Flesh-eating screwworm returns to US after 60-year absence, spreads in Mexico

The confirmation of a New World screwworm infestation in Texas cattle has jolted North American agricultural authorities, marking the first appearance of the flesh-devouring parasite in United States livestock since its eradication in 1966. The U.S. Department of Agriculture detected the fly, *Cochliomyia hominivorax*, in two calves in Zavala County, a short distance north of the Mexican border. The discovery prompted a rapid emergency declaration by Governor Greg Abbott, who warned of an “imminent threat” likely to intensify through the summer months. For Washington, the outbreak revives a costly, decades-old battle thought to have been won.

Ottawa reacted swiftly, imposing a temporary ban on cattle and horses that have been in Texas within the preceding 21 days. The move by the Canadian Food Inspection Agency underscores the parasite’s economic firepower: Texas is the leading beef-producing state in the U.S., and any sustained trade disruption could ripple across integrated North American supply chains. Viewed from London, the incident echoes biosecurity flashpoints increasingly common as climate and land-use changes redraw the distribution maps of dangerous pests.

Yet the American outbreak is only the northern flank of a much wider problem. Mexico, which has long battled the screwworm in its southern regions, now reports more than 2,000 active cases, with Veracruz state bearing the heaviest burden. This contiguous presence along the U.S.-Mexico border raises the stakes for containment. Mexican health and agriculture authorities are intensifying surveillance and wound-inspection protocols, but the parasite’s ability to infest any warm-blooded animal — including humans — makes eradication immensely difficult once it gains a foothold.

The screwworm’s life cycle is a horror of biological efficiency: females deposit up to 300 eggs at the edge of an open wound; the emerging larvae burrow into live tissue, enlarging the wound and attracting more flies. Without treatment, secondary infections often prove fatal. This grisly reality led the U.S. to pioneer the sterile insect technique in the 1950s, releasing irradiated males that successfully drove the fly from the country and then steadily southward. Bioethicists have even debated whether humanity could morally countenance the species’ deliberate extinction — a discussion now revisited as the parasite re-emerges.

Looking ahead, analysts note that the summer heat will likely accelerate the fly’s reproductive cycle, complicating efforts to isolate and sterilise affected zones. The economic vulnerability is acute: the U.S. cattle herd, already at its smallest in decades, could shrink further if herd-health interventions falter. For Mexico, the persistence of the screwworm highlights structural gaps in veterinary surveillance. As global trade and warming temperatures redraw the map of livestock disease, the screwworm’s return is a stark reminder that pathogens do not respect borders — and that battles once declared won rarely stay settled.