The Arizona Department of Agriculture said the infection was detected on Nov. 6. The confirmation prompted officials to expand the designated infestation zone to include Graham County, a rural stretch of southeastern Arizona where livestock and pets often share close quarters with wildlife.

New World screwworm is caused by the larvae of a parasitic fly that lays its eggs in the open wounds of warm-blooded animals, including people. The maggots feed on living tissue, enlarging wounds and, if left untreated, can be fatal. The pest was once eradicated from the United States decades ago through an aggressive sterile-fly release program, but its reappearance in Arizona has alarmed ranchers, veterinarians and public health officials.

The Graham County case follows a cluster of infections in neighboring Cochise County, where the state's first case was recorded in a dog and a containment plan was quickly launched. Officials have since confirmed multiple additional cases in that area, and the University of Arizona has begun distributing testing kits to livestock producers to speed detection.

State veterinarians are urging anyone who owns animals — whether livestock, pets or working dogs — to inspect them regularly for unusual wounds or the presence of maggots. Any suspected case should be reported immediately to the Arizona Department of Agriculture so that containment measures can be taken.

The expansion of the infestation zone means additional movement restrictions and surveillance will likely apply to animals in and around Graham County. For a region already grappling with drought and economic pressure on small farms, the arrival of screwworm adds another layer of uncertainty.

Officials have not said how the Graham County dog became infected, but the case underscores the importance of early detection. Residents who spot suspicious wounds on animals are encouraged to contact their veterinarian and the state agriculture department without delay.