I have followed prion research since the outbreak of mad cow disease in Great Britain three decades ago. With a mad cow variant prion causing the Chronic Wasting Disease epidemic spreading in wildlife, this blog is an overview of a disease I believe carries great risk to man and beast. My new biological thriller, Fatal Feast, is set in Montana, featuring pandemic spread of prion disease.
Hunting in Montana is a way of life. In some families, killing your first deer is a coming of age event. Mounting a trophy on the wall, filling the freezer with venison or elk each fall, and hunting into old age are common. But is it still safe to eat venison, elk, moose and other wild game? Maybe, maybe not.
Across the United States and in Canada the public have been alerted to the epidemic spread of a fatal neurological disease in wildlife. They are cautioned not to eat infected meat, to handle meat with caution, and instructions to limit spread from infected carcasses.
However, the infectious agent is invisible and will contaminate surfaces and tools in contact with blood and other body fluids. All contaminated surfaces should be washed with soap and water, then soaked for five minutes with 40% bleach. Infected tissue must be incinerated to stop infectivity. Prions are not killed by usual sterilization techniques. In fact, people have died after being infected by disease transferred to them from “sterilized” surgical instruments
It is true no humans have been identified with CWD from eating prion-infected meat, but research has shown, both spider monkeys and macaques are susceptible and die from eating infected venison. With these non-human primates having genetic makeup so close to humans, the likelihood of CWD disease jumping the species barrier and infecting humans is possible. CWD is a variant of mad cow disease that killed humans in Great Britain in the 1990s. Humans died after consuming infected beef.
The first CWD positive deer was identified in Montana in 2017. Since that time, the infected animals have been identified on both sides of the Rocky Mountains. Twenty-seven states and three Canadian provinces now have spreading CWD. Alaskan caribou have the genetic makeup risking spread of the disease to them. In Norway, 2,000 reindeer were exterminated in an attempt to stop spread in an expansive herd. In Montana and elsewhere, kill zones, like the one in Libby, are organized to euthanize large herds of animals at risk for spread.
Prions are stable in soil for years and are taken up in growing plants that may be able to transmit the disease. Carcasses left in the forest contaminate the ground for years, sometimes decades, depending on the type of soil. In the wild, prions are spread naturally to scavengers such as mice. Crows are known carriers. Studies show transmission in herds from licking behavior and ground contamination easily spread disease.
Ill animals are easy to identify when the disease has progressed. They appear weak, confused, thin, unafraid of humans, uncoordinated and drooling. Early in the disease process as prions spread through the body, the animal appears normal but is contagious. Friends of mine driving along the west Hungry Horse Dam road stopped their vehicle to watch an ailing doe with twin yearlings. The young ones were lively and beautiful. The doe appeared unstable, thin, and stumbled up to their car and pressed her nose against the side window, peering in at them with vacant eyes. No positive CWD deer have been identified in that hunting zone, but it appears CWD has arrived there, too.
After the unusual protein, a prion, acting like an unstoppable super-bug, enters the body, disease begins in the small intestine concentrating in lymph tissue. Gradually, over about a year and a half in deer, prions spread along nerves to the brain before symptoms are visible.
Clumps of the abnormal protein disrupt nerve function and destroy brain tissue. Microscopic examination of brain tissue shows resulting cell damage and holes making it look like a sea sponge, thus the name spongiform. Mad cow disease is called bovine spongiform encephalopathy. The generic term for an array of prion disorders in animals and humans is transmissible spongiform encephalopathy (TSE). There are many forms. Some human forms are inherited.
CWD information is available on state hunting websites.