West Nile Virus Strain – New York 1999 : How does this strain compare to its Old World siblings?
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West Nile Virus Strain – New York 1999 : How does this strain compare to its Old World siblings?

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    At this time, research indicates that the strain of West Nile virus identified in the New York 1999 outbreak is consistent with Old World West Nile virus strains, from the perspective of human or animal illness.

    Human 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 to apparent 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.

    Bird Illness: 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 experimentation to determine differences in virulence between West Nile virus isolates will be needed to fully answer these questions.

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