A dead crow in the York Region of Ontario, Canada, has undergone testing and is presumed positive for West Nile virus. It is the first presumed positive of the virus for the region.Equine cases haven't been reported in Canada this year, but typically do not turn up until late summer. The first 2003 equine case in the United States was detected in early April in Florida. The virus has been circulating in the North American equine population since 1999, its first appearance in the Western Hemisphere."We anticipated West Nile virus activity this year," said Dr. Hanif Kassam, acting medical officer of health for the York Region. "Knowing where that activity might be allows us to take appropriate action to monitor and prevent the spread of West Nile virus in our community. This information puts our plan in action."Crows are known to be most susceptible to the disease and act as an early warning system for the presence of the virus in a particular area. The more information we have the faster and more effectively we can respond."West Nile virus is a mosquito-borne virus that can cause encephalitis (inflammation of the brain) or meningitis (inflammation of the lining of the brain and spinal cord). The virus is named after the West Nile region of Uganda, where it was first isolated in 1937. The virus was found in the human, equine, and mosquito populations in the York Region in 2002.York Region Health Services has asked residents to report dead crows, with suitable specimens collected and submitted to the Canadian Co-operative Wildlife Health Centre in Guelph for screening.