(WASHINGTON) — All imports of live cattle, horse and bison from the southern border have been banned due to the spread of a flesh-eating pest in Mexico, the U.S. Department of Agriculture (USDA) said on Sunday.

“The protection of our animals and safety of our nation’s food supply is a national security issue of the utmost importance,” USDA Secretary Brooke Rollins said in a press release.

The secretary cited New World Screwworm (NWS), a parasitic fly, as the reason for the suspension of imports. The name refers to the way in which maggots screw themselves into the tissue of animals with their sharp mouth hooks, causing extensive damage and often leading to death.

Panama saw NWS infections among livestock rise from an average of 25 cases annually to over 6,500 in 2023. Since then, the disease has spread further north, breaking a previously established barrier that contained the pest to South America for decades, the USDA said.

Infections have been detected in Costa Rica, Nicaragua, Honduras, Guatemala, El Salvador and Belize.

More recently, a case was reported in Mexico late last year, which also shut down the border for live animal trade. Imports resumed earlier this year after an agreement between the U.S. and Mexico to mitigate the threat of the disease.

The continued spread and threat of NWS led to the current shutdown, which will continue on a month-by-month basis, “until a significant window of containment is achieved,” the USDA said. The disease was recently detected in remote farms about 700 miles from the U.S. border.

Eradicating the disease is possible through a technique in which male screwworm flies are sterilized and then released into the environment to mate with females until the population dies out. This process was used to rid the U.S. of NWS in the 1960s.

The eradication efforts yielded estimated economic benefits of nearly $800 million annually for American livestock producers in 1996, with an estimated $2.8 billion for the wider economy, according to the USDA.

U.S. agriculture officials are working to release sterile flies by both air and ground along parts of Southern Mexico and in other regions in Central America.

“Once we see increased surveillance and eradication efforts, and the positive results of those actions, we remain committed to opening the border for livestock trade,” Rollins said. “This is not about politics or punishment of Mexico, rather it is about food and animal safety.”

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