Update: West Nile Virus in Ontario
An increased number of telephone reports of dead crows have been received by the CCWHC laboratory in Ontario over the past few weeks. This has resulted in a number of submissions, many of which have tested positive for West Nile Virus.
To date, there have been 18 WNV positive avian cases diagnosed in Ontario. The birds most commonly involved, with 9 cases, are crows. However, cases that have tested positive by PCR also include 3 Great Horned Owls, a Red Tailed Hawk, a Blue Jay, an American Robin, a Canada Goose and 2 Mallards that were in a rehabilitation centre.
The geographic range of cases is fairly wide, extending from southwestern Ontario to eastern Ontario southeast of Ottawa to Sault St. Marie in northern Ontario. Many of the areas in between the points of this triangle have not submitted birds, so that their WNV status has not been confirmed.
Public Health Ontario has put its surveillance efforts into monitoring mosquito pools and human cases, which are reported on a weekly basis. Here is a link to the most recent report: http://www.publichealthontario.ca/en/DataAndAnalytics/Documents/PHO_WNV_Weekly_Surveillance_Report_2013_Week_32.pdf
WNV activity, as reflected in positive mosquito pools and in human cases, is down considerably this year over last year. This likely is a result of the cooler weather that has affected much of the province this summer. Interestingly, though, a comparison of the location of positive birds from our WNV testing indicates that there are several parts of the province in which virus is circulating that have not produced either human cases or positive mosquito pools at this time. Testing of corvid species of birds for WNV was initially adopted as a public health surveillance tool because it provided the earliest possible indication of virus activity in a geographic area, and this is likely still the case.