Flesh-Eating Screwworm Spreads Outside Texas as More Cases Detected

U.S. Agriculture Secretary Brooke Rollins announced that a fifth New World screwworm case had been reported in a Texas goat during a joint news conference with Texas Gov. Greg Abbott on June 8 in Kerrville.

The latest case was in Gillespie County, near Fredericksburg, Texas, which is farther away from the border than previous Texas cases. The news came just hours after two other cases were reported, one involving a calf in Texas and the other a dog in New Mexico.

A veterinarian in Andrews County, which borders New Mexico in West Texas, submitted samples from an infected dog, noting that “early reports indicate the dog was recently in Mexico.” That case had originally been reported as a Texas case, but its owners live in New Mexico.

The other case, in La Salle County, about 70 miles north of Laredo, Texas, involved a calf, the U.S. Department of Agriculture (USDA) said, without providing further details. Both cases remain under investigation.

Officials in Texas confirmed two cases last week near the Mexican border. The parasite was found in a 1-month-old calf in Zavala County, Texas, just 5.6 miles from the first confirmed case, involving a 3-week-old calf whose umbilical cord was infected with maggots.

With a growing number of New World screwworm infections in Texas, the state and federal governments are moving rapidly to contain the outbreak amid growing concern.

“We now know what the enemy looks like,” Rollins said. “We now understand what we have to do.”

Abbott said last week during a news conference that Texas needs to act quickly because the parasite tends to expand its footprint during the hot summer months. He has made additional personnel and resources available to speed up the process to produce more sterile flies, including bringing Texas A&M University personnel on board.

​“During the winter months, it may kill off the flies or reduce their number,” he said last week, while stating that additional sterile flies are needed in less than a year. “We cannot make it through a second summer.”

State and federal officials are scrambling to stop the spread of screwworms that can infect animals and, more rarely, humans, causing horrific wounds that can be fatal if left untreated.

​The government’s main tool against the pest is the release of sterile flies, which eradicated the screwworm from Texas during a devastating infestation about 50 years ago, officials said.

​Sterile males mate with females, causing them to lay unviable eggs—a key strategy in past eradications.

​But now only 100 million such flies are produced each week at a single plant in Panama, according to USDA officials.

​The USDA gave Mexico $21 million to renovate a fruit fly production facility in Metapa, Mexico, to provide an additional 100 million sterile screwworm flies. The renovation is expected to be completed by the end of June, with additional flies coming online. The facility is expected to produce 100 million flies by the end of the year, according to USDA officials.

An estimated 500 million sterile flies would need to be released weekly to push the screwworm back to the Darién Gap, a stretch of jungle between Panama and Colombia that was once a natural barrier, according to the USDA.

At the June 8 news conference, Rollins and Abbott said the goal is to speed up production of sterile flies.

On June 5, the USDA activated the sterile fly dispersal facility at Moore Air Force Base in Texas, an $8.5 million project completed earlier this year.

Aerial dispersal flights originating from the base will begin on June 9, according to the USDA.

A second facility under construction at the airbase will produce sterile flies.

Rear Adm. Michael Schmoyer, a member of the USDA’s screwworm response team, said the second facility is expected to be finished in November 2027, producing 100 million flies per week. In 2028, the plant is expected to produce an additional 200 million sterile flies, bringing the total to 300 million.

Scott Hutchins, who serves as undersecretary for the research, education, and economics mission area of the USDA, announced the development of the Novo fly, a new type of sterile fly.

​“It’s going to allow us to almost instantaneously double the number of flies, sterile flies … we put in the fight, because it allows us to produce only male sterile flies,” he said.

Officials stressed that the infections are highly treatable if caught early and that the parasite does not affect food safety.

“The food supply system remains intact and couldn’t be safer,” Rollins said.