Tensions Rise Between US and Mexico over New World Screwworm Threat

Additional screwworm information from the Big Bend Sentinel.

NOTE: this article was originally published to BigBendSentinel.com on May 21, 2025. It was written by Gibran Caroline Boyce, Sandra Sadek and Alfredo Corchado.

EL PASO — Zoom screens lit up across Mexico and Texas as over two dozen agricultural leaders, including those in Mexico’s Department of Agriculture, scrambled into an emergency virtual meeting. Just 24 hours earlier, U.S. Agriculture Secretary Brooke Rollins — on May 11 — abruptly shut down livestock imports at the U.S.-Mexico border, citing the return of the New World screwworm, a deadly flesh-eating parasite threatening cattle, horses, and other vital livestock.

“We are hoping for the best but prepared for the worst,” said Alvaro Bustillos, chairman of the Chihuahua Cattlemen’s Association and president of Vaquero Trading, based in El Paso.

Bustillos expressed frustration with his own government of Mexico and President Claudia Sheinbaum for not doing more to contain the screwworm, calling on the “U.S. government to pressure Mexican authorities to do their job.” He also called for authorities to suspend cattle imports along Mexico’s southern border “until we get ahead of the problem,” he said.

Bustillos spent the next 48 hours after the May 11 announcement calling for a panel of Mexican and U.S. authorities to find ways to address screwworm spread “effectively” and bring “an end to the suspension of operations” on the northern border.  

The pause was to be reconsidered in 15 days. But some are already estimatingmillions in potential profit losses for borderland ranchers amidst an already devastating year due to President Donald Trump’s tariffs.

“The screwworms are advancing,” Bustillos said. “That’s the problem. It has already passed a buffer zone,” referring to the Istmo de Tehuantepec, a large tropical isthmus in the southern Mexican state of Oaxaca. Because “the screwworm surpassed that zone, obviously other actions were needed in response.”

Following the first 15 days, the pause is expected to be renewed indefinitely on a month-to-month basis until “significant containment” is achieved, according to U.S. Department of Agriculture (USDA) officials. The parasitic fly pest poses a catastrophic threat to American agriculture, with officials warning that its last U.S. outbreak took 30 years to eradicate.

The decision to cease livestock border crossings comes just months after the USDA increased restrictions on livestock importation and limited some port of entry access across the southern border back in November and December 2024, following reports of screwworm detections in Central America. At the time, officials increased inspections and quarantine measures, requiring Mexican livestock producers to arrive two days ahead of scheduled crossings for inspection. Sunday’s full suspension marks the most aggressive action taken yet to prevent the parasite from breaching U.S. soil.

According to a press release issued by the USDA, the screwworm is currently found approximately 700 miles away from the southern U.S. border, but is rapidly approaching.

“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,” said Secretary Rollins. “This is not about politics or punishment of Mexico, rather it is about food and animal safety.”

In a statement made via the social media platform X, Mexico’s Secretary of Agriculture, Julio Berdegué, said he spoke with Secretary Rollins, discussing a joint strategy against the screwworm.

“We don’t agree with this measure,” Secretary Berdegué said. “But we’re confident we’ll reach an agreement sooner rather than later.”

Sheinbaum echoed these sentiments in a subsequent press conference, describing the decision as “unfair.”

“Mexico is not anyone’s piñata,” said Sheinbaum. “[There is] collaboration, coordination, but not subordination, nor can we be subjected to what is said each day by the U.S.”

The Director of the National Agricultural Council in Mexico, Luis Fernando Hario, also shared on X, “The reality is that all cattle crossing into the United States are guaranteed to be free of screwworms; the suspension of imports by the U.S. does not solve the problem.”

In 2024, the U.S. imported over one million cattle originating from Mexico. Cattle bred in Mexico using U.S. cattle genes are brought to the U.S. through borders, including San Jeronimo-Santa Teresa, Ojinaga, and Presidio and many more to be fattened up in U.S. pens before being slaughtered into various cuts of meat. Despite having its own cattle supply stateside, the U.S. both imports and exports beef across its borders to meet consumer demand based on how lean and diverse the cuts are. 

U.S. beef tends to be of higher quality and thus more fatty, while Mexican beef is leaner, which is better for creating products like ground beef and other by-products. 

According to the International Atomic Energy Agency (IAEA), estimated losses in South America are almost $4 billion annually from the screwworm. In Mexico, where the parasite remains endemic in parts of the south, outbreaks threaten livestock health and trade stability. The estimated annual cost to the U.S., according to the National Agricultural Library at the USDA, is expected to be about $900 million.

The New World screwworm was onceeradicated from the U.S. in 1966 after a sterilization campaign to contain fly reproduction. The screwworm outbreak cost the U.S. at that time over $750 million, according to the Texas and Southwestern Cattle Raisers Association. While significant, potential losses in animal deaths and treatments from the screwworm were estimated to be even higher. The eradication effort required decades of research and cooperation between the U.S., Mexico, and Central America. Now, as shifts in climate and cross-border trade occur, the reemergence of an outbreak is once again testing pest control diplomacy.

The parasitic fly is known to be found in tropical and subtropical climates. According to Maxwell Scott, a professor of entomology at North Carolina State University and an expert on the New World screwworm, “with a warming planet, the New World screwworm could spread even further north than in the past.”

Scott supports the USDA’s decision to halt border crossings temporarily.

“In general, it is a good idea to stop the movement of infested livestock, something that was clearly not done well in Central America,” Scott said. “It is very unlikely the fly could have made the large jumps that were observed by itself.”

Stateside, cattle associations have voiced support for Secretary Rollins’ latest move to shut down the border to cattle crossings. In astatement, Texas Farm Bureau President Russell Boening said the threat of the New World Screwworm to domestic livestock and wildlife industries should “not be underestimated.” Boening also called for the construction of domestic facilities to sterilize the parasite-carrying fly to combat its spread. 

“Texas Farm Bureau is encouraged that U.S. Secretary of Agriculture Brooke Rollins and the U.S. Department of Agriculture recognize the seriousness of this situation and are taking necessary precautions to safeguard our country from this animal health threat by closing the ports,” Boening said.

National Cattlemen’s Beef Association CEO, Colin Woodall, said in a statement that the association has been working with the USDA for months to sound the alarm on the virus. He blamed weak government participation and efforts from Central America, especially what he described as bureaucratic hurdles by the Mexican government, to curb the spread.

“USDA’s border closure was entirely avoidable,” Woodall said. “The Mexican government’s failure to knock down senseless obstacles has left America with no alternative but a closure of the U.S. border until the outbreak is verifiably stopped and the flies are pushed back south of Panama’s Darien Gap.”

Woodall also acknowledged that the border closure will create economic harm and supply chain disruption in the short run, but the long-term costs of fighting the parasite on U.S. soil will be far more expensive.

Gibran Caroline Boyce and Sandra Sadek reported from New York City. Alfredo Corchado reported from El Paso. This story was produced for Puente News Collaborative in partnership with the Craig Newmark Graduate School of Journalism at the City University of New York (CUNY).