The U.S. Food and Drug Administration (FDA) has authorized the emergency use of the drug nitenpyram to treat infestations of New World screwworms in dogs and cats. This approval comes amid recent cases of screwworm infections resurfacing in livestock and pets in the United States.
What Happened
On June 11, 2026, the FDA issued an emergency use authorization allowing nitenpyram tablets to be administered to dogs and cats weighing at least two pounds and aged four weeks or older to combat New World screwworm infestations. The decision follows confirmed cases of the parasitic infestation in cattle in Texas and in a dog in New Mexico.
Key Facts
- Nitenpyram, initially approved by the FDA in 2000 under the brand name Capstar for flea treatment, is the first generic animal drug authorized against New World screwworm.
- The medication targets larvae that consume live flesh in pets and other warm-blooded animals.
- Studies from Brazil indicated most screwworm larvae were expelled post-treatment with nitenpyram, with remaining larvae dying.
- The FDA advises pet owners to administer a second dose of nitenpyram six hours after the first.
- Screwworm infestations were once eradicated in the U.S. but have resurfaced recently.
Why It Matters
This emergency authorization provides a critical tool for veterinarians and pet owners in addressing potentially severe and fast-progressing screwworm infestations. New World screwworm larvae consume living tissue, posing a serious health threat to afflicted animals. The quick-acting treatment could limit damage and improve animal welfare during outbreaks.
Background
Screwworm, caused by larvae that feed on living flesh of warm-blooded animals, was a major cattle pest in the United States from the 1930s until eradication efforts succeeded by the 1960s. The parasite’s recent reappearance in Texas cattle and a New Mexico dog signals a potential resurgence, prompting regulatory action to control the infestation.
Analysis
The FDA highlighted nitenpyram’s rapid action, noting it kills most screwworm larvae within hours of administration. However, the agency cautioned that the drug’s effects are short-lived and it does not confer ongoing protection against re-infestation. This suggests that veterinary follow-up is necessary to ensure complete removal of the larvae.
Who Is Affected
Veterinarians, pet owners with affected dogs and cats weighing at least two pounds, and livestock owners in regions experiencing screwworm cases are directly impacted by this authorization. The agricultural and animal health sectors also face implications due to the parasite’s threat to livestock.
What Remains Unclear
- The duration of ongoing protection following treatment with nitenpyram is limited and unclear.
- A complete eradication timeline for the current screwworm outbreak in the U.S. has not been established.
- Details on the availability and distribution scale of the drug under emergency authorization remain unspecified.
What Comes Next
Pet owners are advised to administer a second dose six hours after the first dose of nitenpyram. Veterinary intervention may be required to remove live or dead larvae remaining after treatment. State officials have also announced emergency rules aimed at preventing further spread of screwworm in other regions, such as Colorado.
Sources
This article is based on reporting and publicly available information from the following source:
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