Screwworm Invasion Stalling at the Southern Border

The New World Screwworm (NWS) invasion, and the potentially devastating impact it could have on wildlife populations and the ranching industry has stalled, at least temporarily. The U.S. Department of Agriculture (USDA) is confident enough in its defenses—coupled with the cooperation of officials in Mexico—that livestock from Mexico is scheduled to resume entry through the Douglas, Ariz., port on Aug. 24.

“Protecting the United States from NWS and pushing this pest out of Mexico and back to the Darien Gap is a top priority at USDA and has the full attention of the Trump Administration,” U.S. Secretary of Agriculture Brooke L. Rollins said in a press release issued on July 24. “The closure of the Southern ports of entry for the last year has been a tough but necessary action to control the spread of NWS in Mexico and protect the American livestock industry. Thanks to the work across the federal government as well as state, local, and industry partners, it is now safe to reopen the Douglas, Arizona, port in 30 days to resume the hundreds year old movement of cattle.”

Every animal entering the United States through the Douglas port will undergo a full USDA inspection to ensure it is NWS free. Depending on detections, ports in Santa Teresa and Columbus, N.M., could reopen later.  

Douglas is 325 miles from the latest NWS case confirmed in the United States, which was in Texas. Sonora and Chihuahua—which border Arizona and New Mexico—according to the USDA press release are, “… identified as the lowest-risk Mexican states for New World screwworm due to their strong, well-established inspection programs and their geographic distance from southern Mexico, where most cases are concentrated.”

The USDA maintains an online list of domestic detections, with the date, county, state and animals affected. So far this month they are significantly below those in June, when NWS first made its way into Texas.

The stateside invasion of NWS during the 1950s and 1960s is estimated to have reduced the whitetail population in Texas by 50 percent. The common housefly-looking insect lays its eggs in warm-blooded animals, primarily in open wounds or newborn animals in the umbilical region. When larvae develop they feast on the host’s flesh.