infected toward the end of her first trimester, early second trimester, although we have seen birth defects occur all when the mother has been infected in any of the 3 trimesters, it just seems to be worse early on in the pregnancy.

The 1 thing we don't know though is what the full spectrum of disease actually looks like with Zika. What we're finding is, is that some babies that appear to be normal at birth, have developmental problems later on. We don't know what the frequency of this is, but we're quite concerned that there may be a larger cohort of affected babies that are just not initially recognized at birth that may have developmental problems later on or ocular problems or other kinds of problems that we still have to elucidate.

The other the other issue is sexual transmission. We've seen 48 cases of sexual transmission in the continental US, obviously there's probably a lot more that happened because we're only going to recognize the ones where both the male and the female are symptomatic and have been tested. So there's probably many more that's happened than the 48, but this has been really unusual because this is the only mosquito-borne virus that we know of that's sexually transmitted among humans. What we do know about that is, is that the primary risk of transmission is from male to female and because there's very high levels of virus and the sperm, but we also think that that risk is fairly short-lived you know a month or 2 although we can detect viral RNA in semen for much longer, let's say 6 months or even longer than 6 months in some people. So we don't know the absolute risk period, so we are recommending that take precautions against sexual transmission of Zika virus for 6 months.