Screw-worm fly (Cochliomyia hominivorax) that has been coloured with fluorescent powder at a breeding program used to study and help control this parasitic insect. (Science Photo Library | Reuters)

The U.S. Department of Agriculture has confirmed 32 New World screwworm infestations, including 31 in Texas and one in New Mexico, as federal and state officials continue working to contain the flesh-eating parasite.

The newest confirmed Texas case was found in a sheep in Crockett County on July 3.

This tracker is updated as new infestations are confirmed. It also answers common questions about how infestations begin, which animals are at risk and what Texans should know.

Despite its name, the New World screwworm isn’t a worm. It is the larval stage of the fly (Cochliomyia hominivorax), a parasite that feeds on the living tissue of warm-blooded animals.

Infestations begin when an adult female screwworm fly lays eggs in an open wound or natural body opening. Within hours, the eggs hatch and the larvae begin feeding on living tissue, unlike common maggots, which feed on dead or decaying tissue.

As the larvae burrow deeper into tissue, wounds become larger and often infected. Without treatment, infestations can be fatal.

Which animals are at risk?

The screwworm primarily threatens livestock and wildlife, making it a major concern for Texas ranchers and animal health officials.

Animals at risk include:

• Cattle
• Horses
• Sheep and goats
• Pigs
• Deer and other wildlife
• Dogs and, less commonly, cats

Can people get New World screwworm?

Human infestations are rare. Most occur when untreated wounds are exposed in areas where the fly is circulating. The current outbreak primarily affects livestock, wildlife and pets.

Is it safe to eat beef and other meat?

According to the U.S. Department of Agriculture, New World screwworm is not considered a food safety threat. The parasite feeds on living tissue in open wounds — not meat intended for consumers — and animal health and inspection systems are designed to keep infested animals out of the food supply.

Symptoms to watch for

Early detection is critical. Animals infected with screwworm may show:

• Wounds that continue to worsen instead of heal
• Bloody, thick or foul-smelling drainage
• Swelling around an injury
• Visible larvae moving inside a wound
• Signs of pain, restlessness or unusual behavior

Veterinarians recommend inspecting animals regularly after injuries, surgical procedures, branding or any condition that creates an open wound.

Why it matters in Texas

Texas has one of the largest livestock industries in the United States, along with extensive ranchland and abundant wildlife populations, particularly white-tailed deer. That combination makes the state especially vulnerable if screwworm becomes reestablished.

A widespread outbreak could lead to:

• Rapid spread through livestock and wildlife
• Increased veterinary and inspection costs
• Economic losses for ranchers and producers
• Potential impacts on livestock trade
• Threats to wildlife, particularly white-tailed deer
• Greater demand on veterinary and animal health services

The Texas Animal Health Commission and the U.S. Department of Agriculture have expanded surveillance, increased monitoring of animal movement and encouraged rapid reporting of suspected infestations.

A screwworm fly stands on a leaf at a bio-factory as Mexico’s government reconditioned a plant to become the new sterile screwworm fly facility, part of the country’s effort to eradicate the flesh-eating parasite that threatens its livestock industry. (Daniel Becerril | REUTERS) How was it eradicated — and could it come back?

The United States eliminated screwworm using one of the most successful pest control programs in history: the sterile insect technique.

Scientists bred and released millions of sterile male flies. Because female screwworm flies typically mate only once, breeding with a sterile male produces no offspring, gradually collapsing the wild population.

That strategy eradicated screwworm from the United States and much of North America. However, the parasite remains present in parts of Central and South America, meaning the risk of reintroduction never fully disappears.

What should Texans do?

For most Texans, there is no reason to change their daily activities. The greatest risk remains to livestock, pets and wildlife.

Animal owners should:

• Inspect wounds on pets and livestock regularly.
• Contact a veterinarian immediately if a wound worsens or contains larvae.
• Avoid transporting animals with suspicious wounds until they have been examined.
• Report suspected infestations to state animal health officials.

Hunters should also inspect harvested game for unusual wounds or signs of infestation and report suspected cases to wildlife officials.

If you suspect an infestation, contact your veterinarian immediately before transporting the animal.

Where to learn more

For the latest information and guidance, visit:

• Texas Animal Health Commission: New World Screwworm resources
• USDA Screwworm.gov
• USDA Current Status dashboard and confirmed detections
• Your local veterinarian
• Your county extension office

Help us report on screwworm

Have you seen a suspicious wound on livestock, wildlife or a pet? Do you have a question about New World screwworm?

Email the TPR newsroom at letters@tpr.org. Your questions, observations and experiences may help guide future reporting.