Second Screwworm Case Prompts Arizona Animal Warning

On November 2, Arizona officials confirmed a New World screwworm infection in a domesticated horse near Hereford, about 10 miles west of Bisbee. The animal had not traveled. The case is roughly 45 miles from the first Arizona infection, found in a dog near Elfrida, also in Cochise County, less than a week earlier.

The state has designated a 12.4-mile-radius area around the horse’s property as infested. Livestock, horses and pets may not be taken out of the zone unless they are examined by the state veterinarian. Agriculture officials are urging owners to check animals daily, especially for wounds, and report signs of maggot infestation.

New World screwworm flies lay eggs in wounds, and their larvae feed on living tissue. Untreated infestations can kill animals. Veterinarian Chantelle Khambholja said livestock face particular risk of severe outbreaks. Ranchers are also concerned about financial losses: Clay Parsons of Marana Stockyards and Livestock said the loss of cattle could add costs for ranchers and consumers. His stockyards have begun fogging some areas to control flies.

Officials are releasing sterile screwworm flies, which can mate with wild flies and reduce their numbers. The method was used in the U.S. eradication effort in the 1960s. Arizona is the third state to report cases, after Texas and New Mexico; cases have also been reported in neighboring Sonora, Mexico. A USDA-funded $3.74 million grant to the University of Arizona is supporting state preparedness. U.S. and Mexican agencies are expanding sterile-fly production, while enhanced inspection measures are planned for cattle imports from Mexico.