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Mosquito- and tick-borne illnesses like West Nile virus and Lyme disease are already a concern in the summer months, but scientists say human impacts on our climate and environment are making the risks for contracting those diseases even greater. 

In a panel hosted Monday by SciLine and the American Association for the Advancement of Science, researchers said that higher temperatures and greater precipitation lead to faster growth of ticks and mosquitoes and, by extension, greater opportunity for disease to spread. 

Climate change’s effects on mosquitoes 

Erin Mordecai, a researcher at Stanford University studying infectious disease, said knowing a 

 is crucial to understanding the effect climate change has on the diseases they spread.  

Mosquito eggs hatch in standing water, where the larvae grow into adults. Record rainfall and temperatures in recent years have meant ample places for mosquitoes to lay eggs and a shorter growth period, said University of Wisconsin-Madison entomologist Lyric Bartholomay. 

Those wetter and warmer conditions create a better environment for carriers of diseases like dengue fever and even malaria. 

Since West Nile virus was first reported in the U.S. in 1999, its season for transmission — typically in the summer and fall — has grown about 25 days. Mordecai said the disease is being found in greater numbers of mosquitoes and, by extension, more cases in humans. 

In July, mosquitoes found in all seven counties of the Twin Cities metro area 

Ticks now have longer seasons to thrive. But Jean Tsao, a researcher at Michigan State University studying the bacterium that causes Lyme disease, said there are other factors at play. 

“Certainly landscape, land use and wildlife communities play a large role in where these ticks can be. And that’s affected by humans,” Tsao said. 

As humans build new developments on forest land, the kinds of animals that live in those forests change, which in turn affects the species of ticks that feed in those forests.

As a result, a number of tick species expanded their range. The lone star tick, which was initially found in the south, has moved into the southern edge of Minnesota.

Just because diseases like Lyme disease and West Nile virus are ubiquitous doesn’t make them any less serious, said Mordecai. 

The researcher said 2025 is looking like a big year for West Nile virus cases. The disease is spread through mosquito bites and can involve fever, aches or vomiting. 

Dengue fever has also been on the rise in recent years, Mordecai said, with some local transmission in places like Hawaii and Florida, so caution when traveling is advised. Also called “breakbone fever,” dengue can lead to nausea, vomiting and severe aches and pains. 

Disease specialists saw a large rise in dengue cases in 2023 to around 5 million in the U.S. and even more in 2024 — around 10 million.  

Mordecai said it remains to be seen whether cases will go up in 2025. 

Rarer tick-borne diseases have been spotted in Minnesota as well, like 

 which can lead to fever in humans and death in pets, and 

, which can lead to severe illness and death.

Bartholomay said agencies have a number of preventative and reactive measures to respond to mosquitoes, but added that in 2023 only about 20 percent of programs in the U.S. could get to the targeted level of mosquito control. Much of that has to do with organizations not being able to catch up to the shifting mosquito season. 

Researchers said people should be careful when spending time outside in peak tick and mosquito season. Wear clothes that cover your arms and legs, and consider clothes treated with permethrin to repel insects. 

 on bare skin and do routine tick checks after spending time outdoors. 

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Payton Whaley

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Human impacts on climate and the environment affect the number of cases of mosquito- and tick-borne illnesses like West Nile virus, dengue fever and Lyme disease, experts say.

A side by side of two bugs up close on human skin.

Getty Images iStockphoto and Erik Karits via Pexels | MPR News photo illustration

Two deer, or black-legged, ticks crawl around in a glass petri dish.

Mosquito- and tick-borne illnesses are on the rise. Climate change is to blame

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