This disease is carried by two types of mosquitoes. The first is a species called Melanour slideor the blacktail mosquito. This mosquito lives in deciduous swamps and feeds on birds such as robins, herons, and wrens, spreading the virus among them. But the melanura mosquito rarely bites mammals. Another species of mosquito, Coquillettidia perturbansis primarily responsible for most human cases of the disease reported in the U.S. The perturbans mosquito becomes infected with the EEE virus by feeding on birds and then infects humans and horses that it bites. In delayed summer, as mosquito numbers peak and begin competing for available blood, human cases begin to appear.
Andreadis, who a historical retrospective was published in the context of the progression of E. disease in the northeastern USA in 2021, stated that climate change has become a major factor in the causation of this disease.
“We have milder winters, warmer summers and extreme precipitation and droughts,” he said. “The impact that has on the mosquito population is probably quite profound.”
Higher average global temperatures generally result in more mosquitoes, regardless of species.
Studies have shown that warmer air temperatures up to a certain threshold, around 90 degrees Fahrenheit, shorten the time it takes to C. melanoma eggs to hatch. Warmer temperatures in spring and fall extend the number of days mosquitoes have time to breed and feed. They will also feed more often in the summer season if it is warmer — mosquitoes are cold-blooded, meaning their metabolism speeds up at higher temperatures.
Rainfall also plays a role in mosquito reproduction and activity, as mosquito eggs need water to hatch. A warmer atmosphere retains more moisturemeaning that even lithe rainfall today dumps more water than it did in the past century. The more standing water there is in roadside ditches, abandoned car tires, ponds, marshes and potholes, the more opportunities mosquitoes have to breed. And warmer water shortens the incubation period C. melanoma eggs, leading one study to conclude that higher than average water temperatures “increase the likelihood of EEE amplification.”