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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 40 (October 1– October 7, 2017)

Provincial Trends

  • As of week 40, there have been 143 reported (confirmed or probable​) human WNV cases: 25 from TOR, 20 from OTT, 19 from WEC,  ten form YRK (one travel-related), eight from PEEL, seven each from NIA and SMD, six from HAL, five form HAM (one travel-related), four each from EOH, GBO, and LGL, three each from DUR, PTC, and WAT, two each from HKP, 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). There was one WNV positive mosquito pool reported from a First Nations community, Chippewas of Saugeen, which is in GBO.
  • Equine: Seventeen horses have been reported with WNV, four each from GBO and SMD, three from NIA, and one each from ALG, DUR, KFL, REN, SUD and WAT.
  • The majority of mosquitoes species were captured in low numbers across Ontario; with decreasing numbers of Culex pipiens/restuans
Other arboviruses and mosquito species of interest
There have been no reports of horses testing positive for Eastern Equine Encephalitis (EEEV). 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; none were collected in week 40.
  • 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 September 23, 2017):
  • Twelve human cases from Quebec, five from Alberta, three from Manitoba, and one from British Columbia.
  • There have been WNV positive mosquito pools reported from Manitoba (41), Quebec (83) and Saskatchewan (10).
WNV United States (January 1 to October 10, 2017):        
  • The Centers for Disease Control and Prevention (CDC) has reported 1295 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: 12/10/2017 10:48 AM
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