US shuts border to Mexican cattle after detection of pest that infests live animals

The United States has shut its border to live cattle imports from Mexico following the detection of a pest called New World screwworm (NWS).

The US Department of Agriculture (USDA) said the NWS was found in a cow at an inspection checkpoint in the southern Mexican state of Chiapas, close to the border with Guatemala.

“NWS are fly larvae that infest living tissue of warm-blooded animals, causing infection,” the department’s statement said.

“Given the severity of the threat from NWS, [the USDA’s Animal and Plant Health Inspection Service] is restricting the importation of animal commodities originating from or transiting Mexico, effective immediately and pending further information from Mexican veterinary authorities on the size and scope of the infestation.”

Wider impact possible

Mexico has been exporting significant quantities of cattle to the US this year and the sudden closure of the trade could have wider implications, according to meat analyst Simon Quilty.

“US cattle feeder imports are close to 1.03 million head [per] year to date, up 21 per cent on last year,” he said.

“If this ban is prolonged and if [the pest] actually arrived in the US itself, we could see an aggressive and longer period of banning between Mexico and the US, which could lead to fairly sharp increases in pricing as the US market looks to cover the shortage that could occur.”

Major trading partner

The US has been Australia’s largest beef export destination in 2024 and, according to Meat and Livestock Australia (MLA), the US bought more Aussie beef in the third quarter of this year than what remained in Australia’s domestic market.

Mr Quilty said the US successfully eradicated screwworms in 1966 using the sterile insect technique, although there was a constant risk of reintroduction.

According to the USDA, NWS can infest livestock, pets, wildlife, occasionally birds and, in rare cases, people.

“They most often enter an animal through an open wound and feed on the animal’s living flesh,” it said.

“While they can fly much farther under ideal conditions, adult flies generally do not travel more than a couple of miles if there are suitable host animals in the area.”