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It's been a record year for dengue fever in Latin America. The mosquito-borne disease surged across the Americas with nearly 3 million cases reported. That's more than 20% higher than the previous record in 2015. NPR's Pien Huang explores why.
PIEN HUANG, BYLINE: It's been a weird year for rain and one of the hottest on record, and mosquitoes are loving it. Tropical countries like Brazil, Nicaragua and Mexico have all had bouts of heavy rain and flooding and huge spikes in dengue. Leah Katzelnick, who's an epidemiologist at UC, Berkeley, says that after it rains, mosquitoes will lay their eggs in any pool of water.
LEAH KATZELNICK: You're just fighting against everything. The lids on top of your barrels become containers for breeding mosquitoes. Any tiny little piece of trash. They've found that tires are a huge source of larvae.
HUANG: Those larvae grow into hungry mosquitoes of the Aedes aegypti species that infect people with dengue when they bite. In some cases, dengue fever can feel like the flu. In severe cases, it can cause blood vessels to leak and organs to fail. More than 1,300 people have died from dengue in Latin America this year. But mosquito weather is only one reason for the surge. Mauricio Nogueira is a virologist in Sao Paolo, Brazil.
MAURICIO NOGUEIRA: Every outbreak that we have has becoming bigger than the last one.
HUANG: He says it could be that the virus is mutating to become more infectious or because more people are packed into cities, which also makes it easier for mosquitoes to spread dengue. But dengue outbreaks come in cycles, too.
NOGUEIRA: Every three or four years, you have a surge of dengue cases.
HUANG: Nogueira says that people who recover from dengue are immune to it for a couple of years. So after big outbreaks, there's a time of herd immunity, where there's enough people who just had dengue to protect those that haven't. So weather, outbreak cycles, and another reason for this year's explosion is a different virus, Zika. Gabriela Paz-Bailey, epidemiologist at the Center for Disease Control's Dengue Branch in Puerto Rico, says rates of dengue have been super low since the Zika virus swept through in 2016.
GABRIELA PAZ-BAILEY: Zika and dengue are closely related viruses, so it is possible that the Zika outbreak in the Americas provided some short-term protection against dengue.
HUANG: Researchers think the antibodies the immune system's created to fight Zika protect against dengue. But this immune system response is a temporary effect that fades after a few years, which may have primed this year for a big dengue surge. Around the world, nearly 4 billion people are at risk of getting dengue, and climate change and increased air travel means that risk is growing. Researchers are working on better vaccines and ways to hack mosquitoes to control the spread.
Pien Huang, NPR News.
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