MARION, Va. (WJHL) – The Virginia Department of Wildlife Resources (DWR) has found trout infected with whirling disease at a Southwest Virginia fish hatchery.

A release from the DWR states the disease has been detected in catchable-size trout at the Marion Fish Hatchery following regular pathogen testing.

Whirling disease is caused by a parasite that enters the tissue of a fish’s head and spine and quickly begins multiplying, according to the DWR. The parasite causes skeletal deformities, often to the spine and tail which impacts the fish’s swimming ability.

Infected fish sometimes swim in a circular motion due to the deformities, hence the name “whirling disease.”

The DWR reports fish exhibiting symptoms of whirling disease have not been seen in the wild outside of the hatchery.

The department announced Thursday that 40,000 catchable trout were regrettably euthanized at the fishery in order to control the disease.

“This represents about a 20% reduction in normal stocking levels for Southwest Virginia and a 5% reduction statewide,” the DWR stated.

Wildlife officials said this will likely result in a reduced number of trout stocked in Buchanan, Dickenson, Grayson, Lee, Russell, Scott, Smyth, Tazewell and Washington counties. The department is working to reallocate fish to make up for the euthanized number and impact on local waterways.

Whirling disease has been documented in 20 states, which includes Virginia. The DWR reports it is native to Europe and was first detected in the U.S. in the 1950s.

The parasite requires two hosts to complete its lifestyle: small worms then a salmonid fish. Rainbow trout are the most susceptible to the parasite, the DWR reports.

Officials said the parasite does not infect humans, even if infected fish are eaten.