USDA confirms first New World screwworm infection in Texas since 1960s eradication

The US Department of Agriculture has confirmed the first known infection of the New World screwworm in the United States since the pest was eradicated in the 1960s. The case involves a three-week-old calf in Zavala County, Texas, following confirmatory testing at the National Veterinary Services Laboratories in Ames, Iowa. Agriculture Secretary Brooke Rollins announced the finding on Wednesday night, marking the first detected breach of the US-Mexico border by the parasite, which has been migrating north through Central America in recent years.

In response to the confirmed case, the USDA has established a 20-kilometre quarantine zone around the detection site. The agency has deployed a unified Incident Command Team in collaboration with the Texas Animal Health Commission to manage the situation. Immediate containment measures include movement restrictions, enhanced surveillance, fly trapping, and the release of sterile insects via both ground chambers and aerial methods.

The New World screwworm is a parasitic fly whose larvae feed on the living tissue of warm-blooded animals, causing severe, life-threatening wounds in livestock and pets. The United States previously eradicated the pest using the Sterile Insect Technique, which involves releasing large numbers of sterilised male flies to disrupt breeding. This effort, supported by a biological barrier of sterile fly releases in Panama and Colombia, was estimated to save the livestock industry $900 million annually.

The biological barrier was breached in 2022, allowing the parasite to move north from South America. Prior to the Texas confirmation, cases had been detected in Mexico, including a five-year-old goat in Coahuila located 25 miles from the border. The USDA is currently dispersing 100 million sterile insects per week in Mexico and along the US-Mexico border to prevent further advancement.

State Representative Don McLaughlin had previously claimed on social media that a case was found one mile from the border, a statement the USDA and Rollins denied as false information that caused unnecessary panic. McLaughlin later stated that samples from two calves in La Pryor, Texas, were being tested, with one showing larvae in an umbilical cord wound, though he acknowledged the diagnosis was unconfirmed at the time. Reuters reported viewing a photo of larvae in a bloody wound but could not immediately verify it as New World screwworm.

To bolster long-term containment, the USDA is constructing a $750 million sterile fly production facility in South Texas. This week, the agency released 4 million sterile flies by air in the affected area. Dudley Hoskins, USDA undersecretary for marketing and regulatory programs, stated in a press release that the United States has defeated this pest before and will do so again.