Paul R. Webb

A Retrospective Immunohistochemical Study Reveals Atypical Scrapie has Existed in the United Kingdom since at Least 1987

Atypical scrapie is a relatively recent discovery, and it was unknown whether it was a new phenomenon or whether it had existed undetected in the United Kingdom national flock. Before 1998, the routine statutory diagnosis of transmissible spongiform encephalopathy (TSE) in sheep relied on the presence of TSE vacuolation in the brainstem. This method would not have been effective for the detection of atypical scrapie. Currently, immunohistochemistry (IHC) and Western blot are commonly used for the differential diagnosis of classical and atypical scrapie. The IHC pattern of PrP d deposition in atypical scrapie is very different from that in classical scrapie using the same antibody. It is thus possible that because of a lack of suitable diagnostic techniques and awareness of this form of the disease, historic cases of atypical scrapie remain undiagnosed. Immunohistochemistry was performed on selected formalin-fixed, paraffin-embedded (FFPE) blocks of ovine brain from the Veterinary Laboratories Agency archives that were submitted for various reasons, including suspect neurological disorders, between 1980 and 1989. It was found that PrP d deposits in a single case were consistent with atypical scrapie. A method was developed to obtain a PrP genotype from FFPE tissues and was applied to material from this single case, which was shown to be AHQ/AHQ. This animal was a scrapie suspect from 1987, but diagnosis was not confirmed by the available techniques at that time.

Transmission of classical scrapie via goat milk.

FOLLOWING reports that ovine scrapie (referred to here and subsequently as classical scrapie) can be transmitted from dams to lambs via milk (Konold and others 2008, Ligios and others 2011), we subsequently carried out a study to investigate whether caprine scrapie could also be transmitted via milk, using material collected from a field outbreak of scrapie in goats in the UK (Gonzalez and others 2009). Lambs were selected as milk recipients from a closed flock of known scrapie-free status (Simmons and others 2009) because an assured scrapie-free source of goats was not available. Due to the lack of published information about the susceptibility of sheep to caprine scrapie, a pilot study was conducted to determine whether sheep were susceptible to …

The interpretation of disease phenotypes to identify TSE strains following murine bioassay: characterisation of classical scrapie

Mouse bioassay can be readily employed for strain typing of naturally occurring transmissible spongiform encephalopathy cases. Classical scrapie strains have been characterised historically based on the established methodology of assessing incubation period of disease and the distribution of disease-specific vacuolation across the brain following strain stabilisation in a given mouse line. More recent research has shown that additional methods could be used to characterise strains and thereby expand the definition of strain “phenotype”. Here we present the phenotypic characteristics of classical scrapie strains isolated from 24 UK ovine field cases through the wild-type mouse bioassay. PrPSc immunohistochemistry (IHC), paraffin embedded tissue blots (PET-blot) and Western blotting approaches were used to determine the neuroanatomical distribution and molecular profile of PrPSc associated with each strain, in conjunction with traditional methodologies. Results revealed three strains isolated through each mouse line, including a previously unidentified strain. Moreover IHC and PET-blot methodologies were effective in characterising the strain-associated types and neuroanatomical locations of PrPSc. The use of Western blotting as a parameter to define classical scrapie strains was limited. These data provide a comprehensive description of classical scrapie strain phenotypes on isolation through the mouse bioassay that can provide a reference for further scrapie strain identification.

Bovine spongiform encephalopathy: investigation of phenotypic variation among passive surveillance cases.

Bovine spongiform encephalopathy (BSE) is a prion disease of domesticated cattle, first identified in Great Britain (GB) in 1986. The disease has been characterized by histopathological, immunohistochemical, biochemical and biological properties, which have shown a consistent disease phenotype among cases obtained by passive surveillance. With the advent of active surveillance in 2001, immunological tests for detection of the prion protein revealed some cases with different biochemical characteristics and, in certain instances, differences in pathology that have indicated variant phenotypes and the possibility of agent strain variation. This study examines a case set of 523 bovine brains derived from archived material identified through passive surveillance in GB. All cases conformed to the phenotype of classical BSE (BSE-C) by histopathological, immunohistochemical and biochemical approaches. The analyses consolidated an understanding of BSE-C and, by western blotting, confirmed differentiation from the known atypical BSE cases which exhibit higher or lower molecular masses than BSE-C (BSE-H and BSE-L respectively).

The interpretation of disease phenotypes to identify TSE strains in mice: characterisation of BSE using PrPSc distribution patterns in the brain.

In individual animals affected by transmissible spongiform encephalopathies, different disease phenotypes can be identified which are attributed to different strains of the agent. In the absence of reliable technology to fully characterise the agent, classification of disease phenotype has been used as a strain typing tool which can be applied in any host. This approach uses standardised data on biological parameters, established for a single host, to allow comparison of different prion sources. Traditionally prion strain characterisation in wild type mice is based on incubation periods and lesion profiles after the stabilisation of the agent into the new host which requires serial passages. Such analysis can take many years, due to prolonged incubation periods. The current study demonstrates that the PrPSc patterns produced by one serial passage in wild type mice of bovine or ovine BSE were consistent, stable and showed minimal and predictable differences from mouse-stabilised reference strains. This biological property makes PrPSc deposition pattern mapping a powerful tool in the identification and definition of TSE strains on primary isolation, making the process of characterisation faster and cheaper than a serial passage protocol. It can be applied to individual mice and therefore it is better suited to identify strain diversity within single inocula in case of co-infections or identify strains in cases where insufficient mice succumb to disease for robust lesion profiles to be constructed. The detailed description presented in this study provides a reference document for identifying BSE in wild type mice.

Assessing the Susceptibility of Transgenic Mice Overexpressing Deer Prion Protein to Bovine Spongiform Encephalopathy

ABSTRACT Several transgenic mouse models have been developed which facilitate the transmission of chronic wasting disease (CWD) of cervids and allow prion strain discrimination. The present study was designed to assess the susceptibility of the prototypic mouse line, Tg(CerPrP)1536+/−, to bovine spongiform encephalopathy (BSE) prions, which have the ability to overcome species barriers. Tg(CerPrP)1536+/− mice challenged with red deer-adapted BSE resulted in 90% to 100% attack rates, and BSE from cattle failed to transmit, indicating agent adaptation in the deer.

Prevalence of scrapie infection in cull animals from 14 scrapie-affected flocks in Great Britain

Average flock size* 250 125 315 280 290 890 240 170 240 990 380 65 220 45 Number of culls submitted 23 22 31 23 78 68 26 23 51 19 20 9 7 7 Cull rate (%) 9·2 17·6 9·8 8·2 26·9 7·6 10·8 13·5 21·3 1·9 5·3 13·8 3·2 15·6 IHC-confirmed positives 1 1 1 0 12 5 0 1 6 0 0 0 0 0 Crude flock cull prevalence (%) 4·3 4·5 3·2 0 15·4 7·4 0 4·3 11·8 0 0 0 0 0 95 per cent CI 0·1-21·9 0·1-22·8 0·08-16·7 0-14·8† 8·2-25·3 2·4-16·3 0-13·2† 0·1-21·9 4·4-23·9 0-17·6† 0-16·8† 0-33·6† 0-41·0† 0-41·0† Number of culls with known age 23 22 31 23 78 64 26 23 51 19 18 9 6 7 Median of known ages (years) 8 6 4 9 3 3 4 6 4 5 7 3 6 3 Range of known ages (years) 5-9 2-8 1-7 8-10 1-8 1-11 2-8 1-8 3-7 3-7 3-9 3-3 4-8 2-5

Paraffin-embedded tissue blot as a sensitive method for discrimination between classical scrapie and experimental bovine spongiform encephalopathy in sheep:

The paraffin-embedded tissue (PET) blot was modified for use as a tool to differentiate between classical scrapie and experimental bovine spongiform encephalopathy (BSE) in sheep. Medulla (obex) from 21 cases of classical scrapie and 6 cases of experimental ovine BSE were used to develop the method such that it can be used as a tool to differentiate between BSE and scrapie in the same way that differential immunohistochemistry (IHC) has been used previously. The differential PET blot successfully differentiated between all of the scrapie and ovine BSE cases. Differentiation was permitted more easily with PET blot than by differential IHC, with accurate observations possible at the macroscopic level. At the microscopic level, sensitivity was such that discrimination by the differential PET blot could be made with more confidence than with differential IHC in cases where the immunohistochemical differences were subtle. The differential PET blot makes use of harsh epitope demasking conditions, and, because of the differences in the way prion protein is processed in different prion diseases, it can serve as a new, highly sensitive method to discriminate between classical scrapie and experimental BSE in sheep.

Studies of the transmissibility of the agent of bovine spongiform encephalopathy to the domestic chicken.

BackgroundTransmission of the prion disease bovine spongiform encephalopathy (BSE) occurred accidentally to cattle and several other mammalian species via feed supplemented with meat and bone meal contaminated with infected bovine tissue. Prior to United Kingdom controls in 1996 on the feeding of mammalian meat and bone meal to farmed animals, the domestic chicken was potentially exposed to feed contaminated with the causal agent of BSE. Although confirmed prion diseases are unrecorded in avian species a study was undertaken to transmit BSE to the domestic chicken by parenteral and oral inoculations. Transmissibility was assessed by clinical monitoring, histopathological examinations, detection of a putative disease form of an avian prion protein (PrP) in recipient tissues and by mouse bioassay of tissues. Occurrence of a progressive neurological syndrome in the primary transmission study was investigated by sub-passage experiments.ResultsNo clinical, pathological or bioassay evidence of transmission of BSE to the chicken was obtained in the primary or sub-passage experiments. Survival data showed no significant differences between control and treatment groups. Neurological signs observed, not previously described in the domestic chicken, were not associated with significant pathology. The diagnostic techniques applied failed to detect a disease associated form of PrP.ConclusionImportant from a risk assessment perspective, the present study has established that the domestic chicken does not develop a prion disease after large parenteral exposures to the BSE agent or after oral exposures equivalent to previous exposures via commercial diets. Future investigations into the potential susceptibility of avian species to mammalian prion diseases require species-specific immunochemical techniques and more refined experimental models.