West Nile Virus

West Nile Virus

General Information

West Nile virus (WNV) is a member of the family Flaviviridae and is closely related to several mosquito-transmitted flaviviruses that cause human disease on different continents, including St. Louis encephalitis (SLE) virus, a native North American arbovirus. Both WNV and SLE viruses are maintained in a transmission cycle involving birds and mosquitos.
WNV was first isolated in 1937 in the West Nile district of Uganda, Africa. Outbreaks of WNV have occurred in a number of countries including Egypt, Israel, South Africa, and countries in parts of Asia and Europe. Recent outbreaks, outside of North America, have occurred in France and Israel in 2000, Russia in 1999, and Romania in 1996-97.
WNV was first detected in the United States in September 1999 during the investigation of an outbreak of encephalitis in humans in New York City.
WNV is spread to humans by the bite of an infected mosquito. A mosquito becomes infected by feeding on the blood of a bird which carries the virus. Approximately two weeks must elapse after a mosquito has fed on an infected bird before it is capable of transmitting the virus to a human or animal. There is no evidence to suggest that an individual could get WNV from another person. For example, WNV cannot be spread through touching or kissing an infected person, or from exposure to a health care worker who has treated someone infected with WNV.

General Information - Surveillance

The number of bird species in North America that play a role in the transmission of WNV is not known at this time, although the virus has been identified in more than 100 species of birds in the USA during 1999, 2000 and 2001. High mortality rates occur in some bird species, particularly crows, blue jays, gray jays, magpies and ravens. The Canadian Cooperative Wildlife Health Centre is currently involved in collecting dead birds for surveillance of West Nile Virus in Canada. See their URL and associated links.
For general information on WNV, visit Health Canada's website.
For recent updates on WNV surveillance by province and general information provided by Health Canada, click here.

As of 1 January 2003, there have been no positive cases of WNV in either humans or birds in British Columbia.
WNV in adjoining jurisdictions to British Columbia:
- As of December 2002 , there have been no positive cases of WNV in dead birds collected in Alberta. For information, click here.
  - WNV was detected in a human patient in Calgary although it is highly likely that this person became infected while visiting endemic areas in the US southeast within the last several months.
- As of January 2003 , WNV has been detected in two corvids and two horses in Washington state - there have been no reports of humans cases. For information, click here.
- As of October 2002 , WNV has been detected in a horse from Idaho - there have been no reports of humans cases. For information, click here.
- As of November 2002 , WNV has been reported from horses and in two human cases in Montana. For information, click here.