USDA confirms Arizona's first screwworm case, in a Cochise County dog

A dog in Cochise County is Arizona's first confirmed case of New World screwworm, and USDA has set up a 20-kilometer (12-mile) infested zone around it. A local veterinarian examined the dog on October 26th and found a back wound infested with maggots.

USDA's Animal and Plant Health Inspection Service (APHIS) confirmed the diagnosis at its National Veterinary Services Laboratories in Ames, Iowa. USDA did not say where in the county the dog was found.

Reuters reported that USDA's website showed 71 confirmed animal cases since June as of October 28th, with 18 still active. A month earlier, Reuters said, only two were.

The dog should survive and is not the first

The dog has no known history of movement, and state officials said it is receiving treatment and is expected to survive, according to KJZZ. State Veterinarian Ryan Wolker said screwworm "affects all warm-blooded species" but is "very treatable" in comments azfamily reported.

Other livestock on the ranch will be evaluated, Wolker said. Arizona is the third state with cases after Texas and New Mexico.

USDA confirmed a Lea County, New Mexico, dog in a June release, and DTN's case tally lists a dog in New Mexico and one in Texas on October 27th.

"We have been preparing for this possibility for a long while and are acting swiftly," Wolker said in a statement. KJZZ reported that about one million sterile flies have been released in the area since the detection.

The rest of the USDA response covers movement controls inside the zone, more live-animal surveillance and trapping, and outreach to producers, veterinarians and communities.

Owners in the area are asked to check pets daily

USDA is asking owners in the area to inspect animals daily for draining or enlarging wounds, maggots or egg masses, signs of discomfort and lesions around the ears, nose, genital area and umbilicus. Anyone who suspects an infestation should call a veterinarian, a state animal health official or USDA right away.

Pet owners who cross the border have their own paperwork. USDA's traveler guidance for pets says dogs arriving from affected countries, including those returning to the United States, need a health certificate signed by an official government veterinarian confirming an inspection for screwworm within five days of travel.

Pets showing signs may be sent back at the owner's expense.

KJZZ reported that screwworm is spreading in Sonora, south of Arizona, and Newsweek reported that a second New Mexico infested zone sits around 10 miles from the Arizona line.

Cattle imports through Douglas, Arizona, resumed in August, and USDA plans to reopen the Nogales port on November 30th if conditions allow.

FDA has already authorized several screwworm treatments for dogs

FDA issued Elanco an emergency use authorization for Credelio in dogs effective October 24th, 2025, and for Credelio CAT that November. FDA authorized NexGard for dogs on February 18th, 2026, and Zoetis received an authorization for Simparica Trio on August 13th, 2026, for treating infestations in dogs and puppies.

Simparica Trio is a prescription product, so treatment runs through a veterinarian.

Prevention came later. FDA's Timothy Schell, director of the Center for Veterinary Medicine, said none of the authorized products for dogs and cats had been for prevention until the agency authorized Sergeant's Capstar on September 3rd and extended a generic nitenpyram tablet authorization to prevention, dvm360 reported.

We covered the over-the-counter nitenpyram tablets when they cleared. Those can be sold without a clinic visit.

Each authorization lasts as long as the federal emergency declaration.

Source: USDA APHIS