Mexican cattle began crossing at Columbus, New Mexico, on October 26, ending a closure of nearly two years at a port that normally handles about a third of US cattle imports from Mexico. The same week, the USDA confirmed screwworm in a dog in Arizona and reported 71 US cases since June, 18 of them still active.
The USDA has released more than 1.64 billion sterile flies and plans to restart livestock imports at Nogales, Arizona, on November 30 if trade conditions are judged safe. Officials caution that flies can cross borders on their own, so ranchers, hunters and pet owners should keep checking animals for wounds.
Why it matters
Screwworm is now in US wildlife, horses and pets, keeping cattle trade shut and beef prices high.
Questions about this story
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Is this a big risk?
N
Yes — a full outbreak would be a serious economic threat, but the risk of that happening is actively being fought down by a containment response built over the past year.
A widespread screwworm infestation could inflict $1.8 billion in damage to Texas alone, and the state holds the largest cattle herd in the country.
4 details5 sources1 disagreement
—Two confirmed cases in Zavala County, 5.6 miles apart, prompted Governor Abbott to issue a disaster proclamation — a signal the state treats this as more than a contained incident.
—The parasite spreads fast: one female lays up to 3,000 eggs in her lifespan and any wound as small as a tick bite is enough to attract her.
—The USDA's $8.5M sterile-fly facility at Moore Air Base can release 100 million sterile flies per week — the same tool that wiped the pest out in 1966 — and a second production plant broke ground in April 2026.
—Food supply is not at risk: screwworms attack living animals, not meat, so beef in stores is unaffected.
USDA and Secretary Rollins are publicly downplaying food-supply risk to avoid market panic, while Texas ranchers and industry analysts point out that even a partial spread would drive beef prices higher in a market already strained by the year-long import ban on Mexican cattle.
0AI answers with web search. May be wrong.
Key Indicators
71
US animal cases
USDA reported 71 confirmed cases across Texas and New Mexico as of Oct. 28, including cattle, a horse, an elk and a dog in Arizona.
18
Active cases
USDA listed 18 active cases on Oct. 28, up from two a month earlier.
1.64B
Sterile flies released
USDA had released more than 1.64 billion sterile flies as of Oct. 22.
20 km
Quarantine zone radius
Movement controls remain around infected sites; Texas has released parts of some older zones.
$1.8B
Estimated economic damage
USDA estimate of potential damage to Texas if the parasite is not contained.
April 2027
Target for US fly plant
USDA aims to finish construction at Moore Air Base in Edinburg, Texas, then start with 100 million sterile flies a week.
22 events
Latest: October 28th, 2026 · 2 weeks ago
Showing 8 of 22
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October 2026
Screwworm confirmed in an Arizona dog
LatestDetection
The USDA confirmed the parasite in a dog in Arizona. The agency reported 71 US cases since June, 18 of them active.
Columbus, New Mexico, port reopens to Mexican cattle
Policy
Mexican cattle began moving through the Columbus crossing after a closure of nearly two years. About a third of Mexican cattle imported to the US pass through Columbus and Santa Teresa.
USDA passes 1.64 billion sterile flies released
Response
USDA said it had released more than 1.64 billion sterile flies since June.
USDA reports 61 animal cases
Detection
The USDA reported 61 confirmed cases across Texas and New Mexico, including cattle, a horse and an elk.
Screwworm found in US wildlife for first time
Detection
An elk harvested by a hunter in Pecos County, Texas, tested positive, the first wildlife detection in the outbreak.
New Mexico and Texas confirm more cattle cases
Detection
New cases were confirmed in cattle in Otero County, New Mexico, and in Texas.
USDA schedules equine imports at Santa Teresa
Policy
USDA announced the Santa Teresa, New Mexico, port would reopen to equine imports by land on Oct. 26.
Texas releases parts of screwworm zones
Policy
The Texas Animal Health Commission released portions of infested zones in Edwards, Schleicher, Sutton and Val Verde counties from movement restrictions. It kept a smaller Zone 04.E under quarantine.
September 2026
Santa Teresa cattle port reopens
Policy
USDA reopened the Santa Teresa, New Mexico, port to cattle imports from Mexico.
UC San Diego tool tracks screwworm spread
Research
Researchers described a tracking system meant to predict where the parasite could appear next as it moves north.
First US horse case detected in Texas
Detection
A horse in a South Texas border county tested positive, the first US horse case in the outbreak; Reuters reported the finding on Sept. 11.
August 2026
Douglas port reopens to Mexican cattle
Policy
USDA reopened the Douglas, Arizona, port to cattle imports from Mexico as part of a phased restart after the 2025 suspension.
June 2026
Second Texas case detected
Detection
A one-month-old calf about 5.6 miles from the first case tests positive in Zavala County.
Abbott declares statewide disaster for all Texas counties
Policy
Governor Greg Abbott expands an existing state of disaster to cover all 254 Texas counties, creates the Texas New World Screwworm Response Team, and warns of an "extraordinarily challenging summer."
Canada restricts livestock imports from Texas
Policy
Canada's food inspection agency blocks entry of livestock and horses that were present in Texas within 21 days of crossing the border, the first international trade restriction triggered by the outbreak.
First US screwworm case confirmed in 60 years
Detection
Federal labs confirm larvae in a three-week-old calf in Zavala County, Texas. A 20-kilometer quarantine follows.
April 2026
Groundbreaking on US fly production plant
Infrastructure
USDA and the Army Corps break ground on a sterile-fly production facility in the Rio Grande Valley.
February 2026
Texas sterile-fly dispersal plant completed
Infrastructure
An $8.5 million facility at Moore Air Base in Edinburg can release up to 100 million sterile flies weekly.
July 2025
USDA shuts border ports to livestock trade
Policy
A new case in Veracruz, Mexico, prompts a fuller shutdown of southern livestock trade.
May 2025
US closes border to live animal imports
Policy
Secretary Rollins suspends cattle, horse, and bison imports through southern ports as the screwworm spreads.
November 2024
Mexico confirms screwworm cases
Detection
The parasite turns up in southern Mexico and begins moving north toward the US border.
1966
US declares the screwworm eradicated
Milestone
A decades-long sterile-fly campaign clears the parasite from the continental United States.
Scenarios
1
Texas cases contained, no wider spread
Possible
Resolves by End of 2026
Discussed by: USDA APHIS, Texas Animal Health Commission
Sterile-fly releases and the quarantine snuff out the Zavala County cases. The female flies that mate once in their lives draw down to sterile males, eggs fail to hatch, and surveillance traps go quiet. The USDA lifts the infested-zone restrictions and declares the local population eliminated, repeating the 2017 Florida Keys playbook.
2
Screwworm spreads beyond the quarantine zone
Deadline passed (Oct 31, 2026)
Discussed by: CNN, NBC News, cattle-industry groups
More cases appear outside the 20-kilometer zone over the summer. Wildlife and untracked animal movement carry the parasite into new Texas counties faster than sterile-fly output can suppress it. The USDA widens quarantines and scales up releases as the response shifts from containment to a longer campaign.
3
US reopens southern border to live cattle imports
Uncertain
Resolves by Q2 2027
Discussed by: Drovers, Farm Progress, USDA
The USDA judges the Texas cases controlled and the Mexican spread checked, then restarts a phased reopening of southern ports to cattle, bison, and horses. The move would ease supply pressure on US feedlots that has built since the May 2025 suspension.
4
Trade restrictions spread to more US livestock partners
Deadline passed (Q3 2026)
Discussed by: CNBC, Global News, Canadian Food Inspection Agency
Canada moved within days of the second US case to block Texas-origin livestock. If surveillance traps find screwworm outside the Zavala County quarantine zone, other major US livestock trading partners could follow. That would shift the economic impact from a regional containment problem to a national trade dispute.
Historical Context
3 moments from history that rhyme with this story — and how they unfolded.
1 of 3
1957–1966
US screwworm eradication (1957–1966)
Researchers Edward Knipling and Raymond Bushland proved you could collapse a screwworm population by flooding it with sterilized males. Females mate once, so a sterile partner ends their line. The USDA cleared the Southeast by 1959 and the Southwest, including Texas, by 1966.
Then
The parasite was pushed out of the continental United States within a decade.
Now
The sterile insect technique became a model pest-control method; Knipling and Bushland won the World Food Prize in 1992.
Why this matters now
It is the same method, and the same calendar marker, behind today's response. The 1966 date is why this case counts as a 60-year first.
2 of 3
September 2016 – March 2017
Florida Keys screwworm outbreak (2016–2017)
Screwworm turned up in endangered Key deer in the Florida Keys, the first US livestock-region detection in decades. Dozens of deer died before the USDA set up checkpoints and released millions of sterile flies.
Then
Federal and state teams contained the outbreak to the Keys.
Now
The USDA declared Florida screwworm-free in March 2017, showing a fresh incursion could still be beaten quickly.
Why this matters now
It is the closest recent test of the playbook now running in Texas, and the basis for hoping the Zavala County cases can be contained.
3 of 3
1994–present
Panama biological barrier (1990s–present)
The US and Panama built a permanent sterile-fly barrier at the Darién Gap through a joint body called COPEG. A factory there releases sterile flies to hold the screwworm to South America.
Then
The barrier kept screwworm out of Central America and North America for roughly three decades.
Now
Its recent strain, as cases pushed north through Central America and Mexico, set up the current US incursion.
Why this matters now
The Texas case is a sign that this long-standing barrier is under pressure, which is why the USDA is now building fly factories on US soil.
