Screwworm Larvae Found in Horse Imported from Argentina 

Currently there are no confirmed cases of NWS in the United States. however, a horse from Argentina undergoing routine USDA import quarantine at a facility in Florida was recently found to have New World Screwworm (NWS) larvae in an open wound.  The animal was immediately treated; samples were sent to the National Veterinary Services Laboratories for test confirmation. 

Accordingly, the horse will remain in quarantine until it has been reexamined and determined to be free of NWS. This situation does not appear to be associated with the NWS outbreak in Mexico that USDA is currently monitoring; it underscores the vigilance in all of USDA’s coordinated efforts to fight NWS. 

“As with all detections at time of import, our US animal population is safe because the horse remains in import quarantine until the animal is deemed free of screwworm after removal of the screwworm larvae, treatments, and an extensive post-treatment examination,” said Dr. Katie Flynn, senior staff veterinarian for Equine Health at the United States Equestrian Federation. “We applaud the USDA import staff on identifying and preventing entry of a Screwworm infected imported animal.” 

To continue to keep the United States clear of NWS from Mexico, the USDA Animal and Plant Health Inspection service (APHIS) announced a shift in its 100 million per week sterile fly dispersal efforts to stop the northern spread- the northern most active case of NWS is still about 200 miles away from the U.S. border. The USDA will relocate aircraft and sterile insects to reinforce coverage along the U.S.-Mexico border. The new dispersal area will include operations about 50 miles into Texas, along the U.S. border with the state of Tamaulipas, Mexico. 

USDA is asking U.S. animal owners to continue to remain vigilant by checking their pets and livestock for signs of NWS and immediately reporting any signs of NWS infestation include draining or enlarging wounds and signs of discomfort to their state animal health officials or USDA area veterinarian in charge.  This includes looking for screwworm larvae (maggots) and eggs in or around body openings, such as the nose, ears, and genitalia or the navel of newborn animals.

Adult screwworm flies are about the size of a common housefly or slightly larger, with a metallic green or blue body, orange eyes, and three dark stripes down its back. NWS maggots can infest livestock and other warm-blooded animals, including people. They most often enter an animal through an open wound and feed on the animal’s living flesh.  

To learn more about NWS, please visit https://www.equinediseasecc.org/new-world-screwworm