State and federal agriculture officials confirmed the first known Arizona case of the New World screwworm after a domestic dog on a ranch in Cochise County tested positive for the flesh-eating parasite.
A veterinarian examined the animal on Monday, Oct. 26, discovering an open lesion on its back that was heavily infested with larvae, according to the Arizona Department of Agriculture. Subsequent testing verified that the maggots were New World screwworm, the department and the U.S. Department of Agriculture announced Wednesday.
The dog, which has no history of travel outside the area, is receiving medical treatment, AZ Family reported. Other livestock on the ranch are undergoing evaluation to determine if any other animals are infected.
A Resurgent Threat to Animals
The New World screwworm is a parasitic fly whose larvae burrow into the living flesh of warm-blooded creatures using sharp mouth hooks. The resulting condition, known as myiasis, can cause devastating tissue damage, intense suffering and death if untreated. While the pest primarily infests livestock and pets, it can occasionally affect wildlife and humans.
Officials emphasized that public health hazards are minimal. The U.S. has recorded no human cases this year, according to ABC News. Last year, health authorities confirmed an infection in a Maryland resident who had traveled to El Salvador, a federal health spokesperson told the network.
Arizona is now the third U.S. state to identify an animal case during the current regional outbreak, joining Texas and New Mexico. However, agricultural authorities noted this is the nation’s first confirmed detection in a canine. The USDA reported the first animal case in the country on June 3, with previous reports restricted to cattle and sheep, according to AZ Family.
“This was a pest that was previously eradicated from the United States in 1966, and we haven’t seen it in the better part of 50 years. And all that changed this morning,” State Veterinarian Dr. Ryan Wolker said during a virtual press briefing on Wednesday.
Containment Efforts and Next Steps
The insect historically inhabited South America and parts of the Caribbean before spreading northward through Central America and Mexico beginning in 2023. For decades, the U.S. kept populations away by releasing billions of sterile male flies into the wild. Because females mate only once, the sterile pairings caused local populations to collapse without producing viable offspring.
The USDA is responding to the Cochise County detection by setting up an infested zone, expanding surveillance across southeast Arizona, and conducting educational outreach to animal handlers, FOX 10 Phoenix reported. Officials have asked owners in the border region to check their animals each day and report any maggot-infested wounds to local veterinarians or state authorities immediately.
State leaders are also urging the deployment of sterile flies in Cochise County to halt local reproduction before the pest can establish permanent footholds. Earlier this year, the University of Arizona received a $3.74 million federal grant to enhance statewide readiness, and state officials continue to prepare for an upcoming sterile fly distribution facility planned for Douglas, Arizona.
“While it is concerning and it is a pest that, again, affects all warm-blooded species, it is very treatable,” Wolker said. Authorities are coordinating across state lines and with Mexican agricultural agencies to evaluate livestock across the border zone, though it remains unknown whether additional domestic or wild animals in southeastern Arizona have been exposed.
