Are mosquitoes getting more dangerous?

MOSQUITOES SEEM TO BE EVERYWHERE THIS YEAR, AND they're not just a nuisance at outdoor gatherings. Health experts say they're carrying some serious diseases—a fact that's hitting home in the U.S., as some towns in Massachusetts have shut down public parks and other outdoor areas in the evenings, after mosquitoes in the region were learned to be carrying eastern equine encephalitis, a rare but deadly virus. And Dr. Anthony Fauci, the country's former top infectious-disease expert, was recently hospitalized with a West Nile virus infection he is believed to have acquired from a mosquito buzzing through his backyard.

- ALICE PARK

It's not news that mosquitoes carry a number of viruses and parasites that can be harmful to human health, including malaria, dengue, yellow fever, chikungunya, West Nile virus, and eastern equine encephalitis. And it's understood that different species of mosquitoes are adept at spreading different viruses. But is this actually a particularly bad year for mosquito-borne diseases? And what can we expect in the future?

The variety primarily responsible for spreading eastern equine encephalitis, Culiseta melanura, has drawn the most attention lately because of how dangerous and potentially deadly the disease is. But fewer than a handful of cases have been reported so far this year in the U.S., which is pretty much on par with what's reported in New England every year, says Dr. James Shepherd, an infectious-disease expert at Yale University School of Medicine.

The more concerning type of mosquito is actually the most common, says Shepherd. Aedes mosquitoes, which include a variety of different species, cause most of the world's malaria, dengue, yellow fever, and Zika. They live primarily in urban, densely populated areas and can generate hundreds of eggs in as little as a capful of water. With an estimated 80% of people around the world now living in urban settings, "we are concentrating ourselves in much, much denser communities amongst urban mosquitoes," Shepherd says.

When it comes to West Nile virus, data from the U.S. Centers for Disease Control and Prevention show that 38 states have reported more than 370 cases so far in 2024; last year, more than 2,500 cases were recorded nationwide, nearly double the number reported in 2022. Experts note, however, that cases fluctuate depending on mosquito populations and the likelihood of human-mosquito interactions.