Warning for El Paso pet owners as New World screwworm detected nearby

EL PASO, Texas (KVIA) — Despite its name, the New World screwworm isn't actually a worm, it’s a flesh-eating fly larva, and health officials are advising Borderland residents to stay vigilant for their pets.

While no cases of the New World screwworm have been reported in El Paso, Dr. Tony Chacon, a veterinarian with El Paso Animal Services, told ABC-7 that the parasite has recently been detected nearby. Officials confirmed one solitary case in Juárez in mid-August, along with cases further east in Texas.

Dr. Chacon noted that while the name includes the word "new," the parasite is not a novel threat to the United States.

"The United States has seen this in the past," Dr. Chacon said. "It's reemerging."

How NWS spreads

Unlike most flies and maggots that feed strictly on dead tissue, the New World screwworm feeds on live tissue. The fly typically targets preexisting wounds or body openings. It uses mouth hooks to "screw" into the wounds.

"Usually it happens in a preexisting wound we could be looking at eyes, ears, or mouth where it can lay its eggs," Dr. Chacon explained. "The eggs hatch into larvae quickly, usually within 24 to 48 hours. They feed for four to seven days before falling off the animal to pupate in the ground. Then the whole life cycle starts over."

The parasite can infect any warm-blooded mammal, including cattle, sheep, wildlife, pets, birds, and in very rare instances—humans. Dr. Chacon clarified that pet owners cannot directly catch the parasite from their pets, but a human could be affected if a fly lays eggs directly on an open wound.

"The eggs hatch pretty quickly. I think it's within 24 to 48 hours. And then the larva feeds for about four to seven days or so. And then it pupates into the ground. And if the right conditions are present, it then hatches into a fly." Said Dr. Chacon.

Left untreated, the larvae can cause extensive tissue damage and infection, which can lead to septic shock and death. However, Dr. Chacon assured ABC-7 that the condition is highly treatable if caught early.

Symptoms, prevention and treatment

Because screwworm flies look almost identical to common houseflies to the untrained eye, pet owners and livestock handlers must monitor their animals closely rather than trying to spot the insect itself.

Key warning signs to watch for include:

• Foul-smelling or discharging wounds
• Unexplained lethargy or depression in your animal
• Loss of appetite
• Visible maggots inside an active wound

If you suspect an infection, seek immediate veterinary care. Veterinarians can manually remove the larvae and administer emergency-authorized preventive drugs approved by the USDA. Collected maggots are then sent to the Texas Animal Health Commission for formal testing.

Eradication and local preparation

To halt the spread on a broader scale, state and federal governments are utilizing sterile insect technique programs.

"They release a bunch of sterilized male flies," Dr. Chacon said. "Female flies only mate once in their lifetime. If they mate with a sterilized male, they won't produce offspring, which breaks the life cycle."

While government agencies manage regional containment, El Paso Animal Services says local teams are fully prepared for potential cases.

"Right now, it's still a couple of counties to the east of us, and we haven't seen any here so far," Dr. Chacon said. "As long as you stay up to date on preventatives, stay vigilant, and have a vet check out any open wounds immediately, your animals will stay protected."