Phoenix (AZ Family) — At least five states have confirmed human cases this year. Eastern Equine Encephalitis (EEE).

Though rare, it can be transmitted by mosquitoes, humans and some animals, and there has already been at least one fatal case in the United States.

Arizona has had cases of EEE before — a horse in Cochise County tested positive for the virus in 2023 — but the bigger problem, both nationally and here in Arizona, is another mosquito virus, West Nile virus.

There have been 18 reported cases of West Nile virus in Arizona this year, 15 of which have been in Maricopa County, a significantly lower number than the 70 cases during the same period last year.

“Mosquito populations can go from no daytime bites to hundreds of thousands of bites in a week,” said John Townsend, section chief of the Vector Control Division for the Maricopa County Department of Environmental Services.

The hot weather this year is affecting the lifespan of mosquitoes, he said.

“Believe it or not, mosquitoes hate it,” he said.

While the overall insect population may be declining, there are still cases of infected mosquitoes.

“We're receiving a significant number of mosquito samples that are positive for West Nile virus,” Townsend said, “and in years when the virus is really active and we have good monsoon rains, the number of positive mosquitoes can go up by 10-fold or more.”

Each week, crews will install about 860 mosquito traps across Maricopa County.

“The attractant is carbon dioxide, which is released by putting dry ice in a bucket with holes in it,” Townsend explains. “The mosquitoes think there's an animal there, so they come over and get caught in the fan.”

Mosquito bites at night are often cause for concern: West Nile virus has been prevalent in the state since about 2003, but Townsend said they test for other viruses as well.

“We've seen St. Louis encephalitis coinfections since 2016, and just a few weeks ago we found the first St. Louis encephalitis-positive mosquitoes this year,” he said, “so we continue to have the two viruses circulating among mosquitoes at night.”

Townsend says the best way to protect yourself from mosquitoes is to wear long sleeves and long pants when going out at night.

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