On June 3, 2026, the USDA confirmed that New World Screwworm (NWS), a foreign parasitic pest, had entered the United States with a confirmed case in Texas. New World Screwworm (NWS) has the potential to cause serious damage to equine health and the agricultural economy.

Screwworm infestation is caused by fly larvae (maggots) that feed on living tissue of animals and humans. The female flies lay the eggs in a wound. The eggs hatch in roughly 24 hours, and the larvae feed on live tissue for roughly seven days until they drop to the ground, pupate, and become flies.

Screwworm infestations can be aggressive and, if left untreated, can kill an animal. Screwworm flies do not discriminate hosts based on species. This outbreak is particularly concerning because it can impact any animal or human.

You may be familiar with flies that primarily impact horses’ GI tracts, such as bot flies, or other types of flesh-eating flies that impact cattle. The screwworm is different because it is not species-specific and will eat live tissue. It also can attack moist areas with thin skin, such as nostrils, eyes, and genital areas. Umbilical areas of foals and recent surgical incisions can also be attractive to the fly.

A screwworm infestation can kill an animal if left untreated. With quick identification and treatment however, most animals recover.

For recent outbreak information, www.screwworm.gov

Signs and Symptoms
Larvae of screwworm flies are visible to the naked eye, though eggs are difficult to see. You may see small, white maggots in an open wound. Other signs an animal may have a wound that is infested include a foul odor or discharge, a wound that won’t heal properly, or a wound that grows bigger over time. You can find photos of screwworm larvae here.

Prevention
The two best things you can do are to try to monitor your animals closely and try to reduce the fly’s likelihood of spreading.

You should:

• Inspect horses daily for evidence of wounds or larvae, paying attention even to small cuts as well as to vulnerable areas like healing surgical sites, umbilical areas, lips, nostrils, eyes, and genitals. The fly can lay eggs around moist areas with thin skin in addition to wounds.
• Clean and protect wounds immediately and consult with veterinarians on the best products to use for wound care and dressing.
• Use veterinarian-directed fly control on horses, especially vulnerable areas of the body. Use masks, sheets, and other physical barriers to reduce fly access to horses.
• Remain vigilant about manure removal and standing water management to make the property less appealing to flies

More broadly, screwworm has been successfully controlled in the past with the release of sterile male flies, which mate with wild female flies and disrupt the life cycle. This strategy was used in 2016 in Florida, when screwworm appeared in key deer. Sterile flies have been released in huge quantities in Mexico and near the border. Reporting a case of screwworm infestation helps authorities know where they need to schedule a new release and helps protect horses in the area.

What to do If You Find Screwworm on an Animal
If you have an animal with suspected screwworm maggots or whose wound seems suspicious, notify your veterinarian immediately. They will contact state animal health authorities to confirm whether this is a case of screwworm. Your veterinarian will also determine what topical or systemic products should be used on your horse.

If you are at a horse show when you find a suspicious wound, notify the competition veterinarian and your treating veterinarian immediately. Your horse may need to be quarantined while authorities determine whether this is a case of screwworm.

Evolving Situation
Once a case of screwworm is confirmed, state animal health veterinarians and the USDA draw a 20-kilometer or 12-mile radius around the case and consider this an “infested area.” Animals within this area will be allowed to move, but under restrictions. We are still awaiting finalized response protocols from state and federal officials for movement of horses within an infested area. It is possible some states will restrict the gathering of animals in an infested area, so some states could effectively prohibit horse shows in infested areas.

As the situation continues to evolve, US Equestrian remains in contact with state and federal animal health officials and will communicate updates as we receive them.

We expect screwworm will continue to spread in the United States and encourage horse owners to stay informed about its progress, even if the states they live and compete in do not currently have confirmed cases.

Impacts on Competitions
Federal and state animal health authorities have jurisdiction over control requirements for screwworm. Individual states are setting their own policies for movement, inspection, and treatment requirements and these do vary between states. USEF is required to insure that competitions comply with federal and state requirements and have built our competition policies around those state requirements.

If you are bringing your horse to an out of state competition, you should check to see what the state requirements are in your origin and destination states. If you live in a state where screwworm has been confirmed, you may be required to get documentation of veterinary inspection before you depart, immediately upon arrival to a show grounds, or both. The same may apply if your horse has been in a state with a confirmed screwworm case in the past 14 days.

You can find contact information for your state veterinarian's office here.

And get the latest information on confirmed screwworm cases here.

If you are coming from a state where screwworm has been confirmed, your horse will need to be examined for any signs of wounds upon arrival to the competition grounds before they are permitted to enter the stabling area. This also applies to horses who are hauling into the show but not stabling there.

Competition management have been instructed to coordinate with an appropriate inspector, and you should reach out to management to be sure they will be available when you arrive. You may not enter the stabling area without this inspection. The appointed instructor may or may not be a veterinarian, depending on the state requirements. If a wound is found on your horse, they will be referred to a veterinarian for the wound to be examined and possibly treated.

If you brought any other animals with you who were in the trailer with the horse during travel, they will need to be inspected for wounds also.

You should check your horse daily for any signs of wounds or screwworm, and competition staff may ask to check them, too.

If you come from a state where screwworm has been confirmed and your horse has a wound but no signs of screwworm, you will be required to show veterinary records or a
note on your health certificate indicating that you have treated the wound with an FDA-
authorized product for screwworm already, or treat the horse and provide that documentation to the competition and to USEF at [email protected]. This also applies to horses who come from an infested state with a surgical incision that is a week old or less.

You can find a list of FDA-approved products for wound treatment for screwworm here.

Above all, please remain patient with competition organizers and officials as everyone navigates this new threat.

Direct any questions regarding these protocols or New World Screwworm to Dr. Katie Flynn, USEF Equine Health and Biosecurity Veterinarian, 859-225-6991 or [email protected]

This is initial guidance and will be updated once the regulatory entities implement their protocols and procedures for movement of animals into and out of an infested area.