U.S. adds emergency screwworm treatments as cases near border: full analysis

Federal agencies are widening the U.S. treatment toolkit for New World screwworm before the parasite reaches domestic herds. On April 27, EPA granted USDA’s request for a Section 18 emergency exemption to import Tanidil from Brazil, while FDA issued an emergency use authorization for Negasunt Powder, giving APHIS two additional topical options to stockpile and distribute if New World screwworm is detected in U.S. animals. (aphis.usda.gov)

The move comes after months of escalating federal preparation tied to the parasite’s spread in Mexico and Central America. APHIS has said New World screwworm was confirmed in Nuevo León in September 2025, less than 70 miles from the U.S.-Mexico border, and CDC later warned that the outbreak had moved into northern Mexico, including Tamaulipas, which borders Texas. CDC’s current situation page says that, as of May 5, 2026, countries in the region had reported more than 171,700 animal cases and more than 1,830 human cases, even though the fly has still not been detected in the United States. (aphis.usda.gov)

Tanidil’s authorization is notable because the product is not currently available in the U.S. APHIS said it must first be imported from Brazil, then relabeled, a process expected to take roughly 90 to 100 days after the order is placed. The agency also said some states will require separate state-level registration, which could limit where the product is immediately available. Once in country, Tanidil and Negasunt are expected to move through APHIS and the National Veterinary Stockpile, with distribution coordinated alongside state animal health officials and federally recognized tribal agencies. (aphis.usda.gov)

FDA’s Negasunt authorization fills a clear regulatory gap. The agency said Negasunt may be effective for preventing and treating screwworm myiasis in cattle, swine, goats, sheep, horses, donkeys, domestic hybrid equids, and captive wild, exotic, and zoo mammals. FDA also stated there are currently no fully approved animal drugs for New World screwworm, and no adequate, approved, and available alternative for several of those species. In its authorization materials, FDA said residues in food products from treated cattle, swine, goats, sheep, and captive wild and exotic food-producing mammals would not pose a public health concern when the product is used as authorized. (fda.gov)

Industry reaction has centered on readiness rather than immediate field use. Elanco said the authorizations are meant to give veterinarians and livestock producers “a ready-now treatment option” if the fly enters the U.S., noting confirmed cases had been detected as close as 62 miles south of the border at the time of its announcement. The company also emphasized that early detection and immediate treatment of open wounds remain critical, alongside fly and tick control to reduce wound sites that can attract egg-laying flies. (elanco.com)

Why it matters: For veterinary professionals, especially those in large animal, mixed animal, equine, wildlife, and zoo practice, the federal response is shifting from contingency planning to operational readiness. Treatment access is still tightly controlled, but the addition of Tanidil and Negasunt suggests regulators expect clinicians and animal health officials to need more than surveillance, movement controls, and sterile insect releases if the parasite crosses into the U.S. APHIS says New World screwworm is not currently present in the country, yet USDA is already dispersing 100 million sterile insects per week in Mexico and adjusting release areas based on surveillance and modeling. That combination of border defense plus stockpiled therapeutics signals a more layered response strategy. (direct.aphis.usda.gov)

The implications extend beyond cattle practice. New World screwworm can affect a wide range of warm-blooded animals, and CDC has reminded clinicians that the larvae feed on living tissue and can infest wounds and mucous membranes. Veterinarians may not be the first to receive Tanidil or Negasunt directly, but they’re likely to be central to recognition, reporting, wound assessment, treatment orders, and communication with pet parents and producers if suspicious cases emerge. FDA’s authorization documents also make clear that emergency-use products come with fact sheets, safety restrictions, and use conditions, so clinical familiarity with those requirements will matter. (cdc.gov)

What to watch: The next milestones are practical ones: APHIS ordering and importing Tanidil, state-level registrations where needed, additional USDA guidance on tracking and reporting requirements, and any further FDA emergency authorizations as the government continues to build out its screwworm response ahead of the 2026 high-risk season. (aphis.usda.gov)