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 (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.

Previous annual reports

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