Paul Mead, MD, currently works in the CDC’s Emergency Operations Center, focusing on Zika virus. When he’s not working on Zika, he is chief of epidemiology and surveillance for Lyme disease. For the time being, though, he’s leading the team that’s counting Zika cases and watching for something experts think is inevitable — the first U.S. case of Zika infection that doesn’t involve travel. When they find it, it will mean the virus has infected mosquitoes here and that many more Americans could be at risk. The interview was edited for clarity and length.
WebMD: What are you keeping an eye on?
Mead: We’re trying to monitor the overall situation of the number of cases coming in — right now we have 98 cases that have been reported officially to CDC in the U.S. — but we’re also trying to pick out those that suggest something unusual or different.
WebMD: What are those cases of high interest?
Mead: We’re concerned about finding cases in pregnant women because of the virus’s association with birth defects and because it may affect [the women's] care and management. We’re concerned about the potential risk of transmission through blood products, so finding cases related to that. We’re concerned about cases of sexual transmission, which suggests a different form of prevention. We’re concerned about local transmission through vectors [mosquitoes].
WebMD: Have there been any cases of locally transmitted Zika infections in the U.S. yet?
Mead: No. We thought we had one. A doctor in Texas saw microcephaly [a birth defect which causes an unusually small head in babies] on an ultrasound. The mother hadn’t traveled or had sexual contact with a traveler and it was in Brownsville, which is one of the areas that has the Aedes mosquitoes [the mosquito that spreads Zika virus]. But the baby was born and was totally normal, so it was a false alarm.
WebMD: What do you think locally acquired infections will look like here?
Mead: Our best model for this is chikungunya virus. To my knowledge, the only local transmission that was seen was in southern Florida. Between 2014 through September of 2015, there were about 3,000 cases of chikungunya reported in Americans who traveled and came back. But there were only about a dozen or so cases of local transmission. It ended up not being a huge component of the outbreak. And that’s our best model for this, but we never know. That’s why we do surveillance.
WebMD: Right now, there’s a lot of circumstantial evidence—strongly circumstantial, but still circumstantial—that Zika virus causes birth defects like microcephaly–where babies are born with smaller than normal heads and brains– and that it’s triggering cases of paralysis caused by Guillain-Barre syndrome. What’s the piece of evidence that would be the smoking gun that would prove to you that Zika is the cause of these things?
Mead: The evidence is probably pretty strong at this point. We have good evidence from individual cases—children with birth defects and serious problems having virus in their brain tissues. That is pretty suggestive …. We have a spike in Zika virus disease in Brazil followed seven months later by a spike in birth defects. That helps support it. That’s one bit of evidence. We’re running a case control study to look at normal children born at the same time as the microcephaly children.
In some ways, proof is kind of the weight of many different kinds of scientific evidence that’s kind of decided by the scientific community as a whole, when people really become convinced.