A dog in Brewster County, Texas, has been confirmed with New World screwworm, a parasitic fly whose larvae feed on the living flesh of warm-blooded animals. The case, confirmed Oct. 2, raised the national total to 53 animal cases since June, including 51 in Texas and two in New Mexico, according to a Texas Public Radio tracker built on U.S. Department of Agriculture data.

The dog is one of three active cases. The others are goats in Crockett County, Texas, confirmed Sept. 26, and a horse in Grant County, New Mexico, confirmed Sept. 17. Officials also recorded the outbreak's first wild screwworm fly in a Brewster County surveillance trap on Sept. 25.

The detection matters beyond ranching — Brewster County is home to Big Bend National Park and draws hunters, campers, and visitors with dogs, and pet owners anywhere in the affected region now face a practical question: how to spot an infested wound early.

A Slowing Outbreak That Has Not Ended

The pace of new cases has eased. More than a dozen cases were confirmed in July, but only four were recorded in August and three in September, according to a Texas House Agriculture and Livestock Committee hearing summarized by The Texan. Federal officials have said the parasite's northward spread has slowed.

The pressure from the south has not eased. USDA counted 45,216 screwworm cases in Mexico through Sept. 30, according to the same hearing summary. Agriculture Secretary Brooke Rollins has said progress is being made but has warned the threat has not passed, particularly for Arizona and New Mexico.

Fifty-two of the 53 U.S. cases involved domestic animals, and none has been confirmed in wildlife or feral animals. That is significant for Texas, where large white-tailed deer populations could help the parasite persist if it reached them.

The Biology Behind the Flesh-Eating Larvae

Despite its name, the screwworm is not a worm. It is the larval stage of the fly Cochliomyia hominivorax. A female fly lays eggs in an open wound or natural body opening, and within hours the larvae hatch and burrow into living tissue. Ordinary maggots eat dead tissue; screwworm larvae eat healthy flesh, which is why untreated infestations can kill an animal.

The United States eradicated the pest decades ago using the sterile insect technique. Scientists breed and release sterile male flies, and because females typically mate only once, mating with a sterile male produces no offspring. Repeated releases collapse the wild population. USDA says it has released more than 1 billion sterile flies in Texas since February and aims to increase production to 500 million flies a week by next summer.

The approach worked before, but it depends on producing enough sterile flies to outnumber wild ones across a very large area — which is why USDA is racing to expand output.

Warning Signs for Dogs, Livestock and Harvested Game

The animals at highest risk are those with fresh wounds: dogs with scratches or bites, livestock after branding, castration or ear tagging, newborn animals with unhealed navels, and any animal recovering from surgery. Veterinarians advise checking injuries daily rather than waiting for them to heal on their own.

Warning signs include a wound that grows larger instead of healing, bloody or foul-smelling drainage, swelling around an injury, visible larvae moving inside a wound, and restlessness or signs of pain. A dog that keeps licking or scratching one spot, or that suddenly avoids being touched, deserves a closer look.

If you see larvae in a wound, call your veterinarian immediately and do not move the animal until you have spoken with them. Moving an infested animal can carry the parasite to new areas. Suspected livestock cases should be reported to the Texas Animal Health Commission. Hunters should inspect harvested deer and other game for unusual wounds and report anything suspicious to wildlife officials.

For people, the Centers for Disease Control and Prevention said when it activated its emergency response in June that there were no reported human cases in the United States and that "the risk to the public remains low." The agency added in its emergency response statement that "the risk of getting NWS is specific to people and animals in areas where NWS flies are circulating." People with open wounds who spend time around livestock in affected areas should keep wounds clean and covered. According to USDA, screwworm is not a food safety threat, because the larvae feed on living tissue in wounds, not on meat entering the food supply.

Costs for Ranchers and Trade Questions Ahead

Texas has one of the largest livestock industries in the country, and a reestablished screwworm population would raise costs for every producer through added inspections, wound treatments and veterinary bills. Small operations and rural pet owners far from a veterinary clinic face the steepest practical barriers, since early treatment is the most effective defense.

Trade is another pressure point. After the first U.S. detections in June, Mexico prohibited most animals from traveling into the country from any U.S. state, the American Veterinary Medical Association reported. Further trade decisions will depend on whether officials can show the outbreak is contained.

Several questions remain open. Officials have not said how the Brewster County dog was exposed, and a single wild fly detection does not show how many flies are present. It is also too early to know whether cooler fall weather will slow fly activity enough to end transmission this year.

Next Steps From USDA and State Officials

USDA updates its current status dashboard as cases are confirmed or move to inactive status, and the Texas Animal Health Commission publishes zone maps showing where movement inspections apply. Sterile fly releases will continue in affected counties.

Most Texans do not need to change daily routines. Pet owners, ranchers and hunters in West and South Texas should inspect wounds, act quickly when something looks wrong, and rely on state animal health officials rather than social-media posts for case information. Nature World News will update this story as new detections are confirmed.

What Readers Want to Know

What is New World screwworm?

It is the larva of a parasitic fly that lays eggs in open wounds. The larvae feed on the living tissue of warm-blooded animals, including cattle, sheep, goats, horses, deer and dogs.

How many screwworm cases are active in the United States?

As of Oct. 4, three animal cases were active: a dog in Brewster County, goats in Crockett County, and a horse in Grant County, New Mexico. There have been 53 cases since June.

What signs should pet owners look for?

Watch for wounds that worsen instead of healing, foul-smelling or bloody drainage, swelling, visible larvae, and signs of pain or restlessness. Contact a veterinarian right away.

Can people get screwworm?

Human infestations are rare. CDC has said the risk to the public remains low and is specific to areas where the flies are circulating.

Is it safe to eat beef?

Yes. USDA says screwworm is not a food safety threat because the larvae feed on living tissue in wounds, not on meat sold to consumers.

How are officials fighting the outbreak?

USDA is releasing sterile male flies, which prevent wild females from producing offspring. More than 1 billion have been released in Texas since February.