The Carlisle Mosquito Online

Friday, October 7, 2005


Eastern Equine Encephalitis found near Carlisle

On Friday, September 23, the Concord Board of Health received notice that an unvaccinated horse on Virginia Road in northern Concord had been put down after contracting Eastern Equine Encephalitis (EEE,) a rare mosquito-born illness that also affects humans. This is the only confirmed case of EEE in Concord during the last 12 years, according to Michael Moore, Concord's Public Health Administrator. Last year an alpaca in Carlisle tested positive for EEE, and cases were also reported in Billerica and Wilmington.

David Henly of the Eastern Middlesex Mosquito Control Project explained in a phone interview that EEE is primarily a disease of birds. Mosquitoes transmit the disease by biting infected birds and then biting animals or humans. While Massachusetts has not been testing dead birds for signs of EEE, testing in New Hampshire has found over 50 infected birds to date this year.

A EEE vaccine is available for horses, but not for humans, who suffer a 30% fatality rate after contracting the disease. Henly did not know of any cases where dogs or cats ever contracted EEE.

EEE runs in cycles

"EEE was discovered in Massachusetts in 1933, when hundreds of horses died from it." Henly continued, "There has been a major outbreak approximately every 17 years," usually with each episode lasting two to three years. This is the second year of an outbreak in Middlesex County, and there were cases in southeastern Massachusetts in 2003. There may be years in between peaks when there are minor outbreaks with one or two cases. "We may be heading out of a cycle, but we can't be sure," He thought a lot depended on how wet this winter is, because populations of EEE-carrying mosquitoes diminish during droughts.

Mosquitoes inactive below 60°F

"Personal protection is the only thing people can do at this point." The mosquito population is down right now, and people should be aware that mosquito activity stops when temperatures are below 60°F. This is important. If there is an outdoor recreational activity and the temperature is below 60°F, you don't have to worry too much." Henly expected the danger to subside in two or three weeks once frosts arrive.

For more information, see the press release below.

2005 The Carlisle Mosquito