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The mild summer weather across the United States this year has given mosquitoes a perfect climate in which to breed, and the mosquito population has been increasing at a steady rate. With a thriving mosquito population comes a greater risk of being infected with mosquito-borne illnesses. One of the most feared viruses, the deadly eastern equine encephalitis virus (EEE), has made its first reported appearance in Massachusetts in 2014.
The EEE virus was positively identified in a mosquito collected on July 15 in Bridgewater, Plymouth County, by the Massachusetts Department of Health. Last year, the state collected over 6,000 mosquito samples, with 1 percent testing positive for EEE. The positive samples were collected from 27 towns across six counties.
The lethal virus can cause inflammation of the brain in those infected, which leads to death in about 35% of the humans infected, especially in the elderly, children and those whose immune systems are suppressed for various reasons. The only person infected with EEE in Massachusetts last year, an elderly woman of 85, died of the disease. Over the past 10 years, there have been 26 people in the eastern state who contracted the disease. Of those, 12 of the cases were fatal. There is no known cure for the infection.
In contrast, West Nile virus was discovered in over five percent of samples tested by the state in 2013, and eight people were diagnosed with the illness. The virus was discovered in 11 counties and 128 towns.
Unfortunately, not only do mosquitoes carry the eastern equine encephalitis virus, but birds can transport EEE as well – sometimes over hundreds of miles. When a mosquito from one of two species that feeds on the blood of birds bites a bird carrying EEE, the virus will be transferred to the insect, who can then infect humans. According to entomologist Bob Russel, a mosquito’s digestive system is the perfect habitat for viruses such as EEE. Once there, it can be regurgitated or be present in the saliva that a mosquito injects into humans when it bites. Generally, people only become sick through the bite of an infected mosquito.
Eastern equine encephalitis was discovered in Massachusetts in 1831 after 75 horses died of the illness. In 1933, the virus was isolated from the brains of infected horses for the first time. The very first confirmed cases in humans were identified in 1938 after 30 children in the northeastern area of the U.S. died of encephalitis at the same time as horses in the same areas suffered from outbreaks.
Although EEE infects amphibians, birds, mammals and reptiles, it is maintained in nature due to the bird-mosquito cycle. Mammals do not carry enough of the virus in their blood once infected to pass the virus on to mosquitoes.
Americans are advised to stay cautious when outdoors and to take steps to prevent mosquitoes from biting them. Wearing clothing that covers legs and arms in the dusk and dawn hours when mosquitoes are most active is the best way to protect oneself. Staying away from wet, swampy areas is another good practice. As the summer season continues, cases of EEE are expected to increase as the number of birds and mosquitoes infected increase, leading the Mass. Department of Health to issue a warning to citizens to stay alert and to take precautions when outdoors.
By Jennifer Pfalz