Mosquito Diseases


Encephalitis in various forms such as St. Louis, Western Equine, La Crosse, Eastern Equine, and West Nile, which was recently discovered in the Northeast is endemic to the United States and increasing in incidence. Although extremely rare, Eastern Equine Encephalitis has a 30% – 60% mortality rate once contracted. Severe damage to the central nervous system occurs in those that survive the illness.

Eastern Equine Encephalitis (EEE) is maintained in nature through a cycle between the Culiseta melanura mosquito and birds that live in freshwater swamps. Although Culiseta melanura do not bite humans, some mosquitoes will “cross bite”; i.e., bite an infected bird and then bite a human or animal (horse, emu, and other exotic birds), thereby spreading the disease. These mosquitoes are also known as “bridge vectors”. A vector is a species that transmits a disease from one host to another. These bridge vectors may take a meal from a bird and later take another meal from a mammal.

Symptoms usually occur within two to ten days after being bitten by an infected mosquito. These symptoms include high fever, stiff neck, headache, confusion, and lethargy. Encephalitis, swelling of the brain, is the most dangerous symptom. Rhode Island has confirmed five cases of EEE with two deaths in the last thirteen years.


West Nile Virus symptoms include fever, headache, nausea, vomiting, and rash, which are mild symptoms to severe symptoms that include neck stiffness, stupor, disorientation, tremor, coma, vision loss, and paralysis. These severe symptoms could last weeks or could be permanent. The onset of symptoms usually begins three to 14 days after a mosquito bite. Unlike Eastern Equine Encephalitis, 80% of the people who are infected with WNV will show no symptoms at all. 20% will show mild to serious symptoms. People who are mostly likely to show symptoms if bitten by an infected mosquito are infants, the elderly and people with auto-immune difficiencies.

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