The New World screwworm, a parasitic fly whose larvae feed on living flesh, has been confirmed in Arizona for the first time. A dog in Cochise County was the first animal, and a horse and a ram have since been reported. Officials say the risk to most pet dogs and cats remains very low, but they are urging owners to inspect animals daily. Here is what is confirmed, what is still unclear, and what to do.
Key facts at a glance
| What | First detections of New World screwworm in Arizona |
| First case | A dog in Cochise County, announced by USDA APHIS on 28 October 2026 |
| Confirmed by | USDA APHIS National Veterinary Services Laboratories, Ames, Iowa |
| Later cases | A horse and a ram with no known travel history, near Duncan in Greenlee County, per the Arizona Department of Agriculture (reported 4 November) |
| Human cases in Arizona | None reported, per ASU Health Observatory |
| Risk to most US dogs and cats | Very low, per ASU epidemiologist Hayley Yaglom |
| Official tracker | screwworm.gov (Current Status), updated daily |
What happened in Arizona
The US Department of Agriculture’s Animal and Plant Health Inspection Service (APHIS) announced on 28 October that a dog in Cochise County had tested positive, the first New World screwworm detection in the state. Samples were confirmed at the agency’s national laboratory in Ames, Iowa. According to the AVMA, a local veterinarian found a heavily infested wound on the dog’s back. ASU News reports the dog lives on a ranch with livestock and is recovering.
On 4 November, the Arizona Department of Agriculture announced two further cases, a horse and a ram near Duncan in Greenlee County, neither with any known travel history, according to ABC15. A new infested zone has been set up around the Greenlee County finds. State Veterinarian Dr. Ryan Wolker said the state has been preparing for this possibility “for a long while” and is acting swiftly.
How authorities are responding
- A joint response by APHIS and the Arizona Department of Agriculture under the national screwworm response playbook.
- A 20-kilometre infested zone around the first detection, with controls on animal movement.
- More live-animal surveillance and fly trapping, plus sterile fly releases.
- Outreach to producers, veterinarians and local communities.
- Per the AVMA, a sterile fly dispersal facility is planned for Douglas, Arizona.
The bigger picture
Arizona joins Texas and New Mexico. The first US animal case this outbreak was a Texas calf in June 2026. Counts differ by source and date: ASU News cited about 90 US cases across Texas, New Mexico and Arizona as of 3 November, while the AVMA reported 91 confirmed animal detections as of 2 November, 34 of them active, with October the busiest month since early June. Because these figures change daily, check screwworm.gov for the latest number.
We covered the early warning in June: Deadly New World Screwworm Threat Raises Alarm for Pet Owners.
What pet owners should do now
Check daily. USDA advises inspecting animals every day, especially outdoors-going pets and those near livestock.
- Look for warning signs: a draining or enlarging wound, maggots or egg masses, a pet that licks or chews one spot, discomfort or irritability, and slow-healing, swollen or foul-smelling wounds. Check ears, nose, genital area and surgical incisions too.
- Treat small wounds fast: keep cuts clean and dry, and ask your vet about anything that does not heal.
- Remove hazards: wire fencing, sharp vegetation, and metal collars or chains that can cause skin injuries.
- Keep up parasite prevention: ASU’s epidemiologist recommends flea and tick control as part of wound prevention.
- Report suspicions: call your veterinarian, your state animal health official or USDA. In Arizona, suspect wounds can be reported
For people: ASU advises covering wounds, sleeping indoors with windows closed near livestock in affected areas, and using EPA-registered insect repellent. Larvae do not pass directly between animals or to people.
What is still unclear
- Reports differ on the horse: the AVMA described a horse confirmed on 31 October in the same county as the dog, while ABC15 places the horse and ram near Duncan in Greenlee County.
- How the flies reached these animals, since the later cases had no known travel history.
- How many more cases will follow. ASU’s epidemiologist called more detections “very possible.”
Frequently asked questions
What is New World screwworm?
It is a parasitic fly whose larvae feed on the living tissue of warm-blooded animals, entering through wounds. It mainly threatens livestock, but dogs, horses and other animals can be affected.
Can my dog or cat catch it from another animal?
No. Per ASU, larvae do not spread directly between animals. Infestation happens when a female fly lays eggs on a wound.
Is it a risk to humans?
Humans can be affected through open wounds, though no human cases have been reported in Arizona. Cover wounds and use repellent in affected areas.
Where do I find the latest case count?
USDA’s screwworm.gov Current Status page, updated daily.
Sources
- ASU News, 3 November 2026
- USDA APHIS announcement, 28 October 2026
- ABC15 Arizona, 4 to 5 November 2026
- American Veterinary Medical Association (AVMA), 2 to 3 November 2026
- DTN Progressive Farmer, 2 November 2026
Pets News Network is India’s first dedicated media platform for the pet and animal industry. This report is based on public statements and published reports; case numbers change daily, so please verify with official sources and consult a veterinarian for your pet’s health. For breaking global pet news, brand coverage, and advertising enquiries, contact: info@petsnewsnetwork.com
