Subject: Experimental Second Passage of CWD (CWDmule deer) Agent to Cattle
Date: April 25, 2006 at 8:01 am PST
Experimental Second Passage of Chronic Wasting
Disease (CWDmule deer) Agent to Cattle
A. N. Hamir, R. A. Kunkle, J. M. Miller, J. J. Greenlee and J. A. Richt
Agricultural Research Service, United States Department of Agriculture, National Animal Disease Center, 2300 Dayton
Avenue, P.O. Box 70, Ames, IA 50010, USA
Summary
To compare clinicopathological findings in first and second passage chronic wasting disease (CWDmule deer)
in cattle, six calves were inoculated intracerebrally with brain tissue derived froma first-passageCWD-affected
calf in an earlier experiment. Two uninoculated calves served as controls. The inoculated animals began to
lose both appetite and weight 10–12 months later, and five subsequently developed clinical signs of central
nervous system (CNS) abnormality. By 16.5 months, all cattle had been subjected to euthanasia because of
poor prognosis. None of the animals showed microscopical lesions of spongiform encephalopathy (SE) but
PrPres was detected in their CNS tissues by immunohistochemistry (IHC) and rapid Western blot (WB)
techniques. Thus, intracerebrally inoculated cattle not only amplified CWD PrPres from mule deer but also
developed clinicalCNSsigns in the absence of SElesions.This situation has also been shown to occur in cattle
inoculated with the scrapie agent. The study confirmed that the diagnostic techniques currently used for
diagnosis of bovine spongiformencephalopathy (BSE) in theUS would detect CWDin cattle, should it occur
naturally. Furthermore, it raised the possibility of distinguishing CWDfromBSE in cattle, due to the absence
of neuropathological lesions and to a distinctive multifocal distribution of PrPres, as demonstrated by IHC
which, in this study, appeared to be more sensitive than the WB technique.
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The present study and a previous experiment
(Hamir et al., 2005a) have established the biological
characteristics of the CWDmule deer agent in cattle.
However, isolates of CWD from other cervids (e.g.
CWDwhite-tailed and CWDelk) may differ. Transmission
experiments with different CWD isolates
are therefore needed to examine the possibility of
variation in the CWD agent in wild cervids. Such
experiments have recently been initiated at the
National Animal Disease Center (NADC).
Acknowledgments
We thank Dr Katherine I. O’Rourke for providing
the antibody for the IHC procedure. Martha
Church, Kevin Hassall, Dennis Orcutt, Jean
Donald, Sharla Van Roekel, and animal handlers
at the NADC provided expert technical assistance.
This study was carried out under the guidelines of
the institutional Animal Care and Use committee at
NADC. Mention of trade names or commercial
products in this article is solely for the purpose of
providing specific information and does not imply
recommendation or endorsement by the United
States Department of Agriculture.
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