A deadly screwworm threat has emerged just 70 miles from the United States border, prompting federal agencies to issue urgent warnings to pet owners and livestock producers across the southern states. The New World screwworm, a flesh-eating parasite that was eradicated from North America decades ago, has been confirmed in Sabinas Hidalgo, Nuevo León, Mexico, marking the closest the dangerous pest has come to American soil during the current outbreak.
The US Department of Agriculture announced that Mexico’s National Service of Agro-Alimentary Health, Safety, and Quality detected the parasite on September 21 in the Mexican city, which sits along a major highway from Monterrey to Laredo, Texas. This represents the northernmost detection of the pest, with more than 15,000 trucks crossing through the World Trade Bridge daily in this busy trade corridor.
What Makes This Parasite So Dangerous
New World screwworm is particularly aggressive because its larvae don’t wait for dead tissue—they actively create it. A single female fly can lay up to 500 eggs in wounds or natural body openings. Within 12 to 24 hours, larvae hatch and burrow into living tissue, causing severe tissue death. Without treatment, infected animals typically die within one to two weeks from secondary bacterial infections.
The economic implications are staggering. A 2024 USDA report estimates that an outbreak affecting 7.2 million Texas cattle alone could cause $732 million in producer losses and $1.8 billion in total economic damage to the Texas economy. The potential disruption mirrors the fallout from a single US case of mad cow disease in 2003, which temporarily shut down global beef trade.
Emergency Response Measures Activated
In response to the growing threat, the US Department of Health and Human Services issued a declaration on August 19, empowering the FDA to grant emergency use authorizations for animal drugs to treat or prevent screwworm infestations. Currently, no FDA-approved drugs exist specifically for New World screwworm treatment in the United States.
The USDA has implemented a comprehensive five-pronged defense strategy, including investing in new eradication technologies, building sterile fly production and dispersal facilities in Texas, increasing surveillance efforts, launching public awareness campaigns, and coordinating with Mexico and international partners to contain the parasite’s spread.
Critical Warning Signs for Pet Owners
Veterinarians are serving as the frontline early-warning system for detecting potential cases. Pet owners, particularly those in border regions, should watch for several key symptoms: foul-smelling wounds, visible maggots in wounds or body openings, depressed behavior, self-isolation, and umbilical infections in newborn animals. Even minor injuries like tick bites, ear tag wounds, or small abrasions can serve as entry points for the parasites.
The USDA urges all residents along the southern border to regularly inspect their pets and livestock for signs of infestation. Look specifically for draining or enlarging wounds, signs of discomfort, and screwworm larvae in or around body openings such as the nose, ears, genitalia, or naval area of newborn animals.
Because other fly species can co-infest wounds, veterinarians warn against attempting field identification. Instead, any suspected cases should be preserved in alcohol and reported immediately to state or federal animal health officials for proper laboratory confirmation and rapid response measures.