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West Nile Virus
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West Nile Virus is a Flavivirus most commonly found in Africa, Asia and southern Europe. The disease, West Nile Fever, is vectored by mosquitoes and affects humans, other mammals and birds. Among animals, horses are especially susceptible; among humans, elderly and other immunocompromised persons.
Research indicates that the strain of West Nile virus identified in the New York 1999 outbreak, and now spread over the eastern half of the nation, is consistent with the Old World West Nile virus strains, from the perspective of human or animal illness. The New York City human outbreak closely mirrored the Romanian outbreak in 1996. Based on the Queens population-based survey of blood samples, the incidence of infection and ratios of inapparent disease were very similar. Clinical infection and ratios of inapparent disease were very similar. Clinical manifestations were also similar. Originally, it was thought that the flaccid paralysis seen in patients in New York City was unique; however, there were anecdotal reports of similar cases in Romania. Classical West Nile fever typically includes a rash. However, few rash symptoms were observed in either the Romanian epidemic of 1996 or the New York outbreak of 1999.
Similarly, there is experimental evidence in the literature of West Nile virus being lethal to hooded crows. There are many bird species, including crows in the Middle East, that survive West Nile virus infection as evidenced by the presence of live, seropositive birds. Why the crow population was so drastically affected in New York City is not known; however, one theory is that the dry summer stressed the crows and made them more susceptible to infection. Controlled laboratory expirimentation to determine differences in virulence between West Nile virus isolates will be needed to fully answer these questions.