Two potentially deadly diseases spread by the bite of infected mosquitoes are on the rise in New England, prompting an alert by Maine health officials.
The Maine Center for Disease Control and Prevention has warned health care providers to be on the alert for Eastern equine encephalitis and West Nile virus. The relatively rare but serious infections typically crop up at this time of year, said Dr. Stephen Sears, state epidemiologist.
“It tends to be into the last half of the [summer] season and into September. … There has been a lot of West Nile activity in the southern part of New England.”
Mosquitoes pick up the diseases from biting infected birds and then spread them to people.
At least 241 human cases of West Nile virus, including 144 severe cases and four deaths, have been reported in 42 states so far this year. It’s the highest number of serious cases through July since 2004.
Maine is one of the few states that hasn’t recorded any cases of West Nile this year, but the virus has cropped up in mosquitoes in neighboring New Hampshire, Sears said. Milder cases of the disease may have sickened some Mainers but weren’t diagnosed and reported to health officials, he said.
Only about one in five people infected with West Nile gets sick with a fever, body aches, vomiting and join pain. But the virus can cause neurological problems such as brain swelling that can lead to confusion, coma, seizures and even death.
Most of the cases of West Nile, which first appeared in the U.S. in 1999, have occurred in three states — Texas, Mississippi and Oklahoma.
Health officials aren’t sure what’s causing the rise in West Nile this year, but suspect that the mild winter, early spring and hot summer spurred more mosquito breeding.
Eastern equine encephalitis is also on the uptick, showing up in Massachusetts this year. Planes flew over communities in the southeastern part of the state last month spraying pesticides to thin the mosquito population.
Research studies of deer indicate that Eastern equine encephalitis has reappeared in Maine, after killing a number of horses in the state in 2009.
“We know the virus is in the state,” Sears said.
The disease can also sicken people. The symptoms are similar to West Nile, but Eastern equine encephalitis can be more deadly, leading to death in 35 to 50 percent of cases.
There is no treatment or human vaccine for either disease.
Health officials are urging Mainers to avoid being outside at dawn and dusk, when mosquitoes are most active, and to use insect repellant while outdoors. The CDC also recommends installing or repairing screens to keep mosquitoes out and emptying standing water where bugs can breed, such as from flower pots, buckets and kiddie pools.