The U.S. Food and Drug Administration cleared the emergency use of nitenpyram tablets to treat New World screwworm infestations in dogs and cats, a fast-tracked response to the return of a parasite that federal officials thought they had wiped out on American soil decades ago.
The authorization, announced Thursday, makes nitenpyram the first generic animal drug approved for use against the flesh-eating parasite. The FDA said the drug kills most screwworm larvae within hours of the first dose, giving pet owners and veterinarians a tool that did not exist in approved form when the first new domestic cases surfaced.
That the agency had to reach for its emergency powers tells you something about how seriously the federal government is taking this outbreak, and how flat-footed it was when the screwworm reappeared after more than six decades of absence.
New World screwworm was once an annual warm-weather nightmare for cattle ranchers across the South and Southwest from the 1930s through the 1960s. A massive federal eradication campaign, one of the genuine success stories of 20th-century agriculture policy, drove the parasite out of the continental United States.
Now it is back. Government officials have confirmed several new cases in cattle in Texas in recent weeks. A case was also found in a dog in New Mexico, according to a USDA APHIS announcement. Newsmax reported that U.S. officials recently confirmed the first domestic New World screwworm cases in more than six decades in cattle, a goat, and a dog in Texas and New Mexico.
The parasite's biology makes containment urgent. Female New World screwworms lay eggs after mating only once in their monthslong lives. The larvae burrow into open wounds on warm-blooded animals and feed on living tissue, a gruesome process that can kill livestock and pets if left untreated.
Nitenpyram is not a new compound. The FDA first approved it in 2000 under the brand name Capstar for treating flea infestations in dogs and cats. Pet owners may already have it in their medicine cabinets. What changed is the FDA's authorization to use generic, over-the-counter nitenpyram tablets specifically against screwworm larvae, an off-label application that now carries the agency's formal backing.
The FDA stated in its announcement:
"Nitenpyram works quickly, killing most [screwworm] larvae within hours of the first dose."
The agency added that pet owners should administer a second dose six hours after the first. The tablets can be used in dogs and cats that weigh at least two pounds and are at least four weeks old.
Even after treatment, the FDA cautioned, an animal may need to have remaining live or dead larvae removed by a veterinarian. This is not a simple pill-and-forget solution. It is a first-response tool that buys time and reduces suffering while a vet handles the rest.
The authorization did not come out of thin air. Studies conducted in Brazil on cats and dogs with screwworm infestations found that most maggots were expelled after treatment with nitenpyram, while the remaining larvae died, according to an FDA fact sheet. Brazil, where the New World screwworm remains endemic, provided the clinical evidence the FDA needed to move quickly.
The agency relies on emergency use authorizations to speed access to treatments in urgent situations, the same legal mechanism it used during the COVID-19 pandemic for vaccines and therapeutics. In this case, the urgency is an agricultural and veterinary emergency that could spread rapidly through livestock herds and domestic animal populations if the parasite gains a foothold.
The FDA's emergency action addresses treatment. It does not answer the harder question: how did New World screwworm return to the United States after more than 60 years?
The cases in Texas cattle and the New Mexico dog suggest the parasite crossed the southern border, the same border whose security has been a running source of political conflict. Screwworm eradication in the 20th century depended on a sterile-insect barrier maintained along the U.S.-Mexico line and deeper into Central America. Any breakdown in that barrier, whether from funding gaps, reduced monitoring, or simple neglect, creates a pathway for reinfestation.
Federal officials have not publicly explained the source of the new cases. The number of confirmed cattle infections in Texas has not been specified. The date of the New Mexico dog case has not been disclosed. Whether any human cases have been reported remains unanswered. These are not minor details. Ranchers and pet owners in the affected states need clear, timely information, not bureaucratic silence.
For now, the practical takeaway is straightforward. Generic nitenpyram tablets are available over the counter. The FDA has authorized their use against screwworm in pets meeting the minimum weight and age thresholds. Two doses, six hours apart, should kill most larvae. A follow-up veterinary visit may still be necessary to remove dead or surviving larvae from wounds.
The FDA's existing approval page for generic nitenpyram covers the drug's original flea-treatment indication. Pet owners in Texas, New Mexico, and neighboring states should talk to their veterinarians about screwworm risk and keep nitenpyram on hand.
The return of New World screwworm is a concrete reminder that eradication is not the same as permanence. Decades of successful containment can unravel if the systems that maintain it are allowed to erode. The FDA moved quickly on the treatment side. Whether the broader federal apparatus, USDA, border agencies, and state agriculture departments, can move just as quickly on containment will determine whether this outbreak stays small or becomes a lasting problem for American ranchers and pet owners alike.
When a parasite the country spent decades eliminating shows up again without explanation, the government owes the public more than a pill. It owes them an answer.
