Earlier today, the United States Equestrian Federation sent the following email to its members.
On June 3, 2026, the U.S. Department of Agriculture confirmed New World Screwworm in the umbilical area of a calf in Zavala County, Texas. This expansion into the United States is alarming and US Equestrian wants to make sure you know about the potential risks of this parasitic fly to horses.
What is the risk of screwworm to horses?
Screwworm myiasis (infestation) is caused by fly larvae (maggots) that feed on living tissue of any warmblooded animal. Horses, cattle, wildlife, pets, and occasionally people could all be affected, which means rapid detection and response are essential. The larvae are deposited on wounds or superficial body cavities such as the nose and sheath of horses, where they feed and grow. Untreated wounds often develop multiple infestations which are more likely to kill the animal.
How serious of a threat is this parasitic fly?
Widespread screwworm infestation could have serious consequences for animal health, agriculture productivity, and the national economy. A widespread outbreak will disrupt livestock movement and trade, increase veterinary and surveillance costs, and place major burdens on producers, animal health officials, and event organizers. Early detection and response is critical to stop the spread.
What can a horse owner do to protect their horses?
Horse owners can protect their horses from screwworm by checking daily for any wounds, drainage, foul odor, or unusual irritation, and by cleaning and protecting even minor cuts as soon as they are found to reduce the opportunities for the screwworm fly.
Consistent fly control, good stable hygiene, and careful monitoring after injuries or surgery can help reduce risk, since screwworm flies are attracted to open wounds and body openings. If a horse develops a wound that worsens quickly, has a bad smell, or contains visible maggots, the owner should contact a veterinarian immediately so the horse can be evaluated, treated, and reported if needed.
How will this screwworm detection in the United States impact equestrian sports?
Federal and state animal health officials will dictate the procedures around screwworm cases. US Equestrian is here to help competition organizers and participants to be aware of and use their guidance. Horses infected with screwworm or horses in a geographic area with screwworm present are likely to be placed under quarantine. State animal health officials will have the discretion to implement movement restrictions in these situations. States may restrict equine movement and activities such as equestrian events in a geographic area. As this is a recent incursion, the state and federal animal health officials are finalizing the protocols for responding to screwworm incursion. If you live in or are traveling to a state where screwworm has been reported, please visit the website of the relevant state veterinarian for the latest information on screwworm response and prevention.
What is the Federation doing to prepare for a potential screwworm incursion?
USEF veterinarians are working collaboratively with the states to develop a response plan which would allow healthy, safe competition to continue in the event of a screwworm detection in the United States – just as we do for equine infectious diseases. Any protocol for events during a screwworm incursion would be at the discretion of the state veterinarian in the venue state. For this type of disease situation, entry requirements to the event could include a requirement for veterinary examination for issuance of a certificate of veterinary inspection which includes an antiparasitic treatment (ivermectin/dectomectin) statement and examination on arrival. The Federation will continue to work with states on a screwworm response plan for equestrian events and will post updates and protocols on the our dedicated New World Screwworm webpage: New World Screwworm | US Equestrian.
Additional Resources
• Map of Current Outbreak: https://www.aphis.usda.gov/node/7944/current-status?page=1
• Horse Owner Fact Sheet: https://equinediseasecc.org/handler/managedfilehandler.ashx?id=62&ext=pdf
• USDA Myth Buster - Facts About NWS: https://www.aphis.usda.gov/sites/default/files/nws-myth-busters.pdf
• USDA New World Screwworm Webinar for Animal Industry: https://www.youtube.com/watch?v=0ZdBU0mBXKE