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Screwworm Returns, Threatening U.S. Livestock and Human Health

  //health-fitness.news-articles.net/content/2026/ .. -threatening-u-s-livestock-and-human-health.html
  Published in Health and Fitness on Saturday, January 31st 2026 at 13:25 GMT by The Hill
      Locales: UNITED STATES, MEXICO

Saturday, January 31st, 2026 - A once-eradicated parasitic pest, the New World screwworm ( Cochliomyia hominivorax ), is making a concerning comeback, and officials are bracing for potential impacts within the United States. After decades of being absent from the U.S., the screwworm is experiencing a resurgence in Mexico, bringing the threat dangerously close to the border and sparking increased monitoring and preventative efforts.

What is the Screwworm? The New World screwworm is a parasitic fly whose larvae infest warm-blooded animals, including livestock (cattle, sheep, goats, horses) and, critically, humans. The female fly lays its eggs in open wounds or natural body openings on a live host. Upon hatching, the larvae burrow into the flesh and feed on living tissue, creating painful, debilitating, and potentially fatal wounds. The resulting myiasis, or maggot infestation, can lead to severe secondary infections, reduced animal productivity, and significant economic losses for ranchers and farmers.

A History of Eradication and Current Resurgence The United States and Mexico jointly eradicated the screwworm from the U.S. in the 1960s, a monumental achievement credited to the innovative Sterile Insect Technique (SIT). This program involved the mass rearing and release of sterile male screwworms, effectively suppressing the population by preventing viable reproduction. For decades, the SIT program was highly successful, keeping the pest at bay.

However, the program in Mexico faced setbacks in recent years. Experts link the resurgence to a decline in the consistent application of insecticides on cattle populations, which had been a complementary component of the SIT program. This disruption allowed the screwworm population to rebound, and despite ongoing efforts, the pest is spreading northward. Jerome Goddard, a USDA entomologist, emphasizes the seriousness of the situation, stating, "The situation is concerning."

States at Risk A multi-state task force is currently monitoring for screwworm activity, particularly along the southern border. States considered to be at the highest risk include Texas, New Mexico, Arizona, California, Florida, Georgia, Alabama, Mississippi, Louisiana, and Oklahoma. These states possess large livestock populations and geographical proximity to Mexico, increasing the likelihood of screwworm introduction. David Cain, an entomologist with Texas A&M AgriLife Extension, acknowledges the precarious situation, saying, "We've been lucky to be able to keep it out of the U.S. so far."

Impacts on Livestock and Human Health The economic consequences of a screwworm outbreak in the U.S. could be substantial. Infested animals experience significant weight loss, reduced milk production, and increased susceptibility to other diseases. Treatment is costly and labor-intensive, requiring veterinary intervention to remove the larvae and manage secondary infections. Severe infestations can even lead to animal death.

Perhaps even more concerning is the potential for human infestation. While relatively rare, screwworms can and do infest humans, particularly those with limited access to healthcare or who work closely with livestock. The larvae can cause excruciating pain, tissue damage, and potentially life-threatening complications. Unlike animal infestations where preventative measures and veterinary care are typically available, human infestations require immediate medical attention and often surgical intervention.

Current Preventative Measures & Emergency Orders The USDA is taking proactive steps to address the threat. An emergency animal disease traceability order has been issued, aimed at improving the tracking of livestock movements. This allows officials to quickly identify and contain potential outbreaks by tracing the source of infected animals. State agencies are actively inspecting livestock at markets and ranches, and educational programs are underway to inform producers about the screwworm, its signs, and preventative measures. These measures include diligent wound care, proper sanitation, and the use of approved insecticides.

Furthermore, the USDA and its partners are working to bolster the SIT program in Mexico, but consistent funding and effective implementation remain crucial. Researchers are also exploring alternative control methods, including biological control agents and improved diagnostic tools.

The situation underscores the importance of international collaboration in animal health and disease prevention. The screwworm's resurgence serves as a stark reminder that eradicated pests can return, and ongoing vigilance is vital to protect both animal and human populations.