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Preventing The Spread Of West Nile Virus


The Centers for Disease Control and Prevention says this year's outbreak of West Nile virus is on track to be the worst in U.S. history. As of yesterday, 43 people have died from the disease, and over 1,100 cases have been reported to the CDC. Almost half those cases come from Texas. Mississippi, Louisiana, South Dakota and Oklahoma have also been hit. The disease is spread by mosquitoes.

If you have questions about West Nile and how to prevent it, give us a call: 800-989-8255. Email: talk@npr.org. You can also join the conversation on our website. That's at npr.org. Click on TALK OF THE NATION. NPR science correspondent Richard Knox joins us now from his office in Dorchester, Massachusetts. Nice to have you back in the program.

RICHARD KNOX, BYLINE: Hi, Neal. Glad to be here.

CONAN: And why is this year so bad?

KNOX: They don't really know. I mean, there are some ideas out there. But there's a lot of mystery with this virus, which first appeared in this country 13 years ago. And since then, it's spread really widely. I mean, it's everywhere now. Vermont is the only state that's not reporting West Nile this year in people, animals or mosquitoes. That's not quite clear why not.

But everywhere else in the continental U.S. has West Nile virus. But as to why a particular year is particularly bad, they don't really know. One factor probably is an unusually mild winter, which a lot of areas had, including Dallas, which is the real hotspot for West Nile right now. And probably an unusually hot spring and summer, an early or hot summer, because this amplifies the amount of virus that are in mosquitoes, and also it amplifies the number of mosquitoes. It speeds up their life cycle, so they're able to reproduce faster.

CONAN: Why Texas? You mentioned that's the hotspot.

KNOX: Again, not entirely clear. Yesterday, the state health commissioner in Texas said that they seem to have an unusually early spring, and their drought was worse last year than this year - worse last year. And so maybe that's why they're a little bit special. But again, the CDC says they don't really know. And as to why within Texas Dallas is a hotspot, they say often you'll find that it's a very local phenomenon - local mosquito population, local bird population - because that's where the mosquitoes get the virus from, along with climate factors. It's a complicated equation.

CONAN: An email question we have from Ernest: Has the virus reached Virginia? I'll answer that for you. You said yes. It's everywhere except Vermont. How would you know you're infected and what age bracket is more or less likely to become infected?

KNOX: I think that the likelihood of becoming infected is not particularly age-specific. The likelihood of getting really sick is higher among people over 50. Maybe one in every 150 people who gets infected with West Nile gets what is called a neuroinvasive form, which means that it gets into the brain and affects the brain or tissue surrounding the brain. That's a really grave disease. Nearly everybody gets hospitalized. Ten percent of people die. Two-thirds of people who get brain infections and paralysis will have lifelong effects.

But in terms of everybody else, I mean, it's really mostly not going to cause you to become ill. Eighty percent of people who get infected with West Nile don't get sick. Another 20 percent, roughly, will get a flu-like illness, which can be pretty severe, lasting from days to weeks to even months, but then they recover fully. So - and you don't know who you, you know, whether you're more likely to get sick or not get sick before you get exposed.

CONAN: And the severe forms, as I understand, can manifest in different forms, as a form of meningitis or a form of polio.

KNOX: Well, I wouldn't call it polio, which is a very specific disease, but it's like polio in a sense that it can cause paralysis, which polio often did. And, you know, as I said, 10 percent mortality rate is pretty grave for that really severe form of West Nile.

So it's a scary disease, but I think we should put in perspective that out of the 1,100 or so reported cases that the CDC knows about so far this year, you know, that's a tiny fraction of the number of Americans who've been infected, which probably approaches about 100,000 people. And most of them didn't know they had West Nile virus infection. Fortunately for them and for everybody who gets the virus and recovers, they're going to have life-long immunity to it.

CONAN: Let's get some callers in on the conversation. 800-989-8255. Email: talk@npr.org. We'll begin with Mohammad(ph), and Mohammad's on the line with us from Oklahoma City.


CONAN: Hi. You're on the air. Go ahead, please.

MOHAMMAD: Hi. Thanks for taking my call. Yeah. My wife contracted West Nile virus three weeks ago. She's still recovering. I think she's one of the lucky ones. And my question was this, that if this was a prevalence on the state, why cannot the government start spraying for the mosquitoes? And why do they have to wait until so many people died? The - I think the - in some state, they are thinking about doing that.

CONAN: Richard, why can't the prophylactic experience of spraying for mosquitoes?

KNOX: Well, some places are - last Thursday, Dallas County because of the especially severe problem there, began spraying. It's up to the mayors of individual communities to decide whether to permit spraying or not, and some do and some don't. I think it's a local public health decision. The CDC promotes it when the case is sever, or when the situation in a locality is severe.

Oklahoma is one of those five states that account for 75 percent of the cases so far this year. And I personally don't know what the debate has been, if there has been, among, you know, mayors and city councils and counties, state governments in Oklahoma. It is thought to be pretty effective and pretty safe to spray.

CONAN: Mohammad, we hope your wife is doing well. We mentioned - you mentioned the debate in Dallas County. There have been 11 fatalities. That was announced on Monday. Two weeks ago, Mayor Mike Rawlings authorized an aerial spraying program to kill mosquitoes. That spraying sparked a debate among residents concerned about the health risks of the spray.

Sherry Jacobson is a health writer with the Dallas Morning News, and joins us now from her office there in Dallas, which probably people are calling ground zero at this point. Nice to have you with us today.


CONAN: Spraying is identified as the main and best way to stop the spread. Why did people object?

JACOBSON: Well, I think there was a lot of concern, say, by beekeepers who felt that the spray was going to affect their hives, and so they had to cover them up. There were also organic gardeners who didn't like it, and a few people who had fish ponds, because the kind of spray that they're using, the synthetic pyrethroid, is a - is known to kill these things. So - but we really haven't heard anything since we did all this spraying.

CONAN: So there had been no ill effects amongst the bee population or the fish population (unintelligible).

JACOBSON: Well, not detectable to us at least. We were expecting we would get some sort of outcry, but we really haven't seen anything.

CONAN: And is the spray, presumably, it's safe for humans. It's been tested.

JACOBSON: It's the same stuff that we've been spraying from the ground from trucks for the last couple of months, and that the - you know, it's a slightly different version that they use from the planes.

CONAN: And, of course, it's not just local governments and public health workers who can help. Individuals can do stuff, too. I gather the Dallas County judge, Clay Jenkins - who's been in charge of this aerial spreading effort - takes DEET showers every morning

JACOBSON: Yeah. That's what he's telling us. We thought it was kind of funny, but he said that he sprays himself down after every shower - after every morning shower, and that other people ought to do that, as well. I don't know that people are doing it, though.


CONAN: Is everybody there on high alert?

JACOBSON: I think they are. You know, we've had a frantic couple of weeks of this discussion about aerial spraying and everything. Now it's sort of a personal campaign of, you know, get rid of standing water where mosquitoes might be breeding, you know, use DEET if you're going outside, that sort of thing.

CONAN: School is getting set to start. Are they spraying there?

JACOBSON: I think the - yeah. The state of Texas has said it's OK to spray these insecticides around schools. They have been pretty protective about that before, but I think they see the need now.

CONAN: I wonder, are you taking any precautions? Are you using DEET?

JACOBSON: Well, I am every now and then, but, really, I'm just staying inside.


JACOBSON: And I think most people are doing that, too.

CONAN: Most people do that in Dallas at this time of the year, anyway.

JACOBSON: Yeah. Well, it has cooled off in the past couple of weeks. As soon as they started spraying, it started raining, which is not a good thing, but - for the spraying. But, you know, it's gotten nicer, but I still think people are wary about going outside.

CONAN: Sherry Jacobson, thanks very much for your time.

JACOBSON: Oki-doke. Thanks.

CONAN: Sherry Jacobson, a health writer for the Dallas Morning News, with us from her office there. And let's see if we can get another caller in. This is Roger. Roger with us from Milford in Michigan.

ROGER: Yes. Now, one thing I've been hearing as a rule of thumb for West Nile around here is that (unintelligible) stay indoors is that if you have - aside from, like, warnings from CDC, or whatever - if you see a bunch of dead birds around, that's when we should start staying indoors because the disease is much more deadly to birds than it is to people, and that would be a warning sign. Is that a helpful or unhelpful a bit of advice?

CONAN: Richard Knox?

ROGER: And I'll take my answer off the air.

CONAN: OK. Richard?

KNOX: Well, dead birds are - he's right. Dead birds are a signal, and state health departments everywhere are watching for that as one method of indicating how much of the virus is around. They're also testing - capturing and testing mosquitoes all the time to - and testing them for virus, which is another important signal about how much risk there is.

It's important, though, to note that even though it's in birds and mosquitoes practically everywhere, many places do not have any cases. I think 38 states have had human cases. The rest haven't. And in most of those 38 states, there have been just, you know, sort of sporadic cases, such as in Massachusetts, where I live, there has been one case of West Nile so far this year. So, again, it's really not clear how the, you know, why there's such variability from one place to another, even within one state.

CONAN: Well, we get it from mosquitoes. The mosquitoes get it from the birds. Where do the birds get it?

KNOX: The birds get it from each other, I guess, and also from being bitten by mosquitoes. It was introduced into this country - I'm not sure how, possibly by mosquitoes aboard ships, but I'd have to check that - back in 1999. And then it spread really rapidly through, you know, birds go all over the place. They migrate.

CONAN: Yeah. It caused a huge drop in the crow population.

KNOX: Yes. The crows seem to be particularly vulnerable. I don't know why. So, you know, I think we've got to live with it. It's endemic. It's - and it's going to vary from one year to the next, and we're going to be learning more, I suppose, in the future about how much of a factor these especially hot summers are.

CONAN: Richard Knox, NPR science correspondent. We're talking about West Nile virus and the outbreak this summer. You're listening to TALK OF THE NATION, from NPR News.

And here's an email that we have. This is from Lewis(ph): Is there a test to see if you had the West Nile virus? And if so, does that mean you have immunity?

KNOX: The CDC is not recommending to doctors that they test people for West Nile unless people come in with symptoms that indicate the most severe form. They're - you know, you can test for antibodies. You can - there are sophisticated and very sensitive tests that indicate whether you've been infected, but it's not routinely recommended that it be done.

CONAN: Let's go next to Joe, and Joe's with us from Little Rock.

JOE: Yeah. Good afternoon. Your guest stated that once you have the virus, that you're immune for life. Is there a possibility of a vaccine somewhere down the pipe?

KNOX: Very good question. There isn't a vaccine yet. I'm sure they're working on it, because it would be a boon. But I don't know what the scientific problems that they'd have to solve would be. And then you'd have to - you know, it's very tricky to determine once you get an effective vaccine just how to use it. I mean, should everybody get it? At what age? How long-lasting is it? Is it really worth inoculating a big proportion of the population to prevent this disease?

You know, it comes back to one really signal fact here in all of this, which is the best way to avoid getting West Nile virus is to avoid getting bitten by mosquitoes, which is not, you know, it's not easy to do if you have to be outside. But with usual precautions, you can certainly reduce your risk a whole lot.

CONAN: Joe, thanks a lot.

JOE: Thank you.

CONAN: And here's an email from Laura in San Antonio: We've had some new mosquitoes in our area the past few years. They're larger than others and are striped. We've been calling them tiger mosquitoes. Their bite is much more painful and long-lasting. Are there insects contributing to the West Nile outbreak?

KNOX: Hmm, outside of my depth. I don't think there's been any indication that a change in the mosquito population, you know, from one species to another or one subspecies to another is behind this at all. I think that, you know, this is a very familiar mosquito called Culex that transmits this virus. And I don't think we're dealing here with a particularly bad mosquito.

CONAN: Let's go next to Dixon, and Dixon with us from Louisville.

DIXON: Thank you. My family has travel plans to go to Dallas, Texas, in late October, and I'm just curious to know what the projection is for the longevity of the outbreak and if that's still a concern. And I can take my answer off the air.

CONAN: OK, thanks.

KNOX: Hmm, these are good questions, and not easy to answer. Normally speaking, throughout the country, the West Nile season begins to taper off in late September. But I have...

CONAN: When it gets colder, and mosquitoes become less active.

KNOX: Yeah. Usually, mosquitoes get less active. There's frost, and people are inside more, too. So - but I don't know whether I would want to stick my neck out right now and say that October would be safe in Dallas. I think that, you know, you'd want to talk to public health people, and maybe Dixon can find someone or maybe I - if he emails me at rknox@npr.org, I'll look into that for him. The reason being that, you know, it can be hot through September and October in Dallas, and that may be a factor. But that's just my speculation.

CONAN: And one last email question, this from Jared: Can animals, such as a pet dog, contract West Nile? If so, what are the symptoms?

KNOX: Hmm. I've never heard of West Nile dogs, so I don't think that that's a particularly big risk. I think, you know, normally, we talk about birds and mosquitoes. I don't think livestock and horses and dogs and cats are vulnerable, but, again, I would need to check that to be absolutely sure.

CONAN: All right. Well, Richard Knox, thanks very much for your time.

KNOX: Sure. Anytime.

CONAN: NPR science correspondent Richard Knox, with us from his office in Dorchester, Massachusetts.

Tomorrow, it's TALK OF THE NATION: SCIENCE FRIDAY. Ira Flatow will be here. It's the TALK OF THE NATION, from NPR News. I'm Neal Conan, in Washington. Transcript provided by NPR, Copyright NPR.