New World screwworm (NWS) is a parasitic fly that lays its eggs in wounds or around body openings. The larvae (maggots) hatch and feed on the living tissues of the affected animal. Unlike other fly larvae, which typically feed on dead or decaying tissue, New World screwworm larvae preferentially feed on living tissue.
Species affected
New world screwworm can infest any warm-blooded animal, including mammals, birds, and humans, although infestations in birds and humans are less .common
Clinical signs
Affected individuals are typically living animals with maggots in wounds or around other body openings such as the nose, ears, rectum, or the navel of newborn animals. The wounds often have a very foul odor and animals may appear depressed, irritated, or isolated from others. Newborn animals, animals that have recently given birth, or animals with open wounds—including those associated with antler velvet shedding, fighting, or other injuries—may be especially susceptible to infestation
Population signficance
New World screwworm infestations can cause severe wounds, secondary infections, and death in wildlife. Outbreaks have the potential to impact wildlife populations, particularly those that are already affected by other stressors. Infestations may also affect hunters by reducing the condition and meat quality of affected game animals. Cold winter temperatures may reduce the potential for long-term NWS establishment in Minnesota; however short-term outbreaks could still occur. Ongoing surveillance efforts remain essential to detect introductions, assess risk, and guide timely management responses nationwide.
Human and domestic animal health
Livestock, domestic pets, and even humans can be infested with New World screwworm. Seek medical or veterinary care if you suspect New World screwworm in yourself or your domestic animals. If you see suspect cases in free-ranging wildlife, please report it to your local area wildlife office or contact the Minnesota DNR Information Center by phone at 651-296-6157 or 888-MINNDNR (646-6367), or by email at [email protected].
Additional information
United States Animal and Plant Health Inspection Service NWS Website
United States Animal and Plant Health Inspection Service NWS Map