Diseases
Mosquito-borne Diseases
Several of the 48 known species of mosquitoes in Oregon can carry diseases under the right conditions. When a female mosquito takes an animal blood meal, which she uses as nourishment for her developing eggs, she may transmit certain disease causing organisms to humans and other animals. These organisms are taken with blood from the infected human or animal. The mosquito completes the cycle when she bites the next susceptible host, causing infection. The two important diseases affecting humans are encephalitis and malaria.
West Nile Virus
Encephalitis
There are two forms of encephalitis transmitted by mosquitoes in Oregon, St. Louis and Western Equine. Both are carried into the area by wild birds that are infected elsewhere. These birds show no symptoms. Infected birds are then fed on by local mosquitoes that can pass the virus on to humans by future bites. Symptoms of encephalitis range from flu-like illness to severe brain involvement that can cause death. Western Equine Encephalitis can affect horses and other equine animals as well as humans.
Malaria
Malaria is much less likely to occur in Oregon due to the necessity for human reservoirs of the disease. Anopheles mosquitoes, the vectors of malaria, are found in some areas of Oregon, and there have been isolated cases where human reservoirs who have visited other countries temporarily provided a source of malaria infection to local residents.