USDA Detects First Case of New World Screwworm in South Texas

This is the first known case of the flesh-eating parasite in the United States since 2017.

Cattle are held in a corral before being exported to the United States through the Jeronimo-Santa Teresa border crossing after Agriculture Secretary Brooke Rollins announced an agreement with Mexico on the management of the New World screwworm at the Chihuahua Regional Livestock Union facility, outside Ciudad Juarez, Mexico, on April 29, 2025. Jose Luis Gonzalez/Reuters

A case of the New World screwworm has been detected in South Texas—the first known case of the flesh-eating parasite in the United States since 2017—the U.S. Department of Agriculture (USDA) announced June 3.

“The affected animal is a 3-week-old calf and larvae were identified in its umbilical area,” the USDA said. “To date, there have been no further detections.”

The sample was sent to the USDA’s national veterinary laboratory in Ames, Iowa, for confirmation.

“We have already activated personnel on the ground and are working with local partners,” the USDA posted on X.

Fears of an infestation have grown in the past week as confirmed cases of the parasite reached within a few miles of the Texas border. A case was confirmed in a 5-year-old goat in Mexico’s Coahuila state, about 25 miles away from the border, on Tuesday.

Texas Rep. Don McLaughlin urgently requested that Gov. Greg Abbott declare an emergency in the state to prepare for the oncoming threat.

“We are facing a tremendous threat along our southern border in the New World screwworm and normal channels just aren’t moving fast enough,” McLaughlin, who serves on the Texas House Agriculture and Livestock Committee, said in a social media video. “It will be devastating to our country and to our nation. It’s truly an issue that we need to attack.”

Abbott issued a statewide emergency declaration in January to prevent a screwworm infestation. His spokesman, Andrew Mahaleris, released a statement Wednesday afternoon, saying the governor’s New World Screwworm Response Team, composed of the Texas Animal Health Commission and the Texas Parks and Wildlife Department, was working with the USDA and other federal partners to respond to the case.

“If the case is confirmed positive, the NWS Response Team will immediately establish an incident response post, expand fly trapping and surveillance efforts, and restrict animal movement to prevent further spread of the pest,” Mahaleris said in the statement. “Targeted releases of sterile NWS flies will be expedited to eliminate any reproducing populations in the area.”

Abbott’s press office did not return requests for comment about the situation by time of publication.

The New World screwworm—a flesh-eating parasite—infests warm-blooded animals, including livestock, pets, and wildlife, causing severe tissue damage and sometimes death, according to the U.S. Department of Health and Human Services (HHS).

In rare cases, it can also infest humans in the same way. In recent outbreaks across Central America and Mexico, authorities reported at least seven human fatalities linked to screwworm infestations, according to the Centers for Disease Control and Prevention (CDC).

As of June 2, these countries have reported more than 171,100 New World screwworm cases in animals and more than 2,070 human cases. One infected person returned to the United States after traveling to El Salvador, the CDC reported.

Larvae of the screwworm fly, collected from infected cows, at the COPEG sterile fly production plant, which fights the spread of the cattle screwworm, in Pacora, Panama, on June 11, 2025. Reuters/Enea Lebrun/File Photo

The New World screwworm infested the United States in the 1960s. The response at the time was to release 500 million to 600 million sterile flies each week to eradicate them, according to the USDA.

That type of response is not possible today.

“We stopped producing the fly in the United States,” McLaughlin said.

The only facility that produces sterilized flies in North America is the APHIS International Services facility in Pacora, Panama, which can only produce over 100 million pupae per week during an outbreak event, according to the USDA.

The USDA is working on increasing the availability of sterile flies to meet the current demands of an outbreak, the agency said.

McLaughlin also requested President Donald Trump to declare a national emergency to address the situation that he said could destroy livestock, wildlife, human health, and the economy of the region.

“We need every agency and every able body onboard,” McLaughlin said. “This is something that will affect not just the southern states. It will affect the whole United States.”

In August 2025, the HHS issued an emergency declaration that allows the U.S. Food and Drug Administration to issue emergency use authorizations for animal drugs to treat or prevent screwworm infestations.

The declaration applies only to drugs for animals.