Mosquito-borne disease surveillance: Annual reports: Vector-borne disease surveillance in Canada

Human cases overview

• The number of cases was higher compared to the average number of cases reported annually in the previous five years. The average number of cases over the previous five years (2020-2024) was 111, ranging from 46 (2021) to 191 (2024).
• Among the 319 cases, 199 (62%) were neurological², 80 (25%) were non-neurological, 17 (5%) were unspecified, and 23 (7%) were asymptomatic³.
• Almost all of the cases (309 or 97%) acquired their illnesses in Canada; 10 cases were most likely infected when travelling outside of Canada.
• Overall, the incidence rate for reported WNV clinical cases⁴ (n=296) was 0.71 per 100,000 population.

Demographic characteristics

• More than half of the cases were 60 years of age and older (n=213, 67%).
• The rate in females and males were 0.62 and 0.9 per 100, 000 population, respectively.
• Of the 18 deaths with available information, all were in individuals 60 years of age or older.

Seasonality

• The earliest onset date for a human WNV case acquired within Canada during the mosquito season was June 1 (epidemiological week 23).
• The majority (88%) of the reported human cases occurred with episode dates^{Footnote 1} between epidemiological weeks 31 and 38 corresponding to July 27 to September 20, 2025.

Geographic distribution

• The provinces with the highest incidence for clinical cases in 2025 were Ontario and Quebec at rates of 1.04 and 1.24 per 100,000 population, respectively.

One Health surveillance

Testing animals and mosquitoes helps to provide an early warning of disease activity and areas of risk.

West Nile virus

• WNV was detected in 352 dead wild birds⁵:
  • The number of dead wild birds positive for WNV in 2025 was similar to the number of positive birds in 2024 (n = 437), but almost double the 5-year (2020 to 2024) average (n=177).
  • Birds found dead with WNV were found from early March until mid-November in the following provinces:
    • SK (n=118)
    • ON (n=115)
    • QC (n=91)
    • MB (n=28)
• WNV was detected in 50 horses⁵:
  • The number of horses positive for WNV in 2025 was higher (2x higher) than the 5-year (2020-2024) average (n=24).
  • WNV positive horses were reported in the following 6 provinces:
    • BC (n=2)
    • AB (n=12)
    • SK (n=19)
    • ON (n=9)
    • QC (n=6)
    • MB (n=2)
• There were 415 mosquito pools that tested positive for WNV in Manitoba (n=148) and Ontario (n=267)⁶:
  • Overall, this represents 4.7% of the pools tested for WNV.

Eastern equine encephalitis virus (EEEV)

• There were five (5) human cases detected in Ontario and Quebec. This represents the greatest number of EEE cases reported in one year in Canada to date.
• EEEV was detected in 10 horses⁵:
  • The number of horses positive for EEEV in 2025 was lower (0.68x lower) than the 5-year (2020-2024) average (n=15).
  • EEEV positive horses were reported in the following provinces:
    • ON (n=8)
    • QC (n=2)
• There were 48 mosquito pools tested for EEEV in Ontario⁶:
  • No (n=0) mosquito pools tested positive for EEEV.

Previous annual reports

Previous versions of the annual report are available in the table below:

Human cases overview

• The number of cases was higher compared to the average number of cases reported annually in the previous five years. The average number of cases over the previous five years (2019-2023) was 82, ranging from 44 (2019) to 167 (2020).
• Among the 177 cases acquired in Canada, 106 (60%) were neurological, 41 (23%) were non-neurological, 17 (10%) were unspecified, and 13 (7%) were asymptomatic².
• In addition to the 177 WNV cases acquired in Canada^{Footnote 5}, an additional 13 cases were associated with travel outside of Canada.
• Overall, incidence rate for reported WNV clinical cases (n=164) acquired within Canada was 0.40 per 100,000 population. The rate in females and males were 0.32 and 0.58 per 100,000 population, respectively.

Demographic characteristics

• More than half of people were over the age of 60 (n=114,~65%).
• There was one death associated with WNV infection in an individual 70 years of age or older.

Seasonality

• In 2024, the earliest onset date for a human WNV case acquired within Canada during the mosquito season was June 27 (epidemiological week 26).
• Most (~80%) of the reported human cases occurred with episode dates^{Footnote 1} between epidemiological weeks 31 and 37 corresponding to July 28 to September 14, 2024.

Geographic distribution

• The provinces with the highest incidence for 2024 were Ontario and Quebec at rates of 0.74 and 0.67 per 100,000 population, respectively.

One Health surveillance

Testing animals and mosquitoes helps to provide an early warning of disease activity and areas of risk.

West Nile virus

• WNV was detected in 387 dead wild birds:
  • The number of dead wild birds positive for WNV in 2024 was higher than the number of positive birds in 2023 (n=224), and higher than the average number of dead wild birds positive for WNV reported annually in the previous five years (2019 to 2023; average number of cases = 94).
  • Birds found dead with WNV³ were found from early May until late October in the following provinces:
    • SK (n=92)
    • ON (n=123)
    • QC (n=156)
    • MB (n=16)
• In 2024, WNV was detected in 41 horses:
  • The number of horses positive for WNV in 2024 was higher (2.3x higher) than the average number of horses positive for WNV in the previous five years (2019 to 2023; average number of cases = 18).
  • WNV positive horses³ were reported in the following 5 provinces:
    • AB (n=10)
    • SK (n=11)
    • ON (n=11)
    • QC (n=8)
    • MB (n=1)
• In 2024, 343 mosquito pools were tested for WNV in MB (n=125), ON (n=214), and SK (n=4)⁴:
  • Overall, 2.03% of the pools tested positive for WNV.

Eastern equine encephalitis virus (EEEV)

• In 2024, there were four (4) human cases detected in Ontario and Quebec. This represents the greatest number of EEE cases reported in one year in Canada to date. In addition, non-human surveillance indicated there was higher than normal EEEV activity in horse and mosquito populations in this same year.
• In 2024, EEEV was detected in 38 horses:
  • The number of horses positive for EEEV in 2024 was higher (3.5x higher) than the average number of horses positive for EEEV in the previous five years (2019 to 2023; average number of cases = 11).
  • EEEV positive horses were reported in the following provinces:
    • ON (n=23)
    • NS (n=1)
    • QC (n=14)
• In 2024, 101 mosquito pools were tested for EEEV in Ontario⁴:
  • Two (<2%) mosquito pools tested positive for EEEV.

Human cases overview

• The number of cases was lower than the average number reported annually during the previous five years. The average from 2018 to 2022 was 131 cases, ranging from 36 (2019) to 337 (2018).
• Among the 98 cases acquired in Canada, 46 (47%) were neurological, 32 were non-neurological, 13 were clinically unspecified, and 7 were asymptomatic^{Footnote 2}.
• In addition to the 98 WNV cases acquired in Canada^{Footnote 5}, six other cases acquired their infection outside Canada.
• Overall, the incidence rate for reported clinical WNV cases (n=91) acquired in Canada was 0.23 per 100,000 population. The rates among females and males were 0.20 and 0.28 per 100,000 population, respectively.

Demographic characteristics

• More than half of the cases were 60 years of age and older (n=51, 52%).
• Two deaths were associated with WNV infection, both among individuals 70 years of age or older.

Seasonality

• In 2023, the earliest onset date for a human WNV case acquired in Canada during the mosquito season was June 20 (epidemiological week 25).
• Most (75%) of the reported human cases had episode dates^{Footnote 1} between epidemiological weeks 33 and 38, corresponding to August 13 to September 23, 2023.

Data note: The available 2023 epidemic-curve data contain 78 records across acquisition statuses. The curve and table below reproduce those available records and should not be interpreted as all 98 cases acquired in Canada.

Geographic distribution

• The provinces with the highest incidence rates in 2023 were Ontario and Manitoba, at 0.37 and 0.35 per 100,000 population, respectively.

One Health surveillance

Testing animals and mosquitoes helps provide an early warning of disease activity and areas of risk.

West Nile virus

• WNV was detected in 224 dead wild birds:
  • The number of dead wild birds positive for WNV in 2023 was lower than in 2022 (n=360) and similar to the average during the previous five years (2018 to 2022; average=222).
  • Birds found dead with WNV^{Footnote 3} were reported from late April through November in Saskatchewan (n=37), Ontario (n=72), Quebec (n=62), and Manitoba (n=53).
• WNV was detected in 48 horses:
  • The number of horses positive for WNV in 2023 was slightly higher than the average during the previous five years (2018 to 2022; average=33).
  • WNV-positive horses^{Footnote 3} were reported in Alberta (n=25), Saskatchewan (n=10), Ontario (n=6), Quebec (n=6), and Manitoba (n=1).
• In 2023, 357 mosquito pools were tested for WNV in Manitoba (n=52) and Ontario (n=305)^{Footnote 4}:
  • Overall, 2.24% of the pools tested positive for WNV.

Eastern equine encephalitis virus (EEEV)

• EEEV was detected in 22 horses:
  • The number of horses positive for EEEV in 2023 was higher than the average during the previous five years (2018 to 2022; average=9).
  • EEEV-positive horses were reported in Ontario (n=18), New Brunswick (n=2), and Quebec (n=2).
• In 2023, 115 mosquito pools were tested for EEEV in Ontario^{Footnote 4}:
  • No mosquito pools tested positive for EEEV.