KERRVILLE, TEXAS — U.S. Secretary of Agriculture Brooke Rollins is scheduled to receive a briefing on the New World screwworm infestation at the U.S. Livestock Insects Research Laboratory in Kerrville, Texas. This briefing follows the USDA's confirmation of two additional cases of the New World screwworm in Texas.
The new infections were identified in a calf in La Salle County and a dog in Andrews County. These cases bring the total number of confirmed New World screwworm cases in Texas to four. Initial cases were discovered last week in two young calves within a few miles of each other in southern Texas. Federal officials indicated that the infected dog had recently traveled in Mexico.
Canada temporarily suspended imports of cattle, horses, and other livestock from Texas following the confirmation of cases. This fly larva consumes living tissue and can affect cattle, wildlife, pets, and humans. Female screwworm flies deposit eggs in the open wounds of warm-blooded animals.
University of Florida entomologist Edward Burgess said increased surveillance often leads to more detections. "When that first case is seen, everyone is being vigilant and their eyes are on it more intensely. And when you are looking for something, you are more likely to see it," Burgess said.
USDA marketing and regulatory undersecretary Dudley Hoskins said, "While we address these instances that require immediate attention, and continue to sample suspected cases, we are simultaneously working to eradicate the pest entirely." The screwworm was eradicated in the U.S. during the 1960s.
Federal and industry officials implemented containment measures following the pest's detection in Mexico in late 2024. The USDA plans to increase sterile fly production at international facilities and construct a new facility in Texas. Female screwworm flies mate only once, a biological trait that allows sterile male release programs to halt outbreaks, a method previously used to contain screwworm populations in southern Panama for decades.
The USDA stated that poison bait methods for controlling screwworms have not been proven effective and may harm non-target insects, animals, or humans. Twelve government-approved medications are available to treat screwworm infections in livestock. The parasite's reappearance has not substantially altered beef prices, which are already elevated due to a smaller national cattle herd. Screwworm larvae do not infest processed meat or harvested fruit. Screwworms prefer humid environments with temperatures at or above 77 F (25 C). Irradiated sterile male flies can be identified and color-coded using ultraviolet light detection.