Selected zoonotic pathogens and diseases in Ontario identified at the AHL in 2024
Tanya Rossi
Animal Health Laboratory, University of Guelph, Guelph, ON.
AHL Newsletter 2025;29(1):9.
The term One Health - “an integrated, unifying approach to balance and optimize the health of people, animals and the environment” - is a relatively new one in medicine, however, the contribution of veterinarians to public health dates back hundreds of years. This contribution has taken many forms, including using comparative physiology and anatomy to further human health, informing policies involving food safety and ecosystem health, and detection of zoonotic pathogens, among others. AHL participates in many of these initiatives, but our primary contribution is in the surveillance and annual reporting of zoonotic pathogens identified at our laboratory (Tables 1 & 2).
Case numbers for most zoonotic pathogens isolated or identified by the AHL in 2024 are relatively unchanged from the previous year, however some changes were identified. Avian West Nile virus positives have increased again this year, rising from 11 in 2021, 26 in 2022, 50 in 2023 to 76 in 2024. Case counts of equine West Nile virus have also risen from 5 in 2023 to 9 in 2024. Similar increases occurred in Eastern Equine Encephalitis virus positives in equines, and in positive serology submissions for Borrelia burgdorferi in canines and equines. These changes in vector-borne disease may reflect changes in vector populations and distribution that should be investigated further2,3.
After seeing an almost 4-fold increase in isolations of Salmonella enterica in chickens in 2023, case counts have returned to 2022 levels.
The percentage of animals identified as positive for leptospirosis was roughly unchanged in 2024 in cattle, equids, and swine, and the total number of submissions tested were similar as in 2023. However, submissions in canines increased by approximately 50% in 2024 with a moderate increase in percent positivity. These are numerator data reliant upon submission biases to the diagnostic laboratory and cannot be regarded as population prevalence estimates. They do not take into account vaccination status, as all except horses may be routinely vaccinated for leptospirosis.
Table 1. Number of cases* for selected zoonotic pathogens isolated and/or identified at the AHL in 2024.
*Cases may include research samples
**Other species include wild avian species, and other domesticated and wild species
References
1. Adisasmito WB, Almuhairi S, Behravesh CB, Bilivogui P, Bukachi SA, et al. One Health: A new definition for a sustainable and healthy future. PLoS Pathog. 2022;18(6): e1010537.
2. Levy S. Northern trek: The spread of Ixodes scapularis into Canada. Environ Health Perspect 2017;24;125(7):074002.
3. Paz S. Climate change impacts on West Nile virus transmission in a global context. Phil Trans R Soc B 2015;370(1665) https://doi.org/10.1098/rstb.2013.0561 .