ST. LOUIS ENCEPHALITIS
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St. Louis Encephalitis is a virus disease (Flavivirus spp.) that occurs widely in the United States and southern Canada. It was first reported in St. Louis, Missouri in 1933. Subsequently, it also has been found in Central and South America. In the eastern United States it is is primarily an urban disease spread by Culex quinquefasciatus or C. pipiens, and in Florida by C. nigripalpus. Chickens and other pet birds serve as amplifying hosts. In the western United States it is found mainly in rural areas near rice fields with Culex tarsalis as a vector (Service 2008).
The majority of infections produces mild symptoms and go undiagnosed, but the virus can cause severe illness and death in humans, especially the elderly where the fatality rate can reach 30 percent. Children characteristically do not develop serious disease. Humans and domestic mammals can acquire the virus, but are dead-end hosts.
The fowl mite, Dermanyssus gallinae (L.) has been found to be the primary transmitter and reservoir of St. Louis encephalitis virus. The virus is passed through the eggs to the offspring of the mites. As chickens are also reservoirs of this virus and as Culex spp. are common feeders on chickens and humans, Culex spp. are important vectors of the disease to humans. The chicken mite maintains the virus in chickens and the mosquitoes transfer the virus to humans. The mosquitoes may also serve as vectors from chicken to chicken (Matheson 1950). The virus has also been isolated from other bird species, so there are probably other reservoirs including birds that are abundant in the urban-suburban environment, such as the house sparrow, pigeon, blue jay, robin. etc.
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