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The relationship between climate change and rising disease

PIEN HUANG, HOST:

As the planet gets warmer, mosquitoes, fleas and ticks are expanding their reach, and they are disease vectors. They carry in them some viruses and parasites that can make humans very sick. In the U.S., there are at least 17 different vector-borne diseases, and the number of people getting these diseases is rising. Here to tell us more is Dr. Benjamin Beard. He's the deputy director of vector-borne diseases at the Centers for Disease Control and Prevention. Welcome, Ben.

BENJAMIN BEARD: Thank you. It's good to be here today.

HUANG: Yeah. So diseases spread by vectors are on the rise. What vectors are we talking about and what diseases?

BEARD: Yeah. So the vectors that we're talking about, by and large, are ticks and mosquitoes. For ticks, there's really three species of ticks that account for the diseases that we see in the U.S. And then when we're talking about mosquito-borne diseases, really there are a couple of different mosquitoes that are particularly important. One is the species that carries West Nile virus - and there are actually a couple of those. And then the other is the yellow fever mosquitoes, what we used to call it - Aedes aegypti. And it's responsible for dengue and chikungunya virus and some other diseases like that.

HUANG: So what are some of the top diseases that you're concerned about right now?

BEARD: Yeah. So in the U.S., there are 16 some-odd diseases - 16 or 17 - that are what we consider to be reported. There's Lyme disease, anaplasmosis, Rocky Mountain spotted fever or spotted fever rickettsiosis, babesiosis, ehrlichiosis. And we see West Nile virus, which is the most common mosquito-borne disease. And then we see several other diseases that are a little less common. And some are travel-associated.

Lyme disease is - you know, it's a very serious disease. Every year there are fatalities. If you catch it earlier, you diagnose it and you treat it, then it's usually not too eventful. But, you know, it's the summertime flu. You can have arthritis, and people have even died from early Lyme disease - carditis. The biggest problem with Lyme disease - if you don't pick it up early and then it becomes disseminated in your body, and you - then it can become much more difficult to treat.

HUANG: What do we know about why these diseases are on the rise in the U.S.?

BEARD: Just to review some of the numbers, kind of in the last 20 or 25 years, we've seen a huge increase in all of these vector-borne diseases. The numbers of cases really have more than doubled over...

HUANG: Wow.

BEARD: ...The last 20 or 25 years. But with the trends that we see with climate change are - we see sort of milder winters, earlier springs, longer growing seasons, fewer frost days, you know, toward the end of the year. And so what that means that - when these ticks come out, they're coming out earlier in the year and they are probably expanding their geographic distribution into more northern areas. And then with mosquitoes, you got sort of a similar thing. So the warming climate, you know, is having an impact in a number of different ways. But there are a lot of other factors going on at the same time.

HUANG: Yeah. So what are some of the ways that you use to control the mosquito and tick populations? I mean, is it as basic as just setting out a lot of mosquito traps? Like, what is being done?

BEARD: Yeah. Well, it's very different between ticks and between mosquitoes. With ticks, it's interesting because our data actually supports that probably the majority of cases of tick-borne illness occur in people's backyards. And the methods that we recommend for tick control, first of all, is to wear repellents. They can do tick checks. Look for ticks crawling on their body. They can take their clothes - throw them in the dryer on high heat for 10 minutes, and it'll kill any live ticks that are there. And then, of course, if you get a fever or a tick bite, you know, go very promptly to your health care provider.

With mosquitoes, really, we encourage people to wear repellent when mosquito numbers are bad. And we believe that pesticides are a very useful tool for the control of vector-borne diseases, but we use them judiciously. And at the same time we use those, we're looking at a number of novel - more novel types of interventions, like releasing sterile mosquito - sterile male mosquitoes. So they - we'll just release the males. Males don't bite. Only the female mosquitoes bite and transmit disease. So if you release male mosquitoes that are sterile, they can actually mate with those wild female mosquitoes, and then they don't produce any offspring. So it's been actually a way that you can control mosquito-borne diseases without using pesticides. And a lot of those methods are still being developed and evaluated, but it's very promising.

HUANG: That was Dr. Benjamin Beard. He's the CDC's deputy director of the Division of Vector-Borne Diseases. Ben, thanks for speaking with me.

BEARD: Thank you, and have a nice day. Transcript provided by NPR, Copyright NPR.