The number of New World screwworm cases has been rising recently in southwest Texas and New Mexico.

According to the U.S. Department of Agriculture, as of Wednesday, there have been 127 cases total this year with 64 still active in 11 Texas counties, eight New Mexico counties and three Arizona counties. So far, there have been no cases in Oklahoma, but experts at Oklahoma State University are staying on high alert about the issue.

“A couple of interesting things that have happened recently are a domestic cat becoming infested and a chicken, so we are keeping an eye on any animal species that has the potential to be a host,” said Dr. Jonathan Cammack, OSU Extension specialist for livestock entomology and parasitology.

The New World screwworm, native to North, Central and South America, is a fly species that lays eggs along bacterial-infected wounds of livestock and other warm-blooded animals. The eggs hatch, and the larvae feed on the animal’s tissue.

“We typically associate this parasite with livestock because that’s where we see the biggest economic losses, but the screwworm can impact a wide variety of animal species,” Cammack said. “In its scientific name, Cochliomyia hominivorax, hominivorax translates from Latin to English as ‘man-eater,’ so humans can be impacted by this.”

In the past three years, roughly 3,000 of the cases that occurred between Central America and Mexico were in humans.

“It’s really a warm-blooded animal issue, so you’ll mostly see it in mammals,” Cammack said. “This is not a new pest; we’ve dealt with it previously. The last time it was in Oklahoma was in 1976, and it was a problem with livestock production and wildlife.”

Since the fly species likes warm weather, there tend to be seasonal fluctuations with cases.

“Since we are moving into a cooler time of year, natural infestations are not currently something we need to be too concerned about, but something we do need to be concerned about is what’s going to happen in the spring as those temperatures warm back up, and we start to have our spring calving herds,” Cammack said.

Here’s what people can do to prevent NWS in Oklahoma:

• Monitor animals frequently. Keep an eye out for anything that looks out of place with wildlife or domesticated animals
• For livestock in particular, when cattle producers come into the spring calving season, some calves are born later than expected, and those are the animals to watch out for, because when a calf is born, it has an open wound on its navel that is going to take a few days to heal.
• For landowners and hunters, watch for signs that something isn’t right with wildlife, such as a wound that isn’t healing, and reach out to the Oklahoma Department of Wildlife Conservation to report it.
• If you find a case of screwworm in a pet, livestock or wildlife, contact your veterinarian, local county Extension office or the Oklahoma Department of Wildlife Conservation.

“In the meantime, cattle producers can keep an eye out for anything in a pasture that might wound an animal,” Cammack said. “If you’ve got some rusty old equipment that the cattle tend to be near that could scratch or gouge them, get it out of your field.”

For more information or continuous updates on New World screwworm cases, visit screwworm.okstate.edu.

New World screwworm timeline:

• November 2024 – NWS detected in Mexico and USDA suspends cattle and bison imports from Mexico.
• February 2025 – Imports temporarily resume
• May 2025 – Imports suspended again
• June 2025 – USDA announces a five-pronged NWS strategy, including construction of an $8.5 million sterile-fly dispersal facility in South Texas.
• June 2025 – Texas creates the Texas New World Screwworm Response Team to coordinate preparedness, prevention and response.
• August 2025 – USDA announces a $750 million investment in a domestic sterile-screwworm production facility in Edinburg, designed to eventually produce up to 300 million sterile flies per week.
• September 2025 – NWS gets closer to Texas
• January 2026 – USDA shifts its sterile-fly deployment strategy, putting more aircraft and sterile insects along the U.S.-Mexico border and extending dispersal operations 50 miles into Texas.
• February 2026 – Texas sterile-fly dispersal facility opens at Moore Air Base in Edinburg.
• May 2026 – APHIS Strike Team is deployed and surveillance is increased
• June 2026 – The Texas outbreak begins, spreading rapidly across south and west Texas.

How sterile flies stop New World screwworm

The technique is called the Sterile Insect Technique (SIT), and the USDA has used it against the New World screwworm for decades. It helped eradicate the pest from the United States beginning in the 1950s. Here’s the basic idea:

• Scientists produce huge numbers of screwworm flies that are raised in specialized facilities where they are allowed to develop through their normal life cycle until the pupal stage.
• The pupae are exposed to gamma radiation, which makes the adult flies sterile, but this does not prevent the males from finding and mating with females.
• The sterile male flies are released in large numbers into the environment in areas where wild screwworm populations exist or where officials want to create a barrier against their spread.
• The sterile males compete with wild males. A wild female screwworm typically mates only once in her lifetime, so if she encounters a sterile male and mates with him, she won’t mate with another male later.
• The female fly lays eggs that don’t hatch, so no new adult flies emerge.
• The fly population starts collapsing.

Frequently Asked Questions