Screwworm Finding: USDA Halts Animal Exports to Mexico

In response to the detection of New World screwworm in the United States, the U.S. Department of Agriculture has restricted the export of live animals to Mexico. Those changes include horses, as the USDA said it will halt exports from all U.S. states of equine to Mexico for breeding or work, sport or exhibition, or for slaughter. The USDA said the policy is effective immediately and will remain in place until it has further information from Mexico. The restrictions also apply to cattle, wild ruminants (non-bovine), sheep and goats, pet dogs, swine, ferrets, and birds. The response follows the June 3 detection of screwworm in a bovine in Texas. To date, there has not been a detection in equine. The USDA Animal and Plant Health Inspection Service confirmed June 3 the detection of a New World screwworm 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, USDA 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." For more information about the New World screwworm infestation in Texas, the American Horse Council is working to share critical information for horse owners. A June 3 AHC update follows: On June 3 the USDA confirmed New World screwworm in the umbilical area of a calf in Zavala County, Texas. This expansion into the U.S. is alarming and AHC wants to make sure you know about the potential risks of this parasitic fly to horses. While this might seem like an overwhelming and scary situation, we've dealt with this before and have confidence in current science based strategies. The U.S. historically was afflicted with screwworm for hundreds of years before successfully eliminating it from the country in the 1960s using many of the same methods we use now. We've eliminated it before, and have full faith we'll do it again, but only if all horse owners do their part to stay vigilant and follow state guidelines for animal movement. risk to horses? Screwworm myiasis (infestation) is caused by fly larvae (maggots) that feed on living tissue of any warm-blooded 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 that are more likely to kill the animal. How serious a threat? 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? 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. impact on equestrian sports? Federal and state animal health officials will dictate the procedures around screwworm cases. Organizers and participants to be aware of and use the guidance of their related discipline associations and governing bodies such as the United State Equestrian Federation. Further, competitors need to check their home state and destination state animal health official webpages for any movement requirements. 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. AHC Preparations? AHC is working closely with industry partners and has built this webpage dedicated to screwworm updates. We will also be building a link to all state animal health officials to help you understand movement requirements in your area. For now, please review the following trusted resources for any screwworm related information: Additional Resources Map of Current Outbreak Horse Owner Fact Sheet USDA Myth Buster—Facts About NWS USDA New World Screwworm Webinar for Animal Industry