Submitted to: Journal of Wildlife Diseases
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/3/2011
Publication Date: 11/25/2009
Citation: Rhyan, J.C., Spraker, T.R., Mccollum, M., Nol, P., Wolfe, L., Miller, M.W., Davis, T., Creekmore, L., Orourke, K.I. 2009. Resistance of fallow deer (dama dama) to chronic wasting disease under natural exposure in a heavily contaminated environment. Journal of Wildlife Diseases. 47(3):739-744. Interpretive Summary: Chronic wasting disease or CWD is a fatal neurodegenerative disease of deer and elk in North America. The disease is a member of the prion family of disorders and is associated with misfolding of a normal host prion protein. Detection of the misfolded protein is a useful diagnostic test, particularly for animals in early disease. CWD has been diagnosed in wild mule deer (Odocoileus hemionus), white-tailed deer (O. virginianus), Rocky Mountain elk (Cervus elaphus), and Shira's moose (Alces alces). Disease outbreaks in farmed cervids in the US and Canada have demonstrated some differences in relative disease susceptibility associated with changes in the gene for the normal prion protein but no genotype has been linked to disease resistance. However, CWD has not been diagnosed in farmed fallow deer (Dama dama) on farms with infected deer or elk. Fallow deer are susceptible to direct inoculation of infected material into the brain, but the levels of abnormal prion protein in the experimentally infected fallow deer were low. In this study, we investigated the susceptibility of fallow deer to natural disease transmission by housing fallow deer for up to 7 years in pens with mule deer, a highly susceptible species showing strong evidence of prion shedding into the environment. There was no evidence of disease or abnormal prion protein in any of the fallow deer in this study. DNA analysis of the deer in the study demonstrated a naturally occurring genetic mutation that may confer resistance to CWD. If confirmed in follow up studies, fallow deer would be the first CWD resistant cervid species.
Technical Abstract: Chronic wasting disease or CWD is a transmissible spongiform encephalopathy or prion disorder of cervid ruminants in several regions of the US and Canada. The prion disorders are characterized by misfolding of the host cellular prion protein into a relatively protease resistant and potentially neurotoxic disease-associated isoform. CWD is highly transmissible in mule deer (Odocoileus hemionus) with evidence for horizontal transmission and environmental persistence of the infectious agent in the environment. Examination of tissues from depopulated infected herds in the US and Canada has not yet shown evidence of CWD in farmed fallow deer (Dama dama), an imported species raised for meat, antlers, and exhibition purposes. In this study, fallow deer were held in pens with a succession of CWD-infected mule deer for 7 years. Mule deer losses were 100% during that time, with an average incubation time of less than 3 years. In spite of this persisent natural exposure, no evidence of abnormal prion protein was found in the tissues of the fallow deer following 7 years of exposure. Resistance to prion disease in sheep and possibly in goats in associated with single amino acid changes in the normal prion protein. All fallow deer examined to date are homozygous for asparagine (N) at residue 138. Mule deer, white-tailed deer, Rocky Mountain elk, and Shira's moose are all homozygous for serine (S) at that site, although the unexpressed cervid pseudogene encodes 138N. This finding represents the first possible evidence for genetic resistance to CWD in cervids.