Skip to content

New World Screwworm

In response to the U.S. Department of Agriculture confirmation of a case of New World Screwworm (NWS) in Texas, the Colorado Livestock Association released the following statement:

"The Colorado Livestock Association is in close coordination with Dr. Maggie Baldwin, Colorado State Veterinarian. We appreciate all the effort that has gone into preparing for this eventuality, and the efforts to keep our industry informed as the first U.S. case of NWS has been reported in Texas. As this unfolds, we are encouraging producers to remain calm and continue operating as usual while remaining vigilant about their livestock. CLA remains committed to coordinating with CDA and disseminating critical information quickly to keep producers informed."

If you suspect a case of NWS, notify your local veterinarian or the Colorado Department of Agriculture at (303) 869-9130.

CDA will post updates about the response at ag.colorado.gov/NWS.

GIS map of the restricted zones.

To learn more, visit screwworm.gov.

Colorado Increases Readiness After New World Screwworm (NWS) Confirmed in Texas, Urges Vigilance

June 3, 2026

Governor Polis and the Colorado Department of Agriculture’s State Veterinarian’s Office announced today that Colorado is activating its New World Screwworm (NWS) response plan following the confirmed detection of NWS in Zavala County, Texas. The confirmed case involves a 3-week-old calf with an infested umbilical area, and the Texas Animal Health Commission (TAHC) is working with the U.S. Department of Agriculture to establish a robust response.

“The health and safety of our cattle, food supply, and agriculture community is vital and we urge care and vigilance for our producers around the state. Colorado is taking action to ensure readiness for the potential arrival of New World Screwworm in our state and are committed to giving the best guidance and information available to protect producers and their cattle. I have been briefed and am monitoring the situation very closely and evaluating any next steps needed,” said Governor Polis.

Colorado Department of Agriculture

USDA Confirms Presence of New World Screwworm in the United States

June 4, 2026

The U.S. Department of Agriculture’s (USDA) Animal and Plant Health Inspection Service (APHIS) confirmed the detection of a New World screwworm (NWS) in a bovine in Zavala County, Texas. NWS is a serious pest that affects livestock, pets, wildlife, and less commonly, people and birds. NWS larvae (maggots) burrow into the flesh of living animals, causing serious damage to livestock and economic losses.

The affected animal is a 3-week-old calf and larvae were identified in its umbilical area. To date, there have been no further detections.

“All models showed New World Screwworm entering the country in 2025; however, thanks to the hard work across the entire Trump administration and our industry, state, and local partners, we were able to buy time for this moment. Protecting our livestock industry is a national security issue of the utmost importance, and USDA is wasting no time in taking action,” said Dudley Hoskins, Under Secretary for Marketing and Regulatory Programs. “USDA invested heavily in the tools needed to eliminate NWS ever since cases started increasing in Central America and Mexico. The United States has defeated this pest before, and we will do it again.”

USDA

Recognizing the Signs

Key signs in affected animals can include:

  • Irritation and restlessness
  • Depression and separating from the herd
  • Head shaking
  • Decreased appetite & milk production
  • The smell of decay
  • Expanding, odiferous, or infected wounds
  • Evidence of myiasis, also known as fly strike
    • Presence of fly larvae (maggots) in woundsLarvae feed with their heads buried downwards in the wound
    • Only their posterior ends are exposed to the surface
    • Spiracles on the posterior end are used to breathe

Photos of infested animals are available on USDA’s webpage.

Additional Resources

APHIS:

CDC:

FDA:

Herd Management Plan

If a detection is made, the Colorado State Veterinarian’s office will work closely with the impacted livestock owner to help prevent any further spread of NWS.

Here are the goals for any impacted herd:

  1. Eliminate NWS within the affected herd
  2. Prevent the spread of NWS to other animals and premises
  3. Minimize the stress and suffering of affected animals
  4. Ensure proper documentation and reporting

During the response, there are immediate actions a livestock owner will need to take:

  1. Stop animal movements as directed by the State Veterinarian’s office
  2. Separate affected animals from unaffected animals
  3. Undergo a veterinary examination by CDA, APHIS, or an accredited veterinarian under official supervision to examine the herd and assess the extent of infestation, and to collect diagnostic samples

Additionally, we will initiate the treatment for affected animals, herd fly control measures and other biosecurity measures necessary to stop the spread of NWS.

Once the immediate response plan is in action, there will be additional surveillance and monitoring, such as:

  • Daily inspections of all animals in quarantined herds
  • Fly trapping
  • Surveillance of the surrounding premises
Scroll To Top