What are Prions?

white-tailed-deer-doe-and-fawnPrions are the infectious agents that cause chronic wasting disease (CWD). Prions are abnormally folded proteins that are lacking DNA. They replicate by causing other proteins that are normally found in the body to re-arrange themselves into a misfolded structure. The misfolded proteins accumulate in the brain, eventually leading to neurological clinical signs and deficits.

The prions responsible for CWD concentrate primarily in the brain, spinal column, and lymph nodes of infected animals. These prions have also been found, in much lower concentrations, in saliva, urine, feces, blood, and muscle tissue.

Transmission of CWD

Deer can transmit CWD prions to each other through saliva, urine, and feces. This has led to restrictions on the baiting and feeding of deer in many states. Whenever deer are congregated, such as at a feed site, there is increased risk of direct (i.e., nose-to-nose) and indirect (i.e., uninfected deer that ingest feed contaminated with infectious saliva or urine left by infected deer) contact. Increased direct and indirect contact between healthy and infected deer often amplifies disease transmission within a population of susceptible individuals.

sick-deer

One of the difficulties wildlife managers face with CWD is that prions may remain infectious in the environment for years, primarily in the soil. Because of this, the spread of CWD within a population is related to both deer transmitting the disease directly amongst themselves and via environmental contamination with prions excreted by infected deer.

Can Prions be Killed?

Prions are very hearty proteins. They can be frozen and thawed and still remain infectious. In order to destroy a prion it must be denatured to the point that it can no longer cause normal proteins to misfold. Sustained heat for several hours at extremely high temperatures (900°F and above) will destroy a prion.

Hunters are advised to wear gloves when handling deer carcasses and to clean equipment that contacts the carcass. If your deer tests positive for CWD, VDGIF will have additional recommendations.

Prion Diseases

There are a variety of prion diseases, many of which only infect one species. CWD has only been documented in North American cervids, including deer, elk, moose, and caribou. Some prion diseases, such as bovine spongiform encephalopathy, are able to infect multiple species.

Prion Disease Species Affected
Chronic wasting disease North American cervids, including white-tailed deer, black-tailed deer, mule deer, elk, and moose
Scrapie Sheep
Bovine spongiform encephalopathy (Mad Cow disease) Bovines, humans (see New Variant CJD)
Transmissible mink encephalopathy Mink
Creutzfeldt-Jacob Disease (CJD) Humans, occurs spontaneously, in 1 out of every 1 million people
New Variant CJD Humans, the result of BSE “Mad Cow” prions transmitted from a cow to a human
Kuru Humans, an extinct disease of Papua, New Guinea, spread through cannibalism

Incubation

Prion diseases vary in their incubation times. Most CWD research suggests incubation periods ranging from 16 months to four years, with an average of two years. CWD prions may remain infectious in soil for at least two years.

Detection

CWD is very difficult to diagnose in a living animal. The misfolded proteins concentrate in areas such as the brain, spinal column, and hard-to-access lymph nodes. The only USDA-approved methods for diagnosing CWD must be performed on samples that can only be collected from animals that have died; these hard-to-access samples include the obex (a part of the brain) and the retropharyngeal lymph nodes (located inside the neck, near the vocal box). Currently, there is no USDA-approved method for diagnosing CWD in a live animal. Similarly, there is no USDA-approved test to detect CWD prions in substances such as soil, urine, or blood.