New World screwworm confirmed in Tucson-area horse

A horse in the Tucson area has tested positive for New World screwworm, bringing Arizona’s total to seven confirmed cases in three weeks and placing new limits on animal movement in Pima County. State agriculture officials have created a mandatory infested zone extending 12.4 miles, or 20 kilometers, around the property connected to the case. Animals cannot leave that area unless the restrictions are lifted or the state veterinarian grants permission.

The detection means Pima County now joins Cochise, Greenlee and Graham counties as areas with designated screwworm zones. The confirmed cases statewide include four horses, two dogs and one sheep. The parasite is carried by a fly that lays eggs in open wounds. Once the eggs hatch, the larvae feed on living tissue, causing painful infestations that can become serious infections. Officials say the condition is treatable, and animals generally recover quickly once the infestation is addressed.

A separate account of the Southern Arizona response described an earlier case involving a domesticated horse near Hereford in Cochise County. That horse reportedly had no travel history, and the finding led officials to establish another 12.4 mile quarantine zone. Earlier still, the state’s first confirmed case was found in a dog near Elfrida on Oct. 28, 2026. That discovery was reported as being about 45 miles from the Hereford case. The newer Tucson area confirmation is part of the rapid increase in detections that has expanded the state’s response.

For people with horses, livestock, dogs or other animals in and around Tucson, the most immediate concern is movement. Animals inside the new Pima County zone cannot be transported out without state approval. Officials have also suspended self inspections within designated zones, meaning animal owners should not assume they can complete a routine inspection and move an animal without additional authorization. The restrictions apply because moving an infected animal could allow the pest to establish itself in new areas.

State officials are advising owners to examine animals every day, paying particular attention to scratches, cuts and other wounds. Even a small break in the skin can provide an opening for infestation. Livestock owners, veterinarians, hunters and pet owners are being asked to report wounds containing maggots or other signs that could indicate screwworm. Reports can be sent to diseasereporting@azda.gov. The agriculture department also accepts reports by phone at 602-542-4293 during weekday business hours.

Residents who hunt or encounter sick or dead wildlife should take additional care. Wildlife can carry the parasite without obvious signs and may die from extensive tissue damage and infection. Hunters who find potentially infested wildlife are directed to contact the Arizona Game and Fish Department at 623-236-7201 and provide GPS coordinates. Officials are warning against moving animals across state lines, including household pets, because infected animals could transport the parasite before the condition is recognized.

The federal government and Arizona are using sterile insect releases as a principal containment measure. The U.S. Department of Agriculture has already dispersed 3.3 million sterile flies in affected parts of Arizona. The technique is intended to reduce reproduction by releasing sterile insects that limit the number of viable offspring. Federal officials are also working with the U.S. Army Corps of Engineers on a production facility at Moore Air Base in southern Texas. Another federal response account described a specialized dispersal facility being constructed in Douglas.

New World screwworm had been contained south of a zone near Panama, but it has moved northward since 2023. Production facilities are currently operating in Panama and southern Mexico, while the planned Texas facility is expected to expand the supply of sterile flies available for control efforts. Arizona officials say the sterile insect approach is the most effective tool currently available for reducing the parasite population and slowing its spread.

People living inside an infested zone can ask veterinarians about monthly over the counter or prescription treatments for their animals, although those treatments are not required. The state and the University of Arizona’s Arizona Livestock Incident Response Team plan to hold a virtual public information meeting from 5:30 to 8 p.m. Monday, Nov. 16. The session will cover the confirmed cases and containment work, and will give community members an opportunity to ask questions. Until then, officials are urging Tucson area residents to check animals closely, avoid unauthorized movement and report suspected cases promptly.