The recent detection of the New World screwworm in the United States has raised eyebrows among agriculture officials, but experts say residents in Virginia have little reason to worry.
Known scientifically as Cochliomyia hominivorax, the New World screwworm is a parasitic fly capable of infesting livestock, pets, wildlife, and occasionally birds. Since early June, twelve confirmed cases involving domestic animals have been reported across Texas and New Mexico.
Despite the detections, the chance of the screwworm reaching Virginia in the near future is “essentially zero,” according to John Currin, DVM, a clinical associate professor at the Virginia-Maryland College of Veterinary Medicine. “And long term, still incredibly close to zero,” he added.
The fly is typically found in South America and the Caribbean, but has been gradually moving northward through Central America since 2023. The insect is drawn to wounds and body openings, where it deposits eggs that develop into maggots. Those larvae then feed on living tissue, causing severe and potentially fatal injuries to the animals they infect.
Currin cautioned that the number of confirmed U.S. cases is likely just a fraction of the actual total. “We should not be surprised when a lot more U.S. cases are identified,” he said. “There’s more out there than what’s been reported. And it’s hard to monitor in wildlife.”
For now, only those transporting animals to or from Texas are being urged to exercise caution. “People need to be aware, if they’re traveling into that area, to prevent bringing it back,” Currin said. “There are products available for both NWS prevention and treatment for livestock, pets and people who may be traveling there.”
Anyone traveling with animals can speak with a local veterinarian to learn about available preventatives and treatments.
The U.S. Department of Agriculture and the Virginia Department of Agriculture and Consumer Services are actively monitoring the movement of animals across state lines to prevent the spread of infected animals into the region.
Virginia State Veterinarian Dr. Charlie Broaddus expressed confidence in the state’s preparedness while noting a key environmental factor working in Virginia’s favor. “If New World screwworm does find its way to Virginia, we are ready to respond and help protect the health of our animal populations,” he said. “We are fortunate that with NWS not surviving in sustained temperatures below 46 degrees, Virginia is not at risk for NWS to become established here long term.”
Consumers who purchase beef or other meat products can also rest easy, according to Tony Banks, senior assistant director of Virginia Farm Bureau Federation agriculture, development and innovation. “Though NWS is a legitimate problem for wildlife and livestock in southernmost states, there’s absolutely no food-safety risk to consumers,” he said.
Currin also pointed out that Virginia’s climate is generally inhospitable to the screwworm fly. “Hopefully we will be able to get this thing contained before it can even move this far north,” he said. “We’re at least a year away from the new USDA plant in Texas coming online that will produce sterile flies to truly get it under control.”
The screwworm is not a new threat to the United States. After infested cattle were shipped from the Southwest in 1933, the parasite triggered outbreaks across southeastern states. The USDA eventually wiped out the screwworm by 1966 using the Sterile Insect Technique, which involves releasing enormous numbers of sterilized male flies to cause local populations to collapse.
The USDA is currently leading a coordinated national response to the new detections. For more information, visit screwworm.gov or reach out to USDA staff at [email protected].
