MS. INDIRA LAKSHMANANThanks for joining us. I'm Indira Lakshmanan sitting in for Diane Rehm. She's out today. The mosquito-borne Zika virus was first reported in Brazil last May. Cases have now been seen in 21 countries and territories across the Caribbean and North and South America. With me in the studio today to talk about efforts to control the spread of the virus, Dr. Anthony Fauci with the National Institute of Allergy and Infectious diseases and Maggie Fox, health reporter with NBC News.

MS. INDIRA LAKSHMANANAnd joining us by phone from Galveston, Texas, Scott Weaver at the Institute for Human Infections and Immunity at the University of Texas medical branch in Galveston. Welcome, everyone.

DR. ANTHONY FAUCIGood to be with you.

MS. MAGGIE FOXGood morning.

MR. SCOTT WEAVERGood to be with you.

LAKSHMANANAnd to our listeners, as always, we're eager to hear what you think. Are you reconsidering travel to Latin America because of the virus? Call us this hour with your comments and your questions at 1-800-433-8850. You can also send us email at drshow@wamu.org. Join us on Facebook or send us a tweet. So I want to start out, Scott, with you because I think very few people in the U.S. had even heard of the Zika virus just a couple months ago, but it actually originated in Africa more than half a century ago. Tell us the history of the disease.

WEAVERThat's correct. So the virus was first discovered in 1947 when their studies going on in Africa to understand the enzootic or the wildlife cycle for yellow fever virus there and monkeys were placed out in the forest and became infected with Zika virus and also mosquitoes collected in the same region became infected. And then, a small about of additional experimental infection was done, including infection of one human volunteer.

WEAVERBut between that time, 1947 and 2007, there were only 14 human infections documented anywhere in the world with Zika virus so there was very little interest in this virus until very recently.

LAKSHMANANHum. So it actually started in the Zika forest in Uganda more than 60 years ago and then, I think, it spread to Tahiti and other parts of French Polynesia, is that right?

WEAVERThat's right, but we knew long before 2007 that the virus was present all over Africa based on finding antibodies in people who were part of various surveys. We also knew, in Asia, that the virus was present, again based mainly on the presence of antibodies in people. And there were a few infections documented, for example, in Cambodia in 2010. There were infections that were detected by a U.S. Navy research group there and we worked with them to diagnose the cases and characterized the Zika virus as genetically during that small outbreak.

LAKSHMANANAll right. Well, Dr. Fauci, the virus is now spreading through more than 20 countries in Latin America and the Caribbean. It's creeping closer and closer to the United States. We know that malaria is one of the leading causes of death, of communicable disease, in the developing world so how serious is the risk from this, which is another mosquito-borne virus?

FAUCIWell, you have to take a look at the disease itself and its affect on a person who does get afflicted with it. And fundamentally, it's a relatively mild and was considered to be an inconsequential infection from the standpoint of clinical consequences. It gives you fever, arthralgias, it gives you joint ache, it gives you running eyes or conjunctivitis. The reason we have an issue now and why there's so much attention paid to it is that there is an association, not necessarily totally proven to be cause/effect, but likely between infection in pregnant women and the occurrence of sometimes devastating, in fact often devastating, but sometimes leading to death and great disability called microcephaly in the fetus of a woman who has been infected during pregnancy.

FAUCISo that's something that we're seeing now to a considerable degree. The...

LAKSHMANANExplain to us, what is microencephaly (sic) for people who don't know.

FAUCIMicrocephaly, it describes a small size of a brain because the brain is either interfered with developmentally when you develop the cortex of the brain and other parts of the brain. When you get infected, the virus interferes with that development, but could also even later on suspecting that it might even be directly toxic to brains, even as they've gone further in their development. But what results is then you've seen the pictures in the newspapers, the terrible consequence of children who look like they have small heads, but it really is because the brain is either underdeveloped or damaged and that's terrible.

FAUCIYou can have stillborn. You could have babies die and even if they survive, you have terrible neurological consequences in some of them. So in that respect, it's a serious situation. But, in general, as an infection on the general population, it is not a devastating infection for the person who gets infected.

LAKSHMANANSo for adults, not as serious. For an unborn baby, extremely serious.

FAUCIIt could be devastating for an unborn baby, yes.

LAKSHMANANNow, have the links between the virus and microcephaly been definitively proven?

FAUCINot definitively proven, but if you look at a variety of different lines of evidence, you could look at association evidence, the association of the temporal and geographic emergence of Zika at the same time as you had more than a 20 fold increase in the incidents of microcephaly. Also there have been a number of situations where you've had the opportunity of getting a fetus, either a stillborn or a baby that dies soon after birth with a demonstration of virus in the brains of those baby.

LAKSHMANANI see.

FAUCIAgain, it doesn't definitively prove that it caused the microcephaly, but the association is strong enough to assume that it is.

LAKSHMANANBecause the virus was found in the brain of these children.

FAUCIExactly. But definitive proof would require a larger, what we call, case-control studies, where you do the kind of studies comparing a variety of factors. Are there co-factors involved? Is it Zika alone, Zika with something else, or is it something else that's enhanced by Zika? That's the reason why we're reluctant to say there's a definitive proof that it's causing it. But the association is strong enough to lead to the kinds of recommendations that we're seeing regarding travel on the part of pregnant women.

LAKSHMANANAnd these children who have it either die, perhaps before birth, or soon after, is it possible for them to survive at all?

FAUCICertainly, certainly. They can survive. But if they do, they are usually significantly impaired. And the impairment is going to be variable in its severity, but in general, it's usually quite severe.

LAKSHMANANAll right. Well, Maggie, let's talk about some of the impacts for adults who've contracted this disease. Zika has also been suspected to cause Guillan-Barre Syndrome, isn't that right?

FOXThat's right. There's some studies that we've reported on that indicate that there might be an increase, but that's something that a lot of viral infections can cause, that's neurological disorder and it's -- Dr. Fauci will know better than I, but I think it's often reversible or resolves itself. But it can cause temporary paralysis and it's quite a frightening syndrome.

LAKSHMANANUm-hum, all right. Has that tended to be the most serious effect for adults struck with this virus?

FOXThat's what the reports from people who have studied it seem to indicate. And 80 percent of the people who have it, apparently, they don't even know it. It's a very mild virus.

LAKSHMANANAll right. So in other words, it's hard to detect this disease because the symptoms are mild. What does it seem like? Does it feel like having the flu?

FOXI think that would be a bad case. I think most of the time, people don't even know they have it, which is one of the reasons it's flown under the radar. You don't really feel bad at all. I think Dr. Fauci was describing it. You have, like, a muscle ache, you might get pink eye, you might have a headache, you might run a low fever, but it's one of the reasons why it's also hard to know exactly how widespread it is because, of course, you're not going to test somebody who doesn't have symptoms to see if they have it.

LAKSHMANANWell, let me ask you, Dr. Fauci, is there any quick on-the-spot test for Zika virus to be sure?

FAUCIThat's a very interesting issue that can be problematic. So if you're talking about detecting the virus itself, there are tests that are used for a variety of viruses called PCR tests where you can actually definitively and in a very sensitive specific way determine if it's Zika. The problem is the virus doesn't hang around very long so if you get infected, within a few days to a week, you can no longer detect the virus. So the question is, how about detecting the history of having gotten infected, which is an antibody that you get against the virus.

FAUCIYou're not detecting the virus. You're detecting an antibody. The problem with those types of tests is that at this stage in development, there are very few labs that can do it, very specialized labs, and the CDC. Not a lot of laboratories throughout different clinics can do it. That's the first problem. The second problem is that there's cross reactivity because Zika is of a category of virus called flavivirus which is quite similar in the sense, in the same category as dengue, chikungunya, West Nile and yellow fever. And particularly...

LAKSHMANANOkay. A lot of yucky mosquito-borne diseases.

FAUCIWell, exactly. But in an area in which you have a very high prevalence of dengue, like in Brazil, that most of the population has some antibodies against dengue and it's very difficult, unless you go to the next level of test, to determine is this really a Zika antibody or is it a cross reacting antibody with dengue. So the diagnosis after the infection becomes problematic.

LAKSHMANANOkay. Scott, let me ask you in the minute we have before we go to a break, what is the danger of someone having it, being a carrier, not even realizing they have it? Can they communicate it to other humans without the mosquito being involved?

WEAVERWell, there is evidence that the virus is found in several other body fluids besides the blood, including the urine, the saliva and the semen. And there have been two cases fairly well documented of sexual transmission from men to women and so that's another concern for travelers. If a man goes to an endemic country, becomes infected, returns home, he also may not be symptomatic. We don't know whether you have to be symptomatic to transmit sexually. We know that there are many people who have lots of virus in their blood who remain without symptoms.

WEAVERSo it may be that even asymptomatic men could return home, transmit sexually and if their partner is pregnant, that could be a very severe risk as well.

LAKSHMANANAnd so these two cases that you referred to are they definitely again documented as proof of sexual transmission? 'Cause you would think it would be far more widespread than that.

WEAVERWell, there's complimentary evidence in these two. One was a study where scientists working in Senegal in West Africa became infected, returned home and then his wife, with no travel history, became infected. And then, a man in French Polynesia where the virus was actually detected in his semen.

LAKSHMANANAll right. We're going to take a short break. I look forward to hearing your questions and your comments. Stay with us.

LAKSHMANANWelcome back. I'm Indira Lakshmanan sitting in for Diane Rehm. Joining me here in the studio on this snowy day in Washington, they've braved the elements to come in and talk about Zika virus, are, Dr. Anthony Fauci, the director of the National Institute of Allergy and Infectious Diseases at the National Institutes of Health up in nearby Maryland. And Maggie Fox a senior health writer with NBC News. Her reporting on Zika virus can be found at nbcnews.com. Joining us by phone from Galveston, Texas, Scott Weaver of the Galveston National Laboratory at The University of Texas Medical Branch in Galveston.

LAKSHMANANAnd joining us now by phone from Rio de Janeiro, Brazil is Simon Romero. He's the Brazil bureau chief for The New York Times. Nearly 4,000 cases of brain damage, in which babies were born with unusually small heads -- we were talking about this earlier, microcephaly -- have been registered in Brazil in the past year. And disease specialists suspect the Zika virus caused this condition. So Brazilian researchers have been talking about this may also be causing a surge in Brazil of another rare condition, Gillain-Barre syndrome. Simon, thanks so much for joining us.

MR. SIMON ROMEROIndira, thank you for having me.

LAKSHMANANYeah. So I want to ask first about this rare condition of microcephaly with the children whose heads are abnormally small. You have met some of the mothers and reported on some of these 4,000 cases. Tell us a little bit more.

ROMEROWell, it's just an incredibly distressing situation. The epicenter of the epidemic is up in northeast Brazil and the states of Pernambuco, Bahia, Paraiba. And you have many thousands of people who have had Zika at this point up there. And doctors started noticing the sharp increase in microcephaly cases around September and October of last year, so nine months after the outbreak of Zika began...

LAKSHMANANMm-hmm.

ROMERO...to intensify. So it's just an incredible stress on the public health system. It's an incredible stress for many of these families, many of whom are poor and they don't have access to private health plans or to private hospitals.

LAKSHMANANMm-hmm.

ROMEROThey rely on -- entirely on this government-run system. And many of them are just in a state of shock over what to do now.

LAKSHMANANMm-hmm.

ROMEROYou know, some of them already have other children to raise and they're confronting this new challenge. So it's really one of Brazil's most acute health crises in decades.

LAKSHMANANSo these stories are dominating headlines. Are they creating panic among pregnant women as well?

ROMEROMany women are distressed, whether they're pregnant or planning to get pregnant here in Brazil. There's been a run, for instance, on insect repellant. And there's been a black market created for some brands, which have come into short supply as a result of people buying up as much as they can find at this point. This is summer time, of course, here in the Southern Hemisphere in Brazil. So it's the hot months. It's the rainy months. You have a lot of accumulation of water. And standing water is where the mosquitoes that transmit Zika can breed.

LAKSHMANANMm-hmm.

ROMEROSo it's an immense challenge for the authorities to get out and educate the population about the risks involved with these mosquitoes. We had the health minister in Brazil come out and say that they're going to deploy 220,000 troops after Carnival in February, in an effort to go on a door-to-door campaign around the country to try to defeat these mosquitoes. It's become very, very (word?)

LAKSHMANANUsing soldiers to defeat mosquitoes? How does that work?

ROMEROWell, you know, it's often forgotten, but Brazil, at one point back in the '50s, did manage to eradicate the Aedes aegypti mosquitoes that transmit not only Zika but other viruses such as dengue and chikungunya and yellow fever.

LAKSHMANANMm-hmm.

ROMEROIt just so happens that these mosquitoes are incredibly illusive and they adapt very well to urban habitats. So when Brazilian cities experienced explosive growth in recent decades, these mosquitoes did very, very well. And the result was that, you know, Brazil had a huge problem with dengue fever before Zika arrived here recently. So it's been an uphill struggle now in Brazil for years.

LAKSHMANANSo it means that there are soldiers who are actually doing sweeps with pesticides at all times? Is that -- that's, I mean, you know, you don't think of soldiers as doing kind of public health. But that's how they've been employed?

ROMEROIt's gone to this point, that's right. And it's going to become even more intense here in Brazil. So what happens is that public health workers go door to door in Brazilian cities to explain to people why they shouldn't have buckets of water in their backyard. Why they shouldn't have old tires, for instance, where water can...

LAKSHMANANMm-hmm.

ROMERO...accumulate and where these mosquitoes can breed. And soldiers are helping them go into many of these areas. You know, Brazil is a country with really high levels of crime and a lot of very difficult areas to go into. So often these health workers feel more comfortable going in with soldiers.

LAKSHMANANAll right. And the President of Brazil Dilma Rousseff, is she under heat for the spread of this disease? Or are she and other authorities seen -- I'm interested not only in Brazil, but in Colombia, where there's also been a serious outbreak -- are the authorities seen as being effective in trying to stem the spread of this disease?

ROMEROWell, Dilma Rousseff was under a huge amount of (word?) criticism before Zika even came to the fore as a public health crisis.

LAKSHMANANMm-hmm.

ROMEROBrazil is experiencing its sharpest economic downturn in decades at this time, with low commodities prices. There are calls for her to resign over corruption scandals in her government. So she was already facing a lot of criticism. And now it's getting even worse. There's a lot of political intrigue over the top health officials in the country and whether they're up to the job of effectively battling Zika. And if the (word?) speak for themselves, then many political analysts here say that they're not up to the job and they need to be replaced.

LAKSHMANANAnd the Olympics are, of course, coming up in Rio de Janeiro. Are there any special precautions that are being taken to protect not only Brazilians, but the visitors and athletes who will be coming from all over the world?

ROMEROIt's a great (unintelligible). They say that they're going to be inspecting the Olympic venues on a (unintelligible)

LAKSHMANANI'm sorry. We seem to be having trouble with the line there. That's Simon Romero, the Brazil bureau chief for The New York Times. We're going to try to fix that line and get back to him. Thanks for your patience on that. So, Scott, I want to ask you about how these mosquitoes -- how many cases of Zika virus have been reported in various Latin American countries. Simon was telling us about Brazil. I know Colombia has also had thousands of cases. Is there a cumulative number that we can say for Latin America and The Caribbean?

WEAVERWell we can really only make crude estimates because, as we heard earlier, the diagnostics available in most of these countries are very limited. Most people are going to a health care provider. And those health care providers...

LAKSHMANANOkay. We seem to have lost the line for Scott as well. Sorry for the technical difficulties. Maggie, can you help us out with the number of cases that there have been overall in Latin America?

FOXYeah. As Scott was starting to say, it's hard to know because people aren't being tested for it.

LAKSHMANANMm-hmm.

FOXBrazil has reported more than a million cases. Colombia is reporting hundreds of thousands of cases, probably. Again, you're not going to know because most people are not symptomatic and they're not going to be tested. But you can kind of guess how many people will be infected by looking at similar diseases, as Dr. Fauci pointed out. This is a virus that's carried by mosquitoes. There are many other viruses that circulate in that part of the world and are transmitted in exactly the same way. Chikungunya is another new one and it has only been around a few years and it's already spread across the entire region, infecting millions of people. So it's very likely that many, many people will be infected with this virus.

LAKSHMANANAll right. Well, we have Scott back on the line now. So, Scott, I actually want to ask you, with the mosquitoes spreading the virus, these are found throughout North and South America, correct? So is it possible that infected mosquitoes could end up in the United States?

WEAVERIt's possible. Again, we have very limited information, direct evidence, of which mosquitoes are transmitting. But we believe that the majority of the transmission is through Aedes aegypti.

LAKSHMANANMm-hmm.

WEAVERAedes aegypti is a mosquito that lives in very close association with people. The eggs are deposited in water containers, sometimes stored water, sometimes refuse in the backyard. The larvae develop right next to homes and then the adult mosquitoes, the females which bite and transmit these viruses, stay the majority of their lifetime indoors, in people's houses. So we do have Aedes aegypti in the southern United States. And we have had recent histories of small outbreaks of similar viruses to Zika, such as dengue and chikungunya, which as far as we know exist in identical transmission cycles.

WEAVERSo we certainly are at risk in the southern U.S. If a single person returns to the U.S. infected with the virus -- and they may not even know it if they're asymptomatic, like most patients are...

LAKSHMANANMm-hmm.

WEAVER...and a single mosquito bites that person during the phase when they have virus in their bloodstream, that can initiate the transmission cycle. And also we have another mosquito in the U.S. that's probably also a significant vector called Aedes albopictus. And that mosquito can occur further north, the whole way up into the northeastern United States. We don't yet know what the respective roles of these two mosquitoes are or even whether there might be other mosquitoes in the U.S. that could also serve as vectors. But we can definitely say there is some risk for local circulation, as a history of chikungunya and dengue tells us.

LAKSHMANANAll right. We have Simon Romero of The New York Times Rio de Janeiro bureau back on the line. And, Simon, I want to actually give you a question from a caller. Let's go to Fernando from Chapel Hill, N.C., who says he has a question about Brazil. Fernando, you're on the line.

FERNANDOYes. Hi.

LAKSHMANANHi.

FERNANDOI am from Recife, Pernambuco, so he must know we have about half of the cases there. And one of the speculation of the outbreak was the drought that happened -- that very severe in that area: Pernambuco, Paraiba. Those are states in the northeast of Brazil.

LAKSHMANANMm-hmm.

FERNANDOAnd so my question was really to Dr. Fauci, whether or not the U.S. Army has any insight on what the best repellents for these mosquitoes are?

LAKSHMANANOkay. All right. Dr. Fauci, do you have any thoughts on that?

FAUCIIs he asking what the best repellent is? We use zeet.

LAKSHMANANOkay.

FAUCIYou know, high-level zeet 30, zeet insect repellent together with proper clothing to make sure...

LAKSHMANANAnd zeet contains Deet?

FAUCIYeah. Yeah. Deet, I'm sorry.

LAKSHMANANYeah, Deet, okay.

FAUCII'm sorry, Deet. Yes, sure. It's with Deet around 30, at least.

LAKSHMANANOkay. So 30 percent Deet repellent.

FAUCIRight. Right.

LAKSHMANANSo, of course, you know, we hear about that not being necessarily safe for children. So I think that's something that...

FAUCIRight.

LAKSHMANAN...that people are concerned about. Would you use that on your children?

FAUCIWell, again, there are now repellents that are being developed. In fact, the CDC is working on developing one that's really quite mild and safe...

LAKSHMANANMm-hmm.

FAUCI...for use in children but also, that would also be quite effective. But it's not yet ready for prime time.

LAKSHMANANAll right. I'm Indira Lakshmanan and you're listening to "The Diane Rehm Show." If you'd like to join us, you can call in at 1-800-433-8850. Or send us an email to drshow@wamu.org. You can also send us messages on Facebook or Twitter. So, Simon, just to wrap up our conversation we were having about what the authorities in Brazil, Colombia and the rest of Latin America are doing to stop the spread of the disease. Are there any special measures being taken? Are they looking to the United States or other neighbors for help?

ROMEROThere are an array of different measures that are being taken around the region. Here, in Brazil, of course, we have a lot of public health workers and soldiers going door to door on an anti-mosquito campaign. In El Salvador, you have the new policy by the government advising women not to get pregnant until 2018...

LAKSHMANANHmm.

ROMERO...for two years into the future, which is a really big step that's much bolder than what we've seen here in Brazil. Although in Colombia and in Jamaica, authorities there have also advised women not to get pregnant as long as Zika is being transmitted.

LAKSHMANANWell, Simon, we actually have had some listeners who have sent in messages. Ruth from Cleveland, Ohio, wants to know, asking women to not get pregnant for two years -- how is that going to work? Is that even realistic?

ROMEROYou know, it's generating an incredible discussion around the region -- in El Salvador, of course, but in a variety of other countries -- because in many parts of Latin America, birth control is still hard to come by.

LAKSHMANANMm-hmm.

ROMEROSome parts of the region are still very religious.

LAKSHMANANMm-hmm.

ROMEROAnd so birth control is frowned upon.

LAKSHMANANMm-hmm.

ROMEROSo it's going to generate, I think, a lot of debate around Latin America about the accessibility of birth control, what women can do, what their choices are at this time.

LAKSHMANANMm-hmm. All right. That's Simon Romero, the Brazil bureau chief for The New York Times. Thank you so much for joining us.

ROMEROThanks for having me.

LAKSHMANANSo, Maggie, this whole question about the CDC advising pregnant women in the United States to postpone travel to more than 20 countries and territories in Latin America and the Caribbean -- so you have authorities in Latin America advising women not to get pregnant, authorities here advising pregnant women not to travel to Latin America -- again, how does that work? How realistic is that?

FOXWell, I think the CDC has left it up to women to decide what kind of risks they want to take.

LAKSHMANANMm-hmm.

FOXBut given how little is understood about microcephaly and what the causes are, I think what people are saying is better safe than sorry. You don't want to do anything to risk your pregnancy if you really don't know. You don't know at what point in your pregnancy you're most at risk.

LAKSHMANANMm-hmm.

FOXThere's nothing you can do if you know your baby is developing microcephaly and you're pregnant. There's nothing you can do about it. There's not much you can do to help a baby after it's born. So given all that, it's, you know, somebody's life -- a child's life versus a trip down...

LAKSHMANANMm-hmm.

FOX...to a region that's affected. I think some people are concerned that the women who are going to be most at risk are people who are living there, either temporarily or permanently. I think tourists have a little bit less to worry about. But if someone's down as an exchange student or working temporarily, they might have a little less control over something like travel.

LAKSHMANANRight. I think it's something that a lot of our listeners are concerned about. Let's take a call from Steven in Silver Spring, Md. Steven, you're on the air.

STEVENYes. Thank you. I was concerned because I'm wondering if Dr. Fauci or anybody else, if there's any difference in the risk assessment if somebody's in the first, second or third trimester of pregnancy. That's number one. And number two is, someone in my family who is pregnant is planning to go to Colombia. And I'm wondering whether you would have any advice for that person, whether they should go or not?

LAKSHMANANAll right. Good question. Thanks. Dr. Fauci, in the minute before we have our break.

FAUCIOkay. It's a great question and we don't have a definitive answer to that. If you look at viral infections that often have affect on fetuses, in general, the earlier in the pregnancy, first trimester, the more devastating effect, particularly if you're talking about the developmental aspect of it.

LAKSHMANANMm-hmm.

FAUCIHowever, it is possible that there are also direct toxic effects of a virus on a brain that has already well into the development of a fetus.

LAKSHMANANHmm.

FAUCISo I think it is too premature right now to say, if you get infected in the first trimester, you're in trouble. But if you get infected later on, you're not. We just don't know.

LAKSHMANANMm-hmm.

FAUCIAnd that's one of the situations where you have to admit that you don't know. But, fundamentally, historically, first trimester infections of any of these types of viruses generally are the most devastating.

LAKSHMANANShort answer, if you get Zika, can it affect future pregnancies?

FAUCIWe don't have any information about that. But it is unlikely that that's the case. But I don't think we can say anything definitively about that.

LAKSHMANANAll right. We'll take a short break. And when we're back, more of your calls and your questions. Stay with us.

LAKSHMANANWelcome back. I'm Indira Lakshmanan, sitting in for Diane Rehm. We're talking today about the Zika virus with two great guests in the studio, Dr. Anthony Fauci, the director of National Institute of Allergy and Infectious Diseases at NIH, and Maggie Fox, a senior health writer with NBC News. Joining us by phone from Galveston, Texas, Scott Weaver, director of the Institute for Human Infections and Immunity and scientific director of the Galveston National Laboratory at University of Texas Medical Branch in Galveston.

LAKSHMANANSo I want to start off with a great question on our Facebook page, posted by Jonathan. He says, perhaps your panel can put Zika into greater context for listeners. For example, how does Zika compare to a global health issue like antibiotic resistance? Is it spreading more quickly than Dengue Fever, or is this issue, although serious, being exaggerated in its threat? Dr. Fauci, can you help us with that?

FAUCIWell, let's start off with the last question first. I mean, you can't say it's been exaggerated because it's an evolving situation, and we're learning more and more about it. But I think if you want to put it into a broader perspective, as an individual disease on a person, it has been in the past, and might even continue once we understand more about this sequelae that we're seeing with microcephaly, is a relatively clinically insignificant disease.

FAUCIYou've just heard us describe it, you know, it's a rash, it's running eyes, conjunctivitis, fever, aches, et cetera, virtually no mortality of the person who gets infected. If you compare that with dengue, which can be a very serious issue with some people and can kill people, chikungunya, which can give you chronic joint issues that last for months and months, that as a global health threat Zika is not in that class. It is not nearly as serious as the ones that we're talking about.

FAUCIHowever, for the individual situation, where you have a mother who has a baby who has the sequelae of microcephaly, that's devastating. So you want to make sure you understand the difference between a broad, global health threat, where dengue causes disease in many areas of the world, chikungunya we now have in the Caribbean, that is a different story than what we see of Zika itself. But for the women involved, that's very, very serious.

FAUCIThe one thing I think it's important when you think about the potential for diseases, I think people need to understand, because there may be confusion about locally versus imported cases, so when you have dengue in South America and the Caribbean, and you have chikungunya, you have a lot of people that travel back to the United States. With chikungunya, there have been thousands of cases of chikungunya in the United States that have been imported. They didn't originate in the United States. We've seen that with Dengue, the same thing. So those are imported.

FAUCIThen there are certain situations such as we've seen with dengue and chikungunya where you actually have someone who's infected come to the United States, get bitten by a mosquito and then locally transmit it in the United States. We've seen that in Florida with dengue and chikungunya. We've seen that in Texas with dengue. Usually those locally transmitted cases don't result in any significant outbreaks. In fact, the historical scene of locally transmitted cases had been well-controlled by mosquito control, et cetera. So even though that's local outbreak, it isn't the massive outbreak that we're seeing in Brazil, and it is unlikely, you never say never, and you never say always, but it is unlikely that we would see a major outbreak of locally acquired Zika in the United States.

LAKSHMANANThat is a critical distinction. Thank you very much for giving that to us. So it sounds like you're saying although there might be some limited local transmission, what we're seeing in the United States, the I think dozen cases reported by the CDC, are more from travelers coming from overseas.

FAUCIRight, and at the same time you say that, you always leave the window open that you can't be confident that that's not going to happen. You could predict if it acts like Dengue, and it acts like Chikungunya, that those local outbreaks will be contained. But we don't want to be, you know, so cavalier about it as to say we can't -- we shouldn't be vigilant that it might be.

LAKSHMANANOkay, well Maggie, the one case that we know of, of having originated in the United States, as far as I know, is the baby with microcephaly born in Hawaii to a mother who had traveled to Brazil while she was pregnant. What do we know about this case?

FOXWe don't know a lot of details. We know she was living in Brazil in May of 2015, when she became pregnant. It's not clear when she left Brazil and came to Hawaii, but then she gave birth to a baby that had microcephaly, and she also had evidence of having been infected with the Zika virus. But again, that's somebody who she would've been infected in Brazil. She did not become infected in Hawaii. And because she's already over the Zika infection, she's not going to infect any mosquitoes in Hawaii that would then go on to infect anyone else there.

LAKSHMANANI see.

FOXAnd the other cases that we know about, there's a few cases that have happened since we've been aware of the outbreak in Brazil that have come back to the U.S., and they're all travelers, too. I think there's been three in New York state, there's been two reported in Illinois, there have been three reported in Florida. They're all travelers who came back and were sick and went in and got tested. They had Zika virus. But officials don't think there's much of a risk. Perhaps Florida because there's a lot of mosquitoes there, but somebody coming back to New York state in the middle of winter, a mosquito is not very likely to bite them and then infect somebody else. So these are going to be locally contained cases.

LAKSHMANANLocalized cases, yes. All right, so Scott, there is no treatment or vaccine for Zika at this point, but I understand you're working on a vaccine. How long is that going to take? Is there interest from big pharma companies who want to invest in this? In other words, is this going to be a quick road to getting a vaccine or a slow one?

WEAVERWell, I think there's bad news and good news for vaccine development. The bad news is that a few months ago, no one in the world was working on a Zika vaccine at all. So everybody's really just getting started, including our academic group here. But the good news is that a lot of vaccines have been developed for other flaviviruses, these other closely related viruses in the same category, such as Dengue, Japanese encephalitis, West Nile, Yellow Fever, and it's likely that the approaches that have worked for those viruses will also work for Zika. So I think that scientifically we have a good chance of developing vaccines very quickly.

WEAVERThe big question mark, and one of them you raised was commercial interest, I think right now there's a lot of commercial interest. I've talked to several people from big pharma companies who are very interested in developing a vaccine, but the question mark I think is more in the long term because it takes many years to take a license -- a vaccine from the basic research laboratory, where the development begins, the whole way through the clinical trials to the people at risk receiving the vaccine.

WEAVERAnd so the incentive has to remain through that time from the big companies, and we also have to find the right regulatory route to having a vaccine licensed, which means traditionally we have to be able to test it in a place where there's a lot of transmission of the agent, a lot of people becoming infected, to show that it protects them from disease. And we really can't predict in, say, three to five years from now where that situation will exist. Will the virus have spread throughout the Americas very quickly, which I would expect, and be circulating only at a very low level in a few years, where it's much more difficult to detect where it is, how many people it's infecting and conduct these kind of clinical trials?

WEAVERSo those are the big challenges, and they're very similar to what we've seen the past few years with Chikungunya and even with Ebola.

LAKSHMANANAll right, Dr. Fauci, you wanted to jump in there?

FAUCIYeah, actually Scott makes a very good point. We had developed a vaccine into the phase one trial or early trial with West Nile virus, a similar virus, a flavivirus, and the problem we had then is that we didn't have enough pharmaceutical company interest to take it into advanced development. So what we're really saying is that we know how to make flavivirus vaccines. We've shown it with Dengue, which has an approved vaccine in Brazil and now a phase three trial going on in Brazil. We have made up to phase one vaccines with West Nile and with Chikungunya.

FAUCIBut we haven't had the pharmaceutical companies want to really actively partner for advanced development. I think that's going to change because as Scott said, and we're seeing it ourselves right now, that there is considerable interest on the part of pharmaceutical companies because of the intensity of this problem. So hopefully we'll go beyond the early stage of vaccine development and really take it to the goal line of having a vaccine that's safe and effective for future types of outbreaks.

LAKSHMANANJust a quick policy question. Is this something where the government should be getting involved in subsidizing the research if big pharma is not?

WEAVERWe do. We have an organization called BARDA, the Biomedical Advanced Research and Development Agency, which -- Authority, which is part of the Department of Health and Human Services, who actually does that and gets very much involved in advanced development, which we generally don't do as a government. But that organization does do that.

LAKSHMANANOkay. We have a great email from Sean in Grand Rapids, Michigan. We've actually received several emails similar to this. Sean asks, what were the lessons learned during the Ebola outbreak, and how are those being applied to address the Zika outbreak? I don't know who'd like to take that. Dr. Fauci, Scott?

FAUCIWell, there are a number of lessons, but we've got to be careful that we don't try and compare them too closely because people get confused. I think one of the big lessons is that infections emerge, they emerge unexpectedly, you've got to be prepared for them, you've got to be prepared to respond in a global health and public health way, and you've got to be prepared to respond rapidly to develop countermeasures. So that's the reason why you have to have the kinds of networks and collaborations, which allow you do that.

FAUCIEbola taught us a number of lessons in that regard, and I think we've learned from that, and that's the reason why you're seeing people jumping all over the Zika problem now, as opposed to waiting to see what happens.

LAKSHMANANAll right. Let's take a call from Aaron in Lafayette, Indiana. Aaron, you're on the air.

AARONYeah, I was just recently traveling in Haiti for the last week, and coming back now, I have been bit by mosquitoes when I was down there. I'm not showing any symptoms at all, but my wife is pregnant. Is there a risk of me transmitting that, if I had it and didn't know, is there a risk of me transmitting me to my wife, somewhere I could go to get tested, or would I know by just some small symptoms whether I had it or not?

LAKSHMANANOkay.

AARONIs there an incubation period?

LAKSHMANANAll right, scary, scary thought, a man who's been in Haiti who is worried about infecting his wife. What can we tell him? Is -- there doesn't seem to be anywhere where he can go to get tested, but what can he do?

FAUCIWell, first of all, we don't know if a person who's asymptomatic with Zika is going to be able to transmit it. There are a lot of unknowns there, and that's really an important point. I would ask him, when he has returned.

LAKSHMANANWithin the week, he said.

FAUCIWithin the week. So I mean, within two weeks of returning from an area that has Zika, that -- you really need to be careful because you might wind up developing symptoms. You don't know because you can develop symptoms anywhere from one or more weeks beyond. So I wish we could give him definitive information, but we just don't know. And sometimes you just have to admit what you don't know, and we don't really know that risk.

LAKSHMANANAll right, I'm Indira Lakshmanan, and you're listening to the Diane Rehm Show. Scott, go ahead, you wanted to jump in.

WEAVERI just wanted to mention, this is very limited information, but so far the two cases that were diagnosed of men having the virus in their semen, they both had a condition where there was also blood present in the semen, and we don't know yet whether that's truly a predictor of the risk for transmission, but that's one indication that if a person sees that condition, they might want to seek medical consultation, and maybe we'll be able to provide diagnostics once the capacity increases in the U.S. and other places for men like that.

LAKSHMANANOkay, we have another listener who sent in an email. His name is Gerald, and he's asking, please ask Dr. Fauci why Chile and Canada will not be affected by this outbreak. He says he has heard of every country in the Americas being affected except for these aforementioned two. Is that correct?

FAUCIYeah, it's the lack of the mosquito vector in those countries.

LAKSHMANANAll right.

FAUCIThe mosquito vector, the Aedes aegypti there, is just not, and that's the reason why. It really is a disease that can be driven by the kinds of vector that are active, and by vector I mean mosquito, in the particular country.

LAKSHMANANOkay, and we also have a caller, James from San Antonio, Texas, who's concerned about immigration and what viruses could be coming into this country as a result of immigration. Maggie, any thoughts?

FOXThat's a concern that comes up all the time. It was an issue with Ebola. It's constantly an issue. Any traveler could carry a virus to the U.S. What you need is for somebody to be actively infected and for the mosquitoes, and only the species of mosquito that can carry this virus, I think that's something that's hard to understand, there are many, many different species of mosquito, only one or maybe two of these species are known to actually carry the virus. So you have to have the combination of somebody actively infected, the right kind of mosquito, the right place at the right time.

FOXImmigrants aren't any more likely than anyone else to be infected with this virus and to bring it. A tourist is every bit as likely as an immigrant to bring it.

WEAVERI think that's a very important point that people need to understand because sometime the people have particular with immigrants, make that story, but there are, you know, thousands and thousands and thousands of Americans who go someplace where there's disease and then come back to their home, which is in the United States.

LAKSHMANANSo it would be not only block immigrants, you'd have to block travel.

WEAVERBlocking people, exactly.

LAKSHMANANBlock Americans from traveling out of the country and back in.

WEAVERExactly.

FOXAnd not only that, people tend to assume that if you've actually been in a place where the disease is that you're going to get it, and that's very unlikely. Actually your odds of being infected are not very high.

LAKSHMANANSo even if you're pregnant, going to these countries, you're unlikely to get infected, but out of an abundance of caution, that's why the CDC is recommending not to go?

FOXThat's right.

FAUCIWe don't -- we don't know. I mean, I think we'd better be careful we don't go too far. The CDC's recommendation are out of an abundance of caution, based on the evidence that we have, and they continually reevaluate what the situation is, literally in real time continuing to accumulate evidence and data, and then recommendations are made. But as they stand now, the recommendations are, and that people who have any question about that, just go to the CDC website, cdc.gov...

LAKSHMANANSo a lot more information.

FAUCIOh yeah, cdc.gov, and you just click on Zika, and you'll see all the information you need.

LAKSHMANANZika virus. All right.

FAUCIThey've done an excellent job on that.

LAKSHMANANWell, Andy in Williston, Vermont, wants to know, he says, his family is going to be attending a wedding in Mexico in May. They're going to be traveling with their four- and seven-year-old children. And they're worried if they contract Zika virus, could their children be at risk? Are there known or suspected long-term negative impacts related to Zika in children? Scott?

WEAVERWell, as far as we know, children in those age groups are at no higher risk than adults and generally have asymptomatic infections or, as Dr. Fauci described, they have a flu-like syndrome that generally is mild and resolves very quickly. So we're not so much worried about children as we are about pregnant women and men who could sexually transmit to women.

LAKSHMANANAll right, Scott, in just 30 seconds, can you tell us, from your knowledge of other mosquito-borne viruses, can you predict anything about Zika virus could spread?

WEAVERWell, I think it's quite predictable at this point that it's going to spread throughout the Caribbean, throughout all parts of Latin America that are permissive for Aedes aegypti, that is all low-lying areas. High-altitude places in South and Central America don't have Aedes aegypti, but all other areas will be susceptible. And again as Dr. Fauci mentioned earlier, I think we'll probably see some small amounts of sporadic transmission in the U.S., seeded by travelers returning to the country.

WEAVERWe can do a little bit to reduce that risk if we reach the point where we can diagnose some of these patients very quickly. We can do very focused mosquito-control efforts in their home and in surrounding homes, and because Aedes aegypti is a mosquito with a very small flight range, if we do very targeted control efforts, we can reduce the risk of that virus getting loose and circulating.

LAKSHMANANAll right, that is Scott Weaver, director of the Institute for Human Infections and Immunity at The University of Texas Medical Branch in Galveston. Also joining me here in studio for this terrific conversation, Dr. Anthony Fauci from the National Institutes of Health and Maggie Fox of NBC News. Thank you all so much. Thank you to our listeners. I'm Indira Lakshmanan, and this is "The Diane Rehm Show."