Overview: West Nile virus identified in a Greater Sudbury horse
Public Health Sudbury & Districts has confirmed that a horse in the Greater Sudbury area tested positive for West Nile virus (WNV). This marks the third animal to test positive in 2025, following two crows identified in the summer. The last known human case in the region was reported in 2023. While the risk of human infection remains low, health officials warn that late summer and early fall are peak periods for West Nile virus transmission due to higher mosquito activity.
Jonathan Groulx, a manager in Public Health Sudbury & District’s Health Protection division, emphasized the seasonal risk: “Although the overall risk of a person becoming infected remains low, late summer and early fall are typically the time of greatest risk for contracting West Nile virus as mosquitoes can carry higher levels of the virus at this time of year. Therefore, continuing to take precautions even late in the season is important to avoid becoming infected.”
The One Health approach: Linkages between people, animals, and the environment
Ontario’s One Health framework recognizes that human health is connected to animal health and ecological conditions. By monitoring cases in people, animals, and mosquito populations, public health authorities, clinicians, veterinarians, and environmental scientists can predict, prevent, and respond to West Nile virus more effectively. This collaborative approach helps identify risk factors, implement targeted interventions, and protect vulnerable populations across the community.
How West Nile virus spreads and what it means for residents
West Nile virus is transmitted through the bite of an infected mosquito. It does not spread directly from horses to humans or other animals. Most people who become infected experience no symptoms or only mild illness, such as fever, headache, body aches, mild rash, or swollen lymph nodes. In rare cases, the virus can affect the brain, leading to more serious illness. For horses, early signs include fever, muscle twitching, heightened sensitivity to touch or sound, and difficulty standing. Vaccination and boosters remain key preventive measures for horses.
Practical steps to reduce risk at home and in stables
Personal and home protection
- Install or repair window and door screens to keep mosquitoes out.
- Eliminate standing water around the home where mosquitoes can breed.
- Avoid outdoor activities at dusk and dawn when mosquitoes are most active.
- Wear light-colored, long-sleeved shirts and long pants; use an approved insect repellent per label directions.
Guidance for horse owners
- Stabilize horses indoors at dawn and dusk when mosquitoes are active.
- Use fans in barns to deter flying insects.
- Apply veterinarian-approved insect repellents to horses as advised by a veterinarian.
What to do if you’re seeking more information
For more information about West Nile virus and current local guidance, contact Public Health Sudbury & Districts at 705.522.9200 (toll-free 1.866.522.9200) or visit phsd.ca. If you have questions specifically about West Nile virus in horses, your veterinarian is a valuable resource for vaccination schedules and protective measures.
Why continued vigilance matters
Though the current risk to people remains low, warm, humid late summer and early fall create conditions favorable to mosquitoes carrying West Nile virus. Maintaining protective practices across communities—whether you live in a city apartment or a rural farm—helps minimize transmission. The Greater Sudbury case underscores the importance of coordinated monitoring across human, animal, and environmental health, aligning with the One Health approach that public health officials advocate nationwide.
