A devastating outbreak of the flesh-eating New World screwworm (Cochliomyia hominivorax) has killed seven people and infected over 1,190 others across Mexico and South America. The parasite is now aggressively moving northward, prompting the US Centers for Disease Control and Prevention (CDC) to issue an urgent health advisory to doctors, veterinarians, and the public.
With 601 active animal cases currently reported in Mexico—including eight in the border state of Tamaulipas—the “devastating pest” is now just 70 miles from the United States.
What is the New World Screwworm?
The New World screwworm is the larval stage of a specific fly that lives in and feeds on the living flesh of warm-blooded animals. Unlike most maggots that consume dead tissue, these larvae burrow into wounds and mucous membranes, effectively eating their hosts alive.
While cattle, horses, and pigs are the most frequent victims, the parasite also targets dogs, cats, and humans. Furthermore, if left untreated, an infestation can be fatal; the larvae are capable of killing a fully grown cow in as little as one week.
A $1.8 Billion Threat to Texas
The proximity of the outbreak to Texas is causing significant alarm within the US Department of Agriculture (USDA). Texas is the largest cattle-producing state in the country, and a widespread outbreak could cost the industry roughly $1.8 billion.
This economic anxiety is rooted in history. Before the 1960s, cattle farmers in Texas were forced to treat approximately 1 million cases of screwworm every year. While the US successfully eradicated the pest in 1966 and again in 2017, the current northward surge threatens to undo decades of progress.
Why Is the Outbreak Spreading Now?
For years, a biological “wall” in Panama—created by the continuous release of sterile male flies—kept the parasite at bay. However, the worm breached this barrier in 2023. Several factors have contributed to its rapid spread:
- Unregulated Movement: The CDC points to unregulated cattle movement and increased human and animal traffic through the Darien Gap.
- New Farming Areas: The expansion of agriculture into previously wild areas has provided new hosts for the flies.
- Climate Change: Scientists warn that rising global temperatures are expanding the geographic range of the flies and lengthening their peak “boom” periods.
The Fight to Stop the Fly
To control the population, scientists use the “sterile insect technique”. Because female screwworm flies typically mate only once in their 21-day lifespan, researchers release billions of males sterilized by gamma radiation. When these sterile males mate with wild females, the resulting eggs do not hatch, eventually causing the local population to collapse.
Additionally, chemical treatments for livestock and favourable weather conditions have historically helped maintain eradication zones.
Q&A: The Flesh-Eating Screwworm Outbreak
Q: Have there been any cases reported in the US yet? A: No infestations related to this specific outbreak have been reported in the US so far. The CDC alert is a proactive measure to ensure health workers can identify the parasite immediately if it crosses the border.
Q: Can humans really be infected? A: Yes. While less common than animal cases, the larvae can inhabit human wounds or mucous membranes. This current outbreak has already resulted in seven human fatalities across Mexico and South America.
Q: Why is the state of Tamaulipas significant? A: Tamaulipas borders Texas. In September 2025, an infected 8-month-old cow was confirmed just 70 miles from the US border, making the threat more immediate than ever.
FAQ: Frequently Asked Questions
What should I look for in an infection? Look for a wound that does not heal, becomes enlarged, or appears to have movement within the tissue. The larvae feed on the edges and deep inside the wound.
How was the screwworm eradicated before? The US used the sterile insect technique. They released billions of lab-reared sterile flies from planes. This stopped the reproductive cycle of wild populations.
Why is it called a “screwworm”? The name originates from the larvae’s burrowing method. They use their screw-like bodies to move deeper into the host.
What does the CDC recommend for clinicians? The CDC health advisory provides guidance on case identification, specimen collection, and treatment protocols for both human and animal patients.
Is there a risk to my pets? Yes. Dogs and cats are susceptible. Owners should check pets for open wounds and keep them clean, especially in areas where the fly is active.
