What Is Screwworm Infection? The Disturbing Human Symptoms of Flesh-Eating Parasite Found in Texas

A case of the flesh-eating parasite known as New World screwworm has been confirmed in a calf in South Texas, prompting urgent containment measures from US authorities and renewed concern over a rare but dangerous infestation that can destroy living tissue.

The US Department of Agriculture (USDA) said the detection marks the first time the parasite has been found in US livestock in decades, triggering quarantines, surveillance zones and emergency response efforts.

While officials stress the risk to humans remains extremely low, experts warn that the parasite's ability to consume living flesh makes it a serious threat to animals and, in rare cases, people.

First US Livestock Case in Decades

The infestation was confirmed by the USDA's National Veterinary Services Laboratories after testing samples from a three-week-old calf in La Pryor, Texas. Authorities immediately activated field personnel, set up a 20-kilometre containment zone and introduced movement restrictions on livestock in the affected area.

The parasite has been identified as New World screwworm infection, which had previously been eradicated in the United States through large-scale sterile fly programmes. Officials say the reappearance is linked to a wider resurgence of cases in parts of Central and South America, which has raised concerns about cross-border spread.

How Screwworm Infection Attacks Living Tissue

Screwworm infection occurs when female flies lay eggs in open wounds or moist areas on warm-blooded animals. Once hatched, the larvae feed directly on living tissue rather than dead flesh, causing rapidly worsening wounds.

Unlike typical fly infestations, screwworm larvae burrow deeper into the skin, creating enlarging lesions that can quickly become infected. In livestock, this can lead to severe illness, secondary bacterial infections and, in extreme cases, death if untreated. The USDA has warned veterinary teams across Texas, Arizona and New Mexico to monitor animals closely for signs of infestation.

Human Symptoms of Screwworm Infection

Although rare, human cases of screwworm infection can occur when larvae enter open wounds. According to the Centers for Disease Control and Prevention (CDC), early symptoms may include intense pain, swelling, irritation and non-healing sores. As the infestation progresses, patients may experience worsening tissue damage, with larvae feeding deeper into the wound.

In severe cases, the infection can lead to extensive tissue destruction and secondary infections, including potentially life-threatening sepsis if not treated promptly. The CDC also notes that individuals most at risk include livestock handlers, agricultural workers and people with untreated or exposed wounds, particularly in rural or outdoor environments.

Despite these risks, US health officials have repeatedly stated that the current threat to the general public remains very low, and that the parasite does not spread directly from person to person.

Sterile Fly Strategy and Quarantine Zones

In response to the outbreak, the USDA has implemented a series of containment measures designed to prevent wider spread. These include quarantine enforcement, livestock movement controls and enhanced surveillance in high-risk zones.

Authorities are also expanding the use of sterile insect technique, a biological control method involving the release of sterilised male flies to reduce reproduction rates in wild populations. When sterile males mate with females, no offspring are produced, gradually collapsing the local population.

The agency has also increased border monitoring efforts and deployed detection dogs along the US-Mexico border to identify potential infected animals. Emergency veterinary supplies have been prepared for rapid deployment to affected areas.

Economic Risk to US Livestock Industry

Officials warn that a widespread outbreak could have significant consequences for US agriculture, particularly the beef and cattle industry. The parasite has historically been associated with large-scale livestock losses, and experts say any sustained spread could increase production costs and contribute to higher beef prices.

During past outbreaks in the region, eradication efforts required extensive coordination and long-term investment in biological control programmes. Authorities say rapid containment is now critical to preventing a repeat of earlier large-scale infestations that once affected tens of thousands of animals across the southern United States.