ARI SHAPIRO, HOST:
An outbreak of the mosquito-borne disease Eastern equine encephalitis started in Massachusetts last month, and now there are cases across the Northeast. The spread of this rare disease raises a question. Is climate change making EEE and other viruses like it more common? Alejandra Borunda from NPR's Climate Desk reports.
ALEJANDRA BORUNDA, BYLINE: You know the sound that horrifying buzz when a mosquito comes at you for a bite? And right now in the Northeast, that sound is a warning because mosquitoes carry and spread the rare and dangerous disease Eastern equine encephalitis or EEE. Leonard Mermel is a medical expert and researcher at Brown University. His hospital in Rhode Island treated patients in 2019 during an outbreak of EEE.
LEONARD MERMEL: I don't know if it had ever happened before, certainly not in my 30 years there.
BORUNDA: Mermel has seen climate change soften New England winters and make his backyard tomatoes ripen sooner. So he wondered, was warming affecting the virus and its hosts, too? That turns out to be a really tricky question. Because EEE is so rare, it's tough to research. And what drives the outbreaks is more complicated than for some of the other mosquito-borne diseases like malaria, where the climate connection is a little more straightforward. Marta Shocket is a disease ecologist at Lancaster University in the U.K. She says...
MARTA SHOCKET: We should be pretty concerned about the impacts of climate change on diseases like malaria and dengue.
BORUNDA: That's because climate change is often loading the deck in those diseases' favor. For example, Shocket explains the way mosquito-spread disease depends on temperature. Step one...
SHOCKET: They have to bite an infected host to pick up the pathogen.
BORUNDA: Step two...
SHOCKET: The mosquito has to survive long enough for the pathogen to complete its development.
BORUNDA: Step three...
SHOCKET: And then that mosquito has to go on to bite a second host to pass that pathogen on.
BORUNDA: It's a pretty straightforward chain of events, but each of those steps are temperature dependent.
SHOCKET: Because the mosquito itself is cold blooded.
BORUNDA: So more mosquitoes usually equals more disease, at least in the case of diseases like malaria or dengue fever, which bounce back-and-forth between mosquitoes and people. EEE, though, is a little more complicated. The virus circulates between mosquitoes and birds, not people. But occasionally, another species of mosquito gets involved. It bites an infected bird and gets the virus. Then it might go on to bite a mammal like a horse or a human and pass the virus to them. Heidi Brown is an epidemiologist at the University of Arizona. She says climate does have an effect, but it's clearly not the only factor in play.
HEIDI BROWN: You know, there's not a one to one of, you know, we have greater abundance, and now we have more disease.
BORUNDA: That said, climate still matters. Temperature is one way. Precipitation - too much or too little or coming at unusual times of year is probably also an influence. And altogether, Brown says...
BROWN: What's driving the system is infected mosquitoes. And the number of mosquitoes that are out there that are infected, how quickly they become infected, that's going to be driven by the climate that the mosquitoes are experiencing.
BORUNDA: But she stresses that other factors matter a lot too, like how close people live to infected birds and mosquitoes.
BROWN: Some of those things we can control a little bit more easily than we can control, you know, climate change.
BORUNDA: So do the things you can. Dump out all the standing water near your home to get rid of mosquito eggs. And wear bug spray and long sleeves to protect yourself. Alejandra Borunda, NPR News. Transcript provided by NPR, Copyright NPR.
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