Screwworm cases are rising in the US as the outbreak spreads beyond the initial contamination zones.

Twelve animal cases have been confirmed so far, a significant increase from the first case detected in a calf in south Texas on 3 June. The growing number of infections has alarmed agricultural experts, who warn that a wider outbreak could have serious consequences for the Texas beef industry.

Of the 12 reported cases, 11 remain active and one is inactive, according to an update issued last Thursday by the US Department of Agriculture’s animal and plant health inspection service. The most recent case was reported on 12 June in Sutton countyin west Texas, where a sheep was discovered with the infection. Other cases have been identified in the Texas counties of Edwards, Tom Green, Gillespie, La Salle and Zavala, as well as in Lea county, New Mexico.

The infected animals include cattle, goats, sheep and one dog.

The screwworm is a fly larva that burrows into open wounds on livestock and other warm-blooded animals, feeding on living tissue. For nearly six decades, the parasite was rarely seen in the US after being largely eradicated in the 1970s. However, its re-emergence and rapid spread have raised concerns that the parasite is making a comeback at a time when beef prices are at record highs.

USDA officials are urging animal owners to watch for signs of screwworm infection, including draining or enlarging wounds, maggots or egg masses, unusual discomfort, and lesions around the nose, ears, genitals or umbilical area. Suspected cases should be reported immediately to help contain the spread of the parasite, the USDA said.

It added that despite the outbreak, the US food supply remained safe, as the screwworm does not infest meat, fruits, vegetables or other fruit products.

In a statement last week, Texas’s agriculture commissioner, Sid Miller, warned of the spread, saying: “This should set off alarm bells across the country. Every day we delay gives this pest another opportunity to spread.”

Miller called for the deployment of the Screwworm Adult Suppression System (Swass), a USDA-developed program that uses targeted bait to kill fertile adult screwworm flies before they can reproduce.

“You don’t win this battle with one tool, you kill fertile flies with Swass while overwhelming the remaining population with sterile flies. That’s how we built the biological barrier that protected American agriculture for decades. That’s the strategy we should be using today,” he said.

In a press statement last Thursday, the US agriculture secretary, Brooke Rollins, said that the government has released 4 million sterile flies on the ground, as well as 4 million sterile flies in the air to help combat the outbreak.

Despite the outbreak still being restricted to Texas and New Mexico, Pennsylvania’s agriculture department has issued a precautionary quarantine order. The order imposes stricter controls on the import of susceptible livestock from affected areas, requiring veterinary inspections and health documentation. Pennsylvania officials said the measures are intended to reduce the risk of screwworm spreading into the state.

“Taking proactive steps now to strengthen biosecurity and limit unnecessary animal movements from affected areas will help protect our farms and communities,” Pennsylvania’s agriculture secretary, Russell Redding, said.