Screwworm Outbreak Spurs US-Mexico Livestock Safeguards

Mexico City, Mexico — Mexican and U.S. authorities are implementing sanitary measures to contain a plague and protect livestock after the detection of a case of the New World screwworm in the state of Nuevo León.

The neotropical screwworm was detected in Nuevo León, in a case controlled by Mexico's sanitary authorities. U.S. specialists warned that they could implement measures "with or without Mexico" to protect their livestock industry and estimate that the problem could last several years.

Case Detected in Nuevo León

Authorities from the National Service for Agrifood Health, Safety and Quality (SENASICA) applied immediate measures to prevent an outbreak, confirming that the larvae were in an early phase, which reduces the risk of expansion. The affected livestock came from Minatitlán, Veracruz, and was reviewed by Mexican technical personnel and members of the Mexico-United States Commission for the Prevention of Foot-and-Mouth Disease.

Only one animal presented an infection (myiasis), was treated, and all the livestock received Ivermectin as a preventive measure. The case was located less than 113 kilometers from the border with the United States, in a critical corridor for trade into Texas.

Measures Against the Screwworm in Mexico

SENASICA and the Ministry of Agriculture and Rural Development (SADER) established sanitary cordons, fumigation campaigns, and the release of sterile flies. As of July 2025, more than 2,700 cases had been registered in states in southern Mexico, and this latest case in Nuevo León marks an advance of the pest toward the north.

No criminal sanctions have been reported for importers of infected livestock, although there are initiatives at the state level, such as in Chihuahua, where proposals call for 5 to 7 years of prison and fines for those who import or facilitate the spread of the plague.

Actions by the United States

The United States Department of Agriculture (USDA) closed ports to imports of Mexican cattle, buffalo, and horses, and established more than 8,000 traps in Texas, Arizona, and New Mexico, with 13,000 samples analyzed without detecting additional plague.

Brooke Rollins, head of the USDA, stated: "We will take aggressive measures, with or without Mexican cooperation, to protect our livestock industry. This is a national security priority."

The National Cattlemen's Beef Association (NCBA) asked the U.S. government to demand accountability from Mexico, while the National Confederation of Livestock Organizations of Mexico warned that the suspension of imports could generate losses of more than 400 million dollars.

How Monitoring Traps Work

The traps use pheromones as an attractant to capture adult flies on sticky surfaces, placed in auction centers and strategic points.

• They allow for the detection of the screwworm's presence and reduce its reproductive capacity.
• They serve to determine whether livestock exports are authorized from certain regions.

This method is key for epidemiological surveillance and the rapid control of outbreaks.

Future Perspectives

Kevin Shea, former director of the USDA's Animal and Plant Health Inspection Service, warns that the plague could remain for several years. The sterile insect technique (SIT) is effective, but slow and costly: it requires breeding millions of sterilized male flies and releasing them to reduce the population. Mexico has already invested in plants in Chiapas and Texas, which will not be operational until 2026. Explorations with genetic editing promise advances, but are still in an experimental phase and could take years to implement on a large scale.