Mosquitoes unlikely to transmit Lyme

The summer is finally here and it is time to venture outside and appreciate our beautiful country. In almost all parts of the country, tick checks are an essential once you come in from the beautiful outdoors – be it wilderness hiking, a walk in a local park or your backyard. But what about the other bugs that like to suck our blood? The world has an extraordinary number of mosquitoes in it, and they can transmit serious diseases in many parts of the world, although in North America and Europe, they are primarily just an itch-causing nuisance. But what about Lyme disease? Can mosquitoes transmit the bacteria that causes Lyme disease if they feed on an infected animal? And does this pose a risk to humans or domestic animals? 

The biology of mosquitoes is different from ticks, so in theory, mosquitoes should not be able to transmit the Lyme disease bacteria, Borrelia. But nature is usually more complicated than we think and there are so many mosquitoes in the world, it is important to check. That is what a group from the Czech Republic has now done. 

While some studies have even found the Borrelia bacteria in mosquitoes it is important to know how well they can pick it up and, most importantly, whether mosquitoes can pass on the bacteria when they bite a person or animal. The researchers tested three kinds of mosquitoes—Aedes aegypti, Culex quinquefasciatus, and Culex pipiens molestus. They let the mosquitoes bite mice that had the Lyme disease bacteria to see if the mosquitoes could pick up the bacteria from the mice. They also gave the mosquitoes blood filled with the bacteria to see if it stayed in their bodies. The mosquitoes were not good at getting the bacteria from infected animals. When given higher doses of bacteria in infected blood, the mosquitoes did take up the bacteria but the bacteria were quickly destroyed during digestion. When the digestive enzyme trypsin was blocked, the bacteria lived a bit longer. But even so, when the mosquitoes were tested to see if they could pass the bacteria to another animal by exposing uninfected healthy mice to the mosquitoes, even the mosquitoes that had fed on the higher dose blood were not good at passing the bacteria. 

While there are always exceptions, this study does provide strong evidence that mosquitoes are not a significant threat for transmitting the Lyme disease bacteria. So that gives us one less thing to worry about when going outdoors to enjoy our wonderful country. Mosquitoes are still irritating and bug spray is a good way to keep them at bay, and tick checks when you come inside are important.

You can get all the details at Parasites & Vectors.

Citation

Pekľanská, M., Kuníková, K., Vlčková, R. et al. Experimental evidence rules out mosquitoes as vectors of Lyme disease. Parasites Vectors 18, 206 (2025). https://doi.org/10.1186/s13071-025-06823-x