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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. This is the second last week for mosquito surveillance; human numbers will continue to be updated on this page for a few more weeks.

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 (Sept 30-Oct 6, 2018)

Provincial Trends

As of week 40, there have been 121 reported (confirmed or probable) human WNV cases, three of which are travel-related:
​BRN (6) CHK (1) DUR (5)
GBO (2)

HAL (4)
HAM (7)

HDN (4)

HKP (1)
LAM (3)
LGL (2)
MSL (8)
(1 travel-related)
NIA (7)
NPS (1)
​OTT (4)
OXF (1) PEEL (6)
PTC (1) SMD (1) ​SUD (1) ​TOR (36)
​WAT (5)​​
(1 travel-related)
​WEC (12)​ ​YRK (3)​​

As of week 40, 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: Seven WNV equine cases has been reported: HAM, MSL, NIA (2), PDH (2), and WEC, for 2018.

Other arboviruses and mosquito species of interest

As of October 4, 2018 there have been 11 reported equine cases of Eastern Equine Encephalitis (EEEV) one from HAM, four from HDN, and six 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 September 15, 2018):

  • 88 clinical human cases: MB (29), QC (40) and AB (19)
  • 257 WNV positive mosquito pools: MB (168), SK (50), and QC (39)
WNV United States (January 1 to October 2, 2018):        
  • The Centers for Disease Control and Prevention (CDC) has reported 1611 human cases of WNV, with 48 states and the District of Columbia reporting WNV activity (people, birds, or mosquitoes)​.​​​​​​
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Page last updated: 2018-10-09 2:07 PM
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