Authors: Lew Strickland, DVM MS DACT, UT Extension Veterinarian; Becky Trout-Fryxell, Professor, Medical and Veterinary Entomology; and Katy Smith, PhD Candidate, Veterinary Entomology Education Specialist

On June 3, 2026, the USDA Animal and Plant Health Inspection Service confirmed a case of New World screwworm (NWS) infestation in a 3-week-old calf and larvae were identified in its umbilical area in Zavala County, Texas. This area is about 50 miles east of the Texas Mexico border. We share this as an educational awareness update: this was a single calf, the calf has been treated, and no further cases have been identified. Rapid reporting and response are exactly what helps protect animal health and the livestock industry.

These larvae burrow into living flesh of any warm-blooded animal, causing serious tissue damage to livestock and potential economic losses. To date, there have been no further detections.

          To combat and contain any further spread of the NWS fly, the USDA and Texas officials are currently conducting these control measures.

• Establishing a 20 km infested zone around the detection and implementing quarantines, movement controls, and surveillance in this area.
• Expediting targeted release of sterile NWS male flies by immediately deploying ground release chambers in the area, in addition to the 4 million sterile flies per week already being released aerially in the area;
• Increasing trapping for NWS flies along the border and just outside of the dispersal area.
• Implementing NWS surveillance and management strategies in wildlife; and
• Conducting targeted outreach in the local area.

What to know:

– NWS is a parasitic fly; the larvae can infest wounds which include newborn navels, minor cuts, and summer injuries can be risk points—making routine checks especially important.

– If you see a wound that’s worsening quickly, has unusual irritation, or you suspect larvae, contact your veterinarian promptly and follow reporting guidance.

– USDA has a response “playbook” and established procedures for detection, surveillance, and control. Playbook and additional guidance are available through USDA APHIS resources as well (www.screwworm.gov).

– Tennessee producers should start practicing consistent warm-weather routines with more frequent health and welfare checks, prompt wound care, fly control, and prevention steps that reduce summer wounds/injury (fence and facility checks, castration/dehorning site monitoring, navel care, etc.).

– Awareness + good management + timely reporting= keeps incidents small and contained.

Learn more about NWS via these factsheets:

• USDA APHIS NWS myth busters factsheet: https://www.aphis.usda.gov/sites/default/files/nws-myth-busters.pdf
• USDA APHIS NWS Playbook: https://www.aphis.usda.gov/sites/default/files/nws-response-playbook.pdf
• UTIA NWS Factsheet: https://utia.tennessee.edu/publications/wp-content/uploads/sites/269/2025/08/W1338.pdf

We want to reiterate; the U.S. food supply is safe. This larva only infests living tissue, they do not infest meat, fruits, vegetables, or other food sources. 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. Under the Federal Meat Inspection Act (FMIA), FSIS inspection personnel must inspect all eligible animal species unless they are exempt or covered by a state inspection program.

If you have any questions, please feel free to reach out: https://animalscience.tennessee.edu/ask-dr-lew/