Texas’s first New World Screwworm cases did not appear immediately across the border with infested states in Mexico.

Instead, they were confirmed in a smattering of counties north, south and west of San Antonio that do not border each other.

Epidemiologists are scrambling to explain why, particularly when no cases have been confirmed in wildlife and no wild flies have been captured in traps.

But the early days of infestation in Texas offer lessons for Arizona — even if the closest outbreak is still hundreds of miles from our border.

1. It’s tough to predict movement

Screwworms need the right mix of heat, moisture and brush to replicate. But a checkerboard of cases in Texas suggests how difficult it may be to predict where they head next. 

Decades ago, when the screwworm was last in Arizona, mid-elevation grazing lands in southern and eastern Arizona were hit harder than upper-elevation ranches and dairies in central Arizona.

Is that still the case?

Livestock moves more often and over greater distances now, and it’s unclear whether hotter winters and more intense storms will push the fly into new territory.

“The last time we had a New World Screwworm infestation was 50 years ago, when this was a very different Arizona,” said Leigh Combrink, who studies wildlife diseases at University of Arizona. 

She is developing a forecasting tool to help answer those questions, based on one that state health officials already use to predict West Nile virus movements in Arizona. 

The effort is part of a multifaceted $3.74 million federal grant the university received to prepare for the pest’s arrival.

By analyzing complex climate, landscape, livestock and wildlife data, the tool could predict areas at heightened risk of an outbreak and test the outcome of various responses.

2. Don’t wait to minimize risk

That would be welcome help in Texas, where the response to new cases has been more like a game of whack-a-mole.

Thankfully, quick reporting and treatment have helped minimize damage and contain infestations.

Ranchers are rapidly adapting their herd management practices to lower the risk of an outbreak, said Tracy Tomascik, who specializes in livestock health issues at Texas Farm Bureau.

Because screwworms frequently lay eggs in wounds, many Texas ranchers have reduced running cattle through chutes, improved corrals and repaired facilities to minimize the risk of scrapes.

Some have chosen to postpone calving season and are waiting to dehorn or castrate animals until winter, when lower temperatures are expected to suppress fly activity.

Tomascik urged Arizona ranchers to talk with their veterinarian now about a response plan.

“Our recommendation has been to sit down and write out the steps you’ll take if and when you end up in an infestation or surveillance zone,” he said.

3. Staff up now for inspections

According to the federal playbook, which Texas is following and Arizona intends to follow, animal health officials must establish a 12-mile infestation and surveillance zone around a confirmed case.

No warm-blooded animal can leave the zone without an official inspection and permit.

“That was a pain point initially, but more people have become certified inspectors,” Tomascik said. “We’ve learned that you’re never going to have too many people to do inspections and write certificates.”

As part of its grant, University of Arizona plans to train veterinarians and others to follow inspection protocols and collect maggot samples using virtual reality.

“It’s one thing to look at photos,” said Amy Ganguli, a UA extension specialist overseeing the grant. “It’s another to see it in a more realistic setting.”

Researchers also plan to support peer training sessions led by Arizona Cattle Growers’ Association and collect experiences from those who lived with New World Screwworm decades ago to help inform response strategies that are appropriate today.

4. Technology holds great promise

The first confirmed screwworm maggot sample in Texas famously got a police escort to expedite its analysis.

But the process to officially confirm screwworm cases could get cumbersome as cases ramp up, considering that each sample must be visually inspected in an Iowa lab.

If it becomes acceptable to utilize other forms of identification, UA researchers will use part of the grant to develop a quicker DNA test that could be run in batches with a high degree of accuracy.

This technology could help process results more efficiently and may be used in remote areas, further speeding detection and treatment.

The university also is exploring whether virtual fencing technology and satellite-based GPS ear tags can be used to help monitor cattle for signs of screwworm.

Some of these technologies are now able to monitor an animal’s activity or heart rate, said Flavie Audoin, a rangeland extension specialist who is heading up this research.

This information could potentially be used to alert a rancher when an animal grows sluggish or could be in distress, offering real-time monitoring in rugged areas where cattle may not be seen for days.

The prospect caught the attention of Dalton Dobson, an Apache County cow-calf rancher and Arizona Farm Bureau member who was already eyeing GPS ear tags to monitor the output of his bulls.

“It may not be feasible now to put them in every animal,” he said. “But covering even a third or a quarter might have real value, especially if the tags are reusable.”


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