The first confirmed case of New World Screwworm in Arizona was announced on Oct. 28.

And, thankfully, everything happened as it should have once a Cochise County rancher found maggots on the back of a working dog.

The infestation was quickly reported. A sample was quickly collected and sent for examination.

An infestation zone was quickly established once screwworm was confirmed, and a million sterile flies have so far been released in the area.

It played out that way thanks to months of education and a clear playbook for how to respond.

It’s a point worth lauding, even if the milestone behind it is one that no one wants to celebrate.

“We have been preparing for this possibility for a long while and are acting swiftly,” Ryan Wolker, the state veterinarian, said in a statement. 

Cases accelerated in October

The United States and Mexico successfully eradicated New World Screwworm decades ago. 

But the flesh-eating pest has steadily moved north since 2024, with nearly 50,000 cases confirmed in Mexico since then. 

The first American case was confirmed in June, as infestations popped up in checkerboard fashion across south Texas. 

Cases slowed considerably in August and September only to rocket back in October across southern New Mexico. 

Seventy-four cases have been confirmed in the U.S., mostly in cattle but also in dogs, goats, sheep, horses, a cat and an elk.

Twenty-one cases remain active.

“Ranchers didn’t want New World Screwworm, but now that it’s here, we’ll deal with it,” said Sonia Gasho, a rancher and Cochise County Farm Bureau vice president.

She thanked the United States Department of Agriculture for its previous commitment to reopen a sterile fly distribution center in Douglas and urged officials to expedite its opening.

An infested zone was established

Sterile flies are a critical part of controlling this destructive pest. 

They mate with wild flies, whose eggs won’t hatch, crashing the population over time.

Though work is underway on the Douglas facility, an opening date has not yet been set.

Meanwhile, a 12-mile infestation zone was established around the case. It includes Sunizona and parts of Elfrida and McNeal west of Arizona 191.

Animals cannot move outside of this area without an official inspection, preventive treatment and permit. 

A 12-mile surveillance zone also was established around the infestation zone, from Benson to the New Mexico state line and south to the Mexican border.

It includes parts of Benson, Willcox, Tombstone and Bisbee.

Animals can move out of this wider buffer zone without restriction, but owners are asked to check animals frequently for signs of infestation.

Officials also are increasing wildlife surveillance.

What should ranchers look for?

Ranchers should keep close watch on their animals, looking for abnormal behavior, head shaking, clusters of white eggs or maggots in wounds, a foul smell or wounds that don’t heal.

The University of Arizona has developed a guide to help safely perform these inspections.

If you suspect a screwworm infestation in livestock or pets, report it immediately to diseasereporting@azda.gov. 

Call the Arizona Game and Fish Department at 623-236-7201 to report a suspected case in wildlife.

Stay informed

The Arizona Department of Agriculture is hosting a public forum and question-and-answer session from 10 a.m. to noon Oct. 31 at the Willcox Elks Lodge, 247 E. Stewart St. 

Department Director Paul Brierley and state veterinarian Ryan Wolker will discuss the New World Screwworm response in Cochise County so far, as well as animal movement restrictions in the infested zone.

The department also will register Premises Identification Numbers on-site and distribute free electronic ear tags — critical components for moving livestock during the outbreak.


Joanna Allhands writes about water, land use and other issues important to the Arizona Farm Bureau. Reach her at joannaallhands@azfb.org.