Strains Of Scrapie Agent Research Articles

Pathology and pathogenesis of bovine spongiform encephalopathy and scrapie.

In common with other prion diseases or transmissible spongiform encephalopathies (TSEs), scrapie of sheep and bovine spongiform encephalopathy (BSE) are characterized by grey matter vacuolation and accumulation of an abnormal isoform of the host prion protein (PrP) in the central nervous system (CNS). In apparent contrast with human disease, neither neuronal loss nor gliosis are invariable features of the pathology of domestic food animal TSEs. In sheep, accumulation of abnormal PrP may also occur in the lymphoreticular and peripheral nervous systems where it may be detected within months of birth. The involvement of tissues other than CNS is influenced by dose, PrP genotype of the host and strain of TSE agent. Although many different strains of scrapie agent have been isolated in rodents following serial passage of affected sheep brain tissue, the significance of these murine strains for natural sheep scrapie, and the extent to which different sheep scrapie strains occur naturally are uncertain. Whereas the consistent vacuolar pattern in the brains of BSE-affected cattle suggests a single strain of agent, the patterns of vacuolation in sheep scrapie are highly variable and cannot be easily used to define strain. In sheep scrapie, immunohistochemistry can be used to visualize different morphological types of abnormal PrP within individual brains. These different types of PrP accumulation seem to be associated with different brain cell types and with variation in the processing of abnormal PrP. When assessed in whole brain, different patterns of PrP accumulation are helpful in distinguishing between different sheep scrapie strains and also between ovine BSE and natural sheep scrapie.

Gastric acidity protects mice against infection after intragastric administration of the 139A strain of scrapie agent: The potential relevance for variant Creutzfeldt-Jacob disease

Gastric acidity protects mice against infection after intragastric administration of the 139A strain of scrapie agent: The potential relevance for variant Creutzfeldt-Jacob disease

The response of the 22A strain of scrapie agent to microwave irradiation compared with boiling

The response of the 22A strain of scrapie agent to microwave irradiation compared with boiling

A 'unified theory' of prion propagation

There is now very persuasive evidence that the transmissible agent for spongiform encephalopathies such as scrapie, consists of a modified form of the normal host protein PrPc, devoid of any nucleic acid. On the other hand, because there are many different strains of scrapie agent with distinct phenotypes which can be propagated in animals homozygous for the PrPc gene, it has been suggested that a nucleic acid must be a component of the agent. Can the two views be reconciled?

Resistance of the ME7 scrapie agent to peracetic acid

Mouse brain infected with the ME7 strain of scrapie agent was exposed for 24 h to a range of concentrations of PAA, either as fragments of intact brain or as supernates of homogenised brain. Two % PAA inactivated the infectivity in intact tissue but not in a supernate. None of the concentrations tested (up to 19%) was effective with supernates, and this was considered to result from the protection afforded by aggregation of infectivity-containing particles.

Polyclonal increase in certain IgG subclasses in mice persistently infected with the 87V strain of scrapie

Eight different combinations of seven strains of scrapie agent and the three known Sinc genotypes of mice were screened for changes in the concentration of IgG in serum. A single radial immunodiffusion assay was used to measure IgG throughout the incubation period which in different models ranged from an average of 125 days to longer than the maximum observation period of about 600 days. The only major changes occurred with the 87V strain of scrapie injected intracerebrally (i.c.) or intraperitoneally (i.p.) into mouse strains of the Sinc genotype p7p7. IgG concentration reached 1·5 to 2·0 times the control values in i.c. infected mice, which developed clinical disease after 270 to 320 days and also in i.p. infected mice, which did not develop the disease within the 600-day observation period. At very high IgG concentration, the increase was polyclonal; it involved the IgG1 subclass more than the others and was accompanied by an increased rate of IgG clearance from serum. It is suggested that some scrapie infections of mice (and sheep) may upset the control of IgG production. The underlying mechanism may involve cell-pathogen interactions which are common to all scrapie infections, but only lead to gross changes in IgG in some combinations of agent strain and host genotype.

An electron microscopic study of inclusion bodies in synaptic terminals of scrapie-infected animals

Inclusion bodies consisting of vesicles of about 25 nm diameter and occurring in the synaptic terminals of scrapie-infected animals have been described by a number of people. In the present study these inclusion bodies were looked for in the neocortex, hippocampus and corpus callosum in a variety of strains of mice (C3H, LM, RIII, IM, VL) infected with different strains of scrapie agent (22C, 79A, ME7, 87V) after intracerebral inoculation. In plaque-bearing models of scrapie, terminals containing synaptic inclusion bodies were frequently found surrounding the amyloid plaque cores in the neocortex but not in the corpus callosum. In non-plaque-bearing models, terminals containing synaptic inclusion bodies were found in the neuropil of the neocortex and hippocampus. For all models, these bodies were either presynaptic or postsynaptic but were not, as a rule, found on both sides of the same synapse. Fibrillary material was frequently seen in the postsynaptic terminals containing the inclusion bodies in both the plaque- and non-plaque-bearing models. On one occasion fibrillary material was seen, together with the inclusion bodies, in a neuron cell body. Inclusion bodies were also seen in the neocortex of hamsters infected with the 263K strain of scrapie agent and a Cheviot sheep infected with the ME7 strain of agent. The inclusion bodies and the fibrillary material were thought to be derived from the breakdown of neurotubules.

Ionising radiation has no influence on scrapie incubation period in mice

Scrapie has an early non-clinical stage when replication of agent occurs in lymphoreticular organs. Whole-body irradiation failed to alter the incubation or neuropathology of the disease. Many experiments were carried out with different strains of scrapie agent and host, doses and timing of irradiation. The results suggest that mitotically quiescent cells are involved in agent replication.

Primary retinopathy in scrapie in mice deprived of light

Rodents infected with some strains of scrapie develop a severe retinopathy in which the photoreceptor cells are destroyed. The possibility that this results from light-induced damage as a secondary consequence of the disease was tested by maintaining scrapie-infected albino mice in total darkness. Photoreceptor loss occurred in terminal scrapie-infected mice maintained in both total darkness and in normal lighting conditions establishing that the retinopathy is a primary lesion with this strain of scrapie agent.

Chromatin structure in scrapie and Alzheimer's disease.

Scrapie affected brains exhibit a number of pathological features in common with the human neurodegenerative condition, Alzheimer's disease. The present report describes studies on chromatin structure seen in these two disease processes. Chromatin associated proteins influence transcriptional activity of DNA through an effect upon chromatin structure. We examined chromatin structure by: measuring the capacity of the enzyme micrococcal nuclease to release mono- and dinucleosomes from isolated nuclei and measuring DNA-histone interactions by examining the effect of ambient tonicity upon the release of chromatin proteins. In two strains of mice infected with two strains of scrapie agent there was reduced accessibility to micrococcal nuclease and an increased content on dinucleosomes of the histone H1 and H1(0) types. These changes precede clinical signs of scrapie and resemble those found in the human conditions of Alzheimer's and Pick's disease. Scrapie mouse brain differs from Alzheimer brain in that scrapie does not alter histone-DNA interactions as monitored by ionically induced histone release from chromatin. Despite similarities, the scrapie agent appears to operate upon different molecular mechanisms than those found in Alzheimer's disease.

Immunological comparison of scrapie-associated fibrils isolated from animals infected with four different scrapie strains

Scrapie-associated fibrils (SAFs) are abnormal filamentous structures that are uniquely associated with unconventional slow virus diseases. The antigenic relationships of SAFs from animals infected with four biologically distinct scrapie strains were investigated by using antisera raised to purified SAF proteins. Rabbit antisera were raised to SAFs isolated from mice infected with the ME7 scrapie strain and to SAFs isolated from hamsters infected with the 263K scrapie strain. A strong antigenic relationship was shown among SAF proteins (PrPs) isolated from all scrapie-infected animals (ME7, 139A, and 87V in mice and 263K in hamsters), and this relationship was demonstrable regardless of which antiserum was used. SAF proteins were antigenically distinct from those of paired helical filaments or amyloid isolated from patients with Alzheimer disease. Distinct Western blot profiles were demonstrated for SAFs isolated from animals infected with each scrapie strain. Differences seen among SAFs were independent, at least in part, of host species or genotype, implying that certain specific structural and molecular properties of SAFs are mediated by the strain of scrapie agent.

Disinfection studies with two strains of mouse-passaged scrapie agent: Guidelines for Creutzfeldt-Jakob and related agents

A variety of disinfection procedures were tested on two strains of scrapie agent, treated either as brain macerates (autoclaving) or as 10% homogenates (chemical treatments). It is suggested that a given treatment should produce a titre loss, of both strains of scrapie, of at least 10 4 units before it be regarded as useful for the disinfection of the agents of scrapie and Creutzfeldt-Jakob disease (CJD). By this criterion, treatment at room temperature with about 4% Hycolin (0.6% chlorinated phenols), 0.2% permanganate, 5% Tego (dodecyl-di(aminoethyl)glycine) or 5% sodium dodecyl sulphate (SDS) are unsuitable. However, data indicate that SDS might be used to reduce the heat stability of scrapie agent. Hypochlorite (Sterilex) was the only satisfactory chemical reagent tested. At least 10 4–10 5 units of infectivity were lost by treatment with hypochlorite containing 1,000 ppm available chlorine after a 4–16 h exposure, or containing 10,000 ppm available chlorine after a half-hour exposure. The latter result points to the use of concentrated hypochlorite (about 2% available chlorine; approximately 20% Sterilex) to decontaminate surfaces. We suggest that the cleaning action of SDS, or other strong detergents, might also help to decontaminate surfaces, but studies on this are needed. Autoclaving at 126°C for 1–2 h reduced titres by 10 3–10 7 units, depending on the strain of agent. However, total disinfection of brain containing high titres of infectivity was approached only at 136°C when titre losses of about 10 6 units were obtained by autoclaving for 4–32 min. Further studies are needed before we can make simple, general recommendations for the disinfection of CJD agents in hospital practice.

Extraneural competition between different scrapie agents leading to loss of infectivity.

MANY strains of scrapie agent have been isolated which differ in their biological properties, such as incubation period and type of brain lesion1. We have shown previously that competition occurred between different scrapie agents intracerebrally injected into mice2, indicated by an increase in the incubation period of the lethal scrapie agent when a different scrapie agent had also been injected to impede its pathogenesis. We did not establish whether the increased incubation resulted from replication of the lethal agent being hindered throughout or at particular stages of pathogenesis, or whether the increased incubation period resulted from some loss of effective titre.

Scrapie in mice: Agent-strain differences in the distribution and intensity of grey matter vacuolation

Five strains of scrapie agent were used as intracerebral inocula for 2 inbred mouse strains, C57BL and VM, and their F 1 cross. The degree of vacuolation in specified regions of the brain, and the relative distribution of this damage in 9 regions represented as a “lesion profile”, was different for each agent. Any of the 5 scrapie agents could be distinguished from the others with a very high degree of reliability solely on the basis of these histological parameters, using either strain of mouse. The lesion profile was unaffected by the dose of the agent, using doses of ME7 agent ranging over 6 orders of magnitude in C57BL mice. The genotype of mouse had a marked effect on the overall degree of vacuolation and on the shape of the lesion profile: these effects were more profound with some agents than others. In certain areas of the brain, depending upon the strain of agent used, the (C57BL × VM)F 1 cross was found to have either significantly more or significantly less vacuolation than either parental genotype. The genetic control of the lesion profile was found to be too complex for more detailed analysis in these data.

Some factors controlling the incidence of scrapie in Cheviot sheep injected with a Cheviot-passaged scrapie agent

Evidence is given for the occurrence in Cheviot sheep of a gene controlling susceptibility to clinical scrapie following injection with the SSBP/1 strain of scrapie agent. The fully dominant allele confers susceptibility with the clinical signs appearing 197 ± 7 days after intracerebral injection with the particular dose used or 313 ± 9 days when injection was subcutaneous. A number of animals apparently homozygous for the recessive resistant allele of this gene developed scrapie after a very long interval, but these cases were confined to those animals receiving an initial intracerebral challenge. Possible reasons for these long-incubation-period cases are discussed.

Distribution of experimentally induced scrapie lesions in the brain.

LESIONS of scrapie are confined to the central nervous system. Differences in the distribution of these lesions have been described for the two strains of scrapie agent used in goats1 and for the lesions which arise as a result of injecting mice with boiled and unboiled material2. We have also collected unpublished data showing wide variation in the distribution of lesions which result from using different strains of the agent in mice or by inoculating, different genotypes of mice with the same agent.