Texas and federal animal-health officials are working to contain the New World screwworm after the parasite was confirmed in two calves in Zavala County, marking its return to the United States after decades of eradication.
The first case was confirmed June 3 in a three-week-old calf with larvae in its umbilical wound. Texas officials reported a second detection June 5 in another young calf in the same county. No cases have been confirmed outside the immediate area.
Screwworm flies lay eggs in open wounds or body openings. After hatching, the larvae burrow into and feed on living tissue, enlarging wounds and potentially killing untreated animals. Cattle, wildlife, pets and other warm-blooded animals can be infected. Human cases are possible but rare.
The discovery poses a serious threat to Texas’ cattle industry because the flies can spread between herds and wildlife populations. An uncontrolled outbreak could cause animal deaths, increase veterinary and production costs, restrict livestock movement and disrupt domestic and international trade.
Officials stress that screwworm is not a foodborne illness and that the commercial meat supply remains safe. Animals showing signs of infestation would be identified during inspection, and contaminated products would not be allowed into commerce.
The U.S. Department of Agriculture and the Texas Animal Health Commission have established a unified incident command and an infested zone covering portions of Zavala and Uvalde counties. Warm-blooded animals cannot leave the zone without state authorization, inspection, treatment documentation and an official movement certificate.
Officials are increasing surveillance, setting traps, inspecting livestock and wildlife, and releasing sterile male screwworm flies. The sterile males mate with wild females, which generally mate only once, producing eggs that do not hatch and gradually reducing the fly population. USDA says four million sterile flies were already being released weekly in the area before the first detection.
Gov. Greg Abbott has issued a disaster proclamation authorizing state resources and directing the Texas screwworm response team to prioritize Zavala and Uvalde counties.
Texas Agriculture Commissioner Sid Miller has called for additional pesticide bait and criticized the federal response as too slow. USDA says it began expanding sterile-fly production, border surveillance and treatment capacity as the parasite moved north through Central America and Mexico.
Ranchers are being urged to inspect animals daily, keep wounds clean and immediately report suspicious larvae or enlarging wounds.
Guest:
Chad L. Cross is Professor of One Health at Texas Tech University School of Veterinary Medicine. His instruction includes medical & veterinary parasitology, medical & veterinary entomology, clinical and applied epidemiology, biostatistics and quantitative methods.
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