The U.S. Food and Drug Administration (FDA) has issued two Emergency Use Authorizations (EUAs) for drugs to treat New World Screwworm (NWS) in pets. One EUA involves the use of NexGard (afoxolaner), chewable tablets for the treatment of NWS infestations (myiasis) in dogs. The second EUA is for NexGard Combo (esafoxolaner, eprinomectin, and praziquantel topical solution) for the treatment of NWS myiasis in cats.
As Texas Public Radio reports, the emergency authorizations are a precaution according to officials, since there are no reports of NWS detection in the United States thus far, but has been moving closer to the Texas-Mexico Border in recent months. In fact, the nonprofit Borderlands Research Institute, within Sul Ross State University, in Alpine, Texas, released a statement, which reads, in part:
“Recently, reports indicated that New World screwworm was once again dangerously near Texas (located in September 2025 only 70 miles from Laredo, Texas). To delay re-entry, the U.S. has restricted livestock imports from areas affected by the outbreak. Yet such restrictions can only buy time; they cannot fully prevent New World screwworm from eventually crossing the border.”
But, the anti-parasitic pet medications are not without their own set of potential risks, in the form of neurologic adverse reactions. Those may include muscle tremors, ataxia, and seizures [although the FDA explains most dogs and cats have not experienced adverse reactions]. Both products are only available by prescription from a licensed veterinarian. They are typically used to prevent fleas, ticks, and heart worm. They can now be used to treat new world screwworm.
* Monitor your animals closely for open wounds that may attract NWS flies.
* Cover and treat these sites when possible.
* Know the signs of NWS infestations including evidence of fly strike, presence of larvae in wounds, irritated or depressed behavior, etc.
* Report suspicions IMMEDIATELY!
The FDA further stated that, “pets near the border and pets that have traveled to countries with active cases are more likely to be exposed to the screwworm.” The FDA previously issued an Emergency Use Authorization for the drug Credelio to treat screwworm in cats and dogs. It also conditionally approved a similar drug, Credelio Quattro.”
This latest NWS threat comes more than forty years after decades of campaigns on both sides of the U.S.-Mexico border finally led their eradication in the United States. While many flies feed on dead or decaying tissue, the screwworm larvae devour living flesh, once a female lays her eggs in open wounds of warm-blooded animals.
Dr. Jennifer Schleining, a clinical professor and head of the Department of Large Animal Clinical Sciences at the Texas A&M College of Veterinary Medicine & Biomedical Sciences and member of the AgriLife Research New World Screwworm Task Force, explains, “The larvae basically eat the animal from the outside in. It can happen very fast if you don’t catch it early.”
The results on livestock can be catastrophic if swift action is not taken. Speaking on a webinar hosted by the Swine Health Information Center in June 2025, Cody Egnor, DVM, veterinary medical officer with the USDA, cautioned, Untreated [NWS] infestations can be fatal within seven to 14 days, with nearly 100% mortality in newborns with umbilical infestations. NWS is not contagious from animal to animal, but multiple animals in a group can become infested.” A 2024 USDA APHIS report indicates a potential outbreak in Texas could cause $732 million in producer losses and a $1.8 billion impact on the state's economy.
One technique successfully used in the past includes the combination of sterile flies and fluorescent dye. Female screwworm flies mate with sterile male flies resulting in unfertilized eggs that don’t hatch, and are easy to identify with their glowing properties.
Back on Monday, February 9, 2026, USDA leaders and Gov. Abbott announced the completion of a U.S.-based sterile fly dispersal facility in Edinburg, Texas, about 20 miles north of the border. The USDA is now releasing roughly 100 million sterile New World screwworm (NWS) flies per week focused along the U.S.-Mexico border, and about 50 miles into Texas.
