New World Screwworm Confirmed in Zavala County Calf

New World Screwworm Confirmed in Zavala County Calf

June 3, 2026

Media Contact: TPWD News, Business Hours, 512-389-8030

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AUSTIN - On June 3 the Texas Parks and Wildlife Department (TPWD) received confirmation of a detection of New World screwworm (NWS) in Zavala County. A sample collected from a three-week-old calf with an umbilical lesion was identified and confirmed as NWS by the National Veterinary Servies Laboratory (NVSL) in Ames, Iowa. There are currently no further detections in animals in Texas.

This is the first detection of NWS in Texas since northward progression from Central America was observed in 2023. TPWD is working closely with United States Department of Agriculture (USDA), Texas Animal Health Commission (TAHC) and other state officials in a joint incident response. TAHC has established an infested zone in the area, and animal movement restrictions are in effect to prevent further spread of the pest.

"NWS can have devastating impacts on free-ranging wildlife populations and rural communities," said Dr. David Yoskowitz, Executive Director of Texas Parks and Wildlife Department. "TPWD, in partnership with our state and federal partners, will work diligently to respond to suspected cases of NWS, and to urge the public to monitor and report signs of an infestation in warm-blooded animals."

"TAHC has been actively preparing for a resurgence of NWS for over two years," said Dr. Bud Dinges, TAHC state veterinarian and executive director. "We are putting these preparations into action, and we encourage all animal owners and caretakers to continue to remain vigilant for the presence of larvae in animal wounds and immediately report any suspicions."

According to the USDA, the U.S. food supply is safe. USDA's Food Safety and Inspection Service (FSIS) ensures that the nation's commercial supply of meat, poultry, and egg products is safe and properly labeled. NWS do not infest fruits, vegetables, or other food sources such as grains and rice.

NWS are larvae or maggots of the NWS fly (Cochliomyia hominivorax), that cause the painful condition NWS myiasis. NWS flies lay eggs in open wounds or orifices of live tissue. These eggs hatch into dangerous parasitic larvae, or maggots, which burrow or "screw" into flesh with sharp mouth hooks. NWS primarily infest livestock, but can also affect pets, humans, and wildlife including wild mammals and birds.

Targeted releases of sterile NWS flies are being expedited to eliminate any reproducing populations in the area associated with the detection. When combined with enhanced surveillance, movement restrictions, prompt treatment of wounds, and education and outreach efforts, the sterile insect technique is a proven and effective tool for controlling and eradicating this pest.

In addition to frequently monitoring animals, producers should implement enhanced management practices including keeping open wounds clean and covered. Animals infested with NWS should be immediately treated with an appropriate method under the direction of a veterinarian. If you suspect NWS in your livestock or domestic animals, contact the TAHC immediately and do not move any animals. A representative will advise you on current collection protocols for submitting suspicious maggots. Contact the Texas Parks and Wildlife Department (TPWD) for wildlife infestation information and the Texas Department of State Health Services (DSHS) for human infestation information.

Learn more about New World screwworm at screwworm.gov.