Possible New World screwworm case triggers USDA testing in Texas

A possible case of New World screwworm has been reported in South Texas, and the US Department of Agriculture says a sample is undergoing confirmatory testing at its National Veterinary Services Laboratories in Ames, Iowa. Ars Technica reports the USDA posted that it has activated personnel on the ground and is working with local partners, after days of industry chatter that had already unsettled cattle producers.

If confirmed, it would be the first detected breach of the US-Mexico border by the parasite in decades. The screwworm fly was eradicated from the United States in the 1960s through a long campaign that relied on releasing sterile male flies, a method that suppresses reproduction because females typically mate only once. The USDA estimates that preventing screwworms saves the US livestock industry about $900 million annually, a figure that helps explain why even an unconfirmed report can move markets and trigger political attention.

The biology is simple and expensive. Female flies lay eggs in wounds and natural openings of warm-blooded animals; the larvae then feed on living tissue, creating deep infections that can kill livestock if untreated and can also affect humans. The fly has been moving north through Central America for several years, and Ars notes recent detections in Mexico’s Coahuila state, including a case in a goat found not far from the border and other cases in calves.

The early information flow has been messy. Agriculture Secretary Brooke Rollins has warned that false reports create panic, disputing claims that the parasite was closer than official reporting suggested. Ars recounts how a Texas state representative, Don McLaughlin, claimed on social media that a case had been found extremely close to the border and later told Reuters that samples from calves on a Texas ranch were being tested. Reuters was shown an image of larvae in a wound but could not verify it, and Ars says it is unclear whether the USDA’s sample is connected to the politician’s claim.

That gap—between laboratory confirmation and the incentives of elected officials, industry groups, and online rumor—arrives just as the physical barrier is being tested by an insect that does not need a port of entry. The last time the US eliminated screwworm, it did so with an industrial-scale program that treated containment as a permanent operation, not a one-off emergency.

For now, the country is waiting on a lab result in Iowa while ranchers in Texas watch for new wounds.