Zika Virus: Are Climate & Ecological Factors Driving Spread of Viral Diseases in the Americas?

February 04, 2016


Amy Vittor

assistant professor of medicine at the University of Florida’s Division of Infectious Disease.

Anne Schuchat

principal deputy director of the Centers for Disease Control and Prevention.

We look at the spread of the Zika virus, which scientists have linked to rising temperatures from global warming because of the increased incidence of mosquito-borne infections. The illness, while generally not life-threatening, has been linked to the birth defect microcephaly, which causes babies to be born with abnormally small heads. The World Health Organization has declared the Zika virus an international public health emergency, saying the virus is "spreading explosively" and that up to 4 million people in the Americas could be infected by the end of this year. Brazil has been hardest hit by Zika with over 4,000 cases of infants with severe birth defects which could be linked to the virus. Meanwhile, officials in Texas have reported the first case of the virus contracted in the United States, saying it was sexually transmitted. We are joined by Dr. Anne Schuchat, principal deputy director of the Centers for Disease Control and Prevention, and Dr. Amy Vittor, assistant professor of medicine at the University of Florida’s Division of Infectious Disease.


This is a rush transcript. Copy may not be in its final form.

NERMEEN SHAIKH: We turn now to the Zika virus. Brazilian President Dilma Rousseff has declared war on the mosquitoes responsible for spreading the Zika virus. Brazil has been hardest hit by Zika with over 4,000 cases of infants with severe birth defects which could be linked to the mosquito-borne virus. President Rousseff spoke in a televised address Wednesday.

PRESIDENT DILMA ROUSSEFF: [translated] All of us need to take part in this battle. We need the help and goodwill from everyone. Collaborate. Mobilize your family and your community. I will insist, since science has not yet developed a vaccine against the Zika virus, the only efficient method we have to prevent this illness is a vigorous battle against the mosquito.

NERMEEN SHAIKH: Meanwhile, earlier this week, officials in Texas reported the first case of Zika virus contracted in the U.S., saying it was sexually transmitted. If confirmed, it marks only the second known case of Zika transmission through sexual contact. Zika has continued to spread rapidly across Latin America, with Chile reporting its first three cases. The mosquito-borne illness, while generally not life-threatening, has been linked to the birth defect microcephaly, which causes babies to be born with abnormally small heads.

AMY GOODMAN: Earlier this week, the World Health Organization declared the Zika virus an international public health emergency. The World Health Organization says the Zika virus is spreading explosively and that up to 4 million people in the Americas could be infected by the end of this year. World Health Organization Director-General Dr. Margaret Chan spoke at a news conference in Geneva.

DR. MARGARET CHAN: I am now declaring that the recent cluster of microcephaly and other neurological abnormalities reported in Latin America, following a similar cluster of French Polynesia in 2014, constitutes a public health emergency of international concern.

AMY GOODMAN: Scientists have linked rising temperatures from global warming to the increased incidence of mosquito-borne infections such as Zika.

To talk more about this, we’re joined by two guests, but we’re going to start with Dr. Anne Schuchat. She is the principal deputy director for the CDC, the Centers for Disease Control and Prevention, has worked for several decades in the field of public health.

We welcome you to Democracy Now!, Dr. Schuchat. Can you explain what Zika is and what your major concerns are in the United States right now?

DR. ANNE SCHUCHAT: The Zika virus is a mosquito-borne virus that can cause mild illness—or no illness, in most people. But in some people who are pregnant, we believe it can likely cause severe birth defects. This is a mosquito that’s—a virus that’s carried by the Aedes aegypti mosquito, and that’s a mosquito that is widespread in Latin America and is present in the southern United States, as well. Although the virus has been known since 1947, it’s only recently that this possible link with the birth defects has come to rise. And that, of course, has raised major concern around the world, including at the World Health Organization and at the Centers for Disease Control and Prevention.

NERMEEN SHAIKH: Dr. Schuchat, could you talk about the extent of the virus in the United States and the likelihood of its spread here?

DR. ANNE SCHUCHAT: It is extremely likely that we’ll have many cases among travelers. We’ve already had dozens of cases among travelers who return from Latin America with a mild illness and are tested and show to have a history of the virus. We do expect there may be some local transmission here in the U.S., in the southern parts of the U.S., where there in the past has been tiny bits of local spread, mosquito-borne spread, of dengue virus or chikungunya virus, related viruses that are mosquito-borne, as well. But we don’t expect that in the United States we’ll have the large outbreaks that they have seen in parts of South America or Central or Caribbean America. And that’s because the living conditions are so different in the U.S., with air conditioning pretty widespread, screens in use, and not the very dense populations and dense mosquito populations in those southern areas where the mosquito is present.

AMY GOODMAN: Dr. Schuchat, on Wednesday, Florida Governor Rick Scott declared a state of emergency in the four counties where people have been diagnosed with the Zika virus in Florida. What’s your response to this?

DR. ANNE SCHUCHAT: I think it’s important for everyone to be taking this threat very seriously. We know that the mosquitoes are present in some parts of the country, and I think that idea of being on alert and responding quickly to make sure that we don’t get local spread, or that we tamp it down if we have it, is an important tool. CDC is working 24/7 with the state and local health departments to make sure that they can diagnose this disease and recognize it and report it, and also working hard to get guidance out for pregnant women and others who may be at risk. And so, we think it’s really important for the U.S. to be following this story and the Florida reaction, to make sure that they’re on top of any risk that might occur, in terms of local spread.

NERMEEN SHAIKH: Well, some here in the United States have suggested that El Niño is expected to bring heavy rain in the South over the next few months, and this may affect the spread of the virus here.

DR. ANNE SCHUCHAT: You know, the weather conditions are always important in infectious diseases, but I think we believe there are other factors that are more important in the emergence of such a large problem with Zika in parts of South America. We think that globalization, with all the travel that we have, and, in particular, urbanization, is potentially responsible for the large outbreak that Brazil has described. You know, when this mosquito-borne virus gets into very dense urban populations where there’s a lot of mosquitoes and a lot of people living in close proximity, you have a chance for more efficient spread of the mosquito-borne virus.

AMY GOODMAN: I wanted to ask you, an issue not related to this, but because you’re one of the heads of the CDC, Dr. Anne Schuchat, the latest recommendation of the CDC that sexually active women who are not on birth control should refrain from alcohol to avoid the risk of giving birth to babies with fetal alcohol spectrum disorders, even if those women are not pregnant, to which Jezebel wrote a headline, "An Unrealistic Warning from the CDC to Women: Don’t Drink Unless You’re Using Birth Control." Your response?

DR. ANNE SCHUCHAT: Fetal alcohol spectrum disorder is a difficult condition for children and their families. It can cause behavioral, intellectual and physical disabilities that can be lifelong. It’s 100 percent preventable, if the developing baby is not exposed to alcohol. In the United States, one out of two pregnancies is unplanned, and most women don’t know they’re pregnant during the first month or so. And so, if you want to make sure that you avoid alcohol exposure to your developing baby, it’s really important to be taking steps to not get pregnant, or not drinking if you might become pregnant.

So I think, of course, that’s a difficult message for people. But in my experience, most women are really keen to do everything they can to increase the chances they’ll have a healthy baby. And we were pleased to raise awareness that you might be pregnant without even realizing it, so please be careful about your drinking exposure. Over the years, science has advanced, and we realize now there’s no safe level of drinking during pregnancy. People used to think it was OK to have a drink now or then, or it was OK to have wine or beer, but not hard liquor. But actually now we know that any level of alcohol can be risky to the developing fetus. So, of course, women will take that message as they want to, but we really do want to do what we can to help people have the healthiest babies they can have.

AMY GOODMAN: Dr. Anne Schuchat, I want to thank you for being with us, principal deputy director for the CDC, the Centers for Disease Control and Prevention, has worked for decades in the field of public health, as we turn now to an expert in Florida.

NERMEEN SHAIKH: Well, to look more at the Zika virus and its link to climate change, we turn now to our next guest. Dr. Amy Vittor is assistant professor of medicine at the University of Florida’s Division of Infectious Diseases. She’s joining us from Gainesville.

Welcome to Democracy Now!, Dr. Vittor. Could you talk about this virus and how serious it is compared to other mosquito-borne viruses?

DR. AMY VITTOR: Yes, I’d be happy to. Good morning.

Zika virus is, no doubt, serious, just as we heard; however, placed in the larger context of diseases around the world, especially mosquito-borne viruses that are equivalent, it needs to be remembered that, for example, dengue virus causes 100 to 400 million infections a year with about 25,000 deaths. Chikungunya just blew through here—our continent, that is—and that led to about a million different cases, and also in India another million and a half or so cases. So, while Zika is quite important, I think, stepping back, we realize that, actually, this is just a series of viral-borne diseases that are now reaching our continent.

NERMEEN SHAIKH: So what do you think accounts for the fact that the World Health Organization has declared Zika a global health emergency?

DR. AMY VITTOR: No doubt the microcephaly piece spurned that. And it’s quite understandable. With so many unknown factors, it makes sense to try to get ahead of the game and warn people, coordinate efforts. So, with the microcephaly, definitely the stakes have been raised, and fear has definitely been also raised amongst people who are affected, and therefore I think it’s quite reasonable to sound the alarm and ensure that research be undertaken quickly and control measures, especially mosquito-control measures, be undertaken quickly.

AMY GOODMAN: Texas officials, reporting on the first case of Zika virus contracted here in the United States, say it was sexually transmitted. Can you explain this, Dr. Vittor?

DR. AMY VITTOR: Well, we don’t understand the pathogenesis of this, I have to say. It is the second time this has been reported, as far as I’m aware. The first time was actually in Colorado in a traveler who returned from West Africa. And so, it was known that it can occur in the semen, probably, the virus. But how long it stays there and what it does in the genitourinary system, we really don’t understand. Nor do we understand the implications of this in terms of how much the virus can spread sexually, in addition to being mosquito-borne.

AMY GOODMAN: Its relationship to climate change?

DR. AMY VITTOR: Well, this is a very muddled picture. The best data we have is really from the dengue climate change world. There have been many models that have looked to model the transmission of dengue under different climate change projections. And what seems to be the case is that there might be a slight increase in the range of the mosquito vector, Aedes aegypti, and also Aedes albopictus, moving northward in the Northern Hemisphere and southward in the Southern Hemisphere.

Now, I say muddled because there are many different effects of climate change, and they’re very local. Some areas may experience more rainfall and higher temperatures, whereas other places might experience the opposite. Also, some areas that are currently already warm may become too warm for the breeding of the mosquito, so that certainly adds an element of complexity. And furthermore, we don’t really understand how the mosquitoes are going to adapt. There’s been an interesting study looking at the mosquito adaptation to changing climate, and they’re actually very flexible, very plastic, and they seem to be adapting to changing climate in Trinidad, for example, by seeking out new types of breeding sites. And then, furthermore, we’re not sure how humans will react and how we will change the way that we interact with the mosquito. In other words, we may actually increase our use of screens, change our mosquito control policies. And all this together adds for a very confusing picture. And then, of course, for Zika specifically, we don’t have any data.

NERMEEN SHAIKH: In another study you did with your colleagues, you examined the association between deforestation, mosquito vector factors and the susceptibility of migrants compared with indigenous people in affected areas. Could you talk about the results of that research and how that might compare to the potential spread of the Zika virus?

DR. AMY VITTOR: Well, that study that you’re referring to is ongoing, actually, and it’s in relation to a virus called eastern equine encephalitis virus in Panama, now actually renamed Madariaga virus. And it behaves quite differently, though, than Zika virus. But what we are starting to see, following an outbreak in Panama of this disease, is that there seem to be household factors. So, lack of sanitation, for example, appear to be associated with increased risk for having been exposed to this virus. Similarly, having particular agricultural exposure seems to be another risk factor for this particular virus. And what’s interesting in this region is that there’s been a massive movement of people into the Darién province, which was formerly forested. Now, vast swaths are deforested, and they’ve become pastureland for cow and cattle. And how exactly this is going to play out, we don’t understand yet; we’re in the process of figuring that out.

But I think it’s very instructive to understand that West Nile virus, dengue virus, chikungunya and Zika all actually probably originate from the Central African forests. And subsequent to human contact, as humans venture in and encroach upon that forest, it’s possible that the virus and the mosquitoes ultimately adapt to, then, human cycles, and from there it’s able to spread worldwide. So, there are, again, many unknowns in the sequence of events, but I think it’s very prudent to take a closer look at the ecological effects of—the ecological effects that may precipitate further vector-borne illness emergencies.

AMY GOODMAN: Amy Vittor, we want to thank you for being with us, assistant professor of medicine at the University of Florida’s Division of Infectious Disease.

That does it for our broadcast. Happy birthday to Hugh Grand. We also have job openings: broadcast engineer, director of finance and operations and director of development. Check our website.

The original content of this program is licensed under a Creative Commons Attribution-Noncommercial-No Derivative Works 3.0 United States License. Please attribute legal copies of this work to Some of the work(s) that this program incorporates, however, may be separately licensed. For further information or additional permissions, contact us.

Email icon redDaily News Digest