Screwworm Returns After Mexico Shuts Key Fly Plant

Chiapas, Mexico — The resurgence of the cattle screwworm, a devastating pest eradicated decades ago in southeastern Mexico, has been attributed to the closure of a sterile fly production plant in Chiapas during the administration of President Andrés Manuel López Obrador (AMLO). The facility, operational until 2018, played a critical role in controlling the screwworm, which affects livestock, humans, and domestic animals.

A Decades-Long Eradication Effort Undone

For several decades, the sterile fly plant in Chiapa de Corzo ensured southeastern Mexico remained free of the screwworm (Cochliomyia hominivorax), a parasitic larvae that feeds on living tissue. However, upon AMLO’s election, the government of the "Fourth Transformation" (4T) repurposed the facility. Initially converted into a makeshift migrant station—known as El Cupapé II or La Mosca—it was later transformed into a National Guard barracks after human rights organizations protested the conditions there.

Livestock producers and experts, speaking anonymously, argue that the dismantling of the plant, coupled with lax border controls, allowed contaminated animals from Central and South America to reintroduce the pest. José Ismael de los Santos Morales, a rancher in Ocozocoautla de Espinosa, confirmed the screwworm’s return, citing infections in his cattle. "The government is very slow to act," he said. "Budget cuts to institutions like Senasica have worsened the problem."

Human and Animal Health at Risk

The Chiapas Ministry of Health reported 15 cases of screwworm myiasis in humans between April 25 and June 20, primarily in Tapachula. Meanwhile, Senasica confirmed 2,886 screwworm cases since November 2024, with over 2,500 contained as of July 7. Gabriel Ayala, Director of Animal Health Campaigns at Senasica, pledged differentiated controls for remaining cases.

Domestic animals are also affected. Franny Garibaldi, director of the MOC Animal Defense Office, warned that dogs and cats are increasingly vulnerable. "There’s a lack of awareness about this threat," she said, urging faster action from authorities.

Failed Promises and Budget Cuts

Despite government assurances, the sterile fly plant in Chiapa de Corzo remains inactive, its equipment removed. A new facility in Metapa de Domínguez, near the Guatemala border, is slated to open in 2026. Costing $51 million, it promises to produce 60–100 million sterile flies annually.

However, Jorge Esteve, president of the National Agricultural Council, criticized the 42.7% budget cut to Senasica, hampering pest control efforts. Meanwhile, Senasica has released 885 million sterile flies imported from Panama to combat the outbreak.

Border Weaknesses and Livestock Smuggling

Ranchers like José Ismael de los Santos blame insufficient border checks for illegal livestock trafficking, exacerbating the crisis. "Ear tags meant to track cattle are being sold illegally," he said, calling for stricter oversight.

Senasica has since strengthened measures, including Authorized Corrals for Animal Health (CAAMZIFS) in Chiapas municipalities like Benemérito de Las Américas and Palenque. These facilities, operated by the International Regional Organization for Agricultural Health (OIRSA), aim to curb smuggling and disease spread.

A Call for Vigilance

Bernardo Luna Coutiño, a rancher in Ocozocoautla, urged fellow producers to report infections promptly. "Misinformation harms us all," he said, noting that Governor Eduardo Ramírez and Sader Secretary Marcos Barba have provided medications to combat the worm.

As the screwworm continues to threaten livestock, pets, and humans, experts warn that restoring control will require significant resources and time—a challenge compounded by years of neglected infrastructure and funding cuts.