Overview

West Nile Virus (WNV) is a mosquito-borne virus that can cause swelling and inflammation of the brain and spinal cord in horses, birds and humans. Only specific species of mosquitoes spread WNV. In Alberta, the species of mosquito of concern is Culex tarsalis, which becomes infected when feeding on infected wild birds. Wild birds are the primary reservoir of WNV. Most wild birds are not affected by the virus, but rather just carry the virus for a variable period of time.

Only domestic geese, horses, mules and donkeys appear to be severely affected by WNV, and may develop clinical disease. Preventive measures should be discussed with your local veterinarian.

How to report

If you suspect WNV in your livestock, call your veterinarian within 24 hours.

WNV is a provincially notifiable disease for horses, donkeys and mules and must be monitored.

All suspected or confirmed cases must be reported to the Office of the Chief Provincial Veterinarian (OCPV) within 24 hours:

Hours: 8:15 am to 4:30 pm (open Monday to Friday, closed statutory holidays)
Phone: 780-427-3448
Toll free: 310-0000 before the phone number (in Alberta)
After business hours: 1-800-524-0051
Fax: 780-415-0810

WNV in horses surveillance

Table 1. Cases of WNV in Alberta horses (2003 to 2016)

As of *Revised Case definitions, as per the OIE, for equine cases of WNV in 2017.
**total only includes confirmed positive cases from 2017 onwards as per revised case definitions.
Cases reported in 2018: As of October 22 2018, a total of 82 cases had been received. Of these, there are 74 positives cases: 1 for a Saskatchewan horse tested by an Alberta Vet, so 73 Alberta positive cases, 7 possible cases, 1 reactor and 2 suspect cases.
Year Number of confirmed positive cases Number of possible cases Number of reactor cases Number of suspect cases
2003 170 - - -
2004 4 - - -
2005 3 - - -
2006 9 - - -
2007 46 - - -
2008 0 - - -
2009 1 - - -
2010 0 - - -
2011 0 - - -
2012 5 - - -
2013 14 - - -
2014 6 - - -
2015 10 - - -
2016 10 - - -
2017 * 11 2 - 1
2018 73 5 1 2
Total 362 7 1 3
West Nile Virus Cases 2018 to Oct 22, 2018 map

Figure 1. Case Distributions for 2018

This map shows the locations of 71 cases for which submission forms have been received.

View larger map (JPG, 481 KB)

Figure 2 . Case definitions for WNV

The Office of the Chief Provincial Veterinarian was notified of the first confirmed "possible positive" equine case of WNV in 2018 on Thursday July 19 in a horse in the County of Mountain View.

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