FDA issues first-ever emergency use authorization for drug to combat screwworm in dogs

Underscoring the gravity of the New World screwworm (NWS) threat looming just across the U.S.-Mexico border, on October 24 the Food and Drug Administration (FDA) published the first emergency use authorization (EUA) for the antiparasitic drug Credelio (lotilaner).

The is the first time the agency has invoked this emergency authority for an animal drug. In this case, it is for treatment of infestations of NWS in dogs and puppies. While most dogs in the U.S. are at low risk of contracting NWS due to their geographic location, dogs near the U.S.-Mexico border and dogs that travel to countries with active NWS cases are more likely to be exposed.

"When it comes to emerging animal health threats, we need to be proactive, not reactive," FDA Commissioner Marty Makary, MD, said in a press release.

The Food and Drug Administration (FDA) has taken the unprecedented step of issuing an emergency use authorization for a canine flea and tick medication for treatment of New World screwworm (NWS) infestations in dogs and puppies.

Infestation

Screwworm flies target warm blooded animals, including livestock, dogs and other pets, wildlife, and humans, laying eggs in an open wound or orifice. Once the eggs hatch, NWS larvae spend the next several days consuming the host's tissue, before reaching maturation and beginning the cycle again. NWS can cause serious damage to a host, which may die from secondary infection if not treated.

Detections of NWS have been on the rise in Central America and Mexico in recent months. In September, a screwworm case was identified in Sabinas Hidalgo, a Mexican city less than 70 miles from the Texas border, making it the northernmost detection during the current outbreak. A second detection, believed to be an isolated case and not related to the first, was detected in October in Montemorelos, about 100 miles further south in the same state.

U.S. and Mexican officials have heightened surveillance in the border region and the U.S. has closed its southern ports to imports of live cattle, bison, and horses from Mexico since July to prevent the parasite's spread into the U.S., where it has essentially been eradicated since the 1960s.

FDA response

U.S. Health and Human Services (HHS) Secretary Robert Kennedy Jr. in August determined that NWS presents a significant potential for a public health emergency. This declaration allows the FDA to issue EUAs for animal drugs for NWS.

"The FDA is using EUAs to bolster our nation's preparedness for NWS," Timothy Schell, PhD, director of the FDA's Center for Veterinary Medicine (CVM), said in a press release. "We are working expeditiously to review additional product-specific NWS EUA requests for animals that could be affected by NWS, including livestock, companion animals and wildlife."

Credelio, sponsored by Elanco, was originally approved in 2018 for flea- and tick-related indications in dogs and puppies. Lotilaner, the active ingredient in Credelio, belongs to a class of antiparasitic drugs called isoxazolines.

Credelio is available only by prescription from a licensed veterinarian. Information for veterinary practitioners regarding its use for NWS can be found in the "Fact Sheet for Veterinarians: Emergency Use Authorization of Credelio."

Larvae hatch from NWS eggs within about 24 hours. The larvae will then burrow into the infested animal's wound to feed on the living flesh. (Courtesy of the Panama-United States Commission for the Eradication and Prevention of Screwworm Infestation in Livestock)

The FDA says the decision to issue the EUA was based on available clinical data supporting the effectiveness of Credelio against Cochliomyia hominivorax larvae, along with the established safety profile of the drug

The fact sheet cites a study in Brazil that followed 11 naturally infested client-owned dogs with active myiasis caused by NWS larvae.

"The study demonstrated 100% overall effectiveness (number of expelled live and dead larvae and dead larvae mechanically removed) against C. hominivorax larvae at 24 hours posttreatment with expulsion of larvae of 80.5% and 93% at 2 and 6 hours after treatment, respectively. The mean larvicidal effectiveness was 41.1% at 24 hours," according to the fact sheet.

Additionally, the FDA CVM is providing veterinarians with information about approved animal drugs labeled for indications other than NWS that scientific literature indicates may be effective to prevent or treat NWS infestation. Products listed in the table have not been through FDA's drug evaluation process for the prevention or treatment of NWS, and CVM is not endorsing or recommending their use for NWS. However, under the Animal Medicinal Drug Use Clarification Act, veterinarians may review the manuscripts and make a judgement to do so in particular cases.

USDA playbook

Also in October, the U.S. Department of Agriculture's (USDA) Animal and Plant Health Inspection Service (APHIS) made available the "New World Screwworm (NWS) Response Playbook." The publication outlines key approaches, resources, and tools to implement animal health response activities in the event of a U.S. detection of NWS.

"USDA continues to execute our five-pronged plan to keep NWS out of the United States," USDA Secretary Brooke L. Rollins said in a press release. "While we continue to aggressively protect the U.S. border and are working with Mexico to stop the pest from continuing to spread further north, we also have to ensure our domestic response plans are ready to activate if needed."

The NWS Response Playbook outlines response strategies for federal, state, and local responders, including how to:

• Effectively manage a coordinated response and communications with stakeholders and the public
• Reduce spread to noninfested animals and prevent NWS from establishing in new areas
• Manage NWS on infested premises
• Implement NWS surveillance and management strategies in wildlife
• Implement NWS fly surveillance and management strategies

APHIS incorporated initial input from state animal health officials, industry, and veterinary organizations when developing the playbook. According to APHIS, activities outlined in the playbook will allow a "flexible, science-based approach and data-driven decisions to allow responders to plan, act, and adapt across all phases of an outbreak."

APHIS is posting the draft playbook to the NWS Foreign Animal Disease Preparedness and Response website and will continue to gather feedback to help ensure its useability and alignment with what's happening in the field.

Feedback and suggestions can be provided to FAD[dot] PReP[dot] Commentsusda[dot] gov(FAD[dot]PReP[dot]Comments[at]usda[dot]gov.)