08/05/2026
What is New World screwworm (NWS)?
🪱New World screwworm (Cochliomyia hominivorax) is a parasitic fly whose larvae feed on living tissue of warm-blooded animals.
It affects livestock, pets, wildlife, and humans.
Unlike many other maggots, NWS larvae invade healthy tissue, causing rapidly worsening wounds, severe pain, and potentially death if untreated.
𝐂𝐮𝐫𝐫𝐞𝐧𝐭 𝐬𝐢𝐭𝐮𝐚𝐭𝐢𝐨𝐧
♦️NWS was eradicated from the U.S. by 1966 using the Sterile Insect Technique and other control measures.
♦️The biological barrier in Panama was breached in 2023, allowing the parasite to move northward.
♦️On June 3, 2026, USDA confirmed the first U.S. case in decades in a calf in southern Texas.
♦️USDA states that the food supply remains safe because NWS does not infest meat or produce.
𝐇𝐨𝐰 𝐢𝐭 𝐬𝐩𝐫𝐞𝐚𝐝𝐬
NWS can spread through:
♦️Natural movement of adult flies.
♦️Movement of infested livestock, horses, or pets.
♦️Movement of infected wildlife.
♦️Rarely, infected people traveling from endemic areas.
♦️Animals at highest risk
Animals with:
♦️Recent births (especially newborns' umbilical areas).
♦️Open wounds.
♦️Surgical incisions.
♦️Branding, dehorning, castration, or other management wounds.
♦️Signs to watch for
♦️Visible larvae in wounds or body openings.
♦️Egg masses around wounds.
♦️Foul-smelling, enlarging wounds with bloody discharge.
♦️Pain, depression, reduced appetite.
♦️Excessive rubbing, head shaking, or irritation.
♦️Larvae are typically white when young and may become pinkish-red as they mature.
Adult flies typically have:
♦️Orange eyes.
♦️Metallic blue-green bodies.
♦️Three dark stripes on the thorax.
What to do if you suspect NWS
♦️Immediately notify your State Animal Health Official and USDA-APHIS.
♦️The USDA after-hours reporting number is (866) 536-7593.
♦️Isolate affected animals.
♦️Collect larvae (if instructed) in 70% alcohol for laboratory identification.
♦️Animals remain under official movement restrictions until cleared by regulatory veterinarians.
Treatment
Treatment generally includes:
♦️Removing all eggs and larvae.
♦️Cleaning and treating the wound.
♦️Pain management.
♦️Preventing secondary bacterial infections.
♦️Using FDA-approved or authorized antiparasitic medications.
♦️Rechecking within 24 hours to ensure all larvae have been eliminated.
Environmental control
♦️Destroy removed larvae so they cannot pupate.
♦️Treat contaminated areas with approved larvicides.
♦️Clean treated surfaces.
♦️Monitor premises for at least one month after affected animals are released.
Prevention
Veterinarians and producers should:
♦️Inspect animals frequently, especially those with wounds.
♦️Treat wounds promptly.
♦️Report suspicious cases immediately.
♦️Follow state movement restrictions and inspection requirements.
♦️States with restrictions
Many states—including Texas, Florida, California, Colorado, Georgia, Illinois, Louisiana, New York, North Carolina, Oklahoma, Tennessee, Washington, Wisconsin, and many others—have implemented restrictions or enhanced requirements for animals arriving from NWS-affected areas.
Overall, the guidance emphasizes that rapid detection, reporting, isolation, and treatment are essential to preventing the parasite from becoming reestablished in the United States.
Reference: https://agrilifeextension.tamu.edu/new-world-screwworm