The Emergence of West Nile Virus in North America: Ecology, Epidemiology, and Surveillance

Abstract

The discovery of the flavivirus, West Nile (WN) virus, in the summer of 1999 in the USA dramatically altered the landscape of arthropod-borne virus (arbovirus) disease ecology and epidemiology in the western hemisphere. Arboviruses capable of causing human encephalitis exist throughout much of North America, but large epidemics or epizootics have not occurred since the last major outbreak of St. Louis encephalitis (SLE) in the 1970s (Bruetman et al. 1976; Levy et al. 1978; Maetz et al. 1978; Paulson and Brinker 1978; Powell and Blakey 1976, 1977; Powell and Kappus 1978; Zweighaft et al. 1979). Because of the sporadic nature of arboviral diseases, it has been difficult to mobilize political and public support for funding needed to maintain effective arboviral surveillance and control programs. The loss of this infrastructure has made much of the USA potentially vulnerable to new mosquito-borne disease outbreaks. The complex and multi-factorial biology of arboviral diseases makes re-establishing the expertise needed to prevent and control human disease outbreaks very difficult. Therefore, regions of the USA that for years have been spared from these diseases, now must evaluate their need for establishing or rebuilding programs for mosquito-borne disease prevention and control, given the introduction and rapid spread of WN virus in the northeastern USA. WN virus also poses a threat to wildlife and domestic animals, with high fatality rates among a wide variety of avian species and equines. Therefore, wildlife and veterinary health officials need to work in concert with their human health counterparts in responding to WN virus.