New World Screwworm, a devastating parasite that eats cattle and other wild animals alive, is traveling north from Central America to Mexico and has crept past biological barriers that kept the pest contained for decades, experts said.

Washington halted cattle imports from Mexico in May, citing the insect’s spread further into Mexico, about 700 miles from the Texas border. With the U.S. cattle herd already at a multi-decade low, the closure could further elevate record-high beef prices by keeping more calves out of the U.S. cattle supply.

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 U.S. in the 1960s when researchers began releasing massive numbers of sterilized male screwworm flies who mate with wild female screwworms to produce infertile eggs.