Based on an article that first appeared at

New World Screwworm Awareness in TexasNew World Screwworm confirmed in Texas

Current Status:

4 cases

Affected counties: Zavala & La Salle County; Gillespie County (6/8/2026)

Other counties in quarantine: Webb & Uvalde County

Previously reported canine case in Andrews County, updated to New Mexico (Lea County)

***Considered active quarantine zones with no animal movement without prior TAHC authorization

Interstate travel (CVI/Health Certificate):
  • Call the destination state to verify requirements before travel
  • Canada: Banned all travel of horses residing in Texas within the prior 21 days (as of June 5, 2026)
  • CVI: Many are only valid for 72 hours, not 30 days.

New World Screwworms (NWS) larvae are maggots of the fly Cochliomyia hominivorax, which is known to lay eggs on open wounds or orifices of live tissue. As the eggs hatch, they continue to destroy healthy tissue, causing larger wounds and damaging the area. NWS can affect all warm-blooded animals, including horses, cattle, sheep, goats, dogs, cats, and wildlife.

Clinical signs to watch out for:

  • Draining or enlarging wounds
  • Maggots
  • Lesions around orifices (ears, nose, genital area, and umbilicus in newborns)
  • Irritation, rubbing of wounds

Temperature and fly activity

  • NWS is a tropical fly, and its activity is temperature-dependent
  • High risk: 80°+F, 30-70% relative humidity (2-3 weeks life cycle)
  • Moderate risk: Temperate weather (3-4 weeks life cycle)
  • Low risk: Below 59°F (2-3 months or less active life cycle)
  • Current conditions are ideal for NWS activity.
  • Central and North Texas may see slowing activity in the winter months. South Texas may experience year-round risk.

Table: Average high and low temperatures (°F) across the year for central Texas, 2000-2024.
Texas A&M AgriLife Extension.

Suspected cases

If you suspect a case, contact your veterinarian immediately. The larvae/maggots may be used to accurately identify the species involved.

DO NOT MOVE THE ANIMAL OR OTHER ANIMALS

Follow the guidelines set by your veterinarian and the Texas animal health commission (TAHC), or your local state health officials

Treatments

Currently approved treatments include:

  • Dectomax (doramectin) can be used for treatment and prevention in horses (>1 year of age)
  • Negasunt Powder (comuaphos, propoxur, and sulfaminide topical powder) can be used for prevention and treatment (limited distribution to USDA)
  • Ivermectin may be effective in prevention
  • F10 Antiseptic wound spray with insecticide (benzalkonium chloride, polyhexanide, and cypermethrin topical solution) can be used for prevention and treatment

Prevention

  • Keep any open wounds cleaned and covered.
  • Work closely with your local veterinarian and follow all state guidelines.

Image: AAEP, Alert to Equine Practitioners: New World Screwworm Enters The United States.

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