West Nile Virus Surveillance

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 during WNV season. Data from previous years is updated annually.

Supporting Resources

Surveillance Week 44 (Oct 28-Nov 3, 2018)

Provincial Trends

As of week 44, there have been 137 reported (confirmed or probable) human WNV cases, three of which are travel-related:
BRN (6) CHK (1) DUR (5) EOH (1)
GBO (3) HAL (4) HAM (7) HDN (6)
HKP (1) KFL (1) LAM (3) LGL (2)
MSL (11) (1 travel-related) NIA (8) NPS (1) OTT (7) (1 travel-related)
OXF (1) PEEL (6) PTC (1) SMD (1)
SUD (1) TOR (39) WAT (5) (1 travel-related) WEC (13)
YRK (3)

As of week 44, there have been 305 WNV positive mosquito pools:
ALG (2) BRN (12)* CHK (9) DUR (7)*
ELG (1) EOH (3) GBO (1) HAL (29)
HAM (13) HDN (5) HKP (5) HPE (4)*
HUR (3) LAM (5) LGL (4) MSL (11)*
NIA (8) OTT (10) OXF (5) PDH (1)
PEEL (69) SMD (3) TOR (40) WAT (9)
WDG (2) WEC (27) YRK (17)

*There was one additional WNV positive pool from each health unit, located in a First Nation community.

Equine: Eleven WNV equine cases has been reported: ELG, HAM, MSL, NIA (2), OXF (3),PDH (2), and WEC, for 2018.


The graphs below have the following common features including: interactive legend, a scrollbar (when applicable) to navigate the data, zoom in, zoom out, download graph data, annotate graph and export graph as an image.

Other Arboviruses and Mosquito Species of Interest

As of October 30, 2018 there have been 13 reported equine cases of Eastern Equine Encephalitis (EEEV) one each from HAM and HPE, four from HDN, and seven from NIA. There have been no reports of EEEV positive mosquito pools or human cases.

  • 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 (Sardelisetal. 2001).

Vector-Borne Disease Activity in Other Jurisdictions

WNV Canada (January 1 to October 20, 2018):

  • 203 clinical human cases: MB (31), QC (127) and AB (45)
  • 266 WNV positive mosquito pools: MB (168), SK (52), and QC (46)

WNV United States (January 1 to October 30, 2018):

  • The Centers for Disease Control and Prevention (CDC) has reported 2204 human cases of WNV, with 48 states and the District of Columbia reporting WNV activity (people, birds, or mosquitoes).
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Enteric, Zoonotic and Vector-Borne Diseases


Updated 19 June 2019