Is a prion disease of deer and elk.

Chronic wasting disease

Explanation:

The prion disease that is known to affect the deer and elk is known as chronic wasting disease and it is called so as the affected animal undergoes severe weight loss (wasting) along with other neurological symptoms. It is a chronic disease as it takes years for the symptoms to manifest themselves in the infected animal.The disease is fatal to the infected animal and some animals may even die without actually showing any signs or symptoms of the disease. There is no known treatment or vaccine to prevent the disease. 

This is a time line from 685 to 978