CHICAGO – New World screwworm, a devastating parasite that eats cattle and other wild animals alive, travelled north from Central America to Mexico before being confirmed in a Texas calf on June 3, creeping past biological barriers that kept the pest contained for decades, experts said.

Washington has halted cattle imports from Mexico for the past year, citing the insect’s spread further into Mexico.

With the US cattle herd already at a multi-decade low, the closure elevated record-high beef prices by keeping more calves out of the US supply chain.

The first confirmed case in the US during the latest outbreak represents a serious challenge for ranchers and could cause beef prices to rise further.

Screwworms are parasitic flies whose females lay eggs in wounds on any warm-blooded animal. Livestock and wild animals are usually the victims.

Once the eggs hatch, hundreds of screwworm larvae use their sharp mouths to burrow through living flesh – feeding, enlarging the wound and eventually killing their host if left untreated.

When screwworms infect a cow, a tiny scrape, a recent brand or a healing ear tag can quickly become a gaping wound, carpeted with wriggling maggots that put the entire herd at risk of infestation.

Screwworms were eradicated from the US in the 1960s when researchers began releasing massive numbers of sterilised male screwworm flies that mate with wild female screwworms to produce infertile eggs.

The US typically imports over a million cattle from Me...