The New World screwworm, a parasitic fly that targets warm-blooded animals, had long been eradicated in the United States, but recent reports of over 70 animal cases have emerged since June. Arizona recently confirmed its first case with an infested dog in Cochise County, a region adjoining Mexico.
The U.S. Department of Agriculture (USDA) reported this instance, while the Arizona Department of Agriculture verified the dog’s wound as indicative of screwworm, later confirmed through scientific testing. State Veterinarian Ryan Wolker stated, “We have been preparing for this possibility for a long while and are acting swiftly.” Historically, screwworm flies have largely not affected U.S. livestock.
The USDA noted 71 cases in animals from Texas and New Mexico and a first in wildlife. Screwworm larvae, or maggots, can cause severe wounds by burrowing into living animal flesh, posing a danger. The Centers for Disease Control and Prevention (CDC) maintains that there are no human cases yet in the U.S., with low risk anticipated for people.
After a screwworm case was identified in Mexico, the U.S. halted certain cattle imports from the country in November 2024, although some import activities have resumed.