The U.S. Department of Agriculture confirmed a second New World screwworm in a calf in Zavala County, Texas, after the agency earlier detected a case in La Pryor, the first U.S. finding since 1966, and Canada announced a temporary ban on livestock from Texas.
The USDA said the second screwworm was found in a one-month-old calf and was confirmed Friday after the agency tested a number of suspected cases; the second infected animal was about 5.6 miles (9 kilometers) from the first case.
The initial case involved a three-week-old calf that was confirmed Wednesday, with larvae found in its umbilical area; La Pryor is about 30 miles (48 kilometers) from the Mexico border.
Texas State Veterinarian Bud Dinges established a 12-mile (20-kilometer) quarantine zone that prohibits the movement of any warm-blooded animal outside the zone without an inspection, and the USDA described the area as a 20-kilometer-wide control zone and said it had enacted quarantines, movement controls and surveillance there.
The USDA has begun releasing sterilized male flies in the area and officials said they have been dropping millions of sterile flies to mate with wild females because female screwworms generally mate only once and females that pair with sterile males are unable to produce offspring. The department has committed $21 million to convert a fruit-fly breeding facility in southern Mexico for screwworm breeding, plans a new center in southern Texas to disperse sterile flies bred elsewhere, and has started construction on a $750 million screwworm fly factory in Texas; the converted facility in Mexico should be operating next month.
Officials said they would need to breed up to 600 million sterile screwworm flies each week to fight the outbreak, but facilities in the United States and Mexico are currently capable of producing about 100 million sterile flies per week. Agriculture Secretary Brooke Rollins told reporters that since the discovery officials have released four million sterile flies by ground, in addition to another four million released by plane on a weekly basis since February, and experts said the current supply is too low to immediately halt a growing screwworm population.
The U.S. is stationing sniffer dogs at the borders to detect screwworms; those specialized dogs, employed by Customs and Border Protection and the USDA, are known as the Beagle Brigade. The U.S. Centers for Disease Control and Prevention said the latest outbreak has so far resulted in 2,070 cases of screwworms in humans.
Texas Agriculture Commissioner Sid Miller criticized the federal response as slow and incomplete and called on the president to take direct control and "throw every available federal resource at this threat before it becomes a full-blown agricultural disaster." Dudley Hoskins, a USDA under secretary, said, "Protecting our livestock industry is a national security issue of the utmost importance, and USDA is wasting no time in taking action." Dinges urged ranchers and pet owners in the area to respect the quarantine zone. Gov. Greg Abbott declared a state of disaster on Friday over the "imminent threat" the outbreak posed and said, "This is likely to spread over the course of the summer." Abbott also criticized sterile fly production as inadequate.
Canada's food inspection agency announced the temporary ban on livestock from Texas, saying cows and horses that were in Texas anytime within 21 days before crossing the border into Canada would not be accepted. Canadian officials said the parasite is unlikely to become a problem in the country because of the colder climate but urged farmers to monitor livestock for wounds accompanied by discharge or a foul odor and asked residents to check pets if they travel to Texas. The U.S. and Canada have a two-way cattle trade; Canadian officials said 550,000 cattle were imported from the United States in 2025.
U.S. agriculture and health officials have outlined a plan to release hundreds of millions of genetically altered sterile flies to try to halt the population growth, along with using sniffer dogs to identify the parasite in cattle, though some experts questioned whether those tactics will be enough. Screwworm larvae grow into flies that can travel short distances, and officials said long-distance spread has primarily occurred when larvae or flies have been transported by humans.