Seven more deer on a game farm near Brainerd have been confirmed infected with chronic wasting disease, the Minnesota Board of Animal Health said Wednesday.

The infected deer were among more than 100 that either died or were shot and killed on the farm after the owner, three years after the disease was first discovered on the farm, finally allowed authorities to destroy the animals so tests could be conducted.

The only way to test for CWD is to examine the animal's brain tissue. The always fatal disease affects deer, elk and moose and is spread between animals through a rogue protein called prions.

In addition to the seven positive test results, some 82 deer from the farm tested negative for CWD. Another 13 deer were already dead and too decomposed to be tested. It's not clear why they died, but it could have been from CWD.

The Minnesota Department of Natural Resources and several Minnesota lawmakers have called for tougher laws for game farms to help prevent the spread of CWD to wild deer, including improved fencing, more testing and a ban on interstate movement of deer-family animals.

After the first CWD was found on the farm outside Merrifield in 2016 the animal health board monitored the farm but allowed it to keep operating. That changed earlier this year after a wild doe found about a half-mile from the Merrifield farm tested positive for CWD - the first ever CWD confirmed in wild deer in the northern half of Minnesota. The U.S. Department of Agriculture negotiated an agreement with the farm's owner to pay him through a federal reimbursement program to destroy his herd. Officials have refused to say how much the farmer was paid.

"The results give us a clearer picture of the disease prevalence on the farm as we continue our efforts to contain and eliminate any remaining infectious CWD prions in the enclosed property," Dr. Linda Glaser, the animal health board's assistant director, said in a statement.

The wooded farm will remain fenced and monitored for at least five years to reduce the risk of the disease being spread to wild deer off the site, the agency added.

CWD has expanded from a single site in Colorado to more than 26 states over the past 50 years, including several deer farms and more than 20 wild deer in southern Minnesota. In southern Wisconsin where the DNR has stopped trying to control the disease, as many as half of all wild deer shot now test positive for CWD. Minnesota wildlife officials are hoping to cull as many deer in the CWD-infected areas as possible to keep the incidence of CWD low and slow the spread to new areas.

CWD is always fatal to deer, elk and moose. One Canadian study found it could spread to monkeys that are fed CWD contaminated meat. CWD can be spread from deer-to-deer but can also spread through soil and even plants. No case of CWD is known to have infected a person, but researchers and health officials recommend against eating a CWD-positive deer. Because the disease is similar to mad cow disease, which can be fatal to humans, some public health experts say it's only a matter of time before CWD spreads to people.