FDA issues emergency use authorization for antiparasitic to combat screwworm in cats

A month after invoking emergency use authority for an animal drug for the first time to fight the New World screwworm (NWS) threat, the Food and Drug Administration (FDA) has issued another.

On November 21, the FDA issued a second emergency use authorization (EUA) for the use of the antiparasitic drug Credelio Cat (lotilaner) for treatment of infestations of NWS (Cochliomyia hominivorax) larvae in cats and kittens. That came just a month after its October 24 EUA for Credelio for NWS in dogs and puppies, the first time the agency invoked emergency authority for an animal drug.

Screwworm's northward migration from Central America has prompted a massive response from animal health officials, who are calling for heightened vigilance from small and large animal veterinarians to ensure the parasite does not regain a foothold in the U.S.

Since July, Mexico has confirmed several cases of New World screwworm (NWS) within 400 miles of the U.S.-Mexico border. The U.S. Department of Agriculture (USDA) says isolated detections outside of the known affected areas in Mexico are not unexpected, "and the fact that they have been identified and addressed quickly show that our collaborative efforts with Mexico to implement the NWS Action Plan are working." (Map courtesy of USDA).

As of December 3, Mexico had recorded 11,516 cases of NWS in animals, according to Mexican government data. Of those, 894 were active cases, over half of which were identified in cattle (576), though Mexico's National Service of Agro-Alimentary Health, Safety, and Quality (SENASICA) data also showed infestations in dogs (145), pigs (79), and horses (48).

Preventive efforts

Credelio Cat, available only by prescription from a licensed veterinarian, comes in two chewable tablet sizes: one with 12 mg of the active ingredient, lotilaner, for cats 2 to 4 lbs in body weight and another with 48 mg of lotilaner for cats weighing 4.1 to 17 lbs. The minimum dosage is 2.7 mg per lb (6 mg/kg) and must be orally administered with food. Cats over 17 lbs should be administered the appropriate combination of chewable tablets, according to the FDA.

Further information for veterinarians regarding its use for NWS in cats can be found in the "Fact Sheet for Veterinarians: Emergency Use Authorization of Credelio Cat (lotilaner)."

Credelio Cat, sponsored by Elanco Animal Health, was originally approved in 2019 for flea- and tick-related indications in cats and kittens. Lotilaner, the active ingredient in Credelio Cat, also belongs to the class of isoxazolines.

"Most cats in America are at low risk of NWS due to their geographic location," the FDA said. "However, outdoor cats near the U.S.-Mexico border and cats that have traveled to countries with active NWS cases are more likely to be exposed to NWS."

The EUA was based on research evaluating the efficacy of Credelio Cat against Old World screwworm in cats as well as the efficacy of Credelio against NWS in dogs, according to Elanco.

"With confirmed cases of New World screwworm detected as close as 70 miles south of the U.S.-Mexico border, this EUA ensures veterinarians and pet owners have a ready-now treatment option for cats and kittens should the fly enter the U.S.," the company's press release stated.

The EUAs will be effective until it is revoked or the Health and Human Services Secretary terminates the declaration that NWS presents a significant potential for a public health emergency, according to the FDA.

New NWS website

The U.S. Department of Agriculture (USDA) launched a new unified NWS website, screwworm.gov, to centralize information across the federal government, as per USDA Secretary Brooke Rollins's previously announced five-pronged plan earlier this year.

Calling NWS a national security priority, Rollins in a November 21 USDA press release said: "To ensure timely and effective communications, this new unified website will be a one-stop shop for all screwworm-related information and will help our stakeholders be better informed as new information comes available."

Screwworm.gov offers resources for a wide range of stakeholders: veterinarians, animal health officials, wildlife professionals, health care providers, livestock producers, pet owners, researchers, drug manufacturers, and the public. It also includes the latest information on USDA-verified cases, U.S. preparedness efforts, and response activities in Mexico.

Information for veterinarians include an NWS webinar, a fact sheet on how to be prepared, and a standard operating procedure for possible detections in animals.

The unified site also includes information from partner agencies: the FDA, the Department of Energy, the Department of Homeland Security, the Environmental Protection Agency, and the State Department.

Meanwhile, the U.S. One Health Coordination Unit for NWS, co-led by the USDA, the Centers for Disease Control and Prevention, and the Department of the Interior, is working to ensure the U.S. is ready should NWS be detected stateside.