Four deer at a quarantined Crow Wing County farm have been found to be infected with a virulent fatal disease, state officials said Friday.

Chronic wasting disease (CWD) was detected in a nine-year-old female mule deer, a 18-month-old female whitetail deer, a two-year-old male whitetail deer and a two-year-old female mule deer at the central Minnesota farm, the Minnesota Board of Animal Health announced in a Friday news release.

In 2016, two deer from the farm tested positive for the disease and the farm was quarantined. It has been monitored by the board since December 2016. No deer is allowed to leave or enter the farm, located near the town of Merrifield.

"We've been working with the herd owner for the past two years to monitor the deer and look for any new detections of the disease," Linda Glaser, assistant director of the health board, said in the news release. "The biggest change following this new detection will be to extend our deadline to monitor the herd."

CWD is a disease of the deer and elk family caused by an abnormally shaped protein that damages brain and nerve tissue. The fatal disease is most likely transmitted when infected deer and elk shed the protein in saliva, feces, urine and other fluids or tissues.

After the first case was confirmed in 2016, the state's Department of Natural Resources began a three-year sampling process of wild deer near the farm. Currently in its second year, the study has not found the disease in any wild deer.

Also, last weekend, during the first days of firearms deer-hunting season, the DNR tested hunter-killed deer in the county for CWD. Those results are not yet available.

Lou Cornicelli, the DNR's wildlife research manager, said the recent four cases didn't change how the DNR conducted its sampling last weekend, but DNR staff and the board will determine if they need to monitor the wild herd for a fourth year.

"We appreciate all the cooperation hunters provided us during this past opening weekend with surveillance in Crow Wing County," Cornicelli said.