New World Screwworm

New World Screwworm is a parasitic fly whose larvae (maggots) burrow into the host’s living tissue. This differs from other species of fly whose maggots feed on dead tissue. NWS is endemic in Cuba, Haiti, the Dominican Republic, and countries in South America. In early 2025 cases began spreading northward through Mexico. It spreads most quickly through infected animals carrying either flies or larvae, especially animals traveling from affected regions. NWS can affect all warm-blooded animals and most cases are in cattle, sheep and goats. NWS larvae are transmitted when a female fly lays eggs on an open wound. Some common wound examples include insect bites, animal husbandry wounds, wire cuts, and other injuries. The NWS flies also target the navel of newborn animals. NWS infested wounds often attract other female screwworms and many infestations on a single wound are possible.

New World Screwworm has not been confirmed in Minnesota at this time.

U.S. cases were first detected in Texas in June 2026. Additional cases can be found in the "National Cases Dashboard" section of this webpage, which displays the USDA's confirmed NWS cases. Anyone who suspects a case of NWS in Minnesota should contact the Board of Animal Health at either animalhealth@state.mn.us or by phone at 651-296-2942.

The Board has NWS import requirements in place for companion animals.