Screwworm Outbreak Sparks Regional Health Emergency Across Latin America

A deadly livestock parasite once thought to be under control is wreaking havoc across Central America and Mexico, sending shockwaves through the livestock industry and public health systems. The outbreak of the cattle screwworm, Cochliomyia hominivorax, has reached alarming levels in Panama—the heart of sterile fly production—while the United States has just confirmed its first human case in more than 50 years, linked to a traveler returning from Central America.

Since its resurgence in Panama in 2023, the plague has spread relentlessly across the region, threatening cattle herds, wildlife, and humans alike. Panama’s latest epidemiological bulletin recorded nearly 50,000 confirmed cases this year alone, 85% of them in cattle, but also hundreds in humans and dozens across wild and domestic animals—from deer and mules to sloths and even leopards. With outbreaks now confirmed as far north as Mexico’s Veracruz, less than 600 kilometers from the U.S. border, alarm bells are ringing in Washington.

Health officials warn that the screwworm’s spread is being fueled by rapid livestock expansion, unchecked animal movements, and poor animal care practices. Warm and humid conditions in the region provide the perfect breeding ground for the parasite, which thrives on untreated wounds and multiplies with frightening speed. The result is a crisis that threatens not only the livestock industry but also regional food security and public health.

Panama and the United States had once celebrated the eradication of this pest in 2006, after nearly two decades of work and heavy investment. For years, a biological barrier maintained in Darién successfully kept the screwworm at bay. But today, that barrier has collapsed, leaving the region scrambling to scale up sterile fly production and surveillance efforts. COPEG, the Panama-U.S. Commission overseeing eradication, has boosted sterile pupae production from 20 million to more than 100 million per week, but experts say five times that amount is needed to keep the outbreak under control.

Mexico, recognizing the growing threat, has launched construction of a $51 million sterile fly plant with U.S. backing to reinforce containment efforts before the parasite crosses into American soil. Meanwhile, local producers are urged to adopt better husbandry practices and treat livestock wounds promptly to curb infestations.

Experts say the battle against the screwworm is at a “turning point.” Without urgent action and stronger international cooperation, the plague could trigger devastating economic losses, undermine decades of progress, and put millions of people and animals at risk across the Americas.