The cause of<unk>  (like other TSEs, such as scrapie and bovine spongiform encephalopathy) is a prion, a misfolded form of a normal protein, known as prion protein (PrP), that is most commonly found in the central nervous system (CNS) and peripheral nervous system (PNS). The misfolded form has been shown to be capable of converting normally folded prion protein, PrPC ("C" for cellular) into an abnormal form, PrPSc ("Sc" for scrapie), thus leading to a chain reaction.<unk>  is thought to be transmitted by this mechanism. The abnormality in PrP has its genetic basis in a particular variant of the protein-coding gene PRNP that is highly conserved among mammals and has been found and sequenced in deer. The build-up of PrPd in the brain is associated with widespread neurodegeneration. Genetics The allele which encodes leucine, codon 132 in the family of Elks, is either homozygous LL, homozygous MM, or heterozygous ML. Individuals with the first encoding seem to resist clinical signs of<unk> , whereas individuals with either of the other two encodings have much shorter incubation periods. In white-tailed deer, polymorphisms at codons 95 (Q->H) and 96 (G->S) dramatically affect<unk>  progression and prion strain specification. Deer containing the 96S allele have delayed progression to clinical<unk>  onset. When deer with the 95H polymorphism become infected, they select for altered strains of<unk> . Spread Researchers in July 2019 stated that "with all the research on the malignity of prions, and the permanence of prions in the wider environment, and their resistance to destruction and degradation, it is necessary to reduce the potential sources of exposure to<unk> ." In fact an APHIS scientist observed that, while the longevity of<unk>  prion is unknown, the scrapie prion has been measured to endure for 16 years. The PrPCWD protein is insoluble in all but the strongest solvents, and highly resistant to digestion by proteases. PrPCWD converts the normal protein PrPC into more of itself upon contact, and binds together forming aggregates. Prusiner noted in 2001 that: However, it is noted that , although<unk>  prions were transmissible within the cervidae family,<unk>  was not considered transmissible to humans or to cattle. How the prions that cause<unk>  spread is unknown, but recent research indicates that prions can be excreted by deer and elk, and are transmitted by eating grass growing in contaminated soil. Animals born in captivity and those born in the wild have been affected with the<unk> . Transmission of<unk>  is thought to be lateral (from animal to animal). Maternal transmission may occur, although it appears to be relatively unimportant in maintaining epidemics. An infected deer's saliva is able to spread the<unk>  prions. Exposure between animals is associated with sharing food and water sources contaminated with<unk>  prions shed by<unk> d deer. Direct<unk>  may be directly transmitted by contact with infected animals, their bodily tissues, and their bodily fluids. Spread may result from contact with infected deer regardless of if they are symptomatic. Recent research on Rocky Mountain elk found that with<unk> -infected cows, many subclinical, a high rate (80%) of maternal-to-offspring transmission of<unk>  prions occurred, regardless of gestational period. While not dispositive relative to<unk>  development in the fetus, this does suggest that maternal transmission may be yet another important route of direct<unk>  transmission. Modern news stories and anecdotal evidence from treating physicians suggest that a human may have contracted Creutzfeldt-Jakob<unk>  via the consumption of squirrel brains infected with<unk> . Experimental transmission In addition to the cervid species in which<unk>  is known to naturally occur, black-tailed deer and European red deer have been demonstrated to be naturally susceptible to<unk> . Other cervid species, including caribou, are also suspected to be naturally vulnerable to this<unk> . Many other noncervid mammalian species have been experimentally infected with<unk> , either orally or by intracerebral inoculation. These species include monkeys, sheep, cattle, prairie voles, mice, and ferrets. An experimental case study of oral transmission of<unk>  to reindeer shows certain reindeer breeds may be susceptible to<unk> , while other subpopulations may be protective against<unk>  in free-ranging populations. None of the reindeer in the study showed symptoms of<unk> , potentially signifying resistance to different<unk>  strains. Indirect Environmental transmission has been linked to contact with infected bodily fluids and tissues, as well as contact with contaminated environments. Once in the environment,<unk>  prions may remain infectious for many years. Thus, decomposition of<unk> d carcasses, infected "gut piles" from hunters who field dress their cervid harvests, and the urine, saliva, feces, and antler velvet of infected individuals that are deposited in the environment, all have the potential to create infectious environmental reservoirs of<unk> . In 2013, researchers at the National Wildlife Research Center in Fort Collins, Colorado successfully inoculated white-tailed deer with the misfolded prion via the nasal passage, when the prions were mixed with clay. This was important because the prions had already been shown by 2006 to bind with sandy quartz clay minerals. One avian scavenger, the American crow, was recently evaluated as a potential vector for<unk> . As<unk>  prions remain viable after passing through the bird's digestive tract, crows represent a possible mechanism for the creation of environmental reservoirs of<unk> . Additionally, the crows' extensive geographic range presents ample opportunities for them to come in contact with<unk> . This, coupled with the population density and longevity of communal roosting sites in both urban and rural locations, suggests that the fecal deposits at roosting sites may represent a<unk>  environmental reservoir. Conservative estimates for crows' fecal deposits at one winter roosting site for one winter season ranged from 391,552 to 599,032 kg.<unk>  prions adhere so tightly to soil surface particles that the ground becomes a source of infection and may be a major route of transmission due to frequent ground contact when animals in the deer family graze.
Chronic wasting disease
Chronic critical illness
Protein–energy malnutrition
Infection-induced anorexia
Renal osteodystrophy
Protein poisoning
Water intoxication
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