A local veterinarian found a heavily maggot-infested wound on the dog's back. The animal lived on a ranch. A lab confirmed the diagnosis, and the Arizona Department of Agriculture announced the case this week. The dog is under veterinary care, and one report says it has since recovered. Officials have not said where in the county it was found.

"We have been preparing for this possibility for a long while and are acting swiftly," said Ryan Wolker, Arizona's state veterinarian. The state is working with the U.S. Department of Agriculture, the dog's owner, neighboring states and Mexican partners on the investigation. It has set up an infested zone with a 20-kilometer (12.4-mile) radius around the detection site, plus a surveillance area reaching at least another 20 kilometers. The response includes sterile fly releases, more live-animal surveillance, trapping, outreach and restrictions on moving animals. Officials are also advancing plans for a sterile fly dispersal facility in Douglas.

Paul Brierley, director of the Arizona Department of Agriculture, said comparable zones in Texas and New Mexico are now inactive as those states work through their eradication process.

The USDA counts 71 cases nationwide since June 3, 18 of them active. The first was reported in June in Zavala County, Texas. Only one involves U.S. wildlife, a female elk in Texas that a hunter found about a week before the Arizona dog. The outbreak began in Panama and Costa Rica in 2023 and has moved north through Central America and Mexico. Screwworm was once devastating to the cattle industry before it was eradicated from North America.

The Centers for Disease Control and Prevention says the infestation is not contagious and can be treated if caught early. Human cases are rare, and officials describe the risk to the public as low. Officials describe the condition as "very treatable" and say "the survivability is excellent." Signs include a strong odor, cavities in the tissue, and maggots packed in a vertical pattern that resembles the head of a sunflower.

The USDA asks animal owners to check their animals daily for draining or enlarging wounds, maggots or egg masses, signs of discomfort, and lesions around the ears, nose, genital area and navel. Anyone who suspects an infestation should contact a veterinarian, a state animal health official or the USDA right away.

The USDA plans to resume livestock imports from Mexico through Nogales, Arizona, on November 30, if conditions allow.