West Nile Encephalitis
Background
Normally seen in the Middle East, and some parts of Europe and Asia, this flavivirus produced an outbreak of encephalitis in the New York Metropolitan area in 1999. This was the first appearance of West Nile virus in the Western hemisphere. The virus normally circulates in birds and mosquitoes. Humans and other mammals become infected when bitten by an infected mosquito. Most human illness from West Nile infection is mild or asymptomatic. Severe disease is more common in elderly or immunocompromised persons.
Scope of Problem
A total of 62 cases of human encephalitis/meningitis with seven fatalities were diagnosed in New York City and adjacent Long Island and Westchester County. Positive birds and mosquitoes were also identified in New Jersey, Connecticut, New York State and Maryland. In the hardest hit section of Queens, 2.5% of humans tested were found to have been infected with West Nile virus.
Sequelae
There were seven fatalities associated with the outbreak. In addition, more than 20 bird species were found to be infected with West Nile virus, with high fatality rates. Fatal infection was also seen in horses on Long Island.
Challenges
As a newly introduced pathogen, the future range and impact of West Nile virus is uncertain. States on the eastern bird flyway have received federal funding to conduct monitoring activities and perform diagnostic assays. This effort will be expanded nationwide. Humans, birds, and mosquitoes must be monitored. In addition, physicians, laboratorians, veterinarians, and the public must be educated about this infection and how to reduce its impact. The public health infrastructure must be better prepared and equipped to address vectorborne diseases.
Risk Groups
All persons can be infected with West Nile virus, but the elderly and immunocompromised are at higher risk of severe forms of illness.
Research Priorities
- Basic biology of the virus in mosquitoes.
- Alternatives to current pesticides and control measures.
- Therapeutics and vaccines.
- Inter-epidemic behavior of the virus.
May 2000
