US Steps Up New World Screwworm Response as Parasite Nears Border
The US is intensifying its response to New World screwworm as confirmed cases approach within 62 miles of the US-Mexico border. Emergency exemptions allow import of new treatments from Brazil, while sterile fly releases are expanded and a $100 million research initiative is launched. All southern ports of entry remain closed to livestock trade.
The United States is intensifying its response to the advancing New World screwworm parasite, with confirmed cases now reported within 62 miles of the US-Mexico border. Federal and state agencies are implementing emergency measures including new treatment options, expanded sterile fly releases, and infrastructure investments to prevent the flesh-eating parasite from entering the country.
The US Environmental Protection Agency on April 27, 2026, granted an emergency exemption allowing the US Department of Agriculture to import Tanidil (coumaphos, propoxur), a topical powder made by Elanco Animal Health in Brazil. This exemption allows Tanidil to be brought into the national veterinary stockpile before any confirmed US cases. An earlier emergency use authorization from the FDA had approved Negasunt Powder for New World screwworm. Both products contain the active ingredients coumaphos and propoxur, though Negasunt also contains the antibiotic sulfanilamide, placing it under FDA oversight, while Tanidil is regulated by the EPA as a pesticide.
Access to these treatments is currently limited to federal, state, local, and federally recognized tribal agency personnel, along with those working under their supervision. If New World screwworm is detected in the US, authorized use would expand to include veterinarians, personnel at quarantine stations, certified applicators at livestock and game facilities, zoo and wildlife facility staff, animal rehabilitation centers, and other wildlife professionals. The importation and relabeling of Tanidil are expected to take approximately 90 to 100 days once an order is placed, and some states may require their own pesticide registration before the product can be used within their borders.
The sterile fly release efforts, which eradicate the parasite by releasing millions of radiation-sterilized male flies that mate with wild females, have been shifted north of active cases in the Mexican state of Tamaulipas to create a buffer zone. The new dispersal zone includes a roughly 50-mile area in southern Texas along the border with Tamaulipas. The USDA currently disperses 100 million sterile insects per week in Mexico and along the US-Mexico border.
Texas Governor Greg Abbott issued a disaster declaration to marshal all available government resources to strengthen the state's New World screwworm response. The USDA has invested $21 million to support Mexico's renovation of an existing fruit fly facility in Metapa, Mexico, which will double New World screwworm production capacity once complete, with production anticipated to begin as soon as this summer. The USDA completed a sterile fly dispersal facility at Moore Air Base in Edinburg, Texas, in February 2026, and construction of a sterile fly production facility at the base with a targeted maximum capacity of 300 million sterile flies per week is expected to begin this spring.
The USDA has launched the New World Screwworm Grand Challenge, a $100 million initiative through APHIS to support research and development of new tools to detect, control, and ultimately eradicate the parasite. The initiative will fund projects that enhance sterile screwworm fly production, develop new traps and lures, advance therapeutics or treatments for animals, and create additional tools to strengthen preparedness and response. Eligible applicants had until February 23 to submit proposals.
New World screwworm was also found in a horse imported from Argentina at a Florida quarantine facility. An inspector identified an open wound with larvae on the horse during a routine examination, and the larvae were confirmed as New World screwworm by the USDA's National Veterinary Services Laboratories. The horse was treated and will remain in quarantine until determined to be free of the parasite.
Currently, all southern US ports of entry are closed to livestock trade. USDA's Animal and Plant Health Inspection Service provides current status updates on New World screwworm in the United States, Mexico, and Central America. The CDC issued a health advisory in late January to raise awareness about the parasite's potential to spread.