By Tina Reed and Alison Snyder, Axios, Aug. 29, 2024

Almost daily headlines about the spread of rare, potentially deadly insect-borne diseases like eastern equine encephalitis and Oropouche fever highlight the expanding threat that mosquitoes, ticks, and other bugs present.

Why it matters: Longer, hotter, summers, milder winters, and changes in land use and travel are giving insects more time and space to spread diseases or compound the misery in places where they already exist.

Global warming is "changing where mosquitoes and ticks live, and thus what diseases are moving around in different regions," CDC director Mandy Cohen said Wednesday.

Driving the news: The death of a New Hampshire resident from eastern equine encephalitis, or EEE, brought home the threat.

The CDC has also warned this summer about an increased risk of dengue fever, which is spread by the same type of mosquitoes that carry the Zika virus and chikungunya.
West Nile Virus — which was recently blamed for the hospitalization of former NIAID director Anthony Fauci — has become a perennial threat throughout much of the continental U.S.
Malaria, a parasite spread by another species of mosquito, is also on the rise around the world, and several cases were reported in the U.S. last year, though the risk of catching it here remains low.

Zoom in: In the U.S. in particular, experts say the environment for insects has become far more hospitable with temperatures rising further north.

"We're seeing diseases that used to be "tropical." Well, now parts of the U.S. can count," Megan Ranney, dean of the Yale School of Public Health, told Axios.
"Ticks are not dying over the winter because it's not getting cold enough, so it's making Lyme disease spread. And then we're seeing other tick-borne diseases, like Powassan virus, start to spread. It is a predictable but potentially deadly consequence of climate change."

Yes, but: More travel and globalization are key elements that fuel the spread of vector-borne diseases, said Michael Osterholm, director of the University of Minnesota's Center for Infectious Disease Research and Policy.

For example, researchers believe Oropouche fever, which is spread by mosquitoes and midges, was brought to the U.S. and Europe by travelers who had been to Cuba and South America. Officials do not have evidence of local transmission in the U.S.
A proliferation of trash — used tires and old plastic — can also create perfect breeding grounds for mosquitoes, Osterholm said.
Changes in land use also play a role. Lyme disease is believed to be spreading in North America, in large part, due to the suppression of wildfires, which has allowed for the maturation of forests and animals that allow ticks to thrive.

Between the lines: Around the world, there are more — and more severe — outbreaks of arboviruses, which can be spread to people when infected insects bite them. "We're putting out more fires, and it takes more to put them out," says Colin Carlson of the Yale University School of Public Health.

The rise in malaria in Africa and dengue fever in Asia and the Americas have been linked to global warming but it's harder to attribute individual outbreaks or rare diseases to climate change, in part because of limited data, he said.
"It's also important to remember that explosive epidemics of arboviruses are standard fare," says Carlson, who studies whether changes in certain diseases can be linked to climate change. It happened with Zika and chikungunya in the Americas.
"With both Oropouche and EEE, I think it's important to not jump the gun and immediately go to, well, this is climate change in practice," Carlson says.

The intrigue: Some mosquito species are migrating around the world — presumably being transported on shipping routes, says Sadie Ryan, a medical geographer at the University of Florida.

One concern is a mosquito species could be deposited in a habitat that suits them and has "blood meals running around on the streets," Ryan said. If there's a disease there, the new species could pick it up and become part of the transmission cycle, she says.
"These are new paradigms," she adds. There's natural invasion biology happening at the same time as transformations in the landscape and climate change.
The challenge is "not even detecting it where it already exists. It's anticipating where it's coming to next."

What to watch: Insect immunology could offer new avenues for fighting the diseases and is beginning to mature as a field, says microbiologist and National Science Foundation program director Joanna Shisler.

Insects don't have complex immune systems like humans but they have something akin to white blood cells and other immune cells.
By studying how a virus replicates in a mosquito and how the insect's immune system fights it, scientists may be able to understand why some mosquitoes are resistant while others are susceptible to different types of virus infections, Shisler says.

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