MONDAY, APRIL 25, 2011
Experimental Oral Transmission of Atypical Scrapie to Sheep
Volume 17, Number 5–May 2011
Research
Experimental Oral Transmission of Atypical Scrapie to Sheep
Marion M. Simmons, S. Jo Moore,1 Timm Konold, Lisa Thurston, Linda A. Terry, Leigh Thorne, Richard Lockey, Chris Vickery, Stephen A.C. Hawkins, Melanie J. Chaplin, and John Spiropoulos –Weybridge, Addlestone, UK
Suggested citation for this article
Abstract
To investigate the possibility of oral transmission of atypical scrapie in sheep and determine the distribution of infectivity in the animals' peripheral tissues, we challenged neonatal lambs orally with atypical scrapie; they were then killed at 12 or 24 months. Screening test results were negative for disease-specific prion protein in all but 2 recipients; they had positive results for examination of brain, but negative for peripheral tissues. Infectivity of brain, distal ileum, and spleen from all animals was assessed in mouse bioassays; positive results were obtained from tissues that had negative results on screening. These findings demonstrate that atypical scrapie can be transmitted orally and indicate that it has the potential for natural transmission and iatrogenic spread through animal feed. Detection of infectivity in tissues negative by current surveillance methods indicates that diagnostic sensitivity is suboptimal for atypical scrapie, and potentially infectious material may be able to pass into the human food chain.
SNIP...
Discussion This study is still ongoing and will not be completed until 2012. However, the current interim report documents the successful oral transmission of atypical scrapie, confirms that the disease phenotype is retained following transmission by this route in AHQ/AHQ sheep, and indicates that infectivity can be demonstrated in the gut in the absence of detectable PrPSc at least as early as 12 months after exposure.
One sheep (animal 12) culled at 24 months post inoculation displayed abnormalities in behavior and movement suggestive of atypical scrapie. Signs like ataxia with head tremor and circling have been described in experimental (19) and natural (3,30) disease, which was attributed to lesions in the cerebellum and forebrain, respectively, corresponding with PrPSc accumulation in these areas (20,24).
By contrast, animal 11, which had confirmed atypical scrapie based on postmortem tests, was considered clinically normal. The less severe and limited PrPSc accumulation in the brain of this sheep than in animal 12 may explain the absence of clinical abnormalities, which is supported by our findings in goats with scrapie in which more extensive PrPSc accumulation in the brain was usually associated with a more severe clinical disease (25).
Although all TSEs are transmissible after intracerebral challenge to a susceptible host, only some are infectious under natural conditions. Therefore, it was important from a pathogenesis and disease control perspective to establish whether or not oral transmission can be successful. However, the challenge model in this study exposed animals as neonates, when the esophageal groove is operational and the lambs are physiologically monogastric. Exposure of 3-month-old ruminating animals to similar amounts of positive brain by the oral route have so far not resulted in any clinical disease, with all animals still alive >1,500 days post challenge (M.M. Simmons, unpub. data), but most natural cases have been recorded in animals older than this, so these animals may still progress to disease in the next few years. Since this challenge study in older animals has no time-kill component, and no losses caused by unrelated disease have occurred, whether any of these sheep are in a preclinical phase of disease is unknown. Unfortunately, the absence of detectable PrPSc in lymphoreticular tissues of sheep with atypical scrapie precludes the use of biopsies to ascertain early infection in these animals.
Transmission may be more efficient in newborn animals; the incubation periods of sheep orally infected with classical scrapie were significantly shorter in sheep challenged at 14 days of age than those challenged at 6 months of age (31). If, however, oral transmission is only effective in such young animals, then field exposure would most likely have to be through milk, which is known to be a highly effective route of transmission for classical scrapie (32). No data are currently available on the potential infectivity of milk from animals with atypical scrapie.
Successful oral transmission also raises questions regarding the pathogenesis of this form of disease. There must be passage of the infectious agent from the alimentary canal to the brain through one of several possible routes, most likely those that have been suggested and discussed in detail for other TSEs, for example, retrograde neuronal transportation either directly (33–35) or through lymphoid structures or hematogenously (36). Infectivity in the absence of readily demonstrable PrPSc has been reported (37–39), and although the mouse bioassay may detect evidence of disease in other tissues, these data may not be available for at least another 2 years. More protease-sensitive forms of PrPSc may be broken down more efficiently within cells and thus do not accumulate in peripheral tissues (19), enabling atypical PrPSc to transit the digestive tract and disseminate through other systems in small amounts before accumulating detectably in the central nervous system.
Although we do not have epidemiologic evidence that supports the efficient spread of disease in the field, these data imply that disease is potentially transmissible under field situations and that spread through animal feed may be possible if the current feed restrictions were to be relaxed. Additionally, almost no data are available on the potential for atypical scrapie to transmit to other food animal species, certainly by the oral route. However, work with transgenic mice has demonstrated the potential susceptibility of pigs, with the disturbing finding that the biochemical properties of the resulting PrPSc have changed on transmission (40). The implications of this observation for subsequent transmission and host target range are currently unknown.
How reassuring is this absence of detectable PrPSc from a public health perspective? The bioassays performed in this study are not titrations, so the infectious load of the positive gut tissues cannot be quantified, although infectivity has been shown unequivocally. No experimental data are currently available on the zoonotic potential of atypical scrapie, either through experimental challenge of humanized mice or any meaningful epidemiologic correlation with human forms of TSE. However, the detection of infectivity in the distal ileum of animals as young as 12 months, in which all the tissues tested were negative for PrPSc by the currently available screening and confirmatory diagnostic tests, indicates that the diagnostic sensitivity of current surveillance methods is suboptimal for detecting atypical scrapie and that potentially infectious material may be able to pass into the human food chain undetected.
''Epidemiological studies indicate that Nor98-like scrapie is either not transmissible or poorly transmissible under natural conditions. Further, the World Organization for Animal Health (OIE) has determined that Nor98-like scrapie is distinct from classical scrapie and is not a listed disease of trade concern. Animals in Nor98-like scrapie infected flocks are not removed and are free to move once they have been officially identified.''
LMAO! CAN YOU SAY USDA, OIE, TRADE AND MONEY $$$
J Vet Med Sci. 2016 Oct; 78(10): 1619–1624. Published online 2016 Jun 20. doi: 10.1292/jvms.16-0259 PMCID: PMC5095634
Transmission of atypical scrapie to homozygous ARQ sheep
Hiroyuki OKADA,1,* Kohtaro MIYAZAWA,1 Morikazu IMAMURA,1 Yoshifumi IWAMARU,1 Kentaro MASUJIN,1 Yuichi MATSUURA,1 and Takashi YOKOYAMA1
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In this study, the estimated infectivity level in skeletal muscle and lymphoid tissues from animals (n = 4) affected with two different classical scrapie isolates did reach up to 1/10 (weight/weight) of the infectivity found in the CNS from terminally affected sheep. These values are higher than those expected from previous work. This could be explained by the fact that previously available data on prion quantities in peripheral tissues of small ruminants (in particular those related to striated muscle) relied on biochemical measurement of PrPScamount [26] and the cell types accumulating PrPSc and the composition of these tissues may have impact on the PrPSc recovery yield. Also, if in some classical scrapie cases a 3–4 log10 infectivity difference was reported between CNS and some lymphoid tissues using bioassay in conventional mice, in other classical scrapie cases, the same study reported that infectivity in lymphoid tissue was only 1 to 10 fold lower than in CNS [27].
The classical scrapie cases that were investigated in this work cannot be assumed to be representative of all field diversity as only four animal cases of highly susceptible genotypes were used. However, the results indicate that exposure risk to such TSE agents through the unrestricted entry in the food chain of potentially infectious tissues would be significantly higher than previously thought.
In most countries, the identification of Atypical/Nor98 scrapie was a consequence of the implementation of an active surveillance for TSE consisting in random testing for PrPScpresence in brainstem of a fraction of fallen or healthy culled small ruminants [10]. In Atypical/Nor98 scrapie cases, the sensitivity of PrPSc detection tests that are used for initial field screening or confirmation of TSE cases is debated. Several authors reported failure to detect PrPSc in some CNS areas like the obex area [5], [6], [20] from known affected animals or discrepancies in results when applying different diagnostic tests to a same sample [6], [10].
The results obtained in this study by comparing the analytical sensitivity of biochemical PrPScdetection (using an OIE registered WB method and a validated rapid screening test for TSE detection, in small ruminants) and bioassay indicated that CNS samples that would contain up to 107.4.–107.7 ID50/g of Atypical/Nor98 scrapie (according to tg338 IC bioassay) could remain negative for PrPSc detection. In field, Atypical/Nor98 scrapie cases (Table 1) PrPSc positive WB was observed in CNS samples in which infectious titre was estimated (on the basis of incubation period) to be higher than 105.8 ID50/g IC in tg338. Such discrepancies might reflect an individual variability of the PrPSc WB detection limits between atypical scrapie cases. It might alternatively be the consequence of a relative imprecision in estimating the titre of low infectious doses by the incubation period bioassay method.
In contrast to Atypical/Nor98 scrapie cases, using two different classical agents the WB PrPScdetection sensitivity limit was about 102 ID50 IC in tg338 (ie a tissue with a titre of 103.7 ID50/g IC in tg338). These differences strongly support the contention that diagnostic assays based on PrPSc detection have lower performance for identifying Atypical/Nor98 scrapie cases than classical scrapie cases. It is consequently highly probable that a significant number of Atypical/Nor98 cases remain undetected by field testing, leading to an underestimation of Atypical/Nor98 scrapie prevalence in the small ruminant population. It is however not possible on the sole basis of this study to evaluate the importance of such underestimation.
The under detection of Atypical/Nor98 scrapie in the field due to the sensitivity of the current PrPSc based approach would also impact on understanding of the biology of this TSE agent.
While under natural conditions, classical scrapie is known to transmit between individuals, the analysis of data collected through the active TSE surveillance program seemed to indicate that Atypical/Nor98 scrapie could be poorly or not transmissible at all. This is based on the lack of statistical difference of the observed Atypical/Nor98 frequencies between the general population and the flocks where a positive case had been identified [38], [39]. The lower ability to detect Atypical Scrapie incubating animals using the PrPSc based methodologies means that this conclusion should be considered with caution.
Atypical/Nor98 cases are identified in older animals in comparison to classical scrapie [6], [40]. The lack of PrPSc detection in peripheral tissues of reported cases suggested that Atypical/Nor98 scrapie agent could be restricted to CNS. This is supportive of the hypothesis that Atypical/Nor98 scrapie could be a spontaneous disorder of PrP folding and metabolism occurring in aged animals without external cause [6], [38].
However, this hypothesis is questioned by the evidence reported here that a negative PrPSctesting result could be observed in animals harbouring high infectious titre in their brain and that the infectious agent can be present in peripheral tissues of Atypical/Nor98 scrapie incubating sheep. TSE are considered to be transmitted following oral exposure; initial uptake is followed by a peripheral replication phase which is generally associated with a dissemination of the agent in the lymphoid system and the deposition of large amounts of PrPSc. This peripheral replication phase is later followed by the entry of the infectious agent into the CNS through the autonomic nervous system [25], [27], [35], [36]. However, in several situations, like BSE in cattle [41], [42], [43] or classical scrapie in ARR heterozygote sheep [44], [45], the involvement of secondary lymphoid system is marginal, which does not preclude central neuro-invasion through the autonomic nervous system [46]. It could be proposed that Atypical Scrapie/Nor98 might occur following oral exposure to a TSE agent, which would spread marginally in lymphoid tissues before neuro-invasion. The slow propagation of Atypical Scrapie/Nor98 in its host (long incubation period) and the impaired detection sensitivity level of PrPSc based assays would explain the apparent old age of detected cases.
The results presented here are insufficient to rule out the hypothesis of a spontaneous/non contagious disorder or to consider this alternative scenario as a plausible hypothesis. Indeed, the presence of Atypical scrapie/Nor98 infectivity in peripheral tissues could be alternatively due to the centripetal spreading of the agent from the CNS. However, our findings point out that further clarifications on Atypical/Nor98 scrapie agent biology are needed before accepting that this TSE is a spontaneous and non contagious disorder of small ruminants. Assessing Atypical/Nor98 scrapie transmissibility through oral route in natural host and presence in placenta and in colostrum/milk (which are considered as major sources for TSE transmission between small ruminants) [28], [32] will provide crucial data.
The presence of infectivity in peripheral tissues that enter the food chain clearly indicates that the risk of dietary exposure to Atypical/Nor98 scrapie cannot be disregarded. However, according to our observations, in comparison to the brain, the infectious titres in the peripheral tissues were five log10 lower in Atypical/Nor98 scrapie than in classical scrapie. Therefore, the reduction of the relative exposure risk following SRM removal (CNS, head, spleen and ileum) is probably significantly higher in Atypical/Nor98 scrapie cases than in classical scrapie cases. However, considering the currently estimated prevalence of Atypical/Nor98 scrapie in healthy slaughtered EU population [10], it is probable that atypical scrapie infectivity enters in the food chain despite the prevention measures in force.
Finally, the capacity of Atypical/Nor98 scrapie agent (and more generally of small ruminants TSE agents) to cross species barrier that naturally limits the transmission risk is insufficiently documented. Recently, the transmission of an Atypical/Nor98 scrapie isolate was reported into transgenic mice over-expressing the porcine PrP [47]. Such results cannot directly be extrapolated to natural exposure conditions and natural hosts. However, they underline the urgent need for further investigations on the potential capacity of Atypical/Nor98 scrapie to propagate in other species than small ruminants.
Porcine prion protein amyloid and Nor-98 atypical Scrapie
Porcine prion protein amyloid
Per Hammarström & Sofie Nyström Pages 266-277 | Received 01 Jun 2015, Accepted 17 Jun 2015, Accepted author version posted online: 28 Jul 2015, Published online: 28 Jul 2015
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On the other hand, Nor98 scrapie (Atypical scrapie) as well as BSE from both cattle and BoTg mouse model resulted in clinical disease in the PoTg001 mice. However, in the first generation, disease progression was FIGURE 3. Schematic model of prion strain adaptation. (Model adapted from Collinge and Clarke 2007 and Sandberg et al 2011, 2013.31,49,50) The red horizontal line indicates the tolerance threshold for prion toxicity for the respective model, the green vertical line indicates normal lifespan/experimental termination for the mice. The black curves indicate increase in prion titer over time upon prion inoculation. (a) BSE and classical scrapie in wild type mice according to Bruce et al.23 (b) BSE, classical scrapie and Nor98 scarpie in PoTg001 mice according to Espinosa, Torres et al. (2009, 2014).25,26 270 Hammarstrom and Nystr € om€ slow. Incubation time until death was as long as 600 d and the hit rate was low. This indicates that disease has barely developed by the time the mice reach their natural life span limit which in this study was set to 650 d Already in the second passage the hit rate was 100 % and the incubation time was cut in half (Fig. 3b). No further shortening of incubation time was observed upon third passage. This shows that PoPrP is capable of forming infectious and neurotoxic prions in vivo if triggered by a compatible prion strain and if given enough time to develop. Both BSE and Nor98 rapidly adapts to the PoPrP host sequence, resulting in higher penetrance as well as in markedly shorter life span already in the second passage, well within the limits of normal life span for a mouse.
It is known that prion strains need time and serial passages to adapt. Knowing that pigs in modern farming are rarely kept for enough time for clinical signs to emerge in prion infected pigs it is important to be vigilant if there is a sporadic porcine spongiform encephalopathy (PSE) as has been seen in cattle (BASE) and sheep (Nor98). Hypothetically such a sporadic and then infectious event could further adapt and over a few generations have reached the point where clinical PSE is established within the time frame where pigs are being slaughtered for human consumption (Fig. 4). USE OF MATERIALS DERIVED FROM PIG IN VIEW OF PORCINE PrP AMYLOID The pig is the most versatile species used by humans for food and other applications. Over 1,5 billion pigs are slaughtered each year worldwide for human use.32 Besides juicy pork sirloin other parts from pig are used for making remarkably diverse things such as musical instruments, china, leather, explosives, lubricants etc. Pig offal is used for human medicine, e.g., hormone preparations such as insulin and cerebrolysin, in xenographs, sutures, heparin and in gelatin for drug capsules.33,34
Research Project: TRANSMISSION, DIFFERENTIATION, AND PATHOBIOLOGY OF TRANSMISSIBLE SPONGIFORM ENCEPHALOPATHIES
Location: Virus and Prion Research
Title: Disease-associated prion protein detected in lymphoid tissues from pigs challenged with the agent of chronic wasting disease
Author item Moore, Sarah item Kunkle, Robert item Kondru, Naveen item Manne, Sireesha item Smith, Jodi item Kanthasamy, Anumantha item West Greenlee, M item Greenlee, Justin
Submitted to: Prion Publication Type: Abstract Only Publication Acceptance Date: 3/15/2017 Publication Date: N/A Citation: N/A Interpretive Summary:
Technical Abstract: Aims: Chronic wasting disease (CWD) is a naturally-occurring, fatal neurodegenerative disease of cervids. We previously demonstrated that disease-associated prion protein (PrPSc) can be detected in the brain and retina from pigs challenged intracranially or orally with the CWD agent. In that study, neurological signs consistent with prion disease were observed only in one pig: an intracranially challenged pig that was euthanized at 64 months post-challenge. The purpose of this study was to use an antigen-capture immunoassay (EIA) and real-time quaking-induced conversion (QuIC) to determine whether PrPSc is present in lymphoid tissues from pigs challenged with the CWD agent.
Methods: At two months of age, crossbred pigs were challenged by the intracranial route (n=20), oral route (n=19), or were left unchallenged (n=9). At approximately 6 months of age, the time at which commercial pigs reach market weight, half of the pigs in each group were culled (<6 challenge="" groups="" month="" pigs="" remaining="" the="">6 month challenge groups) were allowed to incubate for up to 73 months post challenge (mpc). The retropharyngeal lymph node (RPLN) was screened for the presence of PrPSc by EIA and immunohistochemistry (IHC). The RPLN, palatine tonsil, and mesenteric lymph node (MLN) from 6-7 pigs per challenge group were also tested using EIA and QuIC.6>
Results: PrPSc was not detected by EIA and IHC in any RPLNs. All tonsils and MLNs were negative by IHC, though the MLN from one pig in the oral <6 5="" 6="" at="" by="" detected="" eia.="" examined="" group="" in="" intracranial="" least="" lymphoid="" month="" months="" of="" one="" pigs="" positive="" prpsc="" quic="" the="" tissues="" was="">6 months group, 5/6 pigs in the oral <6 4="" and="" group="" months="" oral="">6 months group. Overall, the MLN was positive in 14/19 (74%) of samples examined, the RPLN in 8/18 (44%), and the tonsil in 10/25 (40%). Conclusions:6>6>
This study demonstrates that PrPSc accumulates in lymphoid tissues from pigs challenged intracranially or orally with the CWD agent, and can be detected as early as 4 months after challenge.
CWD-infected pigs rarely develop clinical disease and if they do, they do so after a long incubation period. This raises the possibility that CWD-infected pigs could shed prions into their environment long before they develop clinical disease.
Furthermore, lymphoid tissues from CWD-infected pigs could present a potential source of CWD infectivity in the animal and human food chains.
CONFIDENTIAL
EXPERIMENTAL PORCINE SPONGIFORM ENCEPHALOPATHY
While this clearly is a cause for concern we should not jump to the conclusion that this means that pigs will necessarily be infected by bone and meat meal fed by the oral route as is the case with cattle. ...
we cannot rule out the possibility that unrecognised subclinical spongiform encephalopathy could be present in British pigs though there is no evidence for this: only with parenteral/implantable pharmaceuticals/devices is the theoretical risk to humans of sufficient concern to consider any action.
Our records show that while some use is made of porcine materials in medicinal products, the only products which would appear to be in a hypothetically ''higher risk'' area are the adrenocorticotrophic hormone for which the source material comes from outside the United Kingdom, namely America China Sweden France and Germany. The products are manufactured by Ferring and Armour. A further product, ''Zenoderm Corium implant'' manufactured by Ethicon, makes use of porcine skin - which is not considered to be a ''high risk'' tissue, but one of its uses is described in the data sheet as ''in dural replacement''. This product is sourced from the United Kingdom.....
snip...see much more here ;
WEDNESDAY, APRIL 05, 2017
Disease-associated prion protein detected in lymphoid tissues from pigs challenged with the agent of chronic wasting disease
spontaneous atypical BSE or spontaneous atypical Nor98 Scrapie, the spontaneous part, or sporadic, no cause, that dog does not hunt anymore. that old folks and old cow disease is BSe at it's finest, just like sporadic CJD, a spontaneous event from nothing in 85%+ of all humans, that's bull shit as well.
AS with atypical BSE type h, type L, and look at France, if atypical BSE was spontaneous, why then does France have an overly abundant cases of atypical BSE in both L type and H type?
must be an epidemic of spontaneous BSE in one given area? i don't think so.
Table 10: Number and proportion of BSE cases subject to discriminatory testing, by case type for the period 2003–2015 in the EU and other reporting countries
see chart page 25;
Table 10: Number and proportion of BSE cases subject to discriminato ry testing, by case type for the period2003–2015 in the EU and other repo rting countries
SAME with atypical scrapie, why then does Portugal of the Russian Federation have an outbreak of the highest documented atypical scrapie cases, if then atypical scrapie is a spontaneous event? look at the chart on page 35, see atypical scrapie cases by country, and someone please tell me why a few of these countries have way over what other countries have of the atypical Scrapie. if it was a spontaneous event, you would think these spontaneous events would be uniform, ...unless there were causes, then they would not be so uniform. look at the chart on page 35
The European Union summary report on data of the surveillance of ruminants for the presence of transmissible spongiform encephalopathies (TSEs) in 2015
European Food Safety Authority (EFSA),Frank Boelaert, Marta Hugas, Angel Ortiz Pelaez, Valentina Rizzi, Pietro Stella andYves Van Der Stede
AND FINALLY, THIS CHART HAS ALL THE PROOF YOU NEED THAT ATYPICAL SCRAPIE IS _NOT_ SPONTANEOUS. IF IT IS, THERE ARE A FEW COUNTRIES WITH AN EPIDEMIC OF ATYPCIAL NOR98 SCRAPIE, THAT OTHER COUNTRIES DON'T HAVE.
Table 14: Annual TSE cases by country, species and case type in 2002–2015 in the EU and other reporting countries
Case type Atypical Classical Year 2002 2003 2004 2005 20062007 2008 2009 2010 2011 2012 2013 2014 2015 Total 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013 2014 2015
Total Sheep
Country
SNIP...SEE FIGURES PAGE 40;
Increased Atypical Scrapie Detections
Press reports indicate that increased surveillance is catching what otherwise would have been unreported findings of atypical scrapie in sheep. In 2009, five new cases have been reported in Quebec, Ontario, Alberta, and Saskatchewan. With the exception of Quebec, all cases have been diagnosed as being the atypical form found in older animals. Canada encourages producers to join its voluntary surveillance program in order to gain scrapie-free status. The World Animal Health will not classify Canada as scrapie-free until no new cases are reported for seven years. The Canadian Sheep Federation is calling on the government to fund a wider surveillance program in order to establish the level of prevalence prior to setting an eradication date. Besides long-term testing, industry is calling for a compensation program for farmers who report unusual deaths in their flocks.
Atypical scrapie in Australia
RW Cook,a* J Bingham,bAS Besier,cCL Bayley,dM Hawes,ePL Shearer,fM Yamada,bJ Bergfeld,bDT Williamsband DJ Middletonb Background Since its initial detection in Norway in 1998, atypical scrapie (‘atypical/Nor98 scrapie’) has been reported in sheep in the majority of European countries (including in regions free of classical scrapie) and in the Falkland Islands, the USA, Canada,New Zealand and Australia.
Case series The diagnosis in Australia of atypical scrapie in four Merino and one Merino-cross sheep showing clinical signs of neurological disease was based on the detection of grey matter neuropil vacuolation (spongiform change) in the brain (particularly inthe molecular layer of the cerebellar cortex) and associated abnormal prion protein (PrPSc) deposition in both grey and white matter. Changes were minimal in the caudal brainstem, the predilection site for lesions of classical scrapie.Conclusion The distinctive lesion profile of atypical scrapie in these five sheep highlights the diagnostic importance of routine histological evaluation of the cerebellum for evidence of neuropil vacuolation and associated PrPSc deposition in adult sheep with suspected neurological disease.
Keywords atypical scrapie; prion disease; sheep; transmissible spongiform encephalopathy
Abbreviations ANZSDP, Australian and New Zealand StandardDiagnostic Procedure; CNS, central nervous system; DMNV, dorsalmotor nucleus of the vagus nerve; H&E, haematoxylin and eosin;IHC, immunohistochemistry; NTSESP, National TSE SurveillanceProgram; PrPSc, abnormal prion protein isomer; TSE, transmissiblespongiform encephalopathy. Aust Vet J 2016;94:452–455 doi: 10.1111/avj.12529
Friday, February 11, 2011
Atypical/Nor98 Scrapie Infectivity in Sheep Peripheral Tissues
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The presence of infectivity in peripheral tissues that enter the food chain clearly indicates that the risk of dietary exposure to Atypical/Nor98 scrapie cannot be disregarded. However, according to our observations, in comparison to the brain, the infectious titres in the peripheral tissues were five log10 lower in Atypical/Nor98 scrapie than in classical scrapie. Therefore, the reduction of the relative exposure risk following SRM removal (CNS, head, spleen and ileum) is probably significantly higher in Atypical/Nor98 scrapie cases than in classical scrapie cases. However, considering the currently estimated prevalence of Atypical/Nor98 scrapie in healthy slaughtered EU population [10], it is probable that atypical scrapie infectivity enters in the food chain despite the prevention measures in force.
Finally, the capacity of Atypical/Nor98 scrapie agent (and more generally of small ruminants TSE agents) to cross species barrier that naturally limits the transmission risk is insufficiently documented. Recently, the transmission of an Atypical/Nor98 scrapie isolate was reported into transgenic mice over-expressing the porcine PrP [47]. Such results cannot directly be extrapolated to natural exposure conditions and natural hosts. However, they underline the urgent need for further investigations on the potential capacity of Atypical/Nor98 scrapie to propagate in other species than small ruminants.
snip...please see full text thanks to the Authors and plospathogens.org/