Protocol to Prevent Screwworm Spread

REDFIELD, Iowa (DTN) -- Prevention is the key to keep New World screwworm (NWS) out of the United States, according to Kathy Simmons, chief veterinarian at the National Cattlemen's Beef Association.

Mexican animal health officials agree. The Mexican Secretariat of Agriculture and Rural Development and the Inter-American Institute for Cooperation on Agriculture (IICA) have expanded their work within Mexico to enhance the prevention and control of NWS, according to a news release.

In November 2024, USDA's Animal and Plant Health Inspection Service (APHIS) halted shipments of live Mexican cattle and bison to the U.S. after a positive detection of NWS in southern Mexico. On Feb. 1, 2025, that restriction was lifted with several protocols in place to help keep the pest out of the U.S.

"The U.S. eradicated New World screwworm in 1966," said Simmons. "Mexico had eradicated it in 1991. The pest has been moving north since last March. There was a biological barrier, and we would like to get that again."

Mike Stepien with APHIS told DTN, "During the first week of reopened imports, 1,317 cattle entered the United States through the ports. Santa Teresa and Douglas Ports of Entry are now open for cattle imports, with Santa Teresa being the first to open."

He assured DTN that cattle and bison will be inspected and treated for screwworm by trained and authorized veterinarians prior to entering the pre-export inspection pens, where they will again undergo inspection by Mexican officials before proceeding to final APHIS inspection then crossing at the Santa Teresa and Douglas Ports of Entry. Cattle and bison approved for importation will also be dipped in a solution to ensure they are otherwise insect- and tick-free.

US, MEXICO DEAL WITH CHALLENGES

The NWS poses challenges to each country's livestock and rural economy. Mexican Agriculture Secretary Julio Berdegue and IICA Director General Manuel Otero agreed to work together to prevent and control the pest within Mexico. As part of this agreement, they will use financial resources to support these actions. Improvements will be made to the offloading and inspection bay at their Federal Verification and Inspection Point in Cosamaloapan, in the Mexican state of Veracruz.

Simmons said sterile male screwworm flies will be used to help control areas where the disease is found. They will drop these sterile males into those areas. Since female flies only mate once, they will die after mating with the sterile males and no eggs will be laid. These flies are produced at a rate of 100 million per week at a Panama facility.

STRICT PROTOCOL MUST BE FOLLOWED

"We want to continue to trade Mexican feeder cattle but have to ensure no New World screwworm or other diseases cross the border, so it is important for the protocol to be followed," said Simmons.

The protocol includes cattle being kept in group lots and penned accordingly on the Mexican side. There they will receive an ivermectin injection in case NWS is present that can't be seen. After three to five days, they will be moved to the next pen and dipped in a wormer solution and inspected and examined for wounds. Once they are inspected by trained and authorized veterinarians of both Mexico and the USDA at the last check pen, the cattle will be allowed to cross the border according to Simmons. She said they may only be able to move the cattle in smaller groups up to 500 at one time to be sure the process is efficient and effective, including having health certificates when they are ready to move.

CATTLE MOVE IN SMALLER AREAS

As part of the protocol signed between the countries, Mexico identified and prepared pre-export inspection pens in San Jeronimo, Chihuahua, and Agua Prieta, Sonora, which were approved by APHIS. Until the process is running smoothly, only two ports of entry will be used for live cattle and bison, at Santa Teresa and Douglas.

IICA said it is committed to strengthening livestock production in the Americas and highlight the importance of international cooperation to tackle the challenges facing the agriculture sector.

"We want to make sure this disease doesn't come to the United States, and we want to get it controlled back to having the biological border. We have had good meetings with Mexico, and they are working with us to make this happen," Simmons concluded.

Jennifer Carrico can be reached at jennifer.carrico@dtn.com

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