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From: TSS ()
Subject: Experimental Second Passage of Chronic Wasting Disease (Cwd-Mule Deer) Agent to Cattle
Date: September 6, 2005 at 9:15 am PST

##################### Bovine Spongiform Encephalopathy #####################


Research Project: Transmission, Differentiation, and Pathobiology of Transmissible Spongiform Encephalopathies
Location: Virus and Prion Diseases of Livestock

Title: Experimental Second Passage of Chronic Wasting Disease (Cwd-Mule Deer) Agent to Cattle


Authors

Hamir, Amirali
Kunkle, Robert - bob
Miller, Janice - ARS RETIRED
Greenlee, Justin
Richt, Juergen


Submitted to: Journal Of Comparative Pathology
Publication Acceptance Date: July 25, 2005
Publication Date: N/A


Interpretive Summary: To compare the findings of experimental first and second passage of chronic wasting disease (CWD) in cattle, 6 calves were inoculated into the brain with CWD-mule deer agent previously (first) passaged in cattle. Two other uninoculated calves served as controls. Beginning 10-12 months post inoculation (PI), all inoculates lost appetite and weight. Five animals subsequently developed clinical signs of central nervous system (CNS) abnormality. By 16.5 months PI, all cattle had been euthanized because of poor prognosis. None of the animals showed microscopic lesions of spongiform encephalopathy (SE) but the CWD agent was detected in their CNS tissues by 2 laboratory techniques (IHC and WB). These findings demonstrate that inoculated cattle amplify CWD agent but also develop clinical CNS signs without manifestation of microscopic lesions of SE. This situation has also been shown to occur following inoculation of cattle with another TSE agent, namely, sheep scrapie. The current study confirms previous work that indicates that the diagnostic tests currently used for confirmation of bovine spongiform encephalopathy (BSE) in the U.S. would detect CWD in cattle, should it occur naturally. Furthermore, it raises the possibility of distinguishing CWD from BSE in cattle due to the absence of microscopic lesions and a unique multifocal distribution of PrPres, as demonstrated by IHC, which in this study, appears to be more sensitive than the WB.
Technical Abstract: To compare clinicopathological findings of first and second passage of chronic wasting disease (CWD) in cattle, a group of calves (n=6) were intracerebrally inoculated with CWD-mule deer agent previously (first) passaged in cattle. Two other uninoculated calves served as controls. Beginning 10-12 months post inoculation (PI), all inoculates lost appetite and lost weight. Five animals subsequently developed clinical signs of central nervous system (CNS) abnormality. By 16.5 months PI, all cattle had been euthanized because of poor prognosis. None of the animals showed microscopic lesions of spongiform encephalopathy (SE) but PrPres was detected in their CNS tissues by immunohistochemistry (IHC) and Western blot (WB) techniques. These findings demonstrate that intracerebrally inoculated cattle not only amplify CWD PrPres but also develop clinical CNS signs without manifestation of morphologic lesions of SE. This situation has also been shown to occur following inoculation of cattle with another TSE agent, scrapie. The current study confirms previous work that indicates the diagnostic techniques currently used for confirmation of bovine spongiform encephalopathy (BSE) in the U.S. would detect CWD in cattle, should it occur naturally. Furthermore, it raises the possibility of distinguishing CWD from BSE in cattle due to the absence of neuropathologic lesions and a unique multifocal distribution of PrPres, as demonstrated by IHC, which in this study, appears to be more sensitive than the WB.

http://www.ars.usda.gov/research/publications/publications.htm?seq_no_115=178318


Research

Title: Experimental Transmission of Chronic Wasting Disease (Cwd Mule Deer) Agent to Cattle by Intracerebral Route

Authors

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


Submitted to: Journal Of Veterinary Diagnostic Investigation
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.

Page Modified: 09/05/2005

http://www.ars.usda.gov/research/publications/publications.htm?SEQ_NO_115=166311


TSS

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