Screwworms are fly larvae (maggots) of certain fly species that burrow (screw) into flesh and feed on living tissue of animals. New World screwworm (NWS, Cochliomyia hominivorax) can infest any warm-blooded animal, including livestock, pets, wildlife, occasionally birds, and rarely humans. Female flies lay eggs in open wounds or the membranes of the mouth, eyes, nose, or genitalia. Infestation can be fatal if untreated.
NWS was eradicated from the United States in 1966 using a biological control technique of sterilizing NWS fly populations. This technique has kept NWS out of the United States and helped eliminate outbreaks. NWS is endemic in many countries of South America and some Caribbean islands. Recently NWS has been moving northward through Central America and was found in Mexico in 2024.
All mammals and birds are potential hosts to NWS, including humans. In Oregon, it is possible for outbreaks to occur from an actively infested animal traveling to Oregon from endemic areas. While NWS does not impact food safety, it may significantly impact our livestock industry, economy, and food supply chain.
See the following pages for more specific information about New World Screwworm in various species:
Outbreak Information and Updates
If you suspect a case of NWS, report it immediately:
For pets or domestic animals:
Oregon State Veterinarian
Phone: 503-986-4711
For wild animals:
Oregon Department of Fish and Wildlife
Phone: 1-866-968-2600
For humans:
Contact your Healthcare Provider
Resources
ODA Resources
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New World Screwworm - What to Expect -
English,
Español
Oregon Department of Agriculture (ODA) New World Screwworm - What to Expect Informational Handout.
Other Resources