FDA Approves Drug to Combat Flesh-Eating Screwworm Amid Outbreak

October 2, 2025 – The U.S. Food and Drug Administration has granted conditional approval for an injectable drug to help fight the reemergence of the New World Screwworm, a flesh-eating parasite that has resurfaced near Texas’ southern border.

The drug, called Dectomax-CA1 (doramectin injection), is designed for use in cattle to both treat and prevent infestations of the screwworm, which feeds on the living tissue of warm-blooded animals. The FDA said the drug has been proven safe and has a “reasonable expectation of effectiveness,” though full approval will require additional data.

Doramectin is a broad-spectrum antiparasitic drug used in veterinary medicine to treat and control internal and external parasites in livestock like cattle, swine, sheep, and deer. It is a macrocyclic lactone derived from the soil organism Streptomyces avermitilis and is available as an injectable solution or pour-on formulation.

The announcement follows months of warnings from ranchers and agricultural officials about the risks posed by the parasite. The screwworm, once eradicated from most of the Americas in the 1960s through eradication programs, has recently reappeared. Just last week, the U.S. Department of Agriculture confirmed an infestation only 70 miles from the border city of Laredo, raising alarms across the livestock industry.

Doramectin is not approved for use in humans.

Texas cattle producers say the approval is critical for protecting herds and preventing the spread of the parasite northward. “Without effective treatment, screwworms can devastate livestock populations and cause massive economic losses,” one ranching association spokesperson said.

The FDA noted that Dectomax-CA1 can prevent reinfestation in cattle for up to 21 days. The agency emphasized that the approval is limited to specific uses in beef cattle, young dairy cattle, pregnant cows, newborn calves, and bulls.

Agricultural leaders welcomed the move but stressed that ongoing vigilance is necessary. “This is a vital tool, but it must be part of a broader strategy to keep the screwworm contained,” said a Texas agriculture official.

For now, the new drug offers ranchers and veterinarians their most promising line of defense against a parasite many had hoped was gone for good.