Arizona agricultural officials have confirmed the state’s first New World screwworm infestation in a dog near the Mexican border, bringing the nationwide total to 71 cases as federal authorities expand surveillance, animal movement restrictions and efforts to contain the parasite.
By yourNEWS Media Newsroom
PHOENIX — Arizona has confirmed its first case of New World screwworm, a flesh-eating parasite that attacks living tissue in animals and can infect humans, making it the third U.S. state to report an infestation during an outbreak that has spread northward from Central America and Mexico.
The Arizona Department of Agriculture announced Wednesday that a veterinarian discovered the parasite in a dog in Cochise County, which borders Mexico, after examining a wound on the animal’s back Monday evening.
The wound was heavily infested with maggots consistent with New World screwworm, prompting the veterinarian to submit samples for testing.
The U.S. Department of Agriculture confirmed the infestation Wednesday after its National Veterinary Services Laboratories in Ames, Iowa, identified the parasite.
The infected dog is receiving veterinary treatment, while state officials are working with its owner and attending veterinarian to determine how the animal became infected and whether other animals in the area may have been exposed.
Arizona State Veterinarian Dr. Ryan Wolker said officials had anticipated the possibility of the parasite reaching the state and had already developed response procedures.
“We have been preparing for this possibility for a long while and are acting swiftly,” Wolker said.
“Because of the extensive outreach, coordination, and surveillance already in place, Arizona producers, veterinarians, and pet owners know what to look for and how to report suspected cases. That preparation is allowing us to move quickly to protect animal health in the state.”
The discovery expands the outbreak into Arizona following confirmed cases in Texas and New Mexico.
According to the USDA’s New World screwworm surveillance data, federal officials had documented 71 animal infestations nationwide since the first U.S. case was reported June 3. Eighteen cases remained active as of the October 28 update.
The number of active cases has increased considerably since September, when only two infestations remained active.
New World screwworm, scientifically known as Cochliomyia hominivorax, is a parasitic fly whose larvae feed on living flesh rather than decaying organic material.
Female flies deposit eggs in open wounds or around vulnerable body openings of warm-blooded animals. Once the eggs hatch, the larvae burrow into living tissue, potentially creating severe injuries and life-threatening infections.
The parasite primarily affects livestock, including cattle, sheep and goats, but can also infest domestic pets, wildlife and humans.
Unlike many other flies whose larvae consume dead or decomposing material, New World screwworm larvae feed directly on healthy living tissue.
Infestations can spread rapidly within an untreated wound, causing extensive tissue damage and potentially killing affected animals.
USDA officials warned that early detection and veterinary treatment are essential to preventing serious complications and limiting further spread.
Following the Arizona confirmation, federal and state animal health officials began establishing a 20-kilometer, or approximately 12.4-mile, infested zone surrounding the detection site.
The containment effort includes restrictions on animal movement within the affected area, increased surveillance of livestock and pets, and additional trapping to determine whether wild screwworm flies are present.
Authorities are also releasing sterile screwworm flies to suppress reproduction.
The sterile insect technique involves breeding male flies that cannot produce viable offspring and releasing them into areas where wild screwworm populations may be present.
When sterile males mate with wild females, the resulting eggs do not develop, gradually reducing the reproductive capacity of the parasite population.
The approach helped eradicate New World screwworm from the United States decades ago and remains a central component of federal efforts to contain the current outbreak.
Arizona officials are coordinating with the USDA, neighboring states and Mexican authorities to monitor the infestation and implement regional control measures.
The state is also continuing preparations for a sterile fly dispersal facility in Douglas, near the international border.
Arizona Department of Agriculture Director Paul Brierley said the state had spent more than a year preparing for a possible detection.
“We’ve not had any cases in Arizona until today’s confirmed case. But it’s something we’ve been working on for over a year to prepare for,” Brierley said, according to KJZZ public radio.
Officials said the infected dog had no known history of travel outside its immediate area, raising questions about whether the infestation originated locally.
Other livestock at the ranch are being evaluated as investigators work to determine the extent of potential exposure.
Approximately 1 million sterile flies have been released in the Cochise County area as part of the initial response, according to state officials.
The Arizona detection follows another significant development in Texas, where federal authorities confirmed the first known New World screwworm infestation in U.S. wildlife.
That case involved a female elk discovered by a hunter in Pecos County, Texas, and was announced Oct. 21.
The discovery demonstrated that the parasite was affecting animals outside livestock and domestic pet populations, complicating surveillance efforts because infected wildlife can be difficult to locate and treat.
The current regional outbreak began spreading through Panama and Costa Rica in 2023 before advancing northward through Central America and Mexico.
The United States had previously eliminated established New World screwworm populations through large-scale sterile insect releases and coordinated eradication campaigns.
However, the parasite’s recent northward spread has prompted renewed concern among livestock producers and agricultural officials.
In 2025, the United States suspended livestock imports from Mexico as a precaution against the outbreak.
According to Reuters, the import restrictions contributed to tighter domestic cattle supplies and higher beef prices.
Federal officials have since resumed livestock trade at three ports of entry in Arizona and New Mexico under enhanced safeguards.
The USDA has indicated that additional livestock imports through Nogales, Arizona, could resume November 30 if animal health conditions permit.
The expansion of screwworm detections into a third state adds uncertainty to those plans as authorities attempt to prevent the parasite from becoming established in the southwestern United States.
Despite the risks, Arizona officials emphasized that infestations are treatable when detected promptly.
State veterinarian Wolker said the parasite can affect all warm-blooded species but does not automatically result in fatal outcomes.
“While it is concerning and it is a pest that, again, affects all warm-blooded species, it is very treatable,” Wolker said, according to AZFamily.
Officials reported that the affected dog was receiving treatment and was expected to survive.
The USDA is urging livestock owners, veterinarians and pet owners to inspect animals daily for wounds that appear to be enlarging, draining or attracting flies.
Other warning signs include visible maggots or egg masses, unusual irritability, discomfort and lesions near the ears, nose, mouth, genital areas or umbilicus.
Anyone who suspects an infestation should immediately contact a veterinarian or state animal health officials.
Arizona residents can report suspected cases to the Arizona Department of Agriculture at 602-542-4293 during business hours or by emailing [email protected].
Hunters and outdoor recreationists who encounter potentially infected wildlife are encouraged to record the approximate location and contact the Arizona Game and Fish Department at 623-236-7201.
The state has also conducted more than 60 training exercises, workshops and educational events involving agricultural producers, veterinarians and other stakeholders to prepare for an outbreak.
Federal officials continue monitoring confirmed infestations through the USDA’s national surveillance system while coordinating containment efforts across the affected states.
The Arizona confirmation represents another expansion of the outbreak, with authorities concentrating on preventing additional infestations and protecting livestock, pets and wildlife from the parasite’s spread.
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