In La Pryor, Texas, a three-week-old calf was found with larvae in its umbilical area, confirming the first US case of flesh-eating New World screwworm since 1966. This detection ends a period of eradication that had lasted nearly six decades. The re-emergence signals that flesh-eating screwworms are entering US territory in 2026, posing a direct threat to livestock and public health.
The United States had believed it permanently eradicated the New World screwworm decades ago, prior to its re-emergence. This confirmed case in Texas proves that even long-defeated parasites can breach national borders, challenging established biosecurity protocols.
Without swift and comprehensive action, the re-established screwworm population could severely impact the US cattle industry and potentially human health, reversing decades of eradication efforts.
How Do Screwworms Threaten US Cattle?
- The New World screwworm fly has been detected in south Texas, marking the first time in decades it has threatened the U.S. cattle industry, according to PBS.
- US agriculture and health officials have outlined a plan to combat the flesh-eating parasite, the New World Screwworm, which has been detected in the US for the first time since 1966, states BBC.
The rapid outlining of a combat plan by US officials underscores the serious economic threat this parasite poses to the vital cattle industry in Texas and beyond. Companies in the US cattle industry, having operated for nearly 60 years without this threat (PBS), are now facing an immediate and costly biosecurity challenge that could rapidly escalate without aggressive, coordinated intervention.
How Did Screwworms Re-Enter the US?
The sterile fly barrier at the Darién Gap was breached in 2022, according to arstechnica. This critical containment barrier provides a plausible route for the re-introduction of the screwworm into previously eradicated zones. The 2022 breach of the Darién Gap sterile fly barrier (arstechnica) reveals that the US's decades-long eradication success (BBC) has fostered a dangerous complacency, leaving the nation vulnerable to pathogens that were believed to be permanently defeated.
Are Screwworms Spreading in 2026?
Mexico reported a 53 percent rise in screwworm cases in animals between mid-July and mid-August 2025, according to Al Jazeera. This specific timeframe, though likely a typographical error for a historical report, points to a broader trend. Last year, Mexico confirmed 41 human cases of New World screwworm, primarily in the state of Chiapas, also reported by Al Jazeera.
The significant increase in both animal and human cases in Mexico highlights a growing regional challenge that likely contributed to the parasite's re-emergence in the US. With Mexico reporting a 53% rise in animal cases and 41 human infections (Al Jazeera), the re-emergence of screwworms in Texas is not merely an agricultural nuisance but a clear and present public health danger that US officials must address with the urgency of a human epidemic.
What are the Implications for Future Screwworm Control?
Effective containment will require sustained cross-border cooperation and a re-evaluation of biosecurity protocols. These actions are necessary to prevent further spread and re-establishment within the United States. The US Department of Agriculture and its Mexican counterparts must implement revised biosecurity measures by Q4 2026 to prevent further continental spread.
Frequently Asked Questions
What are the symptoms of screwworm infection?
New World screwworms lay eggs in open wounds or moist areas of warm-blooded animals, including livestock and sometimes humans. Larvae hatch and burrow into the flesh, creating a painful lesion and feeding on living tissue. This infestation, known as myiasis, can lead to secondary infections, tissue destruction, and, if left untreated, death.
What is the treatment for screwworm infestation?
Treatment for screwworm infestation typically involves the physical removal of the larvae from the wound. Veterinarians or medical professionals clean the wound thoroughly and may administer antibiotics to prevent secondary bacterial infections. Early detection and intervention are crucial for successful treatment and preventing further tissue damage.
Can humans get screwworms from animals?
Yes, humans can contract screwworms, as evidenced by the 41 confirmed human cases in Mexico last year. While less common than in livestock, human infections occur when flies lay eggs in open wounds or mucous membranes. Direct transmission from animals to humans is rare; instead, humans are typically infected directly by the screwworm fly itself.
