What to Do if You Suspect New World Screwworm in Your Herd - Texas A&M AgriLife Extension Service

If New World screwworm (NWS) is suspected in livestock, immediate action is critical to prevent further spread and protect animal health.

This guide outlines the steps to take if NWS is suspected, starting with the core response approach: Inspect. Report. Protect. NWS is known to infest many livestock species, including cattle, goat, sheep, pigs, horses, among other warm-blooded animals.

Immediate Actions

If screwworm infestation is suspected:

Contact authorities:
- Texas Animal Health Commission (TAHC) for livestock and pets: 800-550-8242
- Texas Parks and Wildlife Department (TPWD) for wildlife: 512-389-4505
Notify the animals’ private veterinarian.
Do not delay reporting. Early detection limits spread and minimizes long-term consequences.

For full response procedures and identification steps, see Rethinking Livestock Management to Consider Screwworm (September 2025)

Inspect

It is vital to frequently monitor livestock and look for signs of NWS, such as:

The smell of rotting tissue,
Visible burrowing larvae, and
Sickly looking wounds on both livestock and wildlife.

Suspected cases should be reported even if unsure.

Report

If an NWS case is suspected, report it to the Texas Animal Health Commission (TAHC). Contact a local veterinarian and/or the local AgriLife Extension county agent. Owners will be asked to collect and send in a larval sample using the following procedures:

Collect and remove all larvae, leaving none in the wound.
Place larvae in a clean, secure container.
Either freeze until solid or fill the container with isopropyl alcohol.
Submit samples to TAHC before applying any treatment plan provided by a veterinarian.

Protect

Work with a veterinarian for a treatment plan for the affected animal and the rest of the herd. Always follow the veterinarian’s treatment plan. Potential options can include:

Topical treatments:

Permethrin sprays: Over-the-counter, kills and repels flies.
Permethrin ear tags: Add protection during active months.

Systemic treatments:

Coumaphos: Requires a certified applicator license due to toxicity. Applied topically but works systemically.

Wound care:

Clean wounds thoroughly and apply disinfectant.
Cover if possible during fly season.
Monitor healing daily.

Why Reporting Matters

Early detection enables fast containment.
Delay in reporting could allow widespread infestation.
While temporary movement restrictions will occur with infestations in the United States, long-term industry impact from established populations would be far worse.

Conclusion

Suspecting screwworm? Act quickly to inspect, report, and protect. Call the vet and state officials, collect samples, and follow treatment protocols. Proactive communication and early action can protect livestock and neighbors.

For additional guidance and a detailed action plan, consult Rethinking Livestock Management to Consider Screwworm (September 2025).

Please immediately isolate suspected animals and report instances of New World screwworm as follows:

Livestock: Texas Animal Health Commission
Wildlife: Texas Parks and Wildlife
Small animals: Your local veterinarian

Please send news and media inquiries to [email protected].

¹Professor and Extension Veterinary Specialist, Department of Animal Science, College of Agriculture and Life Sciences, Texas A&M University, Texas A&M AgriLife
²Assistant Professor and Extension Sheep and Goat Specialist, Department of Animal Science, College of Agriculture and Life Sciences, Texas A&M University, Texas A&M AgriLife
³Professor and Extension Livestock Specialist, Department of Animal Science, College of Agriculture and Life Sciences, Texas A&M University, Texas A&M AgriLife
⁴Professor, Department of Animal Science, College of Agriculture and Life Sciences, Texas A&M University, Texas A&M AgriLife
⁵Professor, Department of Entomology, College of Agriculture and Life Sciences, Texas A&M University, Texas A&M AgriLife