Concerns about meat-eating parasites have caused U.S. officials to stop all live cattle, horses and bison imported on the southern border.

Agriculture Secretary Brooke Rollins made the decision Sunday, citing the discovery of the northern spread of New World Screwworms in southern Mexico last year.

"Protecting our animals and the food supply to our nation is the most important national security issue," Rollins said in a statement.

"It has nothing to do with Mexico's politics or punishment, but about food and animal safety," she said.

The screwworms of the New World are fly larvae that drill into wounds or animals’ mucosa and few humans’ mucosa.

The debris feasted on the host's flesh and blood, with tiny mouth hooks on it. Untreated parasitic infections can kill a cow within one to two weeks.

The effort to get rid of pests goes back decades.

In fact, the United States and Mexico were able to eliminate New World Screwworms of the 1960s and 1970s by releasing hundreds of millions of sterile adult flies that would mate with women, ultimately preventing them from laying viable eggs.

This strategy helps create a "barrier zone" that prevents pests from invading the United States and Mexico, although cases still occur from time to time.

In 1976, an outbreak in Texas affected 1.4 million cattle, hundreds of thousands of sheep and goats. If such an outbreak happens now, it is estimated that it will cost Texas economy $1.8 billion, according to a USDA analysis.

The potential impact is why agricultural officials are so shocked that pests have made a comeback in the past few years.

The U.S. Department of Agriculture said on Sunday that cases surged in part of Central America and that "remote farms" about 700 miles from the U.S. border have been found in some "remote farms" in Mexico.

As a result, the United States closed the on-site animal trade at the border in November. This was canceled in February after the United States and Mexico agreed to new measures to avoid parasites.

The USDA said the new ban will continue in "a month" until a major containment window is achieved.