USDA Finds Screwworm Larvae In Imported Horse

USDA identified New World screwworm larvae in an imported horse currently in quarantine at a Florida import facility, prompting swift treatment and continued monitoring to protect U.S. animal health.

The horse, which arrived from Argentina, was undergoing routine import quarantine when larvae were discovered in an open wound. The animal was treated immediately, and samples were submitted to the National Veterinary Services Laboratories for confirmation. The horse will remain in quarantine until it is cleared and confirmed free of infection.

Officials emphasized that there are currently no confirmed cases of New World screwworm in the United States. Because the detection occurred during import quarantine, the situation poses no risk to the domestic animal population. The case is not believed to be connected to the ongoing outbreak in Mexico, but it highlights the importance of strict import protocols and surveillance.

Dr. Katie Flynn, senior staff veterinarian for Equine Health at the United States Equestrian Federation, noted that quarantine procedures are designed to prevent entry of infected animals. She credited USDA import staff for identifying the issue quickly and preventing potential spread.

Meanwhile, the USDA Animal and Plant Health Inspection Service is continuing its aggressive prevention strategy along the southern border. The agency recently shifted its sterile fly dispersal program, which releases roughly 100 million sterile flies per week, to strengthen efforts against the northward movement of screwworm. The current northernmost active cases remain about 200 miles from the U.S. border, and aircraft and resources are being repositioned to reinforce coverage near Texas and along the border with Tamaulipas, Mexico.

Animal owners are being urged to stay alert. USDA recommends regularly checking pets and livestock for warning signs, including draining or enlarging wounds, unexplained discomfort, or the presence of maggots or eggs near body openings such as the nose, ears, genitalia, or the navel in newborn animals. Any suspected cases should be reported immediately to state animal health officials or a USDA area veterinarian in charge.

Adult screwworm flies resemble slightly larger houseflies, with metallic green or blue bodies, orange eyes, and three dark stripes on their backs. The larvae can infest livestock, pets, wildlife, and even humans, entering through open wounds and feeding on living tissue.