Atypical bovine spongiform encephalopathy (BSE) has recently been identified in Europe, North America, and Japan. It is classified as H-type and L-type BSE according to the molecular mass of the disease-associated prion protein (PrP^Sc). To investigate the topographical distribution and deposition patterns of immunolabeled PrP^Sc, H-type BSE isolate was inoculated intracerebrally into cattle. H-type BSE was successfully transmitted to 3 calves, with incubation periods between 500 and 600 days. Moderate to severe spongiform changes were detected in the cerebral and cerebellar cortices, basal ganglia, thalamus, and brainstem. H-type BSE was characterized by the presence of PrP-immunopositive amyloid plaques in the white matter of the cerebrum, basal ganglia, and thalamus. Moreover, intraglial-type immunolabeled PrP^Sc was prominent throughout the brain. Stellate-type immunolabeled PrP^Sc was conspicuous in the gray matter of the cerebral cortex, basal ganglia, and thalamus, but not in the brainstem. In addition, PrP^Sc accumulation was detected in the peripheral nervous tissues, such as trigeminal ganglia, dorsal root ganglia, optic nerve, retina, and neurohypophysis. Cattle are susceptible to H-type BSE with a shorter incubation period, showing distinct and distinguishable phenotypes of PrP^Sc accumulation.

With the use of increasingly sensitive methods for detection of the abnormal isoform of prion protein (PrP^Sc) and infectivity in prion diseases, it has recently been shown that parts of the peripheral nervous system (PNS) of bovine spongiform encephalopathy (BSE)-affected cattle may become infected. It has been reported that prions spread to the central nervous system (CNS) via the PNS in sheep scrapie, but the pathogenesis of BSE in cattle is less well understood. To determine whether parts of the PNS other than those implicated directly in the hypothetical pathogenetic spread of agent from the intestine to the CNS become involved before or after the CNS is affected, PrP^Scdistribution was investigated by a highly sensitive Western blotting technique in dorsal root ganglia, stellate ganglion, phrenic, radial and sciatic nerves, adrenal gland and CNS of cattle that were inoculated orally with BSE-affected brain and culled sequentially. In experimentally BSE-affected cattle, PrP^Scwas first detected in the CNS and dorsal root ganglia; subsequently, PrP^Scaccumulation was detected in the peripheral nerve trunks. PrP^Scwas also detected in the adrenal glands of cattle that showed clinical signs. No PrP^Scwas detected in the PNS of BSE-negative cattle. This study shows that, with respect to dorsal root ganglia, a paravertebral sympathetic ganglion and the somatic nerves examined, PrP^Scis detected in the PNS during the disease course at the same time as, or after, it accumulates in the CNS.

Sheep scrapie is caused by multiple prion strains, which have been classified on the basis of their biological characteristics in inbred mice. The heterogeneity of natural scrapie prions in individual sheep and in sheep flocks has not been clearly defined. In this study, we intravenously injected 2 sheep (Suffolk and Corriedale) with material from a natural case of sheep scrapie (Suffolk breed). These 3 sheep had identical prion protein (PrP) genotypes. The protease-resistant core of PrP (PrPres) in the experimental Suffolk sheep was similar to that in the original Suffolk sheep. In contrast, PrPres in the Corriedale sheep differed from the original PrPres but resembled the unusual scrapie isolate, CH1641. This unusual PrPres was not detected in the original sheep. The PrPres distributions in the brain and peripheral tissues differed between the 2 breeds of challenged sheep. A transmission study in wild-type and TgBoPrP mice, which overexpressing bovine PrP, led to the selection of different prion strains. The pathological features of prion diseases are thought to depend on the dominantly propagated strain. Our results indicate that prion strain selection occurs after both inter- and intraspecies transmission. The unusual scrapie prion was a hidden or an unexpressed component in typical sheep scrapie.

Background: Prions, infectious agents associated with transmissible spongiform encephalopathy, are primarily composed of the misfolded and pathogenic form (PrP^Sc) of the host-encoded prion protein. Because PrP^Sc retains infectivity after undergoing routine sterilizing processes, the cause of bovine spongiform encephalopathy (BSE) outbreaks are suspected to be feeding cattle meat and bone meals (MBMs) contaminated with the prion. To assess the validity of prion inactivation by heat treatment in yellow grease, which is produced in the industrial manufacturing process of MBMs, we pooled, homogenized, and heat treated the spinal cords of BSE-infected cows under various experimental conditions. Results: Prion inactivation was analyzed quantitatively in terms of the infectivity and PrP^Sc of the treated samples. Following treatment at 140°C for 1 h, infectivity was reduced to 1/35 of that of the untreated samples. Treatment at 180°C for 3 h was required to reduce infectivity. However, PrP^Sc was detected in all heat-treated samples by using the protein misfolding cyclic amplification (PMCA) technique, which amplifies PrP^Sc in vitro. Quantitative analysis of the inactivation efficiency of BSE PrP^Sc was possible with the introduction of the PMCA₅₀, which is the dilution ratio of 10% homogenate needed to yield 50% positivity for PrP^Sc in amplified samples. Conclusions: Log PMCA₅₀ exhibited a strong linear correlation with the transmission rate in the bioassay; infectivity was no longer detected when the log PMCA₅₀ of the inoculated sample was reduced to 1.75. The quantitative PMCA assay may be useful for safety evaluation for recycling and effective utilization of MBMs as an organic resource.

Two different scrapie prion strains with different characteristics were obtained from two sheep naturally infected with scrapie in Japan. In mice transmission, one (Tsukuba‐1) showed shorter incubation periods (133±2 days) than the other (Tsukuba‐2) (288±5 days). Spongiform changes and accumulation of an abnormal isoform of prion protein (PrP^Sc) were observed throughout the brain in Tsukuba‐1 inoculated mice, while the lesions and the PrP^Sc accumulation were localized in the brain stem of mice with Tsukuba‐2. Western blot analysis showed that there was no strain‐specific glycoform of PrP^Sc within these two strains. A super‐infection experiment revealed that neither strain interfered with the other's propagation.

In the interspecies transmission of prions, the species barrier influences the susceptibility of the host. Bovine spongiform encephalopathy (BSE) prions affect a wide range of host species but do not affect hamsters. In order to study this species barrier, this study analysed the transmissibility of BSE prions to several lines of transgenic (Tg) mice, including those expressing mouse and hamster chimeric prion proteins (MH2M and MHM2 mice). BSE prions were transmitted to tga20, MHM2 and ICR mice, and the incubation period was approximately 400 days. Thus, these mice were classified as ‘susceptible mice’. However, BSE prions were not transmitted to MH2M and TgHaNSE mice, and these mice were classified as ‘resistant mice’. After the BSE prions were passaged once in wild-type mice, they could be transmitted to resistant mice. The characteristics of the accumulated abnormal isoform of PrP (PrPSc) in susceptible and resistant mice were determined using Western blotting. A BSE-like glycoform pattern of PrPSc was detected in all of the susceptible mice using two different antibodies that recognized either the N- or the C-terminal end of the 27–30 kDa protease-resistant fragment of PrP (PrP27–30) as the epitope. In contrast, proteinase digestion followed by deglycosylation analysis showed that, in addition to PrP27–30, truncated PrPSc fragments existed in resistant mice. These mixed PrPSc fragments may have resulted from the adaptation of resistant mice to BSE prions.