The New World Screwworm — a flesh-eating fly whose larvae burrow into living animal tissue to feed — has now reached 25 confirmed cases in Texas livestock, according to the USDA's Animal and Plant Health Inspection Service. The confirmed cases are all in sheep and cattle in Medina, Crockett, and Edwards Counties in southwest Texas, but the parasitic fly does not discriminate by species.
"NWS can infest any warm-blooded animal," according to CIDRAP's reporting on the Texas expansion — including dogs, cats, and, rarely, humans. Any animal with an open wound in or near the quarantine-affected counties is a potential host.
For pet owners in or near the affected area, that means now is the time to act.
Why This Matters
New World Screwworm (Cochliomyia hominivorax) was eradicated from the United States in 1966 through a decades-long sterile insect release campaign. The 2026 detections in Texas represent the first confirmed NWS cases in the continental U.S. in decades. The parasite's re-establishment would pose a serious threat to the U.S. livestock industry — estimated to have cost $100 million per year before eradication — and a meaningful risk to domestic animals and wildlife.
The parasite's life cycle is aggressive: the adult female fly deposits eggs in open wounds or any moist tissue on a living animal, and the larvae hatch and burrow into living flesh within 12 hours. Left untreated, the infestation expands rapidly and can be fatal within one to two weeks.
What We Know So Far
CIDRAP confirmed on June 25, 2026 that six new NWS cases had been confirmed in Texas, bringing the total to 25. Five of the new cases are in sheep in Crockett and Edwards Counties, and one is in cattle in Medina County. All confirmed cases have been in livestock.
USDA APHIS has established a quarantine zone in the affected counties and is conducting response activities including aerial sterile insect technique (SIT) releases — the same eradication method that was successful in the 1966 campaign. The sterile male flies mate with wild females, preventing reproduction in the wild population.
However, the presence of the fly in Texas means that any animal in or near the quarantine zone is potentially at risk of infestation if it has an untreated wound — including companion animals.
What Pet Owners in the Affected Area Need to Do
The risk to dogs and cats is real but can be significantly reduced with vigilance. Veterinary authorities and the CDC recommend the following for pet owners in or near Medina, Crockett, and Edwards Counties:
Daily wound checks. Inspect your pet's entire body every day, paying particular attention to any wound, surgical site, skin irritation, or cut — even small ones. Check especially warm, moist areas, including the ears, nose, mouth, and genital region.
Prompt wound treatment. Any wound should be kept clean and treated promptly. Consult a veterinarian for any wound that cannot be easily managed at home. Do not allow wounds to remain untreated or exposed in affected areas.
Watch for behavioral changes. Animals with NWS infestations may show behavioral signs before visible larvae are apparent: restlessness, excessive scratching or attention to a specific area, reluctance to eat, or unusual discharge from a wound.
Immediate veterinary attention. If you see larvae in any wound — small white or yellowish worm-like creatures burrowing into tissue — this is a veterinary emergency. Do not attempt to remove larvae yourself without veterinary guidance, as improper removal can cause larvae to burrow deeper.
The FDA-Authorized Treatment Option
According to CIDRAP and CDC guidance, the FDA has authorized emergency use of generic nitenpyram as an over-the-counter treatment option for dogs and cats in affected areas. Nitenpyram is the active ingredient in CapStar, a fast-acting oral flea treatment that kills insects — including NWS larvae — rapidly. It is available without a prescription at pet stores and veterinary offices.
However, nitenpyram is not a substitute for professional veterinary wound care if an infestation has already occurred. It is most useful as a precautionary measure or as part of immediate first response before veterinary evaluation. Any animal with an active wound infestation requires full veterinary wound debridement and management.
What About Human Risk?
NWS infestations in humans (myiasis) are rare but documented. The same biology applies: a human with an untreated or poorly managed open wound in an affected area could theoretically be infested by the fly if they are in locations where the fly is present.
People who are camping, farming, hunting, or working outdoors in the quarantine-affected counties should cover wounds promptly, avoid sleeping outdoors in areas with suspected fly activity if they have untreated wounds, and seek prompt medical care for any wound that shows signs of unusual tissue damage, discharge, or what appears to be larval activity.
What You Can Do Now
- If you live in or near Medina, Crockett, or Edwards Counties, inspect all pets and livestock daily for wounds, skin irritation, or behavioral changes.
- Keep all wounds on pets and livestock clean, treated, and covered.
- Ask your veterinarian about nitenpyram (CapStar) as a precautionary option for dogs and cats in affected areas.
- Report any suspected NWS case in livestock to USDA APHIS at 1-888-702-7020. Report potential companion animal cases to your local veterinarian immediately.
- Monitor the USDA APHIS website at aphis.usda.gov/screwworm for updated quarantine zone boundaries.
What Happens Next
USDA APHIS is conducting ongoing sterile insect releases in the affected area. Quarantine zone boundaries are being monitored and may expand or contract depending on new detections. MedicalDaily will report on any expansion of the quarantine zone, additional cases, or guidance changes from USDA or veterinary authorities.
The Bottom Line
All 25 confirmed New World Screwworm cases in Texas are in livestock, but the parasite can infest any warm-blooded animal with an open wound, including dogs, cats, and rarely humans. Pet owners in or near Medina, Crockett, and Edwards Counties should inspect their animals daily, treat wounds promptly, and contact a veterinarian immediately if they find larvae in any wound. This is an active and evolving animal health situation, and vigilance right now is the most effective prevention.
