The disease is spread by two types of mosquitoes. Hedgehogor black-and-white mosquito. This mosquito lives in broadleaf marshes and spreads the virus by feeding on birds such as robins, herons and wrens. However, the melanula mosquito does not often bite mammals. Another mosquito species, Coquilletidia pelturbansMosquitoes are the primary cause of the majority of reported human cases of the disease in the United States. Mosquitoes that feed on bird blood pick up the EEE virus and transmit it to humans or horses they bite. As summer draws to a close, mosquito populations peak and begin competing for blood. This is when human cases begin to spike.
Andreadis, who published a historical memoir in 2021 about the progression of Triple E in the Northeast United States, said climate change is emerging as a major cause of the disease.
“We have milder winters, warmer summers, and more extreme precipitation and drought,” he says. “The impact of this on mosquito populations is probably quite significant.”
Rising global average temperatures generally lead to an increase in mosquito populations, regardless of species.
Research has shown that when temperatures rise to a certain threshold (around 90 degrees Fahrenheit), C. melanura Mosquitoes take a long time to hatch their eggs. Warmer temperatures in the spring and fall allow mosquitoes to breed and feed for longer periods of time, and warmer temperatures in the summer encourage them to feed more frequently. Mosquitoes are ectotherms, and warmer temperatures speed up their metabolism.
Rain also affects mosquito breeding and activity because mosquito eggs need water to hatch. Higher temperatures hold more water, meaning even small rainfalls produce more water than in the last century. The more water that accumulates in roadside gutters, abandoned car tires, ponds, swamps and holes, the more opportunities there are for mosquitoes to breed. Warmer water also shortens the incubation period for mosquitoes. C. melanura Eggs are more frequent, with one study concluding that warmer than average water temperatures “increase the likelihood of amplifying EEE.”
