New World Screwworm in 2026: What Canadian Cattle Producers Need to Know

Short answer: New World screwworm is a flesh-eating fly larva. As of November 5, 2026, USDA had confirmed 116 animal infestations in the US, 56 of them active, across Texas, New Mexico and Arizona. There are no confirmed cases in Canada, and the cold limits how far north the fly can survive. Still, in June CFIA put emergency restrictions on livestock coming from Texas. The outbreak can affect Canadian producers through trade, prices and imported animals.

Screwworm hasn't been a problem in North American livestock for about 50 years, so most producers have never seen it. Here's what it is, where it is now, and what it means for cattle operations in Canada.

What is New World screwworm?

New World screwworm (Cochliomyia hominivorax) is a fly that lays its eggs in open wounds on warm-blooded animals. The larvae eat living flesh, which makes the wound bigger and draws in more flies. Without treatment, an infested animal can die. It affects cattle, horses, dogs, wildlife and, rarely, people.

The US and Mexico got rid of it decades ago by releasing sterile male flies. Wild females that mate with them lay eggs that don't hatch. In the past few years the fly has spread north from Central America through Mexico.

Where is screwworm now?

The outbreak in the southern US has grown quickly this fall:

Date	US status
Early June 2026	First US livestock case in about five decades, found in Texas
September 2026	Fewer than 50 US cases for the year so far; USDA releases its billionth sterile fly in Texas (KFYR)
November 4, 2026	113 confirmed cases, 36 in October and 24 in early November (KBTX)
November 5, 2026	116 confirmed cases, 56 active, in Texas, New Mexico and Arizona (Texas Public Radio)

The recent cases include cattle in Hudspeth and Mitchell counties in Texas, a horse in Greenlee County, Arizona, and horses, cattle and a dog in New Mexico. Two elk were also infested. Movement restrictions cover parts of 16 Texas counties.

How is Canada responding?

In June 2026, CFIA put emergency import restrictions on all livestock, including horses, coming into Canada from Texas. Under those rules, any animal that started in or passed through Texas within 21 days of reaching the border is refused entry (Fox 7 Austin). Check CFIA's current animal import notices before you buy or move animals from the southern US. The rules can change as the outbreak spreads into new states.

Can screwworm survive in Canada?

The fly needs warm weather and can't survive long Canadian winters. Historically, outbreaks happened mostly in the southern US. The bigger risks for Canadian producers are:

• Imported animals carrying larvae in a wound, including horses and dogs that travelled south.
• Summer spread if the northern edge of the outbreak keeps moving.
• Trade and price effects. Every border decision between the US and Mexico changes feeder supply and prices in North America.

How does screwworm affect cattle prices?

US-Mexico cattle trade normally moves about 1 million head a year. The US closed the border to Mexican cattle for most of the time since late 2024. In July 2026, USDA said it would reopen in phases, starting with Douglas, Arizona, and later two New Mexico ports, with full inspection of every animal (Farm Policy News). In early November, Canfax listed the reopening of the Columbus, New Mexico port to Mexican feeders as a reason Canadian feeder prices were weaker.

The basic pattern:

• Mexican cattle shut out of the US means fewer feeders in US yards and stronger demand for Canadian cattle.
• Mexican cattle allowed in means more US feeder supply and some downward pressure on Canadian feeder prices.

Watch border news alongside Canfax prices. They move together. Read our fall 2026 Canadian cattle market update for current prices.

What signs should I watch for?

US animal health officials list these signs:

• Wounds that get worse instead of healing
• Bloody, thick or foul-smelling drainage
• Swelling around an injury
• Larvae visible in a wound
• Pain, restlessness or unusual behaviour

Check animals closely after branding, castration, dehorning, tagging, calving or any injury, and check newborn navels. Don't move an animal with a suspicious wound until a vet has looked at it. In Canada, screwworm is a reportable disease. If you suspect a case, contact your vet and the nearest CFIA district office right away.

How do good records help?

If screwworm or any other reportable disease shows up near your operation, officials will ask three questions: which animals came from where, when they arrived, and what treatments they had. Producers who can answer quickly lose less time to movement restrictions. Make sure you're keeping:

• Tag numbers and source for every animal bought or brought in.
• Treatment and wound records with dates. See cattle health tracking.
• Movement dates between pastures, yards and buyers. See our 2026 Canadian traceability update.

The takeaway

Screwworm isn't an immediate threat to Canadian herds, but it's already affecting cattle trade and prices across North America, and it could change border rules quickly. Watch CFIA notices, check wounds after processing, and keep tag-level records of where every animal came from. CattleOS lets your crew record treatments, wounds and moves by voice at the chute, so you can answer those questions in minutes if you ever need to.

Hashim Farooq is the CTO and co-founder of CattleOS. Case counts in this article come from USDA data as reported on November 4 and 5, 2026. Always check CFIA and USDA APHIS for the latest numbers.