New World Screwworm (NWS) is a parasitic fly that infests warm-blooded animals including cats and dogs, small mammals, and birds. The female lays eggs in wounds, and the hatching larvae eat living tissue and can lead to death of the animal. NWS was eradicated from the United States in 1966 and periodically returns. The flies are present in Mexico, the Caribbean, Central and South America, and threaten to return to the U.S.
How to recognize New World Screwworm
Wounds as small as a tick bite can be infested with NWS, and they are more likely to be around the face and genitals. Animals will be inappetent, painful, and often exhibit scratching and head shaking. Infested wounds may smell like dead carcass, have dripping bloody discharge or pus, and may suddenly get bigger. The ridged larvae can get up to 17 mm (2/3 in) long and generally burrow too deep to see but they may be visible. White eggs may be seen along the edges of the wound. The flies are the size of a typical house fly with orange eyes and green iridescent bodies.
View USDA's New World screwworm photo gallery for images of flies, maggots, and infested wounds.
How to prevent New World Screwworm
The following preventative actions are most important to implement for pets traveling to areas where NWS is present
- Wound prevention: inspect animal housing for sharp objects It's recommended to delay vaccination/castration in cattle herds, but it probably invites problems to extend the same recommendation to pet owners
- Treat for ticks
- Seek prompt treatment for wounds and keep pets with wounds indoors if possible
- Closely monitor for wounds around face and genitals
If you suspect New World Screwworm
Contact your veterinarian, and report to the ODA State Veterinarian at 503.986.4711.
What to expect if New World Screwworm infestation is confirmed
Animal health officials will quarantine the animal until daily wound care and treatments have successfully eliminated the screwworm larvae. The ODA and USDA investigate cases to determine if additional control measures of environmental treatment or sterile fly release is warranted. The animal(s) may be released from quarantine when it is confirmed that no screwworm larvae remain.
Resources
ODA Resources
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New World Screwworm Information for Pet Owners - English, Español
Oregon Department of Agriculture (ODA) New World Screwworm Information for Pet Owners Informational Handout.
- New World Screwworm - What to Expect - English, Español
Oregon Department of Agriculture (ODA) New World Screwworm - What to Expect Informational Handout.