New World Screwworm infestation reaches Arizona, adding to cases in livestock and pets
The USDA reports the spread of New World Screwworm flies to Arizona, bringing the total U.S. animal cases to 74, including ten domestic pets, as officials urge monitoring and reporting of wounds.
The United States Department of Agriculture confirmed that the New World Screwworm (NWS) infestation has expanded to Arizona, joining New Mexico and Texas as affected states. Since the flies re-entered the country in June, 74 animal cases have been documented, most in livestock, with ten cases involving domestic pets such as dogs and a cat.
In Arizona, the first case was identified in a dog from Cochise County, where a veterinarian observed a wound heavily infested with maggots matching NWS characteristics. The state’s agriculture department said it remains "prepared and vigilant" and urged livestock and pet owners to monitor animals for unusual wounds and report them promptly.
The flies lay hundreds of eggs in wounds or moist body openings, and the emerging maggots feed on living tissue, potentially causing severe or fatal injuries. Historically, the United States eradicated the parasite in the 1960s through aerial releases of sterile male flies. A biological barrier along the Darién Gap had limited re-entry until it was breached in 2022, allowing the flies to move northward from Central America.
While the primary concern is the impact on the livestock industry, the parasites can also affect wildlife, domestic animals, and, in rare instances, humans. Mexico’s Ministry of Health has recorded 806 human cases since the re-emergence, with nine fatalities. The USDA is coordinating a joint response with Arizona authorities to address the expanded outbreak.