ARI SHAPIRO, HOST:
It's been a record-breaking year for dengue cases in Central and South America - almost 10 million cases so far, more than any year on record. The Centers for Disease Control and Prevention is now warning of an increased risk of dengue infections in the U.S. NPR health correspondent Pien Huang is here to tell us about it. Hey, Pien.
PIEN HUANG, BYLINE: Hey, Ari.
SHAPIRO: Any idea why the virus is surging now?
HUANG: So a couple of reasons. No. 1, this is a mosquito-borne virus. And it's been a warm, wet year in South America, so there's a lot more mosquitoes around. Mosquitos are also thriving in more places thanks to climate change, so that's No. 1. No. 2 is that dengue is cyclical. There tend to be big outbreaks every couple of years. The last big one was in 2019. And part of the reason for that is that there's actually four different strains of dengue. People who get one strain are protected for a couple of years, then the immunity wears off and they're susceptible to getting one of the other strains. So this population-level immunity comes and goes in cycles. And then there's also the fact that people in the U.S. are traveling a lot more these days.
SHAPIRO: These days meaning, like, summer vacation? Or just broadly, generally speaking, people travel more?
HUANG: Definitely a lot more since the pandemic. So I spoke with Gonzalo Vazquez-Prokopec, an environmental scientist at Emory University. He says we can't just blame the mosquitoes.
GONZALO VAZQUEZ-PROKOPEC: Human mobility, either short or longer distances, play a significant role in moving the viruses around. So humans are the vector. Humans are the ones that are moving the virus even a longer distance than mosquitoes.
HUANG: He says one of the reasons why things went pretty quiet in the last couple of years is that travel basically shut down during the COVID pandemic. So now that people are traveling more generally - seeing family, old friends, places they haven't been - they're getting bitten by mosquitoes with dengue, and they're bringing it to wherever they're going next.
SHAPIRO: So how bad is it? I have a sense that, like, you'd rather get dengue than malaria, but you don't want to get dengue.
HUANG: Well, dengue is actually one of the world's most common mosquito-spread diseases. And in 75% of the cases, the people who get infected don't actually get very sick.
SHAPIRO: Well, that's good.
HUANG: Yeah, that's good. But in a quarter of those cases, they do, and those symptoms can be pretty awful, Ari. People can get high fevers, debilitating headaches, joint pains. And in some severe cases, it can cause people's blood vessels to leak, and it can lead to shock and even death.
SHAPIRO: Not good. OK, I said the CDC is warning about risk in the United States. How severe is that risk? Who should be worried?
HUANG: Yeah, so it really depends on where you live. The risk is not spread equally across the country. So far this year, there have been about 2,000 cases in the U.S. and most of those cases have been in Puerto Rico, where dengue is endemic. Puerto Rico actually declared a public health emergency over dengue a few months ago. There have also been some cases reported in the U.S. Virgin Islands, some in Florida. In recent years, local transmission has been seen in Texas, Arizona, California.
Gabriela Paz-Bailey, head of CDC's dengue branch, says that people who traveled to Puerto Rico or other places that are experiencing big dengue surges should be aware of the risk. It's especially dangerous for babies, pregnant women and the elderly. But she says that they're not actually expecting big surges of dengue across the continental U.S. the summer. What they do expect to see is more travel-related cases and small chains of transmission related to them. She says that they really want doctors to be on the lookout for cases and to test for it.
SHAPIRO: NPR's Pien Huang. Thank you.
HUANG: You're welcome. Transcript provided by NPR, Copyright NPR.
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