May Have Role in Spread of New Virus West Nile virus, a virus new to the United States, could be spread not only by mosquitoes but also by migrating birds. 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. 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.