New World Screwworm (NWS)

Current Outbreak

On June 3, 2026, New World screwworm (NWS) was confirmed in a calf in Zavala County, Texas. The following week, several more cases of NWS were identified in other Texas locations and one case in a dog in New Mexico.

KDA News Release 6-4-2026

Click here to view the most updated information on the current situation. 

NOTE: NWS does not impact food safety.

What to know before traveling from an infested state:

• Any species that originates from an infested zone will need to meet the movement requirements for the state of origin AND obtain a permit from the Kansas Animal Health Commissioner and a statement of “all animals listed were individually inspected and found free of wounds" on the CVI.
• For additional information or questions call the Division of Animal Health at 785-564-6601, or visit Import Requirements.

Reporting

If you suspect an NWS case, contact your local veterinarian or the KDA Division of Animal Health at 785-564-6601. NWS is a reportable condition and should be reported to the Division of Animal Health.

What Is New World Screwworm?

• New World screwworm (Cochliomyia hominivorax) lays eggs in an open wound, and the larvae (maggots) eat the living flesh, rather than dead tissue like other maggots.
• This causes the wound to become larger and can be fatal to the animal if it’s not treated quickly.
• Prior to June 2026, NWS had been eradicated from the United States since 1966, due to the release of sterilized males into the environment. However, NWS is still found and considered endemic in most of South America, Cuba, Haiti, and the Dominican Republic.

Clinical Signs/How to Identify

• Wounds in living animals infested with maggots
• Smell of decaying flesh
• Head shaking
• Blood-tinged discharge from infected wounds
• Fly strike evidence
• Discomfort
• Depressed/not eating
• Decreased milk production
• Seclusion from herd/flock

Transmission 

• Females are attracted to a live animal's wound and/or opening. This is a prime place to lay eggs. Openings can be anything from a tick bite, nose, eyes, genitalia, or umbilicus in a newborn animal, wounds from dehorning, castration, shearing, barbed wire fences, as well as shedding of antler velvet in deer.
• Females mate once in their lifetime and store sperm from a male to fertilize eggs over time.
• Once females find a wound, in a warm-blooded animal, they can lay anywhere from 200-300 eggs at one time, and possibly up to 3,000 eggs in their lifetime.
• Eggs hatch into larvae, or maggots, and burrow into healthy, living tissue, which is such a problem. The maggots feed for 3-7 days and cause the wound to become bigger. This can cause very serious tissue damage.
• Once the maggots are done feeding, they drop from the animal to the ground to become adults in approximately 7-10 days, and the cycle repeats.

Diagnosis

• NWS only feed on living tissue, which is different from other flies that only feed on dead tissue.
• NWS is identified by larval collection and evaluation.
  • Larvae have spines that point backward around a tapered body, making the larvae appear like a "screw."

Treatment

• KDA flyer about Prevention, Monitoring and Treatment of NWS 
• Consult with your local veterinarian. If any animal is infested with NWS, has myiasis (fly strike), or has a secondary infection, they must be immediately treated by cleaning the wound and applying a topical pesticide or other medication that is effective against NWS larvae. FDA has Conditionally Approved many drugs for the treatment of NWS, which are already approved for other uses.

Prevention

• Keep open wounds clean and covered.
• Treat clothing, gear, and people with proper repellents.
• Check pets and vehicles for NWS flies and larvae if traveling to NWS-infested areas.
• Monitor pets and livestock for clinical signs and report immediately if any suspicions.

Resources

• Guidelines for KDA movement requirements:
  • General Animal Movement Requirements
  • Cattle Movement Requirements
  • Dairy Cattle Movement Requirements
  • Horses and Other Equids Movement Requirements
  • Swine Movement Requirements
• USDA New World screwworm site: Screwworm.gov
• K-State Research and Extension - New World Screwworms Fact Sheet for Producers
• https://www.tahc.texas.gov/news/brochures/TAHCFactsheet_NewWorldScrewworm.pdf
• https://www.merckvetmanual.com/integumentary-system/flies/obligatory-myiasis-producing-flies-of-animals#Treatment-and-Control_v3279271

History of NWS

Prior to entering the U.S., New World Screwworm (NWS) detections in Panama rapidly increased from an average of 25 cases per year to 6,500 cases in one year beginning in 2023. Since then, NWS has been detected in Costa Rica, Nicaragua, Honduras, Guatemala, Belize, El Salvador, and Mexico, north of the biological barrier that's historically successfully contained this pest to South America for decades.