New World Screwworm risk in Minnesota low, but officials warn of transfer

(FOX 9) - Agriculture officials warn that although the risk of infection in Minnesota remains low, those handling animals should be cautious of the spread of New World Screwworm (NWS).

New World Screwworm in Minnesota

What we know:

Once prevalent in the U.S. until eradication in the 1950s to 1980s, the U.S. Department of Agriculture (USDA) says it is working to strengthen measures to keep the pest out of the U.S. after a resurgence in 2025.

Minnesotans are being asked to stay alert for NWS – a fly that lays a destructive maggot capable of inflicting harm to livestock, pets, wildlife, and rarely to humans.

While the risk is lower for the parasite to become established in Minnesota compared to southern states with warmer climates, its spread is still possible due to international animal movements, officials say.

What they're saying:

"Currently there are outbreaks of NWS in Central America and detections in Mexico," said State Veterinarian Dr. Brian Hoefs in a statement. "Many people falsely think our northern climate is a strong enough deterrent to tropical pests like NWS. Unfortunately, our summers and shoulder seasons are warm enough to allow this fly to complete its lifecycle and potentially spread in Minnesota."

What you can do:

Those handling livestock and other wildlife are encouraged to learn the signs of NWS infestation, which include open wounds with maggots, strong odor, irritated animal behavior, and tissue decay.

Infested animals usually separate from the herd and will have visible discomfort.

Cases of infestation should be reported to a veterinarian immediately, officials say.