Environmental Health

West Nile Virus

West Nile Virus Overview

West Nile Virus (WNV) is new to the United States, however, other similar mosquito borne (arboviral) diseases have existed here for many years. These include St. Louis encephalitis, Eastern Equine encephalitis, Western Equine encephalitis, and La Crosse encephalitis. St. Louis encephalitis is the most common; representing about one half of all arboviral encephalitis reported in the U.S. The West Nile and St. Louis viruses are closely related.

States that have historically experienced the highest numbers of arboviral encephalitis have also reported the highest numbers of WNV disease. According to data from the Center for Disease Control, a total of 8,035 cases of St. Louis encephalitis, Eastern Equine encephalitis, Western Equine encephalitis, and La Crosse encephalitis were reported in the U.S. between 1983 and 2000. Only three (3) of the 8,035 cases of arboviral encephalitis reported since 1983 have occurred in Oregon.

That is not to say that WNV will bypass Oregon. Typically, when a new disease enters a region, it finds susceptible hosts and the incidence rate of the disease increases. After a period of time, the number of cases drops to background or “endemic” levels. So far, WNV has followed this typical pattern. States that initially experienced high numbers of WNV disease are, after one or two years, experiencing much lower “endemic” levels of WNV disease.

Avoid Mosquito Bites and Prevent Infection

By taking action to eliminate mosquito breeding areas around your home and protecting yourself and your family from mosquito bites, you will significantly reduce your risk of being exposed to WNV and other arboviral diseases. You can also contribute to community surveillance efforts by reporting dead birds or large areas of standing water.

Public Health Response

Efforts by the Department of Health Services to prevent the spread of WNV include:

• Participating in the statewide disease surveillance network
• Communicating WNV disease risk to the public and medical community
• Providing information about WNV disease and the actions people can take to limit their exposure to WNV
• Coordinating response efforts with other local governments, allied agencies, and the medical community

The level of public health response will be based on the risk of WNV transmission to humans. If surveillance indicates a significant presence of WNV in our area, federal, state and local health authorities will assess the risk of disease transmission to humans. Control measures will be based upon this risk assessment and the availability of resources. Resources will be focused on those areas where the risk of disease transmission to humans is highest.

More Information

With West Nile Virus expected in Oregon within months, public health officials at the Oregon Department of Human Services (DHS) has launched a Toll free telephone information line:
(866) 703-4636 or (866) 703-INFO.

Fight the Bite! Avoid Mosquito Bites to Avoid Infection

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Se espera que el Virus del Nilo Occidental llegue a Oregón dentro de pocos meses. Por esta razón, los funcionarios de salud pública del Departamento de Servicios Humanos de Oregón (DHS) lanzaron hoy una línea gratuita de información telefónica:
(866) 703-4636 u (866) 703-INFO

¡No se deje picar! Evite las picaduras de mosquitos para evitar la infección