Screwworm Threat Prompts Emergency Measures in the U.S.

09/09/2025

The screwworm parasite — eradicated from the U.S. more than half a century ago — has re-emerged at the Mexican border, triggering swift regulatory action. The Food and Drug Administration (FDA) will now be able to issue emergency use authorizations (EUAs) for new veterinary drugs designed to combat outbreaks.

Screwworm flies are notorious for laying eggs in open wounds; the larvae feed on living tissue, leading to severe animal suffering, production losses, and often death. Outbreaks can devastate cattle herds and impose trade restrictions, creating billion-dollar risks to livestock industries.

Alongside the regulatory change, the U.S. Department of Agriculture (USDA) is preparing a major biosecurity investment: up to $750 million for a sterile-insect production facility in Texas. The sterile fly technique, pioneered decades ago, was critical to eliminating screwworm from North America. However, building and scaling such a facility will take years — leaving a gap in short-term defenses (Reuters).

This situation underscores the economic cost of complacency. Maintaining eradication programs is expensive, but resurgence can be far costlier in terms of animal health, veterinary interventions, and lost productivity. For the U.S., the episode is a reminder that biosecurity is not a one-off investment but a continuous commitment.

The screwworm threat may also influence regulatory precedent. If EUAs prove effective for animal health emergencies, similar models could be adopted for other transboundary livestock diseases — creating new dynamics in drug approval and veterinary market access.