As the Zika virus continues to spread through the Americas, health officials in the U.S. are hurrying to learn more about the virus and prepare for cases. Currently, the emergency operations center at the U.S. Centers for Disease Control and Prevention (CDC) is on its highest-level alert for the Zika response — only the fourth time in its history. We spoke to CDC director Dr. Tom Frieden about the ongoing outbreak and what we are learning along the way.
Researchers are working on the connection between Zika and microcephaly. Has a lot been learned in the last month?
Absolutely. Every day we are learning more about this virus and how it is currently behaving. I think we can say that the link between Zika and Guillain-Barré looks strong and would not be at all surprising. We’ve seen similar post-infection complications after many different infections, including some that are quite similar to Zika. The link to microcephaly is also getting stronger. It’s not definitive proof yet. It will take more time, including understanding what happens when Colombia and other countries that have large numbers of infections progress so that the women who were infected in the first trimester deliver. We have another investigation team in Colombia.
We currently have about 500 people working on this response at the CDC. This is a big challenge; it is extraordinarily unusual to identify a new cause of a birth defect, and as far as we know, it's unprecedented to [find] a mosquito-borne cause of a birth defect. So people are concerned, and we understand that. That’s why we are working hard to get as much information as accurately and quickly as possible. We are also now certain that sexual transmission is possible, and this is why we advise men who have sex with women who are pregnant, if they might have a Zika infection because of their travel or residence, to use a condom.
What kind of evidence are you seeing that makes the connection with microcephaly stronger?
We were able to see the actual virus in the brain tissue of infants who had died of microcephaly, and the reaction of the body made it clear that this was a virus that was causing serious problems to the infant. This was likely the cause of the microcephaly in those cases. That doesn’t tell us whether there might have been cofactors, like other infections, that might have led to it, and it doesn’t tell us what proportion of women who get infected may deliver an infected child, but it does suggest the strongest link to date. Also, the epidemiology is suggestive with the peak of Zika being followed a certain number of months later by a peak of microcephaly. I would say the evidence is getting steadily stronger for a causal link.
Lately, people have been talking about whether microcephaly could be linked to larvicide. Is there any truth to this?
We looked at the rumor that was circulating about larvicide, and we never dismiss anything out of hand. We always want to look openly at any suggestion. And we base our recommendations on science. The larvicide that was mentioned in the Internet was used for many years in many parts of the world with no tie to microcephaly. There’s never been a link to microcephaly in humans or animal models. It wouldn’t explain why we are seeing Zika virus in the brains of children who died of microcephaly, and it wouldn’t explain the time course between Zika exposure and microcephaly, and it doesn’t explain the increase in microcephaly in French Polynesia, which doesn’t use that larvicide. So we don’t see evidence that supports that allegation. One thing that many people are thinking about is whether a prior infection with dengue predisposes a pregnant woman to have this complication, but there is zero evidence for that either. We need to learn more. This is a very unusual situation. It's unprecedented, and our commitment is to learn as much as we can as quickly as we can and to communicate what we learn openly and immediately.
What are you seeing in terms of cases of Zika reported in the U.S.?
We really do expect that there will be hundreds, if not thousands, of travel-associated cases in the U.S. There are more than 40 million travelers in the U.S. to Zika-affected countries every year. That’s a lot of people. So far there have been 84 travel-associated reported cases. In Puerto Rico, there are more than two dozen locally transmitted cases. We also have cases officially reported from the U.S. Virgin Islands and American Samoa. We do know of pregnant women who became infected with Zika while traveling who are in the U.S. now. The bottom line for most Americans is, if you’re pregnant, don’t travel to Zika-affected areas. And Americans who live in places like Puerto Rico, who are in areas where Zika is spreading, do everything you can to protect yourself against mosquito bites, with DEET and long sleeves. Stay indoors in air-conditioning, and at least in screened places, if at all possible.
Of the cases in Puerto Rico, have there been any cases of microcephaly?
No, and we would not expect any at this point. We assume that infections in the first trimester or early second trimester are the ones most likely to cause this malformation, and they wouldn’t be due yet, so to speak. We have, however, seen Guillain-Barré cases both in Puerto Rico and in the continental U.S., and we have seen miscarriages as well. There is a strong association between Zika infection and specific Zika virus presence in the placenta and miscarriage.
More than 80% of adults in Puerto Rico are infected with dengue. About a quarter of adults became infected with chikungunya in less than 12 months. If Zika follows the same pattern, we will see a very large number of Zika infections at some point in the coming weeks or months, and it’s not possible to predict exactly when.
How is the CDC getting rapid testing to states in the U.S.?
We have made good progress in the past few weeks. Our lab staff have done a terrific job working around the clock. Currently we are just finishing up the production of reagents that are sufficient to do 100,000 tests for prior infection with Zika. I think we may still in the next two to four weeks be in a situation where somebody will want to get testing and can’t, but within a month or two, there will be ample product available through the state public laboratories through what’s called the laboratory response network.
You recently tweeted about the lack of research for Zika up to this point. Are there other infectious diseases that seem unthreatening now but the world should be paying attention to?
There is so much that we need to do to strengthen our preparedness. One of the things is getting a sense of what’s happening in other parts of the world through better detection systems. Another is understanding certain viruses more. I will give you one example. Through the Global Health Security Agenda work that the President proposed and Congress funded as part of the Ebola supplemental, we are working with 17 countries around the world to strengthen their ability to find and stop health threats. In India, for example, our partners are already beginning to look to see if Zika is a problem, but they are also finding a disease that can be quite severe in a much wider distribution than was previously recognized. It’s called Kyasanur Forest Disease, or KFD, and I am not saying it’s a threat in the U.S., but it’s a tick-borne infection that can cause an Ebola-like syndrome. It does that much less often than Ebola, but the fact that there are a lot of dangerous organisms out there, and with the amount of mobility and travel and trade that we have, we need to expect the unexpected. That’s why it’s so important that we continue to build systems around the world to find, stop and prevent health threats.
President Obama recently announced that he is asking for $1.8 billion to fight Zika. How will that help the CDC efforts?
We need to be able to produce diagnostics in large numbers so that people can find out if they’ve been infected. We need to strengthen the capacity within states to find and stop mosquitoes. We need to advance vector control and figure out better ways to stop mosquito-borne illness. We need to partner with international cooperation efforts to learn more about Zika so that we can be better prepared here and support other countries in their response. We need to monitor for outcomes of women who are Zika-infected, and we will need a robust response in Puerto Rico and other U.S. territories, which are likely to see very large numbers of cases of Zika infection.
Is there anything else about this outbreak Americans should know?
This is another example of why it’s so important for us to be engaged and involved in health threats around the world. It’s the right thing to do, it’s also the best way to keep Americans safe. The sooner we can figure out about problems that are emerging anywhere in the world, the sooner we can figure out how to protect Americans from them. That’s what we are doing here, and that’s why we have to continue to focus on building our public-health programs and cooperation with countries around the world.