In Europe, Asia, and Africa, West Nile virus appears to be spread
mainly by migrating birds; if this pattern holds true in North America, West
Nile could cause outbreaks throughout temperate and tropical regions of the
Western Hemisphere, according to an article in an upcoming issue of Emerging
Infectious Diseases, CDCís peer-reviewed journal, which tracks new and
reemerging infectious diseases worldwide.
Last summer in New York City, there were 62 confirmed cases of the disease
and 7 persons died during the first outbreak of West Nile virus infection in
this country. Humans become infected when they are bitten by mosquitoes that
have bitten infected birds. Recent testing has shown traces of West Nile virus
in mosquitoes that survived the winter in the New York area.
Birds can travel across the Atlantic by normal migration, storms, or legal
and illegal importation. A few birds of some species regularly migrate from
breeding grounds in Europe to wintering grounds along the eastern coast of North
America. These birds could be infected by mosquitoes before they migrate. Each
summer a few birds are swept across the Atlantic by tropical storms; some of
these birds belong to species that can be infected by West Nile virus. During
1999, 17,178 birds were legally imported into New York. Even though a quarantine
period is required, no tests are done for West Nile virus, and birds can be
infected without showing signs of illness.
In North America, spread of the new virus may depend on its survival in birds
that spend the winter in tropical, subtropical, and southern temperate regions.
According to the author, if migratory birds do play a role in virus spread, the next outbreak may not be
in the New York area, but rather in southern wetlands, farmlands, or cities.
These areas could provide a permanent base for the virus, from which it could be
spread north by migrating birds.
Illness in humans can be prevented by intensive monitoring of birds for
abnormal die-offs during fall and winter; collecting and testing dead birds if
die-offs occur; and stringent mosquito control measures at die-off sites. Any
birds taken from one part of the country to another should be tested for West
Nile virus during quarantine.
Access the full article regarding the West Nile Virus, courtesy of the Emerging Infectious Disease Journal at http://www.cdc.gov/ncidod/EID/vol6no4/rappole.htm.