A Parasite’s Resurgence Sparks Alarm
A tiny fly with a devastating impact has put U.S. agriculture on high alert. The New World Screwworm, whose larvae burrow into living animals, has spread rapidly through Mexico, reaching farms in Oaxaca and Veracruz, 700 miles from the U.S. border. Capable of killing livestock in weeks, the pest threatens not just cattle but also wildlife and, in rare cases, humans. Its advance has forced a tough call.
On May 11, 2025, U.S. Secretary of Agriculture Brooke L. Rollins ordered a halt to live cattle, horse, and bison imports at southern border ports. The move aims to shield the nation’s $200-billion livestock industry from a pest that once cost billions to eradicate. At the same time, it disrupts trade with Mexico, a vital partner, raising questions about how to protect animals without harming economic ties.
This isn’t a new fight. The U.S. eliminated screwworm by 1966 using sterile insect releases, but its return in Mexico since 2023 signals a broader challenge. Global trade and shifting climates are speeding up the spread of animal diseases, testing the ability of nations to respond effectively.
The Stakes of the Suspension
The import ban targets a pest that can devastate herds. New World Screwworm larvae infest wounds, causing severe damage and often death. Past outbreaks drained U.S. producers, with losses from treatments and dead livestock reaching millions yearly. The current policy seeks to protect the 92-million-head U.S. cattle herd, a cornerstone of the food supply.
Many in the U.S. livestock sector back the decision, citing the need to prevent economic catastrophe. USDA Tick Riders now patrol border areas to spot infected animals, bolstering biosecurity. The ban also reflects a historical pattern of using trade restrictions to block exotic pathogens, a strategy dating back to the 19th century.
Yet, the policy has downsides. Mexico’s exporters face immediate losses, and smallholder farmers in Central America, already hit by screwworm, may struggle further. The ban’s month-to-month terms create uncertainty, with trade resumption depending on Mexico’s containment progress. Both nations feel the economic pinch, highlighting the complexity of the choice.
Teaming Up Against the Threat
The U.S. and Mexico are tackling the screwworm together. The USDA’s Animal and Plant Health Inspection Service is releasing sterile flies in southern Mexico to disrupt the pest’s breeding. Both countries are also boosting field surveillance and educating farmers to catch infestations early. Daily talks and a planned data review in two weeks show a commitment to collaboration.
History offers hope. The 2011 global eradication of rinderpest proved that coordinated efforts can defeat animal diseases. Recent programs in the Americas have cut transboundary disease rates by 45 percent since 2021, using shared vaccines and disease-free zoning to sustain trade. Still, wildlife crossing borders can spread screwworm, complicating containment.
Some experts push for deeper global teamwork. International health groups argue that shared surveillance systems and emergency vaccine reserves can limit losses and keep markets open. These strategies prioritize animal welfare and economic stability, offering a model for managing future outbreaks.
Navigating Economic and Health Trade-Offs
Trade restrictions like the USDA’s ban often stir debate. World Trade Organization records show that 2024 avian influenza bans cut global poultry trade by 12 percent, costing $7 billion. In East Africa, Rift Valley fever zones slashed smallholder export incomes by 25 percent. The screwworm ban risks similar disruptions for Mexican exporters and U.S. buyers reliant on cross-border livestock.
Allowing the pest to spread, however, could be far costlier. China’s 2018-19 African swine fever outbreak slashed pork output by 40 percent, driving up global prices and reshaping trade. A U.S. screwworm resurgence could trigger similar chaos in meat and dairy markets. The USDA’s careful approach, including inspections for animals in holding, aims to reduce these risks.
Finding equilibrium is tricky. The ban safeguards U.S. agriculture but strains ties with Mexico, a key ally in both trade and pest control. Success depends on Mexico’s eradication progress and the U.S.’s support for those efforts, all while maintaining open communication.
A Path Forward
The screwworm crisis highlights a hard reality: animal diseases don’t respect borders. The USDA’s import ban buys time but isn’t a long-term fix. Lasting solutions require ongoing investment in surveillance, technology, and global partnerships. The UN’s GF-TADs program, started in 2004, shows how early warning systems and shared strategies can curb outbreaks.
For farmers in the U.S. and Mexico, the impact is immediate. The ban protects American livestock but squeezes rural economies on both sides. Its flexible review process offers hope for trade resumption, but clear benchmarks and transparency are essential to ease uncertainty for businesses.
Looking ahead, the screwworm fight points to a larger truth. As trade and climate change fuel disease risks, nations must work together, not apart. By combining science, diplomacy, and vigilance, the U.S. and its partners can safeguard livestock, secure food supplies, and navigate the challenges of an interconnected world.