Skip Ribbon Commands
Skip to main content
West Nile Virus surveillance
To learn more about how to use the features on this page, watch our introductory video.

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. Until June 2016, weekly West Nile Virus surveillance reports were available in PDF form. This data, from 2002 year to the most recent surveillance week, is now available in the graphs below.

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 33 (August 13 – August 19, 2017)

Provincial Trends

  • As of week 33, there have been 14 reported (confirmed or probable) human WNV cases, three from OTT, two from WEC and one each from EOH, HAM (travel-related), HDN, HKP, PTC, REN, SUD, TSK and YRK (travel-related). There have been 264 WNV positive mosquito pools, from 26 different health units: BRN (2), CHK (3), DUR (7), EOH (3), HAL (24), HAM (19), HKP, HPE (9), HUR (2), KFL (2), LAM, MSL (4), NIA (8), NWR, OTT (15), OXF, PDH (5), PEEL (62), PTC, REN (2), SMD, TOR (48), WAT (3), WDG (2), WEC (25) and YRK (13).
  • Equine: Currently, no horses have been reported with WNV.
  • The majority of mosquitoes species were captured in low numbers across Ontario; with higher numbers of Culex pipiens/restuans, Aedes vexans and Coquillettidia perturbans. The Coquillettidia genus is not a major vector of WNV in Ontario, but can be a biting nuisance; it was caught in relatively high numbers in some health units.
Other arboviruses and mosquito species of interest
There have been no reports of mosquitoes, or horses, testing positive for Eastern Equine Encephalitis (EEEV).
  • 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. This species was reported in relatively low numbers in week 33.
  • 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 August 5, 2017):
  • No human cases have been reported.
  • There have been WNV positive mosquito pools reported from Manitoba (30), Quebec (9) and Saskatchewan (3).
WNV United States (January 1 to August 15, 2017):        
  • The Centers for Disease Control and Prevention (CDC) has reported 209 human cases of WNV, with 43 states reporting WNV activity (people, birds, or mosquitoes).
Uncontrolled print copy. Valid only on day of Print: [date]
Page updated on [date/time] 22/08/2017 10:18 AM
© , Ontario Agency for Health Protection and Promotion