West Nile Virus in Canada: 2008
Here's a recap of West Nile virus activity in Canada in 2008.
Humans: There were 36 people diagnosed with disease caused by West Nile virus. Five had neurological disease, 29 had non-neurological disease (i.e. West Nile fever) and in two cases the clinical syndrome was not defined. Most affected people were from Saskatchewan (17) and Manitoba (12), with three from Ontario and two from Quebec. There were single cases in Alberta and British Columbia, and both of those were thought to have been acquired outside of the respective provinces.
Horses: West Nile virus infection is an immediately notifable disease in Canada, whereby the Canadian Food Inspection Agency must be notified of all diagnosed cases in animals. Six positive horses were reported in Canada in 2008, including two in Ontario horses, both in eastern Ontario. Two other cases were reported in Saskatchewan and two more were reported in Quebec. Whether this low number of diagnosed cases is because the disease is now actually this uncommon in canadian horses, or because there is less testing for the disease is unclear. Based on anecdotal information from other veterinarians and horse owners, I suspect that West Nile virus infection in horses is truly rare in Ontario, but is more common in Saskatchewan. This makes sense considering the different types of mosquitoes in the two provinces, as well as the corresponding difference in the number of human cases. These questions highlight the need for proper diagnostic testing to be performed on all horses with neurological disease. The more confidence we have in the surveillance data, the better conclusions we can make about patterns of disease and the need for vaccination.
