JACKSON, Miss. (AP) — A deadly brain disease has been found in or is suspected in 40 Mississippi deer, and the state is asking hunters to continue providing samples through the deer season.

“Deer harvest begins to tail off this time of the season. I hope we will get several hundred more before the season is over, if not a thousand or so,” Russ Walsh, wildlife chief of staff for the Department of Wildlife, Fisheries and Parks, said Thursday.

Chronic wasting disease, or CWD, is a highly infectious disease spread by malformed proteins called prions, like those that cause mad cow disease and the related human infection called Creutzfelt-Jacob disease.

Nearly all the infected and suspected deer were in north Mississippi, including 25 killed or found in Benton County and 10 in adjacent Marshall County, the Mississippi Department of Wildlife, Fisheries and Parks said in a news release. Both counties border southwest Tennessee, where the disease has also been found.

“It’s likely tied in with the cases they have,” Walsh said.

Three of those in Marshall County and 18 in Benton County have been detected since Oct. 1.

But two, including Mississippi’s first and third, were about 160 miles (257 kilometers) away in west-central Issaquena County, along the Mississippi River.

“As we collect more samples and more data, hopefully we’ll be able to connect the dots. It’s still a mystery why those two were there,” Walsh said.

Panola, Pontotoc and Tallahatchie counties, all closer to Benton and Marshall counties, have had one each, according to a department news release.

The department has collected nearly 4,700 heads from hunters, road-killed deer and white-tails reported as diseased. “We still have several hundred of those pending lab testing,” Walsh said.

The news release said, “Continued surveillance is critical, and hunters are the key source for sample collection. MDWFP is relying on hunter-harvested deer for the remainder of the 2019–20 hunting season.”

The gun-with-dogs season runs through Jan. 22 and the archery/primitive weapons season through Jan. 31.

The department has 36 freezers where hunters can leave deer heads.

CWD can be present in a deer’s saliva, feces, urine, blood, and antler velvet for a year or two before symptoms show. It’s been found in most kinds of deer and related species, including moose, elk, and mule deer, and in at least 25 states including Texas and Arkansas. It has not been found in Louisiana, Georgia, South Carolina or Alabama.

No human infections are known but the Centers for Disease Control and Prevention recommend that hunters in areas where CWD has been found have any deer or related species they kill tested for the disease and not eat meat from infected animals.