A dog living on a ranch in Cochise County has become Arizona's first confirmed case of New World screwworm, a flesh-eating parasitic fly that has been creeping north toward the U.S. border for years. The Arizona Department of Agriculture announced the detection on Wednesday, marking the first time the pest has turned up anywhere in the state.
New World screwworm, scientifically known as Cochliomyia hominivorax, is a species of parasitic fly whose larvae feed on the living tissue or flesh of warm-blooded animals and people during part of their life cycle, according to AZ Family. The fly is typically found in South America and parts of the Caribbean, but it has steadily moved northward through every country in Central America, Mexico and now the United States since 2023, per USDA and CDC data cited by the outlet. The U.S. Department of Agriculture separately confirmed the Arizona detection, noting it is the first case reported in the state, as investing.com reported.
First Confirmed Case in a U.S. Dog
Officials said the Cochise County case marks the first U.S. screwworm detection in a dog, a distinction that sets it apart from the string of livestock cases already confirmed in New Mexico and Texas. That timeline stretches back to June 3, when the USDA reported the nation's first animal case, and has since expanded to include multiple sheep and cattle infestations across New Mexico and Texas, the same report notes.
There's a wrinkle in that first-dog claim worth noting. Back in June, Reuters reported that a dog case initially logged in Andrews County, Texas, was reclassified by USDA's Animal and Plant Health Inspection Service as New Mexico's first detected case, after officials determined the animal actually resided at a household in Lea County, New Mexico, which borders Texas, according to Reuters. Arizona and federal officials have described Tuesday's Cochise County case as the first U.S. detection in a dog, even as that earlier reclassification remains on the record.
Cases Piling Up Along the Border
The Arizona find lands amid a fast-moving cluster of new cases just across the state line. As of October 26, New Mexico and Texas each had six active screwworm cases, per Border Report. Four of those were confirmed near El Paso in the span of a week: two cattle cases in Hudspeth County, Texas, on October 23, and a ram and a bull in Doña Ana County, New Mexico, the following day, the outlet reported.
Days later, New Mexico officials announced two more confirmed cases in Doña Ana County — a sheep found on the New Mexico State University campus and a cow at an off-campus location — following four earlier confirmed cases in Otero and Grant counties, according to Source New Mexico. State and federal officials are now expanding surveillance and fly-trapping on the NMSU campus in response, the outlet reported. Earlier in October, two additional cases involving a horse and a cow surfaced in Grant County, New Mexico, as reported by KJZZ.
What's at Stake for Ranchers
The spread has rattled the region's agricultural industry well before it reached Arizona soil. As the pest advanced north through Mexico earlier this year, Texas ranchers began bracing for its possible arrival in the United States, and experts estimated a widespread outbreak could cost that state $1.8 billion in economic damage while devastating wildlife populations, according to Reuters reporting from June.
Arizona's own rules reflect that concern. The Arizona Department of Agriculture requires all veterinarians, livestock producers and animal owners to immediately report suspected infestations, unusual larval sightings or open-wound parasitic activity to the Office of the State Veterinarian. The department has also issued heightened screening, tracking and inspection protocols for cattle originating from Sonora, Mexico, tied to a phased plan to reopen the Douglas port of entry.
Risk to People Remains Low, Officials Say
Despite the fly's grim feeding habits, officials have stressed that no human infestations acquired within the United States have been reported, and that the risk to people remains very low. For now, the focus stays on animals — from the ranches of Cochise County to the pastures around Las Cruces and El Paso — as USDA's Animal and Plant Health Inspection Service continues tracking confirmed detections by county, animal type and status through its national dashboard.
