FDA approves emergency use of medication to treat screwworm in dogs, cats
New World screwworm fly (Cochliomyia hominivorax) on Friday, Jun 06, 2025, in College Station, Texas. (Michael Miller/Texas A&M AgriLife)
The U.S. Food and Drug Administration on Thursday issued an emergency use authorization for a medication to be used to treat New World screwworm infestations in dogs and cats.
Nitenpyram, an over-the-counter medication used to kill adult fleas, was shown to be effective at killing screwworm infestations based on studies in Brazil, officials said.
What they're saying:
"The FDA has spent nearly a year fast-tracking reviews and readying for the arrival of New World screwworm in the U.S.," Acting FDA Commissioner Kyle Diamantas said.
Nitenpyram tablets can be used in dogs and cats that weigh at least two pounds and are at least four weeks old, the FDA said.
New World screwworm flies lay eggs in open wounds or mucous membranes. The larvae can hatch in hours and eat live flesh and fluids instead of dead material. The larvae can infest any warm-blooded animal, including humans in rare instances.
Studies in Brazil showed the drug worked effectively to expel most of the maggots from a screwworm infestation, while the remaining larvae died, the FDA's fact sheet states.
The FDA said a veterinary professional may need to remove remaining larvae following treatment to minimize the risk of infection and provide a plan for wound care.
"Nitenpyram works quickly, killing most NWS larvae within hours of the first dose. Pet owners should administer a second dose six hours after the first," the FDA said.
Officials warned that nitenpyram does not prevent infestation or protect against reinfestation.
Nitenpyram was first approved as a flea treatment for dogs and cats in 2000 under the brand name Capstar.
What is the New World screwworm?
Big picture view:
The New World screwworm is considered one of the most devastating livestock and wildlife pests in history.
The insect gets its name because it’s only found in the Americas.
New World Screwworm larvae (USDA)
It lays its eggs in the open wounds of animals, and its larvae become parasites. Unlike common fly larvae, screwworm maggots burrow into and feed exclusively on the living flesh of warm-blooded animals, causing severe injury, massive economic loss, and death if left untreated.
While rare, they can also infect humans.
The screwworm was mostly eradicated in Texas and the rest of the United States in the 60s. But now, it’s moving north up from Panama and has a known presence a little over 300 miles south of the Texas-Mexico border.
New World screwworm in Texas
Officials have confirmed eight cases of New World screwworm in Texas and another case in New Mexico.
Since June 3, eight cases of New World screwworm have been reported to the USDA. The cases have been found in Zavala, La Salle, Gillespie and Edwards counties. The pest has been found in cattle and goats.
Officials initially reported an additional case involving a dog in Andrews County on June 8. However, after further epidemiological investigation, authorities determined the animal lives in Lea County, New Mexico, and the case was reclassified as New Mexico's first confirmed New World screwworm infection.
The veterinarian who submitted samples from the dog is based in Texas, officials said. Early reports indicated the dog had recently traveled to Mexico.
The Texas Parks and Wildlife Department said updates will be provided as additional cases are confirmed. The agency has established a public information page and said situation reports will be updated daily when new detections occur.
The Source: Information in the article comes from the U.S. Food and Drug Administration, the U.S. Department of Agriculture and previous FOX Local reporting.