Fish, Wildlife and Parks biologist Jay Kolbe drags a deer carcass from a backwater of the Clark Fork River on Wednesday evening to confirm signs of internal hemorrhaging caused by a virus spread among deer by biting gnats. Dozens of deer have died west of Missoula in recent days in what appears to be the first documented case of epizootic hemorrhage disease west of the Continental Divide in Montana.
Wildlife officials are trying to find out why more than 100 whitetail deer have died along the Clark Fork River west of Missoula.

"The deer may show no outward symptoms of disease," said Montana Fish, Wildlife and Parks biologist Vickie Edwards. "People are seeing healthy looking deer fall over dead."

Fishing guides and landowners along the Clark Fork and fields near and downstream of Harpers Bridge started reporting the dead deer on Sunday. Dead deer have also been found in the Mill Creek area northeast of Frenchtown.

By Tuesday, Montana Fish, Wildlife and Parks personnel had confirmed 103 dead deer, with more appearing sick or dying. Biologists have collected lung, spleen and blood samples from affected deer to research the cause.

One possible cause is epizootic hemorrhagic disease, which has hammered deer populations in several eastern Montana regions. Biting midges or gnats transmit the disease, usually in late summer or early fall. The bugs typically die off soon after the first hard frost.

"Hemorrhagic disease viruses are not contagious from one animal to another and are not transmissible to humans," said Jennifer Ramsey, FWP wildlife veterinarian in Bozeman. "Transmission is only known to occur through the bite of the gnat."

The disease poses no threat to humans. Anyone who sees dead or sick deer in the Missoula area is asked to call FWP at 542-5515 with observations and locations.