5 non-travel related cases of malaria have been reported in the U.S.

STEVE INSKEEP, HOST:

Texas and Florida face five cases of malaria.

LEILA FADEL, HOST:

If you're thinking, wait, malaria's gone from the U.S., well, it was all but gone. Its disappearance is one of the great public health stories. Many kids learn in school how this country cut back on the mosquito-borne disease. They used insecticides and window screens and good drainage of standing water. But now it seems to be back.

INSKEEP: And NPR's Pien Huang is covering malaria's reemergence. Good morning.

PIEN HUANG, BYLINE: Good morning, Steve.

INSKEEP: What is unusual about these five cases?

HUANG: Well, Steve, it's really where people got the disease. So each year in the U.S., there's about 2,000 cases of malaria, but all of those are generally travel-related, usually found in people who have come back from countries where malaria is common. These five cases are locally transmitted. So these patients got malaria where they live - four in Southwest Florida and one in South Texas. And this local transmission is something that the U.S. has not seen in 20 years. So that prompted the CDC to send out an alert to doctors, telling them to look out for more cases.

INSKEEP: People have seen so little malaria. I have to ask, for those who don't know, what it is.

HUANG: So it's a disease that's caused by a parasite, and it's carried by mosquitoes. It's transmitted between people through mosquito bites. After someone gets bitten, it can take a week or a few weeks for symptoms to show. Dr. Monica Parise with the CDC says then it can quickly become a medical emergency.

MONICA PARISE: We don't want people to have traveled to a malarious area and then get a fever and just sit at home, or if you seek care and have been given a diagnosis and you're not getting better, you need to go back.

INSKEEP: Do you know what's changed, why we would see these cases now?

HUANG: That's an open question. I mean, experts think that a few factors aligned. So maybe there was an influx of travelers who came back with malaria, got bitten by mosquitoes in the U.S. Maybe that's coincided with a lot of rain, a lot of heat and humidity. These are conditions that mosquitoes and the malaria parasites really thrive under. And, probably, these forces combined to cause a flare in cases.

INSKEEP: You know, I study a lot of history. So, you know, you read about the 19th century. You read about malaria in the United States. I mean, it killed people then or it would just devastate their health for a long time. How dangerous is this?

HUANG: Well, it depends on the country and also the strain. And so specific to the U.S., around 15 out of every 100 people who get malaria get seriously ill. And every year, we do see a few people who die from it. Malaria can be caused by 1 of 5 different parasite species. And these cases in the U.S. are caused by one called Plasmodium vivax. Steve, there's good news and there's bad news that comes with that. So the good news is that this is not the most deadly one, although people still can be laid up for weeks with illness. The bad news is that this is a species that can hide out in a person's liver and come back after a few weeks or a few months. And so that makes it extra important for people to get the right diagnosis and take the right drug so that people can fully kick these parasites.

INSKEEP: Should we expect that malaria is going to become a larger problem in the United States?

HUANG: Well, there's probably more than five cases. But at the moment, the CDC says they're not expecting a huge outbreak. Malaria, as you mentioned, used to be a big problem in the U.S., and it's actually the reason the CDC was founded back in the 1940s. They did a lot of work going door to door, and that led to the disease actually being eliminated from the U.S. by the early 1950s. So in the best-case scenario, these cases are a blip. But they are checking to make sure that they're not a sign of a bigger problem.

INSKEEP: NPR's Pien Huang, thanks so much.

HUANG: You're welcome. Transcript provided by NPR, Copyright NPR.