This serious animal health threat is not currently found in Wisconsin. Sign up for updates from DATCP.
New World Screwworm (Cochliomyia hominivorax/NWS) is a parasitic fly whose larvae feed on living tissue. After being eradicated from the U.S. in 1966, NWS has re‑emerged in Central America and Mexico. According to the U.S. Department of Agriculture (USDA), NWS has been detected in the U.S. and in animals near the U.S.-Mexico border. USDA is working with affected states to respond with sterile fly releases, surveillance, and movement controls.
Fig. 1 NWS Adult | Fig. 2 NWS Larvae
Why It Matters for Wisconsin
Wisconsin receives animals from southern states where NWS risk is highest. Any warm‑blooded animal with an open wound can be affected, including pets, livestock, wildlife, and people. Early detection prevents severe, sometimes fatal, infections.
Who Is at Risk
- Dogs, cats, cattle, horses, swine, sheep, goats, and birds
- Wildlife and imported/illegally trafficked animals
- Humans with untreated wounds or recent travel to affected regions
- Animals recently transported from southern states or countries
Signs to Watch For
- Painful, enlarging, draining, foul‑smelling wounds
- Larvae burrowed deep in tissue (not on the surface like typical maggots, and wounds can be infested with multiple maggot species)
- Sudden discomfort, agitation, or behavior changes in animals
What You Can Do
For Pet and Livestock Owners, Markets, and Dealers
- Inspect animals after travel or intake
- Seek veterinary care for suspicious wounds
- Avoid transporting animals from outbreak areas without inspection
- Maintain compliance with quarantine and inspection requirements
For Shelters and Rescues
- Train staff to recognize NWS
- Inspect all incoming animals, especially from southern regions
- Report suspected cases immediately to DATCP
- Maintain compliance with quarantine and inspection requirements
For Veterinarians
- Review NWS identification and reporting protocols
- Report suspected cases to DATCP
- Use USDA, Food and Drug Administration (FDA), and Centers for Disease Control (CDC) resources for diagnostics, treatments, and training
- Complete NVAP Module 41 on NWS
NWS Communications
June 2026: New World Screwworm: What Wisconsin Needs to Know
September 2025: New World Screwworm: Information for Farmed Deer Producers
July 2025: What Shelters Should Know about New World Screwworm
December 2024: New World Screwworm (NWS) Awareness for Veterinarians