FDA authorizes generic pill to treat screwworm in pets

The Food and Drug Administration authorized emergency use of a generic nitenpyram tablet for dogs, puppies, cats and kittens as New World screwworm cases pushed into the United States and raised the stakes for livestock, wildlife and pet health. The parasite feeds on living tissue through open wounds, so regulators are moving quickly to give veterinarians a way to stop infestations before they spread further.

The emergency authorization applies to animals that weigh at least two pounds and are at least four weeks old. The FDA said nitenpyram works quickly and can kill most screwworm larvae within hours of the first dose, with a second dose recommended six hours later. The move adds another treatment option to a regulatory response that already included emergency authorizations for NexGard in dogs and NexGard COMBO in cats.

The urgency reflects how far the threat has traveled. The Centers for Disease Control and Prevention says the outbreak has moved northward through Central America and Mexico since 2023, while the United States has now recorded its first domestic animal cases in more than six decades in cattle, a goat and a dog in Texas and New Mexico. The first U.S. animal case in the current outbreak was confirmed on June 3 in Zavala County, Texas, in a 3-week-old calf with larvae in its umbilical area.

Screwworm is hard to ignore because a single female fly may lay up to 3,000 eggs, and any warm-blooded animal can become a host. The CDC says cases are less commonly reported from humans, domestic dogs, various wild mammals and birds, but the historic range once extended into the southern and western United States before eradication efforts pushed it southward. No locally acquired human infestations have been reported in the United States.

USDA says the current risk to animals and people in the United States is very low and that the U.S. food supply remains safe, but the agency is treating the outbreak as an active containment problem. USDA and the Animal and Plant Health Inspection Service define active cases as those requiring ongoing mitigation, treatment and wound management until wounds heal. The agency’s current-status page lists recent detections, including New Mexico’s first dog case and additional Texas cases, and says the map and case list are updated on Tuesdays and Thursdays.

The FDA said it is working with animal-drug sponsors on more options and has created a veterinary information page to help clinicians identify and use drugs for New World screwworm myiasis. The emergency authorization shows how fast federal regulators are adapting as a once-rare parasite reappears in a way that could test animal health systems well beyond a single pet case.