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West Nile Virus surveillance
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West Nile Virus (WNV) is a vector-borne disease of public health importance in Ontario. Each week, we analyze provincial mosquito, human and weather data to produce a weekly vector surveillance report. Public health units provide us with mosquito and human data, and Environment Canada is our source for weather data. Updated case counts are available every Wednesday below. Data from previous years is updated annually.

For more information on the graphs, maps, and health unit codes, please read the West Nile Virus surveillance glossary and data caveats. If you have any questions, please contact

Surveillance Week 44 (October 29– November 4, 2017)

Provincial Trends

  • As of week 44, there have been 154 reported (confirmed or probable​) human WNV cases: 28 from TOR, 20 from OTT and WEC, 11 from YRK (one travel-related), nine from PEEL, eight from NIA, seven from SMD, six from HAM (one travel-related) and HAL, five each from EOH and LGL, four from GBO, three each from DUR, HKP, PTC, and WAT, two each from SUD and WDG, and one each from HDN, HPE, KFL, LAM, MSL, OXF, PDH, REN and TSK. There have been 409 WNV positive mosquito pools, from 27 different health units: BRN (2), CHK (3), DUR (10), EOH (5), HAL (36), HAM (31), HKP, HPE (13), HUR (2), KFL (5), LAM (2), LGL, MSL (7), NIA (15), NWR, OTT (35), OXF, PDH (6), PEEL (114), PTC (2), REN (2), SMD (2), TOR (62), WAT (3), WDG (3), WEC (29) and YRK (16). In addition, there was one WNV positive mosquito pool reported from a First Nations community, Chippewas of Saugeen, which is in GBO. All health units have stopped their WNV mosquito trapping for 2017; week 44 is the last update for 2017. No new updates will be posted until the 2018 season.
  • Equine: Twenty-one horses have been reported with WNV, five from GBO, four from SMD, three from NIA,  two from KFL, and one each from ALG, DUR, HAL, OXF, REN, SUD, and WAT.
  • Health units have stopped their mosquito trapping for 2017. 
Other arboviruses and mosquito species of interest
As of October 30, 2017 there have been two reports of horses testing positive for Eastern Equine Encephalitis (EEEV), one each in GBO and SMD. In week 40 one mosquito pool tested postive for EEEV from HUR.
  • Culiseta melanura is an important mosquito vector in the transmission cycle of EEEV as it is responsible for amplifying the virus in the bird population.
  • Although large numbers of Cq. perturbans can be identified in Ontario, this species is not considered a competent vector species in the transmission of WNV due to the presence of a substantial salivary gland barrier (Sardelis et al. 2001).
Vector-borne disease activity in other jurisdictions
WNV Canada (January 1 to October 21, 2017):
  • Fifteen human cases from Quebec, seven from Alberta, four from Manitoba, and one from British Columbia.
  • There have been WNV positive mosquito pools reported from Manitoba (41), Quebec (84) and Saskatchewan (10).
WNV United States (January 1 to October 31, 2017):        
  • The Centers for Disease Control and Prevention (CDC) has reported 1697 human cases of WNV, with 47 states and the District of Columbia reporting WNV activity (people, birds, or mosquitoes).​​​
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Page last updated: 07/11/2017 10:10 AM
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