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From: TSS ()
Subject: A prion disease of cervids: Chronic wasting disease
Date: April 3, 2008 at 12:43 pm PST

Thursday, April 03, 2008

A prion disease of cervids: Chronic wasting disease

1: Vet Res. 2008 Apr 3;39(4):41

A prion disease of cervids: Chronic wasting disease

Sigurdson CJ.

The recent discovery of chronic wasting disease in cervids (CWD) beyond the
borders of Colorado and Wyoming, as far east as New York and including two
Canadian Provinces, has led to the emergence of CWD as a prion disease of
domestic and international importance. The apparent ease of horizontal
transmission, potentially via environmental contamination or by
prion-containing saliva, creates enormous challenges for disease management.
Ongoing studies of CWD interspecies transmission by exposure of domestic and
non-domestic species directly or using transgenic mice have shed light on
species barriers. Transgenic mice expressing cervid PrP have also proven
useful for assessing the genetic influences of Prnp polymorphisms on CWD
susceptibility. Accumulating evidence of CWD pathogenesis indicates that the
misfolded prion protein, PrPSc, seems to be widely disseminated in many
nonneural organs, and CWD infectivity has been recently detected in blood.
This review highlights recent research findings in this disease of
free-ranging wildlife.


3. CWD prion spread and target organs

Collectively, CWD pathogenesis studies have revealed extensive deposition of
PrPSc in the
central nervous system (CNS) and extraneural tissues (Fig. 1). The only
other natural prion
diseases that even approach this degree of systemic involvement are variant
Jakob disease (vCJD) in humans, sheep scrapie, and transmissible mink
[22, 23, 30, 61, 62]. In mule deer, PrPSc is detectable in the
retropharyngeal lymph node
within only 6 weeks following an oral exposure [76]. In a further study of
the kinetics of prion


infection in mule deer, Fox et al. showed that PrPSc is widely distributed
in lymphoid tissues
by 3 months post-oral exposure when it is first detected in brain [17]. By 9
months, PrPSc was
detected in the myenteric and submucosal plexi throughout the
gastrointestinal tract and in
the vagus nerve, and by 16 months, PrPSc deposits were detectable throughout
the brain and
spinal cord. The Prnp genotype seemed to impact the infection kinetics in
that mule deer that
were SF heterozygous at codon 225 showed a delay in PrPSc spread; PrPSc was
detectable in the brain until 16 months post-inoculation which was 13 months
later than the
225SS deer. Perhaps the 225F allele confers a dominant negative effect on
the kinetics of
this CWD strain, as has been described in sheep, where the 171R allele has
been shown to
have a dominant negative effect on prion susceptibility [20, 33].
CWD pathogenesis seems to vary between deer and elk: PrPSc levels have been
found to be
lower in lymphoid tissues of elk compared to deer [66]. In a report of 226
CWD-infected elk,
28 had no PrPSc in lymphoid tissues despite having PrPSc in brain [81].
In addition to lymphoid tissues, PrPSc or infectivity has been detected in
other non-CNS
tissues, including pancreas [17, 77], adrenal gland [17, 77], and skeletal
muscle [2]. Recently
PrPSc was described in cardiac muscle from 7 of 16 (44%) white-tailed deer
and from 12 of
17 (71%) elk [35]. This is the first report of PrPSc in cardiac muscle in
any TSE.
The cellular and molecular mechanisms of systemic prion spread are under
investigation in
many laboratories. A recent report showed that blood from CWD-infected deer
infectivity and could transmit prion disease via a blood transfusion [50].
This finding
recapitulates indirect findings of blood infectivity in vCJD affected humans
[61] and
experimental transfusion studies of scrapie sick sheep [32], and indicates
that prion transport
throughout the body may include the blood as a potential vehicle.


12. Conclusion

CWD in cervids is efficiently transmitted, likely more than any other TSE in
animals or
humans. Therefore, it is unlikely that this TSE can be eradicated, but
perhaps through an
improved understanding of transmission routes, biological factors
influencing pathogenesis,
and the molecular basis of CWD prion conversion, a targeted strategy for
disease spread may be developed.


I thank Drs. Michael Miller, Jason Bartz and Mathias Heikenwalder for
critical review of the

see full text ;

snip...see full text 19 pages and other relating data in full here ;

A prion disease of cervids: Chronic wasting disease 2008

CWD Update 90 March 7, 2008


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