How to Spot Screwworm Infections in Animals

Preventing Screwworm - Tips for Animal Owners

The Florida Department of Agriculture and Consumer Services (FDACS) is alerting veterinarians, livestock owners, and animal health professionals to stay watchful for signs of the New World screwworm, as its spread from Panama to southern Mexico raises concerns about potential entry into the U.S.

The New World screwworm, or Cochliomyia hominivorax, is a parasitic fly whose larvae feed on the living tissue of warm-blooded animals. Unlike typical maggots that consume dead tissue, these larvae invade open wounds and can cause severe, sometimes fatal, infections in livestock, pets, wildlife, and occasionally humans.

The U.S. successfully eradicated the screwworm in 1966, though a 2016 outbreak in Florida’s Key deer population required intervention with sterile fly releases to eliminate the threat.

Currently, there are no active cases in the U.S., but the USDA has suspended imports of live cattle, horses, and bison from Mexico as a precaution.

Infected animals may show signs such as excessive attention to wounds, foul odor, visible maggots, swelling, behavioral changes, and reduced appetite or milk production. Early detection is critical, as wounds may worsen and deepen over time.

Treatment involves veterinary care to remove larvae, while broader control efforts rely on releasing sterilized flies to disrupt reproduction. Animals with outdoor exposure or recent wounds are at higher risk.

FDACS urges anyone suspecting an infection to isolate the animal and contact a veterinarian or the State Veterinarian’s office immediately. Attempting to treat the wound without professional guidance could hinder outbreak control efforts.

Preventive care includes keeping wounds clean and covered and monitoring animals closely for any unusual symptoms.