Mexico has activated emergency controls following the detection of a new New World screwworm case in cattle within the northern border state of Nuevo Leon.
It marks the closest instance to the US frontier since the outbreak began in 2024.
The affected animal, discovered in the town of Sabinas Hidalgo, originated from the Gulf state of Veracruz, according to Mexico's National Health for Food Safety and Food Quality Service.
The last reported case, on July 9 in Veracruz, prompted Washington to suspend imports of live Mexican cattle.
The parasite, a larva of the Cochliomyia hominivorax fly, attacks warm-blooded animals, including humans.
Mexico has reported more than 500 active cases in cattle across its southern states.
The block on cattle imports has created difficulties for Mexico's government, which has already been busy trying to offset the impact of U.S. President Donald Trump's tariff threats this year.
The government and ranchers have sought to get the ban lifted. If it stays in place through the year, Mexico's ranching federation estimates losses up to $400 million.
Mexico's Agriculture Secretary Julio Berdegué said in a post on X that Mexico is "controlling the isolated case of screwworm in Nuevo Leon,” under measures to fight the pest agreed with the U.S. in August.
U.S. Agriculture Secretary Brooke Rollins said Washington will take “decisive measures to protect our borders, even in the absence of cooperation" and said imports on Mexican cattle, bison and horses will remain suspended.
“We will not rely on Mexico to defend our industry, our food supply or our way of life,” she said.
In August, a screwworm was detected in a human for the first time in the U.S., according to the Department of Health and Human Services.
The individual was diagnosed after returning to the U.S. from a trip to El Salvador.
The Department of Health and Human Services said at the time that the Hilliard "risk to public health in the United States from this introduction is very low."
