(VIDEO) Flesh-Eating New World Screwworm Threatens Pets This Summer: Safety Tips

Federal and state officials are urging pet owners and livestock producers across the southern United States to remain vigilant this summer as the New World screwworm, a parasitic fly whose larvae feed on the living tissue of warm-blooded animals, continues to spread following its first confirmed U.S. detection in nearly 60 years.

The parasite, commonly abbreviated NWS, resurfaced domestically on June 3, when the U.S. Department of Agriculture's Animal and Plant Health Inspection Service confirmed a case in a three-week-old calf in Zavala County, Texas, located roughly 50 miles from the Mexico border. Since then, the outbreak has expanded significantly. According to the Centers for Disease Control and Prevention, USDA has confirmed 16 domestically acquired animal cases, spread across multiple Texas counties and Lea County, New Mexico, involving cattle, goats and at least one dog, the first confirmed case in a companion animal since the parasite's reappearance.

New World screwworm infestations begin when a female fly lays eggs on an open wound or body opening, where the eggs hatch into larvae that burrow into the wound and feed on living tissue, according to USDA. The pest affects livestock, pets, wildlife and, less commonly, birds and people, though officials have emphasized that NWS is not contagious and does not spread directly between animals or from animals to humans. Instead, infestations occur individually, when a fly lays eggs on a susceptible wound, meaning even a small, untreated cut can put a pet or farm animal at risk.

According to the USDA, common warning signs of a potential infestation include wounds that appear to be enlarging or draining unusual discharge, visible signs of discomfort in an affected animal, and, in more advanced cases, the presence of larvae or eggs visible in or around body openings such as the nose, ears, genitalia, or the navel area of newborn animals. Officials have stressed that if caught early, NWS infestations are treatable by veterinarians and physicians, underscoring the importance of prompt detection and reporting.

The outbreak stems from the northward spread of screwworm populations that reemerged in Chiapas, Mexico, in November 2024 after having been effectively eradicated from Mexico and Central America for decades through a sustained sterile insect release program. Since that reemergence, every country in Central America and Mexico where NWS had previously been controlled has reported new cases in animals, including livestock, pets and wildlife, as well as in people, according to the CDC. One human case tied to the broader outbreak was confirmed in the United States in August 2025, involving a person who had traveled to El Salvador before returning home, though officials have said there have been no reports of locally acquired human infestations within the United States as the domestic animal outbreak has unfolded.

USDA Under Secretary for Marketing and Regulatory Programs Dudley Hoskins addressed the expanding outbreak in a statement, emphasizing the need for continued public vigilance. "We need the partnership of animal owners across the region. Please stay vigilant, check your animals closely, and report anything that looks suspicious," Hoskins said.

In response to the outbreak, USDA and Texas state officials have activated a unified incident command structure involving 75 personnel on the ground, supported by hundreds of additional staff providing laboratory, logistics and operational assistance nationwide. Under the agency's response protocols, each new confirmed detection triggers a 20-kilometer infested zone around the case, accompanied by quarantines, animal movement restrictions and heightened surveillance in the surrounding area. The Texas Animal Health Commission has established a broader quarantine zone spanning more than 20 counties across South and Central Texas, restricting the movement of animals out of the affected region without prior authorization.

Central to USDA's long-term eradication strategy is the release of sterile male screwworm flies, a technique that helped eliminate the pest from the United States in 1966 and that has been continuously maintained in Central America since to prevent its northward spread. USDA has activated a sterile fly dispersal facility at Moore Air Base in Edinburg, Texas, with aerial dispersal flights underway alongside ground release chambers deploying millions of sterile flies per week near detection zones. According to reporting on the outbreak, more than 129 million sterile flies have been released in the designated release zone since February 2026, though officials have acknowledged that current sterile fly production capacity remains a constraint relative to the scale of the expanding outbreak, with a projected timeline of 18 to 24 months to reach full eradication capacity.

For pet owners specifically, veterinary and public health experts, including those at the CDC and Texas A&M's College of Veterinary Medicine and Biomedical Sciences, have outlined a set of precautions to help reduce the risk of infestation heading into the warmer summer months. Recommendations include keeping any open wounds clean and properly covered, regardless of size or location on the body; sleeping indoors with windows closed or properly screened, or using a bed net or screened tent when camping outdoors; checking pets regularly for wounds or injuries; cleaning and treating any wounds promptly; and closely monitoring surgical incisions or other healing cuts for signs of infection. Officials have specifically warned against attempting to remove suspected screwworm larvae without professional assistance, advising that anyone who notices a foul odor, swelling or irritation around a wound seek medical or veterinary attention immediately rather than attempting self-treatment.

Officials have continued to emphasize that the U.S. food supply remains unaffected by the outbreak. According to USDA's Food Safety and Inspection Service, screwworms do not infest meat, fruits, vegetables or other food products, and any animal found to have an active infestation would be identified during routine food safety inspections, preventing any contaminated product from entering the commercial food supply.

With the outbreak continuing to expand across Texas and into New Mexico, and with health officials cautioning that confirmed cases likely represent only a fraction of actual infestations given how recently the parasite reappeared after nearly six decades of U.S. eradication, veterinarians and agricultural officials are urging both pet owners and livestock producers to maintain heightened awareness throughout the remainder of the summer, when warm weather and outdoor activity increase the likelihood of wounds going unnoticed or untreated. Anyone who suspects a screwworm infestation in a pet, farm animal or themselves is advised to contact a veterinarian, state animal health official or the USDA immediately, rather than attempting to manage the situation without professional guidance.