A prion disease of cervids: Chronic wasting disease 2008
Thursday, April 03, 2008 A prion disease of cervids: Chronic wasting disease 2008 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.
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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 Creutzfeldt-Jakob disease (vCJD) in humans, sheep scrapie, and transmissible mink encephalopathy [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
1 http://www.aphis.usda.gov/vs/nahps/cwd/cwd-distribution.html
5
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 not 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 contained 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.
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6. CWD strains among deer and elk
Prion strains, such as those seen in sheep scrapie, show distinct incubation periods in differentially susceptible inbred mice and lesions target discrete brain regions [11, 18, 19]. CWD in deer and elk has been considered a single disease entity, and western blot glycoform patterns of PrPSc are similar among deer and elk [67]. However, some new data indicate otherwise, suggesting that conformational variants, or strains, may exist. In a study by Raymond et al., Syrian golden hamsters were infected with mule deer or elk CWD, but with an incomplete attack rate; only 2 of 7 and 0 of 7 hamsters developed terminal disease, respectively. Indeed, second and third passage of the mule deer derived strain resulted in a short incubation period of only 85-89 days, whereas the elk-derived strain led to an incubation period of 408-544 days. Surprisingly, when mule deer CWD was first passaged in hamster PrP expressing transgenic mice and then into hamsters, a slowly replicating strain with distinct clinical disease and PrPSc deposition patterns in brain ensued. Therefore two different strains could be passaged from a single mule deer CWD isolate, a rapid and a slowly replicating strain with differing disease phenotypes [70]. Alternatively, these strains could have been generated upon interspecies transmission [6]. We have also observed two strains arising from a single CWD-infected mule deer upon passage in transgenic mice overexpressing murine PrP. Here, mice developed different PrPSc aggregate morphologies in brain, either dense, congophilic plaques or fine, diffuse aggregates which could be selectively passaged [78]. LaFauci et al. have reported that elk PrP expressing transgenic mice developed phenotypically divergent diseases when inoculated with either mule deer or elk CWD, which was also suggestive of different strains [44]. In each of these studies, it is not clear whether mule deer and elk possess heterogeneous PrP aggregates (strain mixture), or whether the strains may have developed in the new host. However, Safar et al. have reported differing conformational characteristics for PrPSc from CWD-infected white-tailed deer and elk directly, using a conformation dependent immunoassay (CDI) [71], which supports the existence of CWD strains. The possible existence of CWD strains is perhaps not entirely surprising, considering that there are genetic Prnp differences among deer and elk that could influence PrPSc conformation [34, 36, 58].
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7. Interspecies CWD transmission
Wild predators and scavengers are presumably feeding on CWD-infected carcasses. Skeletal muscle has been shown to harbor CWD prion infectivity [2], underscoring that other species will almost certainly be exposed to CWD through feeding. However, CWD has not been successfully transmitted by oral inoculation to species outside of the cervid family, suggestive of a strong species barrier for heterologous PrP conversion. Ferrets (family Mustelidae) can be infected with deer CWD after intracerebral (ic) but not oral exposure [5, 80]. Raccoons resisted even ic infection for up to 2 years thus far [24]. Mountain lion (Puma concolor) susceptibility to experimental feeding of CWD prions is currently under investigation (M. Miller and L. Wolfe, personal communication). Could wild rodents colonizing CWD- or scrapie-infected pastures serve as an environmental reservoir of prion infectivity? Interestingly, bank voles (Clethrionomys glareolus), are readily infected with CWD and sheep scrapie by intracerebral inoculation ([64]; U. Agrimi, unpublished data) and are considered as a potential reservoir for sheep scrapie [64]. Many vole species occur in North America [65, 83] and further research may determine whether voles enhance CWD or scrapie spread through environmental contamination. Given that environmental contamination with CWD prions likely occurs [55], domestic ruminants may be exposed to CWD through common grazing areas. However, sheep and cattle appear to be poorly susceptible to mule deer CWD: ic inoculation with mule deer CWD succeeded to infect only 2 of 8 sheep [28]; likewise cattle have not been infected after cograzing with CWD-infected mule deer, or after a direct oral exposure (over 6 years) (M. Miller, personal communication). Even direct ic inoculation led to CWD infection in only 5 of 13 cattle (38%) after 2-5 years [26]. In contrast, cattle are highly susceptible to white-tailed deer CWD with 12 of 14 animals developing neurologic disease and PrPSc by only 22 months post-ic inoculation (+/-0.5 months) [29]. Further studies are planned to determine whether cattle are susceptible to white-tailed deer prions after an oral exposure (J. Richt, personal communication). The differential susceptibility of cattle to CWD from mule deer versus whitetailed deer suggests that CWD strains exist, and that CWD may differentially cross species barriers depending on the strain. Nevertheless, to date, natural CWD infections have been detected only in cervids. Is the converse true, are cervids susceptible to sheep scrapie? Only one study has been performed on cervid susceptibility to sheep scrapie by the ic route, and showed that 3 of 6 elk developed neurologic signs, spongiform encephalopathy and PrPSc in brain [25]. Further experiments to address this question may be interesting since sheep scrapie is considered a possible source for CWD in North America [89, 91].
8. Human susceptibility to CWD
Millions of North Americans hunt deer and elk (U.S. Department of the Interior, Census Bureau), and there is no doubt that people have been exposed to CWD through venison consumption, particularly in light of recent data showing CWD prions in muscle [2]. Human susceptibility to CWD or to other newly emerging animal TSE [9, 14] is still unclear, although we can be somewhat reassured in that there have been no large scale outbreaks of human TSE cases in Colorado and Wyoming, where CWD has existed for decades [51]. Up until approximately 10 years ago, autopsies were not performed on suspect human TSE cases in many states due to biosafety concerns, therefore the diagnosis of potential new TSE strains has been hampered. This indicates that clinical TSE diagnoses in humans were not confirmed, nor was any strain typing done to look for the appearance of potentially subtle or unusual pathological or biochemical phenotypes of a new TSE strain. Fortunately, the autopsy rate for suspect cases is improving. At the National Prion Disease Pathology Surveillance Center at Case Western Reserve University (Cleveland, Ohio), Creutzfeldt-Jakob disease (CJD) suspect cases are studied and classified by CJD subtype. Thus far,
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*** twenty-seven CJD patients who regularly consumed venison were reported to the Surveillance Center***,
however there have been no unusual or novel prion subtypes that might indicate the appearance of a new prion strain [7, 41]. Other indirect studies of human susceptibility to CWD also suggest that the risk is low. In biochemical conversion studies, Raymond et al. [68] showed that the efficiency of CWD to convert recombinant human PrP into amyloid fibrils was low, but similar to that of both BSE and scrapie fibrils to do the same. These results suggest that there is a molecular incompatibility in the conversion of human PrPC by CWD, sheep scrapie, or BSE, and that cross species infections in humans may be rare events. To determine whether common PrPSc strain features may link CWD and CJD, histopathology and the PrPSc biochemical characteristics from deer and elk were compared with that of humans with sporadic CJD (sCJD) cases that are methionine homozygous at codon 129 of the Prnp gene by Xie et al. [96], although strain features including histologic profile, target organs, and glycoform patterns will not necessarily remain the same upon crossing species barriers [6, 5, 8, 57]. The PrPSc form is cleaved by proteinase-K (PK) at different sites depending on the conformation of the protein and may aid determination of whether the PrPSc conformation is similar. By western blot (SDS-PAGE) of elk CWD, the unglycosylated PK-resistant PrPSc migrated at 21 kDa, similar to sCJD (MM1 subtype) and the PK cleavage site was the same, occurring at residues 78 and 82 as assessed by N-terminal sequencing. Conformational stability was evaluated by measuring the PrPSc stability under partially denaturing conditions and also showed no significant difference between elk CWD and sCJD MM1 PrPSc. However, elk CWD and human sCJD MM1 strains exhibited distinct glycoform patterns by two dimensional gel electrophoresis, suggesting that the strains differed. Future studies may utilize luminescent conjugated polymers, which were recently shown to distinguish naturally- and experimentally-derived prion strains [79]. To study elk-human prion species barriers, Kong et al. inoculated elk CWD into transgenic mice expressing either human PrP or elk PrP. Whereas the elk PrP expressing mice developed disease after only 118-142 days post-inoculation, human PrP expressing mice (129M) did not develop any features of TSE after more than 657 or more than 756 days [41]. In accordance with these results, Tamgüney et al. also reported that human PrP overexpressing mice were not susceptible to 9 CWD isolates from mule deer, white-tailed deer, and elk [84]. However, mice have a limited lifespan and further passages may be necessary to detect low levels of prion infectivity that may be present subclinically. Although indirect evidence is accumulating that there may be a robust species barrier for CWD transmission to humans, one report indicates nonhuman primate susceptibility to CWD. Intracerebral inoculation of squirrel monkeys (Saimiri sciureus) demonstrated a positive CWD transmission [49]. Among non-human primates, however, the Prnp sequence of the new world monkeys are the most distant from humans [72], and therefore may not indicate that human prion conversion would occur by CWD.
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11. Disease control challenges posed by CWD
Evidence is building that indicates efficient horizontal transmission occurs in CWD, indeed a complicating aspect in disease control [91]. Potential transmission mechanisms range from spread via direct contact among animals to environmental exposure through grazing in areas contaminated by prion-infected secretions, excretions (saliva, urine, feces), tissues (placenta), or decomposed carcasses. Recently, in a breakthrough finding, saliva from CWD infected deer was shown to transmit prion disease [50]. An additional experiment by Miller and colleagues showed that CWD-infected carcasses allowed to decay naturally in confined pastures can lead to CWD infections in captive deer, demonstrating the potential for environmental contamination to spread infection [55]. Modelling studies have provided further
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support that environmental contamination is likely playing a significant role in transmitting CWD [56, 53]. Additionally, infectious prions have been demonstrated to bind soil particles and remain infectious to animals by both intracerebral and oral exposure routes [38, 37]. Prion infectivity has been recovered from soil more than two years after experimental exposure to prions, suggesting the soil may serve as a reservoir for CWD prions [75]. Taken together, these results indicate that there may even be multiple sources for CWD exposure, perhaps through direct contact and environmental routes. Significant challenges to CWD eradication exist in free-ranging cervids. Infected deer and elk range over a broad geographic region, and even previously surmised geographic barriers such as the Continental Divide have proven passable by infected animals. Ridding the environment of CWD-contaminated soil or even CWD-infected carcasses is not possible. Moreover, the available ante-mortem diagnostic tests for surveillance are laborious and impractical for large numbers of free-ranging animals [74, 88, 95]. Therefore for a wildlife manager, this disease is costly to survey and difficult to control.
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 interrupting disease spread may be developed.
Acknowledgements
I thank Drs. Michael Miller, Jason Bartz and Mathias Heikenwalder for critical review of the manuscript.
snip...see full text 19 pages ;
http://www.vetres.org/index.php?option=article&access=standard&Itemid=129&url=/articles/vetres/pdf/2008/04/v08092.pdf
Research Project: Strain Typing of Chronic Wasting Disease (Cwd) and Scrapie by Intracerebral Inoculation into Transgenic and Inbred Mouse Lines Location: Animal Diseases Research
Project Number: 5348-32000-026-07 Project Type: Specific C/A
Start Date: Sep 28, 2007 End Date: Sep 27, 2012
Objective:
To identify and differentiate typical and atypical case samples of CWD and Scrapie by characterizing the biologic phenotype and pathologic profile of these agents when administered to susceptible lines of transgenic and inbred mice.
Approach:
Tissue samples from deer, elk, sheep and goats with Transmissible Spongiform Encephalopathy (TSE) will be administered to mice by intracerebral injection. Multiple tissue types will be included, such as samples of brain, lymph node, blood, urine, feces, antler velvet and muscle. Mouse models used as recipient hosts will include both preexisting and recently created transgenic and inbred mouse lines. Recipient mouse phenotype will be evaluated by measuring clinical response, population disease rate, incubation time, and pathologic profile within the central nervous system (CNS). Pathologic profile of CNS lesion foci is assessed by evaluating anatomic localization, spongiform change, astrocytic gliosis, and deposition of protease resistant prion protein. BSL-1; 9-4-06. Documents SCA with U. of WA.
http://www.ars.usda.gov/research/projects/projects.htm?accn_no=411895
Research Project: Strain Typing of Chronic Wasting Disease (Cwd) and Scrapie by Intracerebral Inoculation into Transgenic and Inbred Mouse Lines Location: Animal Diseases Research
2007 Annual Report
1a.Objectives (from AD-416)
To identify and differentiate typical and atypical case samples of CWD and Scrapie by characterizing the biologic phenotype and pathologic profile of these agents when administered to susceptible lines of transgenic and inbred mice.
1b.Approach (from AD-416)
Tissue samples from deer, elk, sheep and goats with Transmissible Spongiform Encephalopathy (TSE) will be administered to mice by intracerebral injection. Multiple tissue types will be included, such as samples of brain, lymph node, blood, urine, feces, antler velvet and muscle. Mouse models used as recipient hosts will include both preexisting and recently created transgenic and inbred mouse lines. Recipient mouse phenotype will be evaluated by measuring clinical response, population disease rate, incubation time, and pathologic profile within the central nervous system (CNS). Pathologic profile of CNS lesion foci is assessed by evaluating anatomic localization, spongiform change, astrocytic gliosis, and deposition of protease resistant prion protein. BSL-1; 9-4-06. Documents SCA with U. of WA.
3.Progress Report
This report serves to document research conducted under a specific cooperative agreement between ARS and the University of Washington. Additional details of research can be found in the report for the parent project 5348-32000-026-00D Transmissible Spongiform Encephalopathies: the role of genetics, strain variation, and environmental contamination in disease control. The purpose of this new SCA is to identify and differentiate typical and atypical case samples of CWD and scrapie by characterizing the biologic phenotype and pathologic profile of these agents when administered to susceptible lines of transgenic and inbred mice. There will be weekly interactions between the ADODR, ADRU scientists and University of Washington collaborators through personnel visits, conference calls and emails.
http://www.ars.usda.gov/research/projects/projects.htm?ACCN_NO=411895&showpars=true&fy=2007
From: TSS (216-119-163-189.ipset45.wt.net)
Subject: CWD aka MAD DEER/ELK TO HUMANS ???
Date: September 30, 2002 at 7:06 am PST
From: "Belay, Ermias" To: Cc: "Race, Richard (NIH)" ; ; "Belay, Ermias" Sent: Monday, September 30, 2002 9:22 AM
Subject: RE: TO CDC AND NIH - PUB MED- 3 MORE DEATHS - CWD - YOUNG HUNTERS
Dear Sir/Madam,
In the Archives of Neurology you quoted (the abstract of which was attached to your email), we did not say CWD in humans will present like variant CJD.
That assumption would be wrong. I encourage you to read the whole article and call me if you have questions or need more clarification (phone: 404-639-3091). Also, we do not claim that "no-one has ever been infected with prion disease from eating venison." Our conclusion stating that we found no strong evidence of CWD transmission to humans in the article you quoted or in any other forum is limited to the patients we investigated.
Ermias Belay, M.D. Centers for Disease Control and Prevention
-----Original Message-----
From:
Sent: Sunday, September 29, 2002 10:15 AM
To: rr26k@nih.gov; rrace@niaid.nih.gov; ebb8@CDC.GOV
Subject: TO CDC AND NIH - PUB MED- 3 MORE DEATHS - CWD - YOUNG HUNTERS
Sunday, November 10, 2002 6:26 PM ......snip........end..............TSS
also,
A. Aguzzi - Chronic Wasting Disease (CWD) also needs to be addressed. Most serious because of rapid horizontal spread and higher prevalence than BSE in UK, up to 15% in some populations. Also may be a risk to humans - evidence that it is not dangerous to humans is thin.
http://www.tseandfoodsafety.org/activities/bse_conference_basel_april_02/2summary_of_conference.htm
Chronic Wasting Disease and Potential Transmission to Humans
Ermias D. Belay,* Ryan A. Maddox,* Elizabeth S. Williams,† Michael W. Miller,‡ Pierluigi Gambetti,§ and Lawrence B. Schonberger* *Centers for Disease Control and Prevention, Atlanta, Georgia, USA; †University of Wyoming, Laramie, Wyoming, USA; ‡Colorado Division of Wildlife, Fort Collins, Colorado, USA; and §Case Western Reserve University, Cleveland, Ohio, USA
Suggested citation for this article: Belay ED, Maddox RA, Williams ES, Miller MW, Gambetti P, Schonberger LB. Chronic wasting disease and potential transmission to humans. Emerg Infect Dis [serial on the Internet]. 2004 Jun [date cited]. Available from:
http://www.cdc.gov/ncidod/EID/vol10no6/03-1082.htm
--------------------------------------------------------------------------------
Chronic wasting disease (CWD) of deer and elk is endemic in a tri-corner area of Colorado, Wyoming, and Nebraska, and new foci of CWD have been detected in other parts of the United States. Although detection in some areas may be related to increased surveillance, introduction of CWD due to translocation or natural migration of animals may account for some new foci of infection. Increasing spread of CWD has raised concerns about the potential for increasing human exposure to the CWD agent. The foodborne transmission of bovine spongiform encephalopathy to humans indicates that the species barrier may not completely protect humans from animal prion diseases. Conversion of human prion protein by CWD-associated prions has been demonstrated in an in vitro cell-free experiment, but limited investigations have not identified strong evidence for CWD transmission to humans. More epidemiologic and laboratory studies are needed to monitor the possibility of such transmissions.
snip...full text ;
http://www.cdc.gov/ncidod/EID/vol10no6/03-1082.htm
Volume 12, Number 10–October 2006
Research
Human Prion Disease and Relative Risk Associated with Chronic Wasting Disease
Samantha MaWhinney,* W. John Pape,† Jeri E. Forster,* C. Alan Anderson,‡§ Patrick Bosque,‡¶ and Michael W. Miller# *University of Colorado at Denver and Health Sciences Center, Denver, Colorado, USA; †Colorado Department of Public Health and Environment, Denver, Colorado, USA; ‡University of Colorado School of Medicine, Denver, Colorado, USA; §Denver Veteran's Affairs Medical Center, Denver, Colorado, USA; ¶Denver Health Medical Center, Denver, Colorado, USA; and #Colorado Division of Wildlife, Fort Collins, Colorado, USA
Suggested citation for this article
The transmission of the prion disease bovine spongiform encephalopathy (BSE) to humans raises concern about chronic wasting disease (CWD), a prion disease of deer and elk. In 7 Colorado counties with high CWD prevalence, 75% of state hunting licenses are issued locally, which suggests that residents consume most regionally harvested game. We used Colorado death certificate data from 1979 through 2001 to evaluate rates of death from the human prion disease Creutzfeldt-Jakob disease (CJD). The relative risk (RR) of CJD for CWD-endemic county residents was not significantly increased (RR 0.81, 95% confidence interval [CI] 0.40–1.63), and the rate of CJD did not increase over time (5-year RR 0.92, 95% CI 0.73–1.16). In Colorado, human prion disease resulting from CWD exposure is rare or nonexistent. However, given uncertainties about the incubation period, exposure, and clinical presentation, the possibility that the CWD agent might cause human disease cannot be eliminated.
snip... full text ;
http://0-www.cdc.gov.mill1.sjlibrary.org/ncidod/EID/vol12no10/06-0019.htm
full text ;
http://chronic-wasting-disease.blogspot.com/2006_12_01_archive.html
CWD
http://chronic-wasting-disease.blogspot.com/
CJD QUESTIONNAIRE
http://cjdquestionnaire.blogspot.com/
Monitoring the occurrence of emerging forms of CJD
http://cjdusa.blogspot.com/
Singeltary, Sr et al. JAMA.2001; 285: 733-734.
Diagnosis and Reporting of Creutzfeldt-Jakob Disease
Since this article does not have an abstract, we have provided the first 150 words of the full text and any section headings.
To the Editor:
In their Research Letter, Dr Gibbons and colleagues1 reported that the annual US death rate due to Creutzfeldt-Jakob disease (CJD) has been stable since 1985. These estimates, however, are based only on reported cases, and do not include misdiagnosed or preclinical cases. It seems to me that misdiagnosis alone would drastically change these figures. An unknown number of persons with a diagnosis of Alzheimer disease in fact may have CJD, although only a small number of these patients receive the postmortem examination necessary to make this diagnosis. Furthermore, only a few states have made CJD reportable. Human and animal transmissible spongiform encephalopathies should be reportable nationwide and internationally.
Terry S. Singeltary, Sr Bacliff, Tex
1. Gibbons RV, Holman RC, Belay ED, Schonberger LB. Creutzfeldt-Jakob disease in the United States: 1979-1998. JAMA. 2000;284:2322-2323. FREE FULL TEXT
http://jama.ama-assn.org/cgi/content/extract/285/6/733?maxtoshow=&HITS=10&hits=10&RESULTFORMAT=&fulltext=singeltary&searchid=1&FIRSTINDEX=0&resourcetype=HWCIT
JOURNAL OF NEUROLOGY
MARCH 26, 2003
In light of the findings of Asante and Collinge et al, there
should be drastic measures to safeguard the medical and surgical arena
from sporadic CJDs and all human TSEs. I only ponder how many sporadic
CJDs in the USA are type 2 PrPSc?
http://www.neurology.org/cgi/eletters/60/2/176#535
TSS
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.
snip...
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 Creutzfeldt-Jakob disease (vCJD) in humans, sheep scrapie, and transmissible mink encephalopathy [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
1 http://www.aphis.usda.gov/vs/nahps/cwd/cwd-distribution.html
5
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 not 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 contained 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.
snip...
6. CWD strains among deer and elk
Prion strains, such as those seen in sheep scrapie, show distinct incubation periods in differentially susceptible inbred mice and lesions target discrete brain regions [11, 18, 19]. CWD in deer and elk has been considered a single disease entity, and western blot glycoform patterns of PrPSc are similar among deer and elk [67]. However, some new data indicate otherwise, suggesting that conformational variants, or strains, may exist. In a study by Raymond et al., Syrian golden hamsters were infected with mule deer or elk CWD, but with an incomplete attack rate; only 2 of 7 and 0 of 7 hamsters developed terminal disease, respectively. Indeed, second and third passage of the mule deer derived strain resulted in a short incubation period of only 85-89 days, whereas the elk-derived strain led to an incubation period of 408-544 days. Surprisingly, when mule deer CWD was first passaged in hamster PrP expressing transgenic mice and then into hamsters, a slowly replicating strain with distinct clinical disease and PrPSc deposition patterns in brain ensued. Therefore two different strains could be passaged from a single mule deer CWD isolate, a rapid and a slowly replicating strain with differing disease phenotypes [70]. Alternatively, these strains could have been generated upon interspecies transmission [6]. We have also observed two strains arising from a single CWD-infected mule deer upon passage in transgenic mice overexpressing murine PrP. Here, mice developed different PrPSc aggregate morphologies in brain, either dense, congophilic plaques or fine, diffuse aggregates which could be selectively passaged [78]. LaFauci et al. have reported that elk PrP expressing transgenic mice developed phenotypically divergent diseases when inoculated with either mule deer or elk CWD, which was also suggestive of different strains [44]. In each of these studies, it is not clear whether mule deer and elk possess heterogeneous PrP aggregates (strain mixture), or whether the strains may have developed in the new host. However, Safar et al. have reported differing conformational characteristics for PrPSc from CWD-infected white-tailed deer and elk directly, using a conformation dependent immunoassay (CDI) [71], which supports the existence of CWD strains. The possible existence of CWD strains is perhaps not entirely surprising, considering that there are genetic Prnp differences among deer and elk that could influence PrPSc conformation [34, 36, 58].
7
7. Interspecies CWD transmission
Wild predators and scavengers are presumably feeding on CWD-infected carcasses. Skeletal muscle has been shown to harbor CWD prion infectivity [2], underscoring that other species will almost certainly be exposed to CWD through feeding. However, CWD has not been successfully transmitted by oral inoculation to species outside of the cervid family, suggestive of a strong species barrier for heterologous PrP conversion. Ferrets (family Mustelidae) can be infected with deer CWD after intracerebral (ic) but not oral exposure [5, 80]. Raccoons resisted even ic infection for up to 2 years thus far [24]. Mountain lion (Puma concolor) susceptibility to experimental feeding of CWD prions is currently under investigation (M. Miller and L. Wolfe, personal communication). Could wild rodents colonizing CWD- or scrapie-infected pastures serve as an environmental reservoir of prion infectivity? Interestingly, bank voles (Clethrionomys glareolus), are readily infected with CWD and sheep scrapie by intracerebral inoculation ([64]; U. Agrimi, unpublished data) and are considered as a potential reservoir for sheep scrapie [64]. Many vole species occur in North America [65, 83] and further research may determine whether voles enhance CWD or scrapie spread through environmental contamination. Given that environmental contamination with CWD prions likely occurs [55], domestic ruminants may be exposed to CWD through common grazing areas. However, sheep and cattle appear to be poorly susceptible to mule deer CWD: ic inoculation with mule deer CWD succeeded to infect only 2 of 8 sheep [28]; likewise cattle have not been infected after cograzing with CWD-infected mule deer, or after a direct oral exposure (over 6 years) (M. Miller, personal communication). Even direct ic inoculation led to CWD infection in only 5 of 13 cattle (38%) after 2-5 years [26]. In contrast, cattle are highly susceptible to white-tailed deer CWD with 12 of 14 animals developing neurologic disease and PrPSc by only 22 months post-ic inoculation (+/-0.5 months) [29]. Further studies are planned to determine whether cattle are susceptible to white-tailed deer prions after an oral exposure (J. Richt, personal communication). The differential susceptibility of cattle to CWD from mule deer versus whitetailed deer suggests that CWD strains exist, and that CWD may differentially cross species barriers depending on the strain. Nevertheless, to date, natural CWD infections have been detected only in cervids. Is the converse true, are cervids susceptible to sheep scrapie? Only one study has been performed on cervid susceptibility to sheep scrapie by the ic route, and showed that 3 of 6 elk developed neurologic signs, spongiform encephalopathy and PrPSc in brain [25]. Further experiments to address this question may be interesting since sheep scrapie is considered a possible source for CWD in North America [89, 91].
8. Human susceptibility to CWD
Millions of North Americans hunt deer and elk (U.S. Department of the Interior, Census Bureau), and there is no doubt that people have been exposed to CWD through venison consumption, particularly in light of recent data showing CWD prions in muscle [2]. Human susceptibility to CWD or to other newly emerging animal TSE [9, 14] is still unclear, although we can be somewhat reassured in that there have been no large scale outbreaks of human TSE cases in Colorado and Wyoming, where CWD has existed for decades [51]. Up until approximately 10 years ago, autopsies were not performed on suspect human TSE cases in many states due to biosafety concerns, therefore the diagnosis of potential new TSE strains has been hampered. This indicates that clinical TSE diagnoses in humans were not confirmed, nor was any strain typing done to look for the appearance of potentially subtle or unusual pathological or biochemical phenotypes of a new TSE strain. Fortunately, the autopsy rate for suspect cases is improving. At the National Prion Disease Pathology Surveillance Center at Case Western Reserve University (Cleveland, Ohio), Creutzfeldt-Jakob disease (CJD) suspect cases are studied and classified by CJD subtype. Thus far,
8
*** twenty-seven CJD patients who regularly consumed venison were reported to the Surveillance Center***,
however there have been no unusual or novel prion subtypes that might indicate the appearance of a new prion strain [7, 41]. Other indirect studies of human susceptibility to CWD also suggest that the risk is low. In biochemical conversion studies, Raymond et al. [68] showed that the efficiency of CWD to convert recombinant human PrP into amyloid fibrils was low, but similar to that of both BSE and scrapie fibrils to do the same. These results suggest that there is a molecular incompatibility in the conversion of human PrPC by CWD, sheep scrapie, or BSE, and that cross species infections in humans may be rare events. To determine whether common PrPSc strain features may link CWD and CJD, histopathology and the PrPSc biochemical characteristics from deer and elk were compared with that of humans with sporadic CJD (sCJD) cases that are methionine homozygous at codon 129 of the Prnp gene by Xie et al. [96], although strain features including histologic profile, target organs, and glycoform patterns will not necessarily remain the same upon crossing species barriers [6, 5, 8, 57]. The PrPSc form is cleaved by proteinase-K (PK) at different sites depending on the conformation of the protein and may aid determination of whether the PrPSc conformation is similar. By western blot (SDS-PAGE) of elk CWD, the unglycosylated PK-resistant PrPSc migrated at 21 kDa, similar to sCJD (MM1 subtype) and the PK cleavage site was the same, occurring at residues 78 and 82 as assessed by N-terminal sequencing. Conformational stability was evaluated by measuring the PrPSc stability under partially denaturing conditions and also showed no significant difference between elk CWD and sCJD MM1 PrPSc. However, elk CWD and human sCJD MM1 strains exhibited distinct glycoform patterns by two dimensional gel electrophoresis, suggesting that the strains differed. Future studies may utilize luminescent conjugated polymers, which were recently shown to distinguish naturally- and experimentally-derived prion strains [79]. To study elk-human prion species barriers, Kong et al. inoculated elk CWD into transgenic mice expressing either human PrP or elk PrP. Whereas the elk PrP expressing mice developed disease after only 118-142 days post-inoculation, human PrP expressing mice (129M) did not develop any features of TSE after more than 657 or more than 756 days [41]. In accordance with these results, Tamgüney et al. also reported that human PrP overexpressing mice were not susceptible to 9 CWD isolates from mule deer, white-tailed deer, and elk [84]. However, mice have a limited lifespan and further passages may be necessary to detect low levels of prion infectivity that may be present subclinically. Although indirect evidence is accumulating that there may be a robust species barrier for CWD transmission to humans, one report indicates nonhuman primate susceptibility to CWD. Intracerebral inoculation of squirrel monkeys (Saimiri sciureus) demonstrated a positive CWD transmission [49]. Among non-human primates, however, the Prnp sequence of the new world monkeys are the most distant from humans [72], and therefore may not indicate that human prion conversion would occur by CWD.
snip...
11. Disease control challenges posed by CWD
Evidence is building that indicates efficient horizontal transmission occurs in CWD, indeed a complicating aspect in disease control [91]. Potential transmission mechanisms range from spread via direct contact among animals to environmental exposure through grazing in areas contaminated by prion-infected secretions, excretions (saliva, urine, feces), tissues (placenta), or decomposed carcasses. Recently, in a breakthrough finding, saliva from CWD infected deer was shown to transmit prion disease [50]. An additional experiment by Miller and colleagues showed that CWD-infected carcasses allowed to decay naturally in confined pastures can lead to CWD infections in captive deer, demonstrating the potential for environmental contamination to spread infection [55]. Modelling studies have provided further
10
support that environmental contamination is likely playing a significant role in transmitting CWD [56, 53]. Additionally, infectious prions have been demonstrated to bind soil particles and remain infectious to animals by both intracerebral and oral exposure routes [38, 37]. Prion infectivity has been recovered from soil more than two years after experimental exposure to prions, suggesting the soil may serve as a reservoir for CWD prions [75]. Taken together, these results indicate that there may even be multiple sources for CWD exposure, perhaps through direct contact and environmental routes. Significant challenges to CWD eradication exist in free-ranging cervids. Infected deer and elk range over a broad geographic region, and even previously surmised geographic barriers such as the Continental Divide have proven passable by infected animals. Ridding the environment of CWD-contaminated soil or even CWD-infected carcasses is not possible. Moreover, the available ante-mortem diagnostic tests for surveillance are laborious and impractical for large numbers of free-ranging animals [74, 88, 95]. Therefore for a wildlife manager, this disease is costly to survey and difficult to control.
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 interrupting disease spread may be developed.
Acknowledgements
I thank Drs. Michael Miller, Jason Bartz and Mathias Heikenwalder for critical review of the manuscript.
snip...see full text 19 pages ;
http://www.vetres.org/index.php?option=article&access=standard&Itemid=129&url=/articles/vetres/pdf/2008/04/v08092.pdf
Research Project: Strain Typing of Chronic Wasting Disease (Cwd) and Scrapie by Intracerebral Inoculation into Transgenic and Inbred Mouse Lines Location: Animal Diseases Research
Project Number: 5348-32000-026-07 Project Type: Specific C/A
Start Date: Sep 28, 2007 End Date: Sep 27, 2012
Objective:
To identify and differentiate typical and atypical case samples of CWD and Scrapie by characterizing the biologic phenotype and pathologic profile of these agents when administered to susceptible lines of transgenic and inbred mice.
Approach:
Tissue samples from deer, elk, sheep and goats with Transmissible Spongiform Encephalopathy (TSE) will be administered to mice by intracerebral injection. Multiple tissue types will be included, such as samples of brain, lymph node, blood, urine, feces, antler velvet and muscle. Mouse models used as recipient hosts will include both preexisting and recently created transgenic and inbred mouse lines. Recipient mouse phenotype will be evaluated by measuring clinical response, population disease rate, incubation time, and pathologic profile within the central nervous system (CNS). Pathologic profile of CNS lesion foci is assessed by evaluating anatomic localization, spongiform change, astrocytic gliosis, and deposition of protease resistant prion protein. BSL-1; 9-4-06. Documents SCA with U. of WA.
http://www.ars.usda.gov/research/projects/projects.htm?accn_no=411895
Research Project: Strain Typing of Chronic Wasting Disease (Cwd) and Scrapie by Intracerebral Inoculation into Transgenic and Inbred Mouse Lines Location: Animal Diseases Research
2007 Annual Report
1a.Objectives (from AD-416)
To identify and differentiate typical and atypical case samples of CWD and Scrapie by characterizing the biologic phenotype and pathologic profile of these agents when administered to susceptible lines of transgenic and inbred mice.
1b.Approach (from AD-416)
Tissue samples from deer, elk, sheep and goats with Transmissible Spongiform Encephalopathy (TSE) will be administered to mice by intracerebral injection. Multiple tissue types will be included, such as samples of brain, lymph node, blood, urine, feces, antler velvet and muscle. Mouse models used as recipient hosts will include both preexisting and recently created transgenic and inbred mouse lines. Recipient mouse phenotype will be evaluated by measuring clinical response, population disease rate, incubation time, and pathologic profile within the central nervous system (CNS). Pathologic profile of CNS lesion foci is assessed by evaluating anatomic localization, spongiform change, astrocytic gliosis, and deposition of protease resistant prion protein. BSL-1; 9-4-06. Documents SCA with U. of WA.
3.Progress Report
This report serves to document research conducted under a specific cooperative agreement between ARS and the University of Washington. Additional details of research can be found in the report for the parent project 5348-32000-026-00D Transmissible Spongiform Encephalopathies: the role of genetics, strain variation, and environmental contamination in disease control. The purpose of this new SCA is to identify and differentiate typical and atypical case samples of CWD and scrapie by characterizing the biologic phenotype and pathologic profile of these agents when administered to susceptible lines of transgenic and inbred mice. There will be weekly interactions between the ADODR, ADRU scientists and University of Washington collaborators through personnel visits, conference calls and emails.
http://www.ars.usda.gov/research/projects/projects.htm?ACCN_NO=411895&showpars=true&fy=2007
From: TSS (216-119-163-189.ipset45.wt.net)
Subject: CWD aka MAD DEER/ELK TO HUMANS ???
Date: September 30, 2002 at 7:06 am PST
From: "Belay, Ermias" To: Cc: "Race, Richard (NIH)" ; ; "Belay, Ermias" Sent: Monday, September 30, 2002 9:22 AM
Subject: RE: TO CDC AND NIH - PUB MED- 3 MORE DEATHS - CWD - YOUNG HUNTERS
Dear Sir/Madam,
In the Archives of Neurology you quoted (the abstract of which was attached to your email), we did not say CWD in humans will present like variant CJD.
That assumption would be wrong. I encourage you to read the whole article and call me if you have questions or need more clarification (phone: 404-639-3091). Also, we do not claim that "no-one has ever been infected with prion disease from eating venison." Our conclusion stating that we found no strong evidence of CWD transmission to humans in the article you quoted or in any other forum is limited to the patients we investigated.
Ermias Belay, M.D. Centers for Disease Control and Prevention
-----Original Message-----
From:
Sent: Sunday, September 29, 2002 10:15 AM
To: rr26k@nih.gov; rrace@niaid.nih.gov; ebb8@CDC.GOV
Subject: TO CDC AND NIH - PUB MED- 3 MORE DEATHS - CWD - YOUNG HUNTERS
Sunday, November 10, 2002 6:26 PM ......snip........end..............TSS
also,
A. Aguzzi - Chronic Wasting Disease (CWD) also needs to be addressed. Most serious because of rapid horizontal spread and higher prevalence than BSE in UK, up to 15% in some populations. Also may be a risk to humans - evidence that it is not dangerous to humans is thin.
http://www.tseandfoodsafety.org/activities/bse_conference_basel_april_02/2summary_of_conference.htm
Chronic Wasting Disease and Potential Transmission to Humans
Ermias D. Belay,* Ryan A. Maddox,* Elizabeth S. Williams,† Michael W. Miller,‡ Pierluigi Gambetti,§ and Lawrence B. Schonberger* *Centers for Disease Control and Prevention, Atlanta, Georgia, USA; †University of Wyoming, Laramie, Wyoming, USA; ‡Colorado Division of Wildlife, Fort Collins, Colorado, USA; and §Case Western Reserve University, Cleveland, Ohio, USA
Suggested citation for this article: Belay ED, Maddox RA, Williams ES, Miller MW, Gambetti P, Schonberger LB. Chronic wasting disease and potential transmission to humans. Emerg Infect Dis [serial on the Internet]. 2004 Jun [date cited]. Available from:
http://www.cdc.gov/ncidod/EID/vol10no6/03-1082.htm
--------------------------------------------------------------------------------
Chronic wasting disease (CWD) of deer and elk is endemic in a tri-corner area of Colorado, Wyoming, and Nebraska, and new foci of CWD have been detected in other parts of the United States. Although detection in some areas may be related to increased surveillance, introduction of CWD due to translocation or natural migration of animals may account for some new foci of infection. Increasing spread of CWD has raised concerns about the potential for increasing human exposure to the CWD agent. The foodborne transmission of bovine spongiform encephalopathy to humans indicates that the species barrier may not completely protect humans from animal prion diseases. Conversion of human prion protein by CWD-associated prions has been demonstrated in an in vitro cell-free experiment, but limited investigations have not identified strong evidence for CWD transmission to humans. More epidemiologic and laboratory studies are needed to monitor the possibility of such transmissions.
snip...full text ;
http://www.cdc.gov/ncidod/EID/vol10no6/03-1082.htm
Volume 12, Number 10–October 2006
Research
Human Prion Disease and Relative Risk Associated with Chronic Wasting Disease
Samantha MaWhinney,* W. John Pape,† Jeri E. Forster,* C. Alan Anderson,‡§ Patrick Bosque,‡¶ and Michael W. Miller# *University of Colorado at Denver and Health Sciences Center, Denver, Colorado, USA; †Colorado Department of Public Health and Environment, Denver, Colorado, USA; ‡University of Colorado School of Medicine, Denver, Colorado, USA; §Denver Veteran's Affairs Medical Center, Denver, Colorado, USA; ¶Denver Health Medical Center, Denver, Colorado, USA; and #Colorado Division of Wildlife, Fort Collins, Colorado, USA
Suggested citation for this article
The transmission of the prion disease bovine spongiform encephalopathy (BSE) to humans raises concern about chronic wasting disease (CWD), a prion disease of deer and elk. In 7 Colorado counties with high CWD prevalence, 75% of state hunting licenses are issued locally, which suggests that residents consume most regionally harvested game. We used Colorado death certificate data from 1979 through 2001 to evaluate rates of death from the human prion disease Creutzfeldt-Jakob disease (CJD). The relative risk (RR) of CJD for CWD-endemic county residents was not significantly increased (RR 0.81, 95% confidence interval [CI] 0.40–1.63), and the rate of CJD did not increase over time (5-year RR 0.92, 95% CI 0.73–1.16). In Colorado, human prion disease resulting from CWD exposure is rare or nonexistent. However, given uncertainties about the incubation period, exposure, and clinical presentation, the possibility that the CWD agent might cause human disease cannot be eliminated.
snip... full text ;
http://0-www.cdc.gov.mill1.sjlibrary.org/ncidod/EID/vol12no10/06-0019.htm
full text ;
http://chronic-wasting-disease.blogspot.com/2006_12_01_archive.html
CWD
http://chronic-wasting-disease.blogspot.com/
CJD QUESTIONNAIRE
http://cjdquestionnaire.blogspot.com/
Monitoring the occurrence of emerging forms of CJD
http://cjdusa.blogspot.com/
Singeltary, Sr et al. JAMA.2001; 285: 733-734.
Diagnosis and Reporting of Creutzfeldt-Jakob Disease
Since this article does not have an abstract, we have provided the first 150 words of the full text and any section headings.
To the Editor:
In their Research Letter, Dr Gibbons and colleagues1 reported that the annual US death rate due to Creutzfeldt-Jakob disease (CJD) has been stable since 1985. These estimates, however, are based only on reported cases, and do not include misdiagnosed or preclinical cases. It seems to me that misdiagnosis alone would drastically change these figures. An unknown number of persons with a diagnosis of Alzheimer disease in fact may have CJD, although only a small number of these patients receive the postmortem examination necessary to make this diagnosis. Furthermore, only a few states have made CJD reportable. Human and animal transmissible spongiform encephalopathies should be reportable nationwide and internationally.
Terry S. Singeltary, Sr Bacliff, Tex
1. Gibbons RV, Holman RC, Belay ED, Schonberger LB. Creutzfeldt-Jakob disease in the United States: 1979-1998. JAMA. 2000;284:2322-2323. FREE FULL TEXT
http://jama.ama-assn.org/cgi/content/extract/285/6/733?maxtoshow=&HITS=10&hits=10&RESULTFORMAT=&fulltext=singeltary&searchid=1&FIRSTINDEX=0&resourcetype=HWCIT
JOURNAL OF NEUROLOGY
MARCH 26, 2003
In light of the findings of Asante and Collinge et al, there
should be drastic measures to safeguard the medical and surgical arena
from sporadic CJDs and all human TSEs. I only ponder how many sporadic
CJDs in the USA are type 2 PrPSc?
http://www.neurology.org/cgi/eletters/60/2/176#535
TSS
posted by Terry S. Singeltary Sr. at
2:23 PM
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