What to know about screwworm as U.S. suspends Mexican cattle imports

• "When NWS fly larvae (maggots) burrow into the flesh of a living animal, they cause serious, often deadly damage to the animal," according to a U.S. Department of Agriculture statement Sunday.
• Rollins noted on X: "The last time this devastating pest invaded America, it took 30 years for our cattle industry to recover. This cannot happen again."

Driving the news: NWS was "recently detected in remote farms with minimal cattle movement as far north as Oaxaca and Veracruz" in Mexico, some 700 miles from the U.S. border, per the USDA. The first case was reported to the U.S. in November.

• The U.S.' import suspension will remain in effect "on a month-by-month basis, until a significant window of containment is achieved," according to the USDA.
• U.S. and Mexican officials reached an agreement last month on screwworm eradication efforts, which the USDA said were continuing in good faith.
• "However, despite these efforts and the economic impact on both countries due to this action, there has been unacceptable northward advancement of NWS and additional action must be taken to slow the northern progression of this deadly parasitic fly," per Sunday's USDA statement.

What they're saying: Mexican Agriculture Secretary Julio Berdegué said on X that Rollins had told him the border would be closed to live cattle exports for 15 days as officials reviewed the situation.

• "We don't agree with this measure," Berdegué said, but added he's hopeful of reaching an agreement sooner rather than later.

Yes, but: The National Cattlemen's Beef Association welcomed the USDA's action. NCBA CEO Colin Woodall in a statement noted "America's cattle and livestock producers spent years" in the 1960s and "millions of dollars to eradicate" NWS from the U.S. and in recent months they've been urging Central American officials "to take stronger action to stop the spread."

Threat level: Although screwworm primarily affects livestock, it can impact pets, wildlife and occasionally birds and people, according to the USDA.

• "NWS infestations are very painful," the CDC notes. "If you have an NWS infestation, you may see maggots (larvae) around or in an open wound. They could also be in your nose, eyes, or mouth."
• They're "attracted to and lay eggs on and in open wounds," per the CDC.

• People who spend time among livestock animals, sleep outdoors and have an open wound are at greater risk of becoming infested with NWS in areas where this parasite is present, the CDC notes.

Zoom in: Per the CDC, symptoms can also include:

• Unexplained wounds or sores on the skin that don't heal or that "worsen over time," with bleeding from open sores possible.
• "Feeling larvae movement within a skin wound or sore, nose, mouth, or eyes" or seeing maggots "around or in open sores."
• A "foul-smelling odor" from the point of the infestation.
• "Secondary bacterial infections sometimes occur and may cause fever or chills," the CDC notes.

The big picture: Screwworm flies are typically found in South America and the Caribbean, but the USDA notes they've spread north throughout Panama and into Costa Rica, Nicaragua, Honduras, Guatemala, El Salvador, Belize, and Mexico over the past two years.

• "The first case of NWS in Mexico was reported to the U.S. in November 2024," according to the USDA.

What we're watching: The USDA's Animal and Plant Health Inspection Service is releasing sterile flies through aerial and ground release "at strategic locations," with a focus on Southern Mexico and other areas in Central America.

Editor's note: This article has been updated with comment from the National Cattlemen's Beef Association.