06/11/2026
⚠️ Screwworm Alert: What Ontario Horse Owners Need to Know
You may have seen recent news about New World Screwworm and wondered whether it is a concern for your horse. Here's what Ontario horse owners should know.
What is screwworm?
Screwworm is the larval (maggot) stage of a specific type of fly. Unlike typical maggots that feed on dead tissue, screwworm larvae feed on living tissue, causing painful and potentially severe wounds.
How do horses become infected?
Adult flies are attracted to:
🐴 Cuts and scrapes
🐴 Surgical incisions
🐴 Castration sites
🐴 Umbilical areas of newborn foals
🐴 Tick bites and other skin wounds
The fly lays eggs in the wound, and the larvae hatch and burrow into healthy tissue.
What signs should owners watch for?
🔹 A wound that is not healing normally
🔹 Increased swelling or inflammation around a wound
🔹 Bloody or foul-smelling discharge
🔹 Visible maggots within a wound
🔹 Pain, irritation, or excessive attention to the area
Affected wounds often worsen over time rather than improve.
Is screwworm in Ontario?
At this time, New World Screwworm is not established in Canada. The risk to horses in Ontario remains very low. However, recent detections in the southern United States and Mexico have prompted increased surveillance and import restrictions to help prevent its spread. The CFIA recently announced temporary restrictions on livestock, including horses, entering Canada from Texas following confirmed cases there.
How can you protect your horse?
✅ Check horses daily for wounds
✅ Clean and monitor injuries carefully
✅ Use appropriate fly control measures
✅ Contact your veterinarian promptly if a wound appears unusual or contains maggots
The bottom line:
There is no reason for alarm in Ontario, but awareness is important. Early recognition and treatment are critical if a case were ever to occur. If you notice a wound that is worsening instead of healing, contact your veterinarian for assessment.
📚 Learn more:
CFIA Animal Health Information
USDA Screwworm Information Hub