In the eastern United States, eastern equine encephalitis (EEE) and West Nile Virus have been transmitted from mosquitoes to people. Most cases of encephalitis in the northeast occur from June through September, when mosquitoes are most active.
The viruses commonly live in the insect's salivary glands and are injected into the person or animal when the insect bites. People can develop diseases from the viruses, but usually can't pass the virus on to other people or animals.
The majority of people infected with the viruses have no symptoms and may not even develop the disease. Symptoms may come on slowly or suddenly and might include:
Because there is no cure for encephalitis, doctors can only react to problems the virus causes, such as loss of the ability to breathe involuntarily, and treat complications like bacterial pneumonia. Because encephalitis causes swelling in the brain, it can result in permanent neurological problems and sometimes death. Only a small proportion of people who are infected develop the disease.
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