A horse in the Tucson area has a confirmed case of New World screwworm, the Arizona Department of Agriculture reported Friday.
It's the seventh case of infection in just three weeks since the parasitic fly was found in Arizona.
A new infested zone was established with the finding, creating a mandatory 12.4-mile radius around the reported case. No animals may leave the area until restrictions are lifted or under the direction of the state veterinarian.
There are now four infested zones in the state, in Cochise, Greenlee, Graham and Pima counties.
The new case raises the count of cases to four horses, two dogs and a sheep.
New World screwworm cases are transmitted by the fly, which lays its eggs on open wounds. Larvae then hatch and feed from live tissue, causing animals severe pain. Infestations are easily treatable.
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Taking animals carrying the parasite across state borders, including pets, presents risks. Once the larvae get to a mature state, they drop in the ground and pupate in the soil, eventually becoming flies and repeating the cycle.
Small wounds, even scratches, can increase the risk of infection. Checking animals daily is advised. While not required, pet owners living inside the infested zones can give their animals monthly over-the-counter or prescription treatment to prevent screwworms. When treated, animals recover quickly from maggot infestation, myasis and infections caused by the parasite.
Unlike pets and cows, wildlife can carry the parasite without detection and die from expansive myasis and infection.
Containment efforts involve restrictions to livestock and domestic animal movement and the dispersal of New World screwworm sterile flies. The U.S. Department of Agriculture has dispersed 3.3 million sterile flies in affected parts of Arizona to date, a spokesperson to the agency wrote to The Republic.
Sterile insect technique is the best tool available to reduce the population of the parasite, which has spread north of a containment zone near Panama since 2023. There are two production plants currently active, one in Panama and another in southern Mexico. USDA is partnering with the U.S. Army Corps of Engineers to build a third production plant in Moore Air Base, in southern Texas.
Arizona officials urge pet owners, ranchers and hunters to report all suspected New World screwworm cases immediately to diseasereporting@azda.gov.
The agency and the University of Arizona’s Arizona Livestock Incident Response Team will hold a virtual informational meeting to inform the public about the detected cases and response efforts, and allow community members to ask questions on Monday, Nov. 16, from 5:30 p.m. to 8 p.m.
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