Lyle Petersen, MD, MPH, director of the Division of Vector-Borne Diseases at CDC’s National Center for Emerging and Zoonotic Infectious Diseases. Photo by CDC.

Since the Zika outbreak was announced in late 2015, the U.S. Centers for Disease Control and Prevention has been instrumental in responding to the virus. We checked in with Lyle Petersen, MD, MPH, director of the Division of Vector-Borne Diseases at CDC’s National Center for Emerging and Zoonotic Infectious Diseases, for an update on what we’ve learned in the past year about Zika and how we can better address vector-borne threats in the future.

Q: It’s been just over a year since alarm grew around the spread of Zika. What was the tipping point that spurred U.S. action?

CDC started working with the Brazilian Ministry of Health in November 2015, shortly after local investigators reported microcephaly possibly associated with Zika. After additional evidence that microcephaly was associated with Zika virus infection, CDC activated its Emergency Operations Center in January 2016 based on the experience with chikungunya and dengue, viruses spread by the same mosquito vector as Zika virus, indicated that Zika would rapidly spread throughout the Americas. CDC also issued the first travel notices to alert travelers about the risk of Zika virus transmission. I believe the tipping point that subsequently galvanized public attention was the discovery of Zika virus in fetal brain tissues and CDC’s subsequent report in the New England Journal of Medicine that concluded a causal relationship between Zika and birth defects. CDC’s Emergency Operations Center remains at a Level 1 response, the highest level, after more than a year of activation.

Q: What was most surprising or unexpected in the response?  

This outbreak has been unusual on a number of fronts. Zika is the first mosquito-borne virus known to cause severe birth defects and the first such virus known to be sexually transmitted. In addition, although we expected some local transmission in South Florida, we didn’t expect to see significant outbreaks in downtown Miami based on our past experiences with similar viruses, such as dengue and chikungunya. These factors among others have made the fight against Zika one of the most complex epidemic responses that we’ve seen at CDC. It has required expertise from across the agency, including subject matter experts in pregnancy and birth defects, mosquito control, laboratory science, travelers’ health, virology, transfusion medicine and communication science. On the other hand, we accurately predicted the rapid spread of the virus and that the virus could also be spread through blood transfusions.

Q: We’ve learned a lot in a year. What else do we need to learn about Zika? 

I’ve already mentioned some of our big advances from the past year, but we do have a long road ahead until we fully comprehend Zika virus. Mostly, we still need to understand the full range of effects of Zika virus infection during pregnancy, and we know that the necessary studies to reach this understanding may take years to observe and understand. We need to understand how long Zika virus can persist in areas of the body, especially semen, so that we can provide better guidance to reduce the risk of transmission. We also need improved rapid and accurate diagnostics to provide pregnant women and their health care providers with information about current or recent Zika virus infection. We will need to assess the long-term epidemiology of Zika, which will have major effects on future travel recommendations, measures to reduce blood transfusion transmission and vaccination policy once a vaccine becomes available.

Finally, to understand the full risk of and respond to Zika, we need to learn more about the mosquitoes that spread Zika virus. We need a more complete map of where these mosquitoes live in the United States, so that we can better predict the risk of local transmission in areas throughout the country. We also need to know, at the local level, whether these mosquitoes are resistant to certain insecticides and to use that information to make informed decisions about what mosquito control methods are used. We also need to find more and better ways to control the mosquitoes that spread Zika virus.

Q: What other vector-borne threats concern you most? 

We are seeing an accelerated threat from mosquito-borne diseases overall. Over the past few decades, we have seen a resurgence of dengue and the introduction of West Nile virus, chikungunya virus and now Zika virus into the Western Hemisphere. Out of the more than 200 other arboviruses out there, we know of 86 that can hurt people. It is very hard to determine which one might come next – Zika virus wasn’t on anyone’s radar screen before it became an international threat. What we do know is that in this age of globalization, more will be coming – we just don’t know from where or when. Mayaro virus, a mosquito-borne virus, sprang up in Haiti for the first time in September 2015. We do not know if Mayaro virus will appear in other new locations or what the effect might be. Usutu virus, which is similar to West Nile virus, has been spreading throughout Europe and if introduced into the United States, has the potential to spread widely. Japanese encephalitis virus could also be introduced into the U.S., as mosquitoes that could spread the virus exist here. We have seen a resurgence of bacterial and viral tick-borne diseases as well. Although the tick-borne diseases do not cause large outbreaks and consequently often don’t make headlines, we have seen a geographic expansion of Lyme disease and about 300,000 cases now occur annually.

Q: After a year of Zika response, are we better prepared now for the next vector-borne threat? 

We have learned a lot; we truly have. And I believe that knowledge will help us to respond faster and better to the next threat as we continue to build on this experience and develop tools to respond. Thanks to the Zika supplemental funding that we received in the fall of 2016, we’ve been able to provide advanced support to state and local health departments in the areas at highest risk for transmission in the upcoming mosquito season. Given the recent history of mosquito-borne diseases in the U.S., we do need to think about how to maintain long-term, sustained epidemiology, laboratory and entomology capacity in state and local health departments.

We also need to think about and evaluate our local mosquito control tools to ensure that state and local jurisdictions have what they need to combat threats such as Zika. A trained and prepared workforce, including entomologists, is also critical to ensure that vector control measures are carried out consistently and effectively from county to county and state to state. Right now, we see a lot of variance in this area, which makes it harder for us to be fully prepared for the next threat. But, all in all, I would say – absolutely, we are better prepared now than we were a year ago. We intend to do all that we can to make additional improvements as we learn more about vector-borne viruses like Zika.