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R F Marsh

Publications and source records attributed to R F Marsh.

At least 19 recordsLinked to original sources
PubMed2000

Adaptation and selection of prion protein strain conformations following interspecies transmission of transmissible mink encephalopathy.

Interspecies transmission of the transmissible spongiform encephalopathies (TSEs), or prion diseases, can result in the adaptation and selection of TSE strains with an expanded host range and increased virulence such as in the case of bovine spongiform encephalopathy and variant Creutzfeldt-Jakob disease. To investigate TSE strain adaptation, we serially passaged a biological clone of transmissible mink encephalopathy (TME) into Syrian golden hamsters and examined the selection of distinct strain phenotypes and conformations of the disease-specific isoform of the prion protein (PrP(Sc)). The long-incubation-period drowsy (DY) TME strain was the predominate strain, based on the presence of its strain-specific PrP(Sc) following interspecies passage. Additional serial passages in hamsters resulted in the selection of the hyper (HY) TME PrP(Sc) strain-dependent conformation and its short incubation period phenotype unless the passages were performed with a low-dose inoculum (e.g., 10(-5) dilution), in which case the DY TME clinical phenotype continued to predominate. For both TME strains, the PrP(Sc) strain pattern preceded stabilization of the TME strain phenotype. These findings demonstrate that interspecies transmission of a single cloned TSE strain resulted in adaptation of at least two strain-associated PrP(Sc) conformations that underwent selection until one type of PrP(Sc) conformation and strain phenotype became predominant. To examine TME strain selection in the absence of host adaptation, hamsters were coinfected with hamster-adapted HY and DY TME. DY TME was able to interfere with the selection of the short-incubation HY TME phenotype. Coinfection could result in the DY TME phenotype and PrP(Sc) conformation on first passage, but on subsequent passages, the disease pattern converted to HY TME. These findings indicate that during TSE strain adaptation, there is selection of a strain-specific PrP(Sc) conformation that can determine the TSE strain phenotype.

Adaptation, Physiological↗
PubMed1998

The host range of chronic wasting disease is altered on passage in ferrets.

Chronic wasting disease (CWD), a member of the transmissible spongiform encephalopathies (TSEs), was first identified in captive mule and black-tail deer in 1967. Due to the failure to transmit CWD to rodents, we investigated the use of ferrets (Mustela putorius furo) as a small animal model of CWD. The inoculation of CWD into ferrets resulted in an incubation period of 17-21 months on primary passage that shortened to 5 months by the third ferret passage. The brain tissue of animals inoculated with ferret-passaged CWD exhibited spongiform degeneration and reactive astrocytosis. Western blot analysis of ferret-passaged CWD demonstrated the presence of PrP-res. Unlike mule deer CWD, ferret-passaged CWD was transmissible to Syrian golden hamsters (Mesocricetus auratus). Increasing the passage number of CWD in ferrets increased the pathogenicity of the agent for hamsters. This increase in host range of a field isolate on interspecies transmission emphasizes the need for caution when assessing the potential risk of transmission of TSEs, such as bovine spongiform encephalopathy, to new host species.

Animals↗
PubMed1995

Experimental infection of cattle with the agents of transmissible mink encephalopathy and scrapie.

Cattle are susceptible to experimental infection with the Stetsonville isolate of the transmissible mink encephalopathy (TME) agent. To determine if they are susceptible to other TME isolates, two groups of calves were inoculated intracerebrally with homogenate of mink brain containing the Hayward isolate or the Blackfoot isolate. For comparison, a third group was inoculated with a brain homogenate from a steer infected with the Stetsonville isolate in its primary cattle passage and a fourth group was inoculated with a pool of brain homogenate from three cattle experimentally infected with a sheep and goat scrapie agent in its primary cattle passage. Clinical signs of neurological disease appeared in each steer of every group between 15 and 25 months after inoculation. An encephalopathy characterized by severe spongiform change and pronounced astrocytosis occurred in the three groups inoculated with the TME agent. In contrast, the neurohistological changes in the steers inoculated with the cattle-passaged scrapie agent were slight and subtle. Analysis of the octapeptide repeat region of the bovine protease-resistant protein (PrP) gene showed that variations in incubation period, clinical signs, and neurohistological changes were unrelated to the homozygous or heterozygous condition of six or six/five octapeptide repeats.

Animals↗
PubMed1994

Physicochemical and biological characterizations of distinct strains of the transmissible mink encephalopathy agent.

Inoculation of the Stetsonville, Wisconsin source of transmissible mink encephalopathy (TME) into Syrian hamsters has identified two strains of the TME agent having distinct biological properties and producing disease-specific prion proteins (PrPTME) having different physicochemical properties. Although several strains of the sheep scrapie agent have been identified in Great Britain, this is the first indication that agents producing transmissible spongiform encephalopathies in the United States also are capable of producing distinct strains.

Animals↗
PubMed1994

Transmissible mink encephalopathy species barrier effect between ferret and mink: PrP gene and protein analysis.

Experimental infection of transmissible mink encephalopathy (TME) in two closely related mustelids, black ferret (Mustela putorius furo) and mink (Mustela visa), revealed differences in their susceptibility to the TME agent. When challenged with the Stetsonville TME agent, a longer incubation period was observed in ferrets (28 to 38 months) than mink (4 months). Western blot analysis of ferret and mink prion proteins (PrP) demonstrated no detectable differences between the proteins. Northern blot analysis of ferret brain RNA indicated that PrP mRNA abundance is similar in infected and uninfected individuals. We amplified the PrP coding region from ferret DNA using the polymerase chain reaction and compared the deduced amino acid sequence of the ferret PrP gene with the mink PrP gene. This comparison revealed six silent base changes and two amino acid changes between mink and ferret: Phe-->Lys at codon 179 and Arg-->Gln at codon 224, respectively. These changes may indicate the region of PrP that is responsible for the species barrier effect between mink and ferret.

Amino Acid Sequence↗
PubMed1994

Experimental infection of mink with bovine spongiform encephalopathy.

To determine whether the aetiological agent of bovine spongiform encephalopathy (BSE) is pathogenic for mink, standard dark mink were inoculated with coded homogenates of bovine brain from the U.K. Two homogenates were from cows affected with BSE. The third was from a cow that came from a farm with no history of having had BSE or having been fed ruminant-derived, rendered by-products, the proposed vehicle for introduction of the BSE agent. Each homogenate was inoculated intracerebrally into separate groups of mink and a pool of the three was fed to a fourth group. Signs of neurological disease appeared in mink an average of 12 months after intracerebral inoculation and 15 months after feeding. Decreased appetite, lethargy and mild to moderate pelvic limb ataxia were the predominant clinical signs, quite unlike the classic clinical picture of transmissible mink encephalopathy (TME). Microscopic changes in brain sections of most affected mink were those of a scrapie-like spongiform encephalopathy. Vacuolar change in grey matter neuropil was accompanied by prominent astrocytosis. Varying greatly in severity from one mink to another, the degenerative changes occurred in the cerebral cortex, dorsolateral gyri of the frontal lobe, corpus striatum, diencephalon and brainstem. Although resembling TME, the encephalopathy was distinguishable from it by less extensive changes in the cerebral cortex, by more severe changes in the caudal brainstem and by sparing of the hippocampus. The results of this study extend the experimental host range of the BSE agent and demonstrate for the first time the experimental oral infection of mink with a transmissible spongiform encephalopathy agent from a naturally infected ruminant species.

Animals↗
PubMed1994

Distinct PrP properties suggest the molecular basis of strain variation in transmissible mink encephalopathy.

The molecular basis of strain variation in scrapie diseases is unknown. The only identified component of the agent is the posttranslationally modified host prion protein (PrPSc). The biochemical and physical properties of PrP from two strains of transmissible mink encephalopathy (TME), called hyper (HY) and drowsy (DY), were compared to investigate if PrP heterogeneity could account for strain diversity. The degradation rate of PrPTME digested with proteinase K was found to be strain specific and correlated with inactivation of the TME titer. Edman protein sequencing revealed that the major N-terminal end of HY PrPTME commenced at least 10 amino acid residues prior to that of DY PrPTME after digestion with proteinase K. Analysis of the brain distribution of PrPTME exhibited a strain-specific pattern and localization of PrPTME to the perikarya of specific neuron populations. Our findings are consistent with HY and DY PrPTME having distinct protein conformations and/or strain-specific ligand interactions that influence PrPTME properties. We propose that PrPTME conformation could play a role in targeting TME strains to different neuron populations in which strain-specific formation occurs. These data are consistent with the idea that PrPTME protein structure determines the molecular basis of strain variation.

Amino Acid Sequence↗
PubMed1993

Immunolocalization of scrapie amyloid in non-congophilic, non-birefringent deposits in golden Syrian hamsters with experimental transmissible mink encephalopathy.

Transmissible mink encephalopathy (TME), a naturally occurring subacute spongiform encephalopathy in commercially ranch-reared mink (Mustela vision), is characterized neuropathologically by spongiform changes in the neuropil, intracytoplasmic neuronal vacuolation and astrocytic hypertrophy and hyperplasia. Amyloid deposits have not been observed in brain tissue sections from animals with natural and experimental TME using conventional histochemical stains such as Congo red. To determine if amyloid deposits be visualized by immunocytochemical techniques, we stained formalin-fixed, formic acid-treated brain tissue sections from several animal species with natural and experimental TME, using a rabbit antiserum directed against scrapie amyloid (PrP27-30). Scrapie amyloid-immunoreactive deposits were found in golden Syrian hamsters experimentally infected with TME, but were absent in mink with natural and experimental TME, as well as in ferrets and squirrel monkeys with experimental TME. The scrapie amyloid-immunoreactive deposits, which were non-congophilic and non-birefringent, were distributed in the subependymal, subpial and perivascular regions of the brain, as in hamsters infected with the 263K strain of scrapie. Ultrastructurally, scrapie amyloid-immunoreactive deposits revealed a collection of degenerating neurites with numerous abnormal mitochondria and degenerating synapses. Amyloid fibrils were not observed. Anti-scrapie amyloid antibodies immunoabsorbed with scrapie amyloid abolished immunostaining. Our data indicate the presence of scrapie amyloid lacking the molecular conformation of amyloid fibrils in hamsters with experimental TME.

Animals↗
PubMed1993

Bovine spongiform encephalopathy: a new disease of cattle?

Bovine spongiform encephalopathy (BSE) was first recognized in Great Britain in 1985. Most believe that the disease is of recent origin initiated by feeding rendered animal protein from scrapie-infected sheep to cattle, then perpetuated by feeding rendered infected cattle to other cattle. This paper explores an alternative hypothesis that BSE existed in cattle populations in an unrecognized form for a much longer time until amplified by changes in the rendering process that allowed cattle to cattle transmission to occur. This viewpoint is supported by observations that transmissible mink encephalopathy, a disease that first occurred 45 years ago, is likely caused by feeding downer cows to mink, and that the sporadic form of Creutzfeldt-Jakob disease occurs spontaneously with no evidence of natural transmission. This epidemiologic scenario on the origin of BSE has important implications for prevention of the disease in BSE-free countries. Mainly, emphasis needs to put on practices of feeding animal protein to cattle rather than in reducing the prevalence of sheep scrapie. If BSE is already present in the cattle population, the major threat becomes feeding cows to cows.

Animal Feed↗
PubMed1993

Immunohistochemical detection of prion protein in sheep with scrapie.

Prion protein (PrP), which is involved in the pathogenesis of scrapie, occurs in 2 forms. The form extracted from scrapie brain is protease resistant (PrP-res), whereas PrP from normal brain is protease sensitive (PrP-sen). This study examined whether PrP-res could be detected in brains of sheep with scrapie by immunohistochemistry (IHC). A suitable IHC procedure was developed using brain tissue from hamsters that had been inoculated with the transmissible mink encephalopathy agent. Tissue samples were fixed in PLP (periodate, lysine, paraformaldehyde) that contained paraformaldehyde at a concentration of 0.125%. Before application of the IHC technique, tissue sections were deparaffinized and treated with formic acid to simultaneously enhance PrP-res immunoreactivity and degrade PrP-sen. Primary antibody was obtained from a rabbit immunized to PrP-res extracted from brains of mice with experimentally induced scrapie. Brain from 21 sheep with histopathologically confirmed scrapie were examined by IHC. In all 21 brains, PrP-res was widely distributed throughout the brain stem. Staining was particularly intense in neuronal cell bodies and around blood vessels. The IHC technique successfully detected PrP-res in brain samples that had been frozen or that were severely autolyzed before fixation in PLP. Brains from 11 scrapie-suspect sheep that were not considered histologically positive were also examined by IHC. PrP-res was found in 4 of these brains. Sections of brains from 14 clinically normal sheep did not have detectable PrP-res. Results of this study indicate that IHC detection of PrP-res is equivalent, and perhaps superior, to histopathology for the diagnosis of scrapie in sheep. Furthermore, IHC is applicable to tissues that have autolytic changes or processing artifacts that prevent satisfactory histopathologic evaluation for lesions of scrapie.

Animals↗
PubMed1993

Epidemiologic and experimental studies on transmissible mink encephalopathy.

Transmissible mink encephalopathy (TME) is a rare foodborne disease of ranch-raised mink produced by an as yet unidentified contaminated feed ingredient. Because of the clinicopathologic similarities to scrapie and the indistinguishable physicochemical properties of their transmissible agents, it was initially assumed that TME was caused by feeding mink scrapie-infected sheep. However, subsequent studies testing the oral susceptibility of mink to scrapie were unsuccessful. Epidemiologic investigations of individual incidents of TME have not identified an association between the occurrence of disease and the feeding of any particular ingredient. However, there are two incidents in which the rancher was confident that sheep were not fed. The most recent of these was in Stetsonville, Wisconsin in 1985 where the meat portion of the diet was composed almost exclusively of downer dairy cows. To examine the possibility that cattle may have been the source of infection on the Stetsonville ranch, mink brain was experimentally inoculated intracerebrally into two Holstein steers. Both of these animals developed fatal spongiform encephalopathies 18 and 19 months after inoculation. These findings are compatible with the Stetsonville incident of TME being caused by feeding mink infected cattle tissue and they suggest the presence of an unrecognized BSE-like disease in the United States. Further experimental studies on the Stetsonville source of TME have identified two distinct strains of the transmissible agent in Syrian hamsters. These strains vary in length of incubation period, clinical signs, endstage brain infectivity titre, and pathogenicity for mink.(ABSTRACT TRUNCATED AT 250 WORDS)

Animal Feed↗
PubMed1992

Identification of two biologically distinct strains of transmissible mink encephalopathy in hamsters.

Experimental transmission of the Stetsonville, Wisconsin, U.S.A. source of transmissible mink encephalopathy (TME) to outbred Syrian golden hamsters resulted in two distinct syndromes, termed hyper (HY) and drowsy (DY), that diverge by the third hamster passage. The syndromes differed with respect to clinical signs, incubation period, brain titre, brain lesion profile and pathogenicity in mink. HY hamster TME had an incubation period of 65 +/- 1 days and was characterized by clinical signs of hyperaesthesia and cerebellar ataxia. Lethargy and the absence of hyperexcitability or cerebellar ataxia were representative of DY hamster TME which had an incubation period of 168 +/- 2 days. At endstage, HY and DY infected animals had brain titres of 10(9.5) LD50/g and 10(7.4) LD50/g of tissue, respectively, indicating that the replication kinetics of these two strains is different. Hamster TME passaged back into mink revealed that only DY retained mink pathogenicity. This suggests that the DY agent is the major mink pathogen in the Stetsonville TME source that is also pathogenic in hamsters after a long incubation period. The HY agent is likely to be a minor component of the original TME mink brain that replicates more rapidly than DY agent in hamsters, but alone is non-pathogenic in mink. The presence of the HY and DY strains of agent that retain their biological characteristics on repeated hamster passage in the Stetsonville TME source requires that the informational molecule encoding these transmissible agents has the capacity to account for this biological diversity.

Animals↗
PubMed1992

Biochemical and physical properties of the prion protein from two strains of the transmissible mink encephalopathy agent.

Transmissible mink encephalopathy (TME) has been transmitted to Syrian golden hamsters, and two strains of the causative agent, HYPER (HY) and DROWSY (DY), have been identified that have different biological properties. During scrapie, a TME-like disease, an endogenous cellular protein, the prion protein (PrPC), is modified (to PrPSc) and accumulates in the brain. PrPSc is partially resistant to proteases and is claimed to be an essential component of the infectious agent. Purification and analysis of PrP from hamsters infected with the HY and DY TME agent strains revealed differences in properties of PrPTME sedimentation in N-lauroylsarcosine, sensitivity to digestion with proteinase K, and migration in polyacrylamide gels. PrPC and HY PrPTME can be distinguished on the basis of their relative solubilities in detergent and protease sensitivities. PrPTME from DY-infected brain tissue shared solubility characteristics of PrP from both uninfected and HY-infected tissue. Limited protease digestion of PrPTME revealed strain-specific migration patterns upon polyacrylamide gel electrophoresis. Prolonged proteinase K treatment or N-linked deglycosylation of PrPTME did not eliminate such differences but demonstrated the PrPTME from DY-infected brain was more sensitive to protease digestion than HY PrPTME. Antigenic mapping of PrPTME with antibodies raised against synthetic peptides revealed strain-specific differences in immunoreactivity in a region of the amino-terminal end of PrPTME containing amino acid residues 89 to 103. These findings indicate that PrPTME from the two agent strains, although originating from the same host, differ in composition, conformation, or both. We conclude that PrPTME from the HY and DY strains undergo different posttranslational modifications that could explain differences in the biochemical properties of PrPTME from the two sources. Whether these strain-specific posttranslational events are directly responsible for the distinct biological properties of the HY and DY agent strains remains to be determined.

Animals↗
PubMed1992

Transmissible mink encephalopathy.

Transmissible mink encephalopathy (TME) is a rare disease of ranch-raised mink caused by exposure to an as yet unidentified contaminated food ingredient in the ration. The clinical and pathological similarities between TME and scrapie, together with the indistinguishable physicochemical characteristics of their transmissible agents, suggest that sheep may be the source of infection. However, experimental testing of oral susceptibility of mink to several different sources of sheep scrapie have been unsuccessful. These results indicate that either the feeding of scrapie-infected sheep tissues to mink is not the cause of TME, or that there exists a strain of sheep scrapie having high mink pathogenicity that remains unknown. Additional sources of sheep scrapie need to be tested in mink, and epidemiological investigations of new incidents of TME need to emphasise obtaining a thorough history of past feeding practices.

Animals↗
PubMed1991

Epidemiological and experimental studies on a new incident of transmissible mink encephalopathy.

Epidemiological investigation of a new incident of transmissible mink encephalopathy (TME) in Stetsonville, Wisconsin, U.S.A. in 1985 revealed that the mink rancher had never fed sheep products to his mink but did feed them large amounts of products from fallen or sick dairy cattle. To investigate the possibility that this occurrence of TME may have resulted from exposure to infected cattle, two Holstein bull calves were injected intracerebrally with mink brain from the Stetsonville ranch. Each bull developed a fatal spongiform encephalopathy 18 and 19 months after inoculation, respectively, and both bovine brains passaged back into mink were highly pathogenic by either intracerebral or oral inoculation. These results suggest the presence of a previously unrecognized scrapie-like infection in cattle in the United States.

Animal Feed↗