New World Screwworm is a parasitic fly whose larva invade wounds and body openings of animals and humans. They can cause extensive damage to livestock.
Current Situation
Animals: The first case of NWS in U.S. livestock was found in Texas on June 3, 2026, followed by other cases in texas and New Mexico.
Humans: No locally acquired infestations in humans in the United States have been reported as of June 2026.
The risk of NWS infestation in people within the United States remains low and is currently limited to areas where NWS flies are present. Federal agencies, including the CDC, USDA, and Department of the Interior, are working closely with state, local and tribal partners to monitor the situation and prevent further spread among people and animals.
Latest Information
About New World Screwworm
- The New World screwworm (NWS) is a parasitic fly whose larvae (maggots) feed on the living tissue of warm-blooded animals.
- When larvae from the fly get into a wound or opening in the body, they cause myiasis, or an infestation of fly larvae. Unlike typical maggots that feed on dead tissue, screwworm larvae invade healthy tissue, causing severe wounds with their sharp mouth hooks, infection, and possibly death if untreated.
- NWS infestations are treated by having the larvae removed by a veterinarian (in animals) or healthcare professional (in humans).
- Screwworms primarily affect livestock, but can also infest pets, wildlife, and rarely humans. Screwworm infestation in cattle can lead to the animal's death and can damage the ranching and agricultural industries.
Screwworms are spread by screwworm flies, the movement of infested animals, and travelers returning from areas affected by New World screwworm. They do not spread directly from person to person or animal to person.
The adult New World Screwworm fly has large orange eyes, a yellow face, and blue body with three stripes along the back.
(Photo: USDA)
Screwworm larva
(Photo:CDC)
Screwworm larva showing mouth hooks that embed into animal tissue.
(Photo: John Kucharski, USDA)
Symptoms
In Animals
- Non-healing or worsening wounds
- Visible maggots in living tissue
- Foul-smelling discharge
- Swelling, bleeding, or tissue damage
- Behavioral changes such as restlessness, irritation, or reduced feeding
In Humans (rare)
- Painful or worsening skin lesions
- Sensation of movement in a wound, sore, ears, nose, eyes, or mouth
- Seeing larvae around or in open sores
- Drainage or bleeding from wounds
- Foul smelling odor from the site of the infestation
- Possible fever or secondary infection.
Guidance for Specific Groups
General
- Clean and cover all wounds immediately.
- Seek medical care for wounds that worsen or do not heal.
- Larvae should not be thrown in the trash or outside while they are alive. Kill larvae by immersing them in isopropyl alcohol.
Guidance for:
Travelers
- Wear protective clothing in at-risk areas.
- Use an EPA registered insect repellent.
- Treat clothing and gear with products containing 0.5% permethrin (an insecticide/repellent).
- Keep open wounds clean and covered.
- Sleep indoors or in screened shelters.
- Monitor any wounds carefully after travel.
Veterinarians
- Inspect wounds carefully in animals.
- Report suspected cases immediately to the Mississippi Board of Animal Health. See Reporting
Wildlife professionals and hunters
- Inspect animals for unusual wounds.
- Inspect harvested animals carefully.
- Report abnormal wounds or infestations to the Mississippi Department Wildlife, Fisheries and Parks at 601-432-2400.
Farmers and ranchers
- Inspect animals regularly for wounds.
- Treat injuries immediately.
- Maintain fly control practices.
- Report suspicious cases quickly to your veterinarian and the Mississippi Board of Animal Health. See Reporting
Pet owners
- Check pets regularly for wounds.
- Keep injuries clean and protected.
- Seek veterinary care promptly.
Healthcare providers
- Consider travel history in wound cases.
- Remove larvae and treat infection.
- Any larvae collected for identification should be submerged in 70% alcohol (ethanol or isopropanol) in a plastic container with a screw cap that can be tightly sealed.
- Report suspected cases to the Mississippi State Department of Health at 601-576-7725
Reporting Cases of NWS
Cases in Livestock
Report suspected cases to a veterinarian and to the Mississippi Board of Animal Health: msstatevet@mdac.ms.gov or 1-888-646-8731.
Cases in Wildlife
Report abnormal wounds or infestations to the Mississippi Department of Wildlife, Fisheries and Parks at 601-432-2400.
Cases in Humans
Report suspected cases to the Mississippi State Department of Health at 601-576-7725.
For Veterinarians
Coordinate with Mississippi Board of Animal Health:
- By phone during office hours: 601-359-1170
- By phone after hours: 1-888-646-8731
- By e-mail: msstatevet@mdac.ms.gov
Resources
Mississippi Board of Animal Health
- New World Screwworm Information
- Information for Veterinarians PDF
- Brochure: New World Screwworm Essential Information PDF
USDA
- Stop ScrewwormInformation on the Screwworm Eradication Program
- Fact Sheet: New World Screwworm PDF
- Brochure: NWS (What You Need to Know) PDF
- Brochure (Spanish): NWS (What You Need to Know) PDF
- Poster: Screwworm Life Cycle and Identification PDF
