Federal officials have approved the emergency use of ivermectin in certain horses as part of the nation’s expanding effort to slow the spread of the New World screwworm, an invasive parasite that poses a serious threat to livestock, wildlife and even people.
The U.S. Food and Drug Administration issued an Emergency Use Authorization allowing veterinarians to prescribe ivermectin for horses that have recently foaled or suffered fresh wounds. The treatment is intended to provide short term protection during the period when animals are most vulnerable to screwworm infestation.
New World screwworm flies lay their eggs in open wounds or the umbilical area of newborn animals. Once the eggs hatch, the larvae feed on living tissue, causing severe injuries that can become fatal if left untreated. Cattle and horses are common hosts, but the parasite can also affect sheep, goats, wildlife, pets and, in rare cases, humans.
Federal officials say the authorization is another step in the nationwide response aimed at preventing the pest from becoming established in the United States. Agriculture and health agencies have increased surveillance, quarantine efforts and sterile fly releases following confirmed detections in South Texas earlier this summer.
The FDA said ivermectin under this authorization must be prescribed by a licensed veterinarian. The medication may be administered orally and is intended only as a temporary preventive measure immediately after foaling or when a horse has an open wound.
Veterinary officials emphasized the treatment does not provide long lasting protection. The preventive effect lasts no more than 24 hours, making wound care, bandaging, fly repellents and aggressive fly control essential parts of any screwworm prevention plan.
The New World screwworm remains one of the livestock industry’s most feared parasites because larvae consume healthy tissue rather than dead tissue. Infestations can rapidly worsen without treatment, leading to severe tissue damage, secondary infections and death.
Health officials also remind producers and the public to keep wounds covered whenever possible and seek veterinary or medical attention immediately if screwworm infestation is suspected. People should never attempt to remove larvae themselves because improper removal can increase tissue damage and complicate treatment.
The emergency authorization comes as state and federal agencies continue working to contain the parasite in Texas and prevent its spread into additional livestock producing regions.