Chronic wasting disease (CWD) affects cervid species in North America. This includes the white-tailed deer (Virginianus odocoileus), mule deer (Odocoileus hemionus), elk (Cervus canadensis), reindeer (Rangifer tarandus) and moose (Alces alces). The disease is a transmissible spongiform encephalopathy (say that five times, fast!). These diseases occur due to an incorrectly folded protein called a prion. In animals, we recognize three of these diseases: mad cow disease, scrapie, and chronic wasting disease. In the body, all proteins must undergo folding, but these prions got messed up somewhere along the way. The problem is that when prions are present in an animal’s nervous system, they can cause other proteins to become incorrectly folded, just like them. All of these altered proteins, when plentiful, cause neurologic disease. They are infectious, but unlike bacteria, protists, and fungi (and depending on who you ask, viruses), they are not alive.
Prion diseases are unique in their pathophysiology and are poorly understood. Some scientists still debate whether people can contract CWD from eating game. So it should come as no surprise that the government takes high precautions when dealing with this disease. Herds of farmed elk or deer with the disease are quickly put under quarantine. The disease is usually noted in older animals, due to the time it takes for the prion proteins to accumulate. This makes diagnosis hard, and it usually has to occur post-mortem.
I had an externship last summer that involved a potential CWD case. We got a call for a reindeer that had been losing weight over the past few months, while her herdmates were thriving. After catching her in the most non-stressful way we could (deer get really stressed during capture, and can get ill or even die from capture myopathy) we checked her out. Sure enough, she was skinny. When asking about CWD, the owner did not know much about it. Heck, the reindeer didn’t even have any papers stating where she was from! Who knows what state she came from! Because it could have been an animal with CWD, handling of the animal was more involved. It is one of those diseases that you hope you never see as a vet, especially if you are in an area that is CWD-free. Regardless, you always have to be thinking of it when dealing with the species that it affects.