Short answer: New World screwworm — a fly whose larvae eat living flesh — has returned to the United States for the first time in about 60 years. The USDA confirmed the first case on June 3, 2026, in a calf in South Texas; by September 15, 2026 it had confirmed 49 cases in domestic animals in Texas, including four dogs and one horse. The outbreak has continued: on October 21, 2026 the USDA confirmed the first detection in US wildlife, an elk in Pecos County, Texas. For pet owners, the practical steps are simple: check wounds daily, get any wound with maggots seen by a vet the same day, and keep pets on year-round parasite prevention. The CDC rates the risk to people as very low.
What Screwworm Is — and Why It’s Different From Ordinary Maggots
The adult screwworm fly lays eggs in open wounds or moist body openings — a cut, a surgical site, a navel, the nose or ears. The larvae burrow in and feed on living tissue, which is what makes them dangerous. Common maggots, by contrast, feed on dead or decaying tissue. Screwworm wounds get bigger and deeper rather than healing, and an untreated infestation can kill an animal.
The US eradicated screwworm in 1966 by releasing billions of sterile male flies — wild females mate once, so they produce no offspring. The same method is being used now, with a new sterile-fly facility under construction in Edinburg, Texas.
Where the 2026 Outbreak Is
| Date (2026) | What USDA confirmed |
|---|---|
| June 3 | First US case: a calf in Zavala County, Texas |
| June 8 | First dog case — reported as a dog in Andrews County, TX; some later tracking placed a dog case in Lea County, NM the same day |
| Aug 26 | 47 total infestations: 46 in Texas, 1 in New Mexico |
| Aug 31 | Fourth dog case (Crockett County, TX) |
| Sept 15 | 49 cases in Texas animals, including the first horse (Presidio County) |
Reported detections fell from about 30 in June to four in August, and Texas began lifting restrictions on some counties from August 31 — but the slowdown did not hold. Texas released a set of infested zones on October 13, 2026, and then, after the USDA confirmed screwworm in a hunter-harvested elk in Pecos County on October 21, the Texas Animal Health Commission moved to modify a previously established infested zone while the USDA and Texas Parks and Wildlife ran extra wildlife surveillance in the area. A wildlife reservoir matters to pet owners because it is far harder to treat than ranched livestock. Counts and zones change quickly; check the USDA Stop Screwworm page for the current picture.
Signs to Watch For in Dogs and Cats
- A wound that gets worse instead of healing
- Bloody, thick or foul-smelling discharge
- Swelling around a cut or opening
- Maggots visibly moving inside a wound
- Pain, restlessness, or constant licking or scratching at one spot
Pay attention to small cuts, recent surgical or spay sites, hot spots, and moist areas such as the ears, nose, eyes and genital area. Any wound with maggots in it — especially in Texas, New Mexico or after travel to Mexico — needs a vet visit the same day, because screwworm has to be ruled out.
Treatment
A veterinarian removes the larvae, treats the wound, and gives medication to kill any that remain. In 2026 the FDA moved quickly to authorize options for pets:
- Dogs: Credelio Quattro-CA1 received conditional approval; Credelio (lotilaner) and Simparica Trio were authorized for emergency use.
- Dogs and cats: generic nitenpyram tablets were authorized for emergency use on June 11, 2026 for pets at least 2 lbs and 4 weeks old; Credelio Cat was also authorized for cats.
Your vet chooses the treatment. Screwworm is a reportable disease, so the clinic will notify state and federal animal-health officials — that’s part of how the outbreak is tracked, not something that gets you in trouble.
Prevention for Pet Owners
- Keep pets on year-round flea and tick prevention. The Companion Animal Parasite Council recommends year-round ectoparasite control, and a veterinary parasitologist told dvm360 that the isoxazoline products many pets already take also help guard against screwworm. (Year-round prevention matters for other reasons too — see our fall hazards guide.)
- Clean and cover wounds and check them daily until healed.
- Keep pets with fresh wounds indoors where possible, away from flies.
- Watch pets closely after travel to Mexico, Central America or affected Texas counties.
- Report suspect cases through your vet.
Travel With Pets
Pet dog travel to Mexico was briefly halted after the first US cases and then restored on June 10, 2026. Dogs entering the US from Mexico need a certificate from an authorized Mexican veterinarian, issued within five days of travel, stating the dog is free of screwworm or has been treated and quarantined until clear. Rules can change at short notice — check USDA APHIS before booking, and see our guides to pet health certificates for international travel and the CDC’s dog import rules.
What About People?
The CDC says the risk to people in the US is very low. There have been no US-acquired human cases; the only US human case on record, in August 2025, was a traveler returning from El Salvador. The USDA stresses screwworm doesn’t infest meat, fruit, vegetables or other food. People can be affected through open wounds in areas with flies, so the same wound care applies to you.
The Bottom Line
Screwworm is a serious livestock and animal-health problem in parts of Texas right now, and dogs are among the animals affected — but it’s preventable and treatable when caught early. Daily wound checks, prompt vet visits for any maggots, and year-round parasite prevention cover almost all of the risk for pets.
This article is for informational purposes only and does not replace guidance from your veterinarian. Domestic-animal case counts are as reported through September 15, 2026, with the October 2026 wildlife detection noted above; check USDA for updates.
Sources
- USDA APHIS — USDA Confirms Presence of New World Screwworm in the United States, June 3, 2026; Two additional cases, June 8, 2026; Stop Screwworm, updated September 18, 2026
- CDC — New World Screwworm Outbreak: Situation Summary, updated August 11, 2026
- dvm360 — First US horse case of New World screwworm in 60 years; fourth dog case also reported, September 15, 2026; New World screwworm live updates
- AAHA — USDA reverses course on pet dog travel to Mexico, June 2026
- Houston Public Media / Texas Public Radio — Texas New World screwworm tracker, August 2026
- Medical Daily — No locally acquired human screwworm cases as animal detections slow, September 18, 2026
