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United States Department of Agriculture

Agricultural Research Service

Title: Experimental Transmission of Chronic Wasting Disease Agent to Cattle by Intracerebral Route

Authors
item Hamir, Amirali
item Kunkle, Robert
item Cutlip, Randall - ARS RETIRED
item Miller, Janice - ARS RETIRED
item O'Rourke, Katherine
item Williams, Elizabeth - UNIVERSITY OF WYOMING
item Miller, Michael - COLORADO DIV WILDLIFE
item Stack, Mick - VET SERVICES AGENCY, UK
item Chaplin, Melanie - VET SERVICES AGENCY, UK
item Richt, Juergen

Submitted to: Journal of Veterinary Diagnostic Investigation
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: January 3, 2005
Publication Date: May 1, 2005
Citation: Hamir, A.N., Kunkle, R.A., Cutlip, R.C., Miller, J.M., Orourke, K.I., Williams, E.S., Miller, M.W., Stack, M.J., Chaplin, M.J., Richt, J. 2005. Experimental transmission of chronic wasting disease agent to cattle by intracerebral route. Journal of Veterinary Diagnostic Investigation. 17:276-281.

Interpretive Summary: This communication reports final observations on experimental transmission of chronic wasting disease (CWD) from mule deer to cattle. Thirteen calves were inoculated into the brain with brain suspension from mule deer naturally affected with CWD. Three other calves were kept as uninoculated controls. The experiment was terminated 6 years post inoculation (PI). During that time, abnormal prion protein was demonstrated in the brain and spinal cord of 5 cattle by laboratory tests. However, consistent clinical signs and microscopic changes were not seen in any of these cattle. Age related changes were seen in both inoculated and control cattle. Findings of this study show that only 38% of the inoculated cattle were positive for CWD agent. Although inoculation directly into the brain is an unnatural route of exposure, and is the most severe challenge possible, this experiment shows that CWD transmission in cattle could have long incubation periods (up to 5 years). This finding suggests that oral exposure of cattle to CWD agent, a more natural potential route of exposure, would require not only a much larger dose of inoculum, but also, may not result in amplification of CWD agent within brain and spinal cord tissues during the normal lifespan of cattle. It is possible that a second bovine passage of material (cattle brain infected with CWD) from this study may result in a larger incidence of affected cattle with a shortened incubation time, and may produce different clinical and pathological findings. Such a study is now in progress. Also, experimental inoculations of cattle with CWD isolates from white-tailed deer and elk are needed to compare findings with the present study and these studies will be initiated in the near future. Impact: Results of this study show that although cattle inoculated directly into the brain with CWD succumb to the disease, the attack rate was rather small (38%) with this unnatural route of transmission. It is speculated that the oral route of infection may not result in replication of the agent during normal lifespan of cattle.

Technical Abstract: This communication reports final observations on experimental transmission of chronic wasting disease (CWD) from mule deer to cattle by the intracerebral route. Thirteen calves were inoculated intracerebrally with brain suspension from mule deer naturally affected with CWD. Three other calves were kept as uninoculated controls. The experiment was terminated 6 years post inoculation (PI). During that time, abnormal prion protein (PrPres) was demonstrated in the central nervous system (CNS) of 5 cattle by both immunohistochemistry (IHC) and Western blot (WB). However, microscopic lesions suggestive of spongiform encephalopathy in the brains of these PrPres positive animals were subtle in 3 cases and absent in 2 cases. The 3 uninoculated control cattle and 8 other inoculated animals euthanized during this time did not have PrPres in their CNS. Degenerative changes indicative of neuroaxonal dystrophy (NAD) were seen in dorsal medulla oblongata and appeared to be related to advancing age in both inoculated and control cattle. Analysis of the gene encoding bovine PRNP revealed homozygosity for alleles encoding 6 octapeptide repeats, serine (S) at codon 46 and S at codon 146 in all samples. Findings of this study show that although PrPres amplification occurred following direct inoculation into the brain, none of the affected animals had classic histopathologic lesions of spongiform encephalopathy. Furthermore, only 38% of the inoculated cattle demonstrated amplification of PrPres. Although intracerebral inoculation is an unnatural route of exposure, and is the most severe challenge possible, this experiment shows that CWD transmission in cattle could have long incubation periods (up to 5 years). This finding suggests that oral exposure of cattle to CWD agent, a more natural potential route of exposure, would require not only a much larger dose of inoculum, but also, may not result in amplification of PrPres within CNS tissues during the normal lifespan of cattle.

Last Modified: 10/21/2014
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