Tracking Viruses From Animals To People

Sep 7, 2012



I'm Ira Flatow. This is SCIENCE FRIDAY. We're going to talk now about West Nile virus, it showed up in 48 states, reports in viruses in either people or birds or mosquitoes, and it's not exactly clear just why the virus is so widespread this year or why the state of Texas has been particularly hard-hit.

It's also not the only instance of a virus crossing from animals to humans and causing problems this summer, with visitors to one Yosemite campground exposed to the hantavirus carried by mice. And there's a discovery of a previously unknown tick-borne virus in Missouri. A lot of really interesting animal-to-human transmission going on this year.

And joining me now to talk about it is Maria Diuk-Wasser. She is assistant professor of epidemiology, of microbial diseases, at Yale School of Public Health New Haven. Welcome to SCIENCE FRIDAY.

DR. MARIA DIUK-WASSER: Thank you, Ira, I'm glad to be here.

FLATOW: Thank you. Is this surprising to you, too, as a virus expert?

DIUK-WASSER: It's actually not that surprising. I mean, we have - I mean, viruses can emerge and have emerged in history. This particular year yet seems to be - you know, there's been this new virus in ticks, which is new, but the other viruses have been here for a - West Nile virus has been here for a few years.

The particularly high levels of this year are somewhat surprising, but, you know, there's a few possible explanations, although nothing is certain, really, of why this particular year.

FLATOW: Well, what would be the possible explanations?

DIUK-WASSER: Well, the weather this year has been particularly - the winter has been very mild, and then there's been a pretty wet spring and then a pretty hot summer. And that are the ideal conditions, really, for this particular mosquito species, the house mosquito that tends to like those conditions.

They basically - the water in the spring will allow breeding, and then the heat will allow the development of the mosquitoes, and also they like very organic matter. So if the water dries out a little, and you have very - you know, puddles, very dirty water, that definitely increases the production of this mosquito.

We don't know for sure if that's the reason, but the conditions kind of fit, you know.

FLATOW: Right, right. What is the life cycle of the disease? How does it get spread around?

DIUK-WASSER: So the disease gets spread between the mosquitoes on the birds and back to mosquitoes, back to birds. So it's a cycle in nature. It just cycles, you know, between a large number of mosquito species, actually, and a large number of birds.

So it really gets to people only occasionally, quote-unquote. When you get a mosquito that bites a bird, gets infected from a bird and then bites a human. So that's only for mosquitoes that really like to bite both birds and humans, which is not all the mosquitoes.

So that's one of the mysteries of this disease, is how it really - in some cases you may get a lot of virus in nature, but you don't get enough of this jumping to humans, so you don't see it. It's kind of - we call it enzootic, in nature only.

FLATOW: Wow, so there must be a lot of research. So it must be a very hot area of research with a lot of funding going on.

DIUK-WASSER: Yeah, actually not very well-funded, unfortunately. I mean, unfortunately, the way this cycle goes with some of these diseases, it was really - you know, got a lot of attention when it first started, and it was introduced in 1999, and then it moved through the states up to 2003. And that was a huge alert. Everybody was watching.

But it's been going somewhat down for a few years, and it's been - kind of fell off the attention. So unfortunately, you know, there's been a big drop in the funding for it and the research. So we're kind of unprepared to - for this, in a way.

I mean, some areas have continued funding, but really it hasn't - you know, it's throughout the whole country. So there's very focal studies in a few areas that have been conducted.

FLATOW: Where does the funding come from that was discontinued?

DIUK-WASSER: Well, mostly CDC funding that has funded - initially there was a big problem. West Nile virus was almost completely cut. So that also funded a lot of state agencies that were partly funded, you know, by the state and partly by CDC. They were also severely cut, so only certain programs can continue doing research on this. There's almost no NIH funding, unfortunately.

There's some NSF funding from one particular program that looks at the ecology of this virus that has funded really interesting research in the Chicago area. But most - you know, it's very hard to get funding to study West Nile, interestingly.

FLATOW: Yeah, it's very interesting. The virus came here from elsewhere, but you don't hear much about it in other countries. Is it different here? Do the birds here not have resistance to it?

DIUK-WASSER: Yeah, there's some debate as to why it is, but, you know, it is so much worse in the U.S. One of the ideas is that the virus has mutated, so the virus that initially came to New York has mutated to a new variant that seems to do a lot better, you know, than the previous one.

So that's been, you know, better adapted just in terms of transmitting the virus. Then the birds of course were not immune at all. They had never encountered that virus. But they were not resistant to it, either. So that was interesting to see that all these birds could get infected. And then as the birds develop immunity, you know, the virus kind of goes down at least for a little bit of time.

But then the birds, you know, the baby birds will not be immune. So then it can come back. So it kind of cycles around. You would expect that, you know, after a year of a lot of virus, you should see a low because most of us are immune. But then it can come back. So that's why we shouldn't, you know, feel OK, we're safe.

You know, we don't know really very well how these cycles are going to go, but it's not surprising that it comes back.

FLATOW: So what about all these spraying efforts? They tell people go indoors, we're spraying your neighborhood this evening.

DIUK-WASSER: Yeah, spraying, it's kind of like a last resort. I mean, ideally we want to control the virus earlier, you know, by controlling the breeding sites. That is an ideal situation, and it's done in some places.

But again, you know, a lot of the cuts or the lack of attention has, you know, reduced that. So you want to go to the breeding sites and, you know, there are some pretty safe larvaecides that can be put in the water, and that is ideal because then you don't get a large population of mosquitoes.

So once epidemic has taken place, that's usually when the agencies get really alarmed and start spraying, and that probably reduces, you know, the number of human cases. But it's a little bit late in the game, unfortunately. You know, in a case like Texas, I think there's no option. I mean, there's people dying, so I think you have to do that.

But the effectiveness of that, we're not entirely sure because also it's - usually it sprays at the end of the epidemic. You know, and maybe it will start going down anyway very soon. So there's no good studies to determine is it really effective.

FLATOW: Well, there's no money being used, so there are no good studies.


FLATOW: So you're saying to me, in as nice language as you can phrase it, is that it's too late. By the time the epidemic is out there, it's too late, that spraying is really not going to do that much.

DIUK-WASSER: Well, spraying, you know, yeah. I mean...

FLATOW: It's more of a...

DIUK-WASSER: We'll kill some of the adult mosquitoes that are infected. It's not that, you know, it will have no effect. But, you know, hopefully we would have done something before the epidemic.

FLATOW: And as you're saying, if the disease seems to abate after the spraying, you're going to say it's because of the spraying, right, you're going to connect the dots, when actually it's probably going down on its own.

DIUK-WASSER: Yeah, it's possible, yeah. That's a problem with really determining the effectiveness of these studies. There's no control. You know, we don't know what would have happened if we hadn't sprayed, like in a similar situation. There's no, you know, control studies to determine that.

So sometimes, you know, it is something that is a necessary almost political decision that it has some effectiveness, but we don't really know how effective it is.

FLATOW: It would be nice to use some science here, wouldn't it?

DIUK-WASSER: Yeah, definitely.

FLATOW: 1-800-989-8255. Let's go to Judith(ph) in Chico, California. Hi, welcome to SCIENCE FRIDAY.

JUDITH: Yes, I'd like to know, I understand that there are any number of people who are being bitten and infected but show no symptoms. What I want to know is in those cases, if they are then bitten by mosquitoes, can the mosquitoes pick up the virus from them and transmit to another human? And I'll take your response off the air.

FLATOW: Thank you.

DIUK-WASSER: No, humans cannot transmit the virus. So the human - the amount of virus in human blood is not enough for a mosquito to get infected from us.

FLATOW: Let's talk about this new tick-borne illness in Missouri. I know you study tick-borne illnesses. They're calling it the Heartland Virus.

DIUK-WASSER: Yeah, it's a very, you know, new virus. We don't know very much about it, just that it's present, and it's present in this Lone Star tick. So it's a different species of tick than the one transmitting Lyme disease. And so, you know, it's pretty - and we don't really know at this point the actual distribution, right?

Unfortunately, the way we detect a lot of these viruses, when we see people dying, and then we're like oh, maybe there's a problem, and we go check the ticks and check in nature, rather than doing it the other way around, really understanding what's there and what the risks are.

And so now it's - you know, we're looking and trying to determine. CDC is doing quite a bit of work. We also have a big tick collection that we may screen for this virus and determine really where it is. And there's a lot of studies obviously to do, to determine what their host - you know, what's the animal host, for example, and what is the actual symptoms. And, you know, it's all new, to be discovered.

FLATOW: Is it sort of like when Lyme disease first showed up in ticks, something new that...

DIUK-WASSER: It could be, yes. Yeah, it's - you know...

FLATOW: Well, being there in Yale, near Lyme, I mean Connecticut...


DIUK-WASSER: Yeah, definitely.

FLATOW: You're aware that - I'm fascinated by your tick collection. You actually collect the ticks and store them for later study?

DIUK-WASSER: Yeah, so we did a very large study in half the U.S. to do a Lyme disease risk. So we collected all the ticks that we could get in more than 300 locations and produced a map of the risk of Lyme disease, so you can kind of get a sense of what's your risk based on where you live. And most of our emphasis was in the deer ticks, you know, for Lyme disease...

FLATOW: Right.

DIUK-WASSER: ...but then we collected any tick we got. So we have a lot of monster ticks, you know, that carry this new virus, carry (unintelligible) and then so they also have their own pathogens, other pathogens that we don't understand very well in what they do. But, yeah, so we're storing them. You know, we're using it, but then as research comes up, you know, we can refer to it too, you know, address new questions or tests for new organisms.

FLATOW: So it would be naive to assume that we've discovered all the tick viruses. There have got to be others out there, right?

DIUK-WASSER: Certainly, yes. And the ticks carry a lot of, you know, all of these organisms carry viruses, you know, that aren't typically not known to be pathogenic to humans, but we don't know for sure sometimes. So there's another - another organisms, another type of borrelia that's been found that we don't know if it's - it causes disease or not. You know, that's similar to the Lyme disease organism but kind of very different. So we keep finding these organisms, and so, you know, whether it requires studies to determine whether they can make people sick or not, you know?

FLATOW: Is there much surveillance for the rise of these possible new tick diseases?

DIUK-WASSER: Well, there's unfortunately not very - not that much. I mean, there are networks of mosquito surveillance in several states, non nationwide, but there's no really systematic tick surveillance in most places. So...

FLATOW: Another funding issue?

DIUK-WASSER: Yeah. Pretty much. And that's pretty much the case. I mean, CDC would typically be responsible for surveillance type of studies. NIH will typically fund more, you know, like a hypothesis-based study or more, you know, when you have - they typically won't fund like surveillance type of studies or in fact ecological studies. I mean, it's just hard to find - fund any study that involves going to nature, understanding nature. A lot of the emphasis in (unintelligible) and vaccines and pharmaceutical, you know, more...


DIUK-WASSER: ...classic-type of medical interventions.


DIUK-WASSER: So, yeah. So when these things appear, we're not very well trained, and we're not very well equipped to address it often.

FLATOW: Let's talk a little bit - I know this is not your specialty but perhaps you can tell us a little bit about the hantavirus carried by the mice at Yosemite.

DIUK-WASSER: Yes. So hantavirus, you know, are - again, it's another disease. We don't know the exact distribution. It, you know, it shows up occasionally, like in this occasion, we don't know really well how it's distributed. So in this case, it's transmitted, you know, by rodent - in contact with rodent feces and so in indoor areas. But it's hard because, again, there's really not a lot of surveillance to know where it is. So it's not entirely surprising that this happened.

I'm not sure, you know, again, there's not that extensive studies...


DIUK-WASSER: ...on that anymore. You know, it kind of falls off the radar. People follow funding. And, you know, it comes back and then we - we're not very well prepared to respond and to really explain why this case. I mean, there's only a couple of cases, but, of course, it's a lot for the human population.


DIUK-WASSER: But in terms of doing statistics and really understanding patterns, it's kind of hard to do. So you really need to go to the animal population and understanding the dynamics of the virus in nature and then, you know, humans will only be the tip of the iceberg, you know?

FLATOW: Right, right.

DIUK-WASSER: It doesn't explain what's going on, really, in terms of the distribution and ecology.

FLATOW: Right. Talking with Maria Diuk-Wasser on SCIENCE FRIDAY from NPR. I'm Ira Flatow hearing that - this - the word we don't know, we don't know, we don't know, we don't know, Dr. Diuk-Wasser, over and over again. There's a lot of stuff we don't know.

DIUK-WASSER: Yeah. Unfortunately.


DIUK-WASSER: And many more that are yet to come. I mean, these are very complex diseases and very - locally, they're very different in every place. I mean, there are certain general patterns, but, you know, you need to really study them intensively in...


DIUK-WASSER: ...certain places to really understand what's going on.

FLATOW: Do you think that global warming may have anything to do with the spread or the different places they're showing up?

DIUK-WASSER: Well, you know, it's hard to tell exactly if the warming itself, you know, may be causing this, but certainly, climate is - we expect climate in general to be linked to these diseases. I mean, these are, you know, these - the mosquitoes and ticks, they're exotherms. They depend on temperature in their development and all their cycle are - it's very sensitive to temperature.

FLATOW: Right.

DIUK-WASSER: So really, you would expect climate to influence them in some way, exactly in which way, we, again, we don't know.


DIUK-WASSER: So we don't even know, you know, the current climate sometimes how it's affecting them. The change would certainly affect, you know, affect them even more. But we definitely think, you know, we need more studies and...


DIUK-WASSER: ...again, funding and, again, you know, looking into the future of how this is going to influence these diseases. It's hard.

FLATOW: How did this - how did the outbreak this year compare with other years?

DIUK-WASSER: Well, it seems to be going to be a record year or either the record year or similar to the 2003. That was the huge epidemic. It's not done yet. But apparently, this first week of September is going to be a record year. And, yeah, and again, I mean, we kind of expect that from the climate but not necessarily why in that particular location in Texas or in those states where it's been more prevalent. There are certainly, you know, people doing studies, and there are certain things we would like to look at and - but it's pretty complex. There's different species of mosquitoes in different places, different birds that are involved so...

FLATOW: Right. So it's hard to make even a vaccine then for West Nile or anything?

DIUK-WASSER: Yeah. But there - yeah. There's - it's - there is a vaccine for horses, actually, but there hasn't been one for humans in - and...

FLATOW: Because...

DIUK-WASSER: I think it's just not recommend - it doesn't seem "profitable," quote, unquote. I mean, a lot of people are asymptomatic, and a lot of people are not exposed. So I'm not sure it would be the most effective thing to vaccinate the whole population against that disease that's so rarely, you know, really severe, overall. So there hasn't been, you know, a lot of development. There are some studies for the vaccine, but it's not going to...

FLATOW: Didn't they say that about Lyme disease when it first showed up?

DIUK-WASSER: Same thing. There was a Lyme disease vaccine, and it was taken off the market. So that kind of history, you know. And in the case of Lyme disease, it was also because there was this sense that it had, you know, side effects and so forth. There was a different kind of debate. But still, this is for the zoonotic infections that depend - especially for Lyme disease. They depend on being exposed to ticks or West Nile it might be, you know, there's mosquitoes everywhere. So most people should be concerned, I would say.

FLATOW: All right. Dr. Diuk-Wasser, thank you very much. Very interesting. And we're going to follow you, have you back, talk more about it. Have a good weekend.

DIUK-WASSER: Thank you. Thank you very much.

FLATOW: You're welcome. Dr. Maria Diuk-Wasser, assistant professor of epidemiology of microbial diseases. That's at the Yale School of Public Health in New Haven, Connecticut. We're going to take a break. When we come back, a trip off the Oregon coast where a new renewable power project is setting up using wave energy, ocean from the ocean. Stay with us. We'll be right back. I'm Ira Flatow. This is SCIENCE FRIDAY from NPR. Transcript provided by NPR, Copyright NPR.