A review of the epidemiological and clinical aspects of West Nile virus

The resurgence of West Nile virus (WNV) in North America and Europe in recent years has raised the concerns of local authorities and highlighted that mosquito-borne disease is not restricted to tropical regions of the world. WNV is maintained in enzootic cycles involving, primarily, Culex spp. mosquitoes and avian hosts, with epizootic spread to mammals, including horses and humans. Human infection results in symptomatic illness in approximately one-fifth of cases and neuroinvasive disease in less than 1% of infected persons. The most consistently recognized risk factor for neuroinvasive disease is older age, although diabetes mellitus, alcohol excess, and a history of cancer may also increase risk. Despite the increasing public health concern, the current WNV treatments are inadequate. Current evidence supporting the use of ribavirin, interferon α, and WNV-specific immunoglobulin are reviewed. Nucleic acid detection has been an important diagnostic development, which is particularly important for the protection of the donated blood supply. While effective WNV vaccines are widely available for horses, no human vaccine has been registered. Uncertainty surrounds the magnitude of future risk posed by WNV, and predictive models are limited by the heterogeneity of environmental, vector, and host factors, even in neighboring regions. However, recent history has demonstrated that for regions where suitable mosquito vectors and reservoir hosts are present, there will be a risk of major epidemics. Given the potential for these outbreaks to include severe neuroinvasive disease, strategies should be implemented to monitor for, and respond to, outbreak risk. While broadscale mosquito control programs will assist in reducing the abundance of mosquito populations and subsequently reduce the risks of disease, for many individuals, the use of topical insect repellents and other personal protective strategies will remain the first line of defense against infection.