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 CWD, 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 CWD progression and prion strain specification. Deer containing the 96S allele have delayed progression to clinical disease onset. When deer with the 95H polymorphism become infected, they select for altered strains of CWD. 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 CWD." In fact an APHIS scientist observed that, while the longevity of CWD 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 CWD prions were transmissible within the cervidae family, CWD was not considered transmissible to humans or to cattle. How the prions that cause CWD 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 disease. Transmission of CWD 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 CWD prions. Exposure between animals is associated with sharing food and water sources contaminated with CWD prions shed by diseased deer. Direct CWD 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 CWD-infected cows, many subclinical, a high rate (80%) of maternal-to-offspring transmission of CWD prions occurred, regardless of gestational period. While not