Sheinbaum praises bilateral steps to combat flesh-eating screwworm

MEXICO CITY (CN) — Mexican President Claudia Sheinbaum praised on Monday the newly inaugurated sterile fly plant in the southern Mexican border state of Chiapas as a good example of bilateral cooperation between the U.S. and Mexico to fight the New World screwworm. The Mexican government invested $30 million for the plant, and the U.S. government $21 million, with more on the way to end the flesh-eating parasite.

Screwworms are fly larvae that can destroy livestock populations, costing ranchers millions. The maggots burrow into the wounds of infested livestock, feeding as they go like a screw into wood. The flesh-eating parasite can also cause significant harm to humans or death.

“It is a good example of development cooperation; it is the example of how cooperation should be between the United States and Mexico. In this case, it is in two ways: scientific and technological development, and on the other hand, joint application to eradicate something that can greatly affect cattle,” said Sheinbaum during her Monday press conference.

Sheinbaum explained the new sterile fly production plant in Metapa de Domínguez, Chiapas, that began operations on Sunday will produce 28 million sterile flies per week by mid-July.

By the end of 2026, the plant will increase production to 100 million.

“There is a similar plant in Panama,” said Sheinbaum. “We receive — I don’t know if they call them pupae or larvae — but it arrives to the factory in Chiapas and then comes the process of reproducing the fly. Then the process to make them sterile begins. This process lasts some weeks — from when the fly enters until when it leaves.”

The sterile flies are then flown on a special airplane to the border state of Tamaulipas.

“From there they will begin to be released,” she said. Because they are sterile, the screwworm population decreases, with hopes it will die out.

Sterile insect technique is a highly effective way to combat screwworm and has been implemented in various programs and agreements between Mexico and the United States since 1958.

This four-step process begins when New World screwworm pupae are exposed to gamma radiation in specialized facilities. These sterile flies are then released into areas affected by screwworm. Wild screwworm flies mate with sterile flies, but their eggs do not hatch, and the pest population eventually dies out.

Multiple diplomats and secretaries from both sides of the border attended the inauguration of the Chiapas sterile fly plant on Saturday.

U.S. Ambassador to Mexico Ronald D. Johnson pledged that the U.S. government will contribute an additional $83.8 million against the screwworm plague.

“The goal is clear: to eliminate this pest to protect livestock, trade and food security in the U.S. and Mexico,” he said Saturday.

In her speech at the Saturday inauguration, U.S. Agriculture Secretary Brooke Rollins praised Sheinbaum and vowed to continue working together to defeat the plague that is devastating livestock.

“From the moment I met President Sheinbaum, I knew she understood and was fully focused, and would be such an extraordinary ally for the United States. And this plant, this inauguration ceremony today, is an example of how this alliance can work beautifully together,” she said.

Secretary of Agriculture and Rural Development Columba Jazmín López Gutiérrez also vowed her dedication to eradicating screwworm.

“We recently met with the Secretaries of Agriculture and Rural Development from the country’s 32 states to announce and work on the new strategy for the prevention, control, and eradication of the screwworm in Mexico. The aim is to transition from an emergency response to a national campaign that enables the coordination, monitoring, and evaluation of activities involving outreach, training, surveillance, movement control, and the production and release of sterile flies,” she said in a speech Saturday.

The Texas & Southwestern Cattle Raisers Association also praised the plan.

“Every sterile fly produced helps the U.S. get closer to eradicating NWS and establishing a biological and geographical barrier to protect Texas ranchers and landowners,” Texas & Southwestern Cattle Raisers Association President Stephen Diebel said in a statement Saturday.

In April 2025, Rollins warned hundreds of screwworm cases in Mexico were threatening the safety of U.S. livestock.

Rollins sent a diplomatic letter to then-Secretary of Agriculture and Rural Development Julio Berdegué urging Berdegué to eliminate restrictions on U.S. Department of Agriculture aircraft that employ sterile insect technique.

A month later, tensions flared when Rollins suspended live animal imports through ports of entry along the southern border after cases in Mexico shot up.

Sheinbaum responded by saying that Mexico is not anyone’s piñata but assured an agreement would be reached.

A sterile screwworm fly production plant in Tuxtla Gutiérrez, Chiapas, ceased operations in 2012 after the Mexican Secretariat of Agriculture and Rural Development and the United States Department of Agriculture agreed toterminate their 1972 binational agreement to eradicate screwworm. Both governments agreed that the objective of eradicating the screwworm from the national territory was met.

The original production plant was built in 1974 as a result of the 1972 agreement.

As of June 27, there are 1,735 active cases of screwworm in Mexico, according to Mexico’s National Agro-Alimentary Health, Safety and Quality Service, and 20 active cases in the U.S., according to the U.S. Animal and Plant Health Inspection Service.

The Mexican government confirmed its first cases of screwworm in November 2024 and the U.S. on June 3.

According to the latest Secretariat of Health Epidemiological Bulletin, there have been a total of 443 confirmed cases of screwworm infections in humans — which can be deadly — in Mexico since the first one in April 2025. There were 34 new cases between June 7 and June 13.