CNBC – U.S. cattle ranchers will soon have a new way to protect their dwindling herds from the threat of the parasite screwworm, which is decimating cattle in Mexico.
Animal Health for the prevention and treatment of New World Screwworm. It can also be used as a treatment and control for the cattle fever tick.
“The conversation started in July with the FDA, and because there is an element of human food safety, there was a big data package we had to generate,” said Holger Lehmann, vice president of pharmaceutical research and development for Merck Animal Health.
“This approval is a significant undertaking. The U.S. has received the product, and Mexico received it in early November, where it is being used,” Lehmann said.
Each dose is effective for 21 days before a new dose would need to be applied. The FDA has approved it with a 98-day withholding period to ensure no residue in meat.
Merck Animal Health is prioritizing sending the product first to U.S. distribution partners located in areas along the U.S.-Mexico border that are more likely to have an immediate need, by the end of the year.
The treatment will be available more broadly to veterinarians and producers in mid-January 2026. Previously, Merck had said it would be more broadly available Dec. 20.
Screwworm is spread by hatching fly eggs in the open wounds of cattle, which feed on their living tissue. Humans can also get infected.
To protect the U.S. cattle herd and to stop the spread of the parasitic fly, the U.S. Department of Agriculture has closed the border to Mexico for imports of live cattle, bison, and horses, on and off, since 2024 …
