Atypical transmissible spongiform encephalopathies in ruminants: a challenge for disease surveillance and control

Short incubation periods of atypical H-type BSE in cattle with EK211 and KK211 prion protein genotypes after intracranial inoculation

In 2006, a case of atypical H-type BSE (H-BSE) was found to be associated with a germline mutation in the PRNP gene that resulted in a lysine substitution for glutamic acid at codon 211 (E211K). The E211K amino acid substitution in cattle is analogous to E200K in humans, which is associated with the development of genetic Creutzfeldt-Jakob disease (CJD). In the present study, we aimed to determine the effect of the EK211 prion protein genotype on incubation time in cattle inoculated with the agent of H-BSE; to characterize the molecular profile of H-BSE in KK211 and EK211 genotype cattle; and to assess the influence of serial passage on BSE strain. Eight cattle, representing three PRNP genotype groups (EE211, EK211, and KK211), were intracranially inoculated with the agent of H-BSE originating from either a case in a cow with the EE211 prion protein genotype or a case in a cow with E211K amino acid substitution. All inoculated animals developed clinical disease; post-mortem samples were collected, and prion disease was confirmed through enzyme immunoassay, anti-PrPSc immunohistochemistry, and western blot. Western blot molecular analysis revealed distinct patterns in a steer with KK211 H-BSE compared to EK211 and EE211 cattle. Incubation periods were significantly shorter in cattle with the EK211 and KK211 genotypes compared to the EE211 genotype. Inoculum type did not significantly influence the incubation period. This study demonstrates a shorter incubation period for H-BSE in cattle with the K211 genotype in both the homozygous and heterozygous forms.

Early and Pre-Clinical Detection of Prion Seeding Activity in Cerebrospinal Fluid of Goats using Real-Time Quaking-Induced Conversion Assay

Since 2005, two cases of natural bovine spongiform encephalopathies (BSE) have been reported in goats. Furthermore, experimental transmissions of classical (C-BSE) and atypical (L-BSE) forms of BSE in goats were also reported. To minimize further spreading of prion diseases in small ruminants the development of a highly sensitive and specific test for ante-mortem detection of infected animals would be of great value. Recent studies reported high diagnostic value of a second generation of cerebrospinal fluid (CSF) Real-Time Quaking-Induced Conversion (RT-QuIC) assay across a wide spectrum of human prions. Here, we applied this improved QuIC (IQ-CSF) for highly efficient detection of TSEs prion protein in goat cerebrospinal fluid. IQ-CSF sensitivity and specificity were evaluated on CSF samples collected at disease endpoint from goats naturally and experimentally infected with scrapie or bovine isolates of C-BSE and L-BSE, respectively. Next, CSF samples collected from L-BSE infected goats during pre-symptomatic stage were also analysed. PrP^L-BSE associated seeding activity was detected at early time points after experimental inoculation, with an average time of 439 days before clinical symptoms appeared. Taken together these data are indicative of the great potential of this in vitro prion amplification assay as ante-mortem TSE test for live and asymptomatic small ruminants.

Presumptive BSE cases with an aberrant prion protein phenotype in Switzerland, 2011: Lack of prion disease in experimentally inoculated cattle and bovine prion protein transgenic mice

Bovine spongiform encephalopathy (BSE) is caused by different prion strains that are discriminated by the molecular characteristics of the pathological prion protein. In 2011, Switzerland reported two presumptive cases of BSE in cattle with a prion protein phenotype different from previously described strains, and it was unclear whether these findings were related to a transmissible disease and have implications on animal and public health. In this study, brain tissues of these cases were inoculated into transgenic mice expressing the bovine prion protein (BoPrP-Tg110) and into cattle. Clinical and pathological investigations as well as molecular testing did not provide evidence for the presence of BSE in the Swiss cases after two passages in BoPrP-Tg110 mice and a challenge period of 3.5 years in cattle. This lack of disease transmission suggests that the Swiss 2011 cases were not affected by a prion disease and were unrelated to the feed-born BSE epidemic.

Neuropathological survey reveals underestimation of the prevalence of neuroinfectious diseases in cattle in Switzerland

Neuroinfectious diseases in livestock represent a severe threat to animal health, but their prevalence is not well documented and the etiology of disease often remains unidentified. The aims of this study were to generate baseline data on the prevalence of neuroinfectious diseases in cattle in Switzerland by neuropathological survey, and to identify disease-associated pathogens. The survey was performed over a 1-year period using a representative number of brainstem samples (n=1816) from fallen cattle. In total, 4% (n=73) of the animals had significant lesions, the most frequent types of which were indicative of viral (n=27) and bacterial (n=31) etiologies. Follow-up diagnostics by immunohistochemistry, PCR protocols and next-generation sequencing identified infection with Listeria monocytogenes (n=6), ovine herpesvirus 2 (n=7), bovine astrovirus CH13 (n=2), bovine herpesvirus 6 (n=6), bovine retrovirus CH15 (n=2), posavirus 1 (n=2), and porcine astroviruses (n=2). A retrospective questionnaire-based investigation indicated that animals' owners observed clinical signs of neurological disease in about one-third of cases with lesions, which was estimated to correspond to approximately 85 cases per year in the adult fallen cattle population in Switzerland. This estimate stands in sharp contrast to the number of cases reported to the authorities and reveals a gap in disease surveillance. Systematic neuropathological examination and follow-up molecular testing of neurologically diseased cattle could significantly enhance the efficiency of disease detection for the purposes of estimating the prevalence of endemic diseases, identifying new or re-emerging pathogens, and providing "early warnings" of disease outbreaks.

In vitro amplification of H-type atypical bovine spongiform encephalopathy by protein misfolding cyclic amplification

The in vitro amplification of prions by serial protein misfolding cyclic amplification has been shown to detect PrP^Sc to levels at least as sensitive as rodent bioassay but in a fraction of the time. Bovine spongiform encephalopathy is a zoonotic prion disease in cattle and has been shown to occur in 3 distinct forms, classical BSE (C-BSE) and 2 atypical BSE forms (L-BSE and H-BSE). Atypical forms are usually detected in asymptomatic, older cattle and are suggested to be spontaneous forms of the disease. Here, we show the development of a serial protein misfolding cyclic amplification method for the detection of H-BSE. The assay could detect PrP^Sc from 3 distinct experimental isolates of H-BSE, could detect PrP^Sc in as little as 1×10⁻¹² g of brain material and was highly specific. Additionally, the product of serial protein misfolding cyclic amplification at all dilutions of seed analyzed could be readily distinguished from L-BSE, which did not amplify, and C-BSE, which had PrP^Sc with distinct protease K-resistance and protease K-resistant PrP^Sc molecular weights.

Encefalopatia espongiforme bovina atípica: uma revisão

RESUMO: A encefalopatia espongiforme bovina (EEB), causada por um príon infectante, surgiu na década de 1980 na Europa como uma nova doença nos rebanhos bovinos e, desde então, estão sendo tomadas várias ações para sua prevenção e controle. A restrição da alimentação de ruminantes com subprodutos de origem animal e a remoção e destruição dos materiais de risco específico para a doença das carcaças em frigoríficos se mostraram efetivas medidas para o controle da doença, além de reduzirem a exposição humana ao agente, pois se trata de uma importante zoonose. No entanto, em 2004 os primeiros casos atípicos de EEB foram diagnosticados, nos quais os agentes causais apresentavam alterações de peso molecular na prova de Western blot, em relação ao agente da forma clássica. Além das diferenças moleculares dos agentes, as apresentações clínicas mostraram-se diferenciadas nas formas atípicas, acometendo principalmente bovinos com idade superior a oito anos. Por se tratar de uma nova forma da doença, muitos estudos estão sendo conduzidos buscando elucidar a patogenia, epidemiologia e seu potencial zoonótico. Objetivou-se neste estudo revisar os principais aspectos relacionados às EEB atípicas enfatizando sua etiologia, epidemiologia, sinais clínicos, diagnóstico e medidas de controle.

L-BSE experimentally transmitted to sheep presents as a unique disease phenotype

Apart from prion protein genotype, the factors determining the host range and susceptiblity for specific transmissible spongiform encephalopathy agents remain unclear. It is known that bovine atypical L-BSE can transmit to a range of species including primates and humanised transgenic mice. It is important, therefore, that there is as broad an understanding as possible of how such isolates might present in food animal species and how robust they are on inter- and intra-species transmission to inform surveillance sytems and risk assessments. This paper demonstrates that L-BSE can be intracerebrally transmitted to sheep of several genotypes, with the exception of ARR/ARR animals. Positive animals mostly present with a cataplectic form of disease characterized by collapsing episodes and reduced muscle tone. PrP accumulation is confined to the nervous system, with the exception of one animal with lymphoreticular involvement. In Western blot there was maintenance of the low molecular mass and glycoform profile associated with L-BSE, irrespective of ovine host genotype, but there was a substantially higher N-terminal antibody signal relative to the core-specific antibody, which is similar to the ratio associated with classical scrapie. The disease phenotype was maintained on experimental subpassage, but with a shortened survival time indicative of an original species barrier and subsequent adaptation. Passive surveillance approaches would be unlikely to identify such cases as TSE suspects, but current statutory active screening methods would be capable of detecting such cases and classifying them as unusual and requiring further investigation if they were to occur in the field.

A Comparison of Classical and H-Type Bovine Spongiform Encephalopathy Associated with E211K Prion Protein Polymorphism in Wild-Type and EK211 Cattle Following Intracranial Inoculation

In 2006, a case of H-type bovine spongiform encephalopathy (BSE-H) was diagnosed in a cow that was associated with a heritable polymorphism in the bovine prion protein gene (PRNP) resulting in a lysine for glutamate amino acid substitution at codon 211 (called E211K) of the prion protein. Although the prevalence of this polymorphism is low, cattle carrying the K211 allele may be predisposed to rapid onset of BSE-H when exposed or to the potential development of a genetic BSE. This study was conducted to better understand the relationship between the K211 polymorphism and its effect on BSE phenotype. BSE-H from the US 2006 case was inoculated intracranially (IC) in one PRNP wild-type (EE211) calf and one EK211 calf. In addition, one wild-type calf and one EK211 calf were inoculated IC with brain homogenate from a US 2003 classical BSE case. All cattle developed clinical disease. The survival time of the E211K BSE-H inoculated EK211 calf (10 months) was shorter than the wild-type calf (18 months). This genotype effect was not observed in classical BSE inoculated cattle (both 26 months). Significant changes in retinal function were observed in H-type BSE challenged cattle only. Cattle challenged with the same inoculum showed similar severity and neuroanatomical distribution of vacuolation and disease-associated prion protein deposition in the brain, though differences in neuropathology were observed between E211K BSE-H and classical BSE inoculated animals. Western blot results for brain tissue from challenged animals were consistent with the inoculum strains. This study demonstrates that the phenotype of E211K BSE-H remains stable when transmitted to cattle without the K211 polymorphism, and exhibits a number of features that differ from classical BSE in both wild-type and heterozygous EK211 animals.

Emergence of a novel bovine spongiform encephalopathy (BSE) prion from an atypical H-type BSE

The H-type of atypical bovine spongiform encephalopathy (H-BSE) was serially passaged in bovinized transgenic (TgBoPrP) mice. At the fourth passage, most challenged mice showed a typical H-BSE phenotype with incubation periods of 223 ± 7.8 days. However, a different phenotype of BSE prion with shorter incubation periods of 109 ± 4 days emerged in a minor subset of the inoculated mice. The latter showed distinct clinical signs, brain pathology, and abnormal prion protein profiles as compared to H-BSE and other known BSE strains in mice. This novel prion was transmitted intracerebrally to cattle, with incubation periods of 14.8 ± 1.5 months, with phenotypes that differed from those of other bovine prion strains. These data suggest that intraspecies transmission of H-BSE in cattle allows the emergence of a novel BSE strain. Therefore, the continuation of feed ban programs may be necessary to exclude the recycling of H-BSE prions, which appear to arise spontaneously, in livestock. Such measures should help to reduce the risks from both novel and known strains of BSE.

Atypical H-type bovine spongiform encephalopathy in a cow born after the reinforced feed ban on meat-and-bone meal in Europe

The significance of atypical bovine spongiform encephalopathies (BSE) in cattle for controlling the BSE epidemic is poorly understood. Here we report a case of atypical H-type BSE in a cow born after the implementation of the reinforced feed ban in Europe. This supports an etiology of H-type BSE unrelated to that of classical BSE.

Squirrel monkeys (Saimiri sciureus) infected with the agent of bovine spongiform encephalopathy develop tau pathology

Squirrel monkeys (Saimiri sciureus) were infected experimentally with the agent of classical bovine spongiform encephalopathy (BSE). Two to four years later, six of the monkeys developed alterations in interactive behaviour and cognition and other neurological signs typical of transmissible spongiform encephalopathy (TSE). At necropsy examination, the brains from all of the monkeys showed pathological changes similar to those described in variant Creutzfeldt-Jakob disease (vCJD) of man, except that the squirrel monkey brains contained no PrP-amyloid plaques typical of that disease. Constant neuropathological features included spongiform degeneration, gliosis, deposition of abnormal prion protein (PrP(TSE)) and many deposits of abnormally phosphorylated tau protein (p-Tau) in several areas of the cerebrum and cerebellum. Western blots showed large amounts of proteinase K-resistant prion protein in the central nervous system. The striking absence of PrP plaques (prominent in brains of cynomolgus macaques [Macaca fascicularis] with experimentally-induced BSE and vCJD and in human patients with vCJD) reinforces the conclusion that the host plays a major role in determining the neuropathology of TSEs. Results of this study suggest that p-Tau, found in the brains of all BSE-infected monkeys, might play a role in the pathogenesis of TSEs. Whether p-Tau contributes to development of disease or appears as a secondary change late in the course of illness remains to be determined.

Individual factors associated with L- and H-type Bovine Spongiform encephalopathy in France

BACKGROUND

Cattle with L-type (L-BSE) and H-type (H-BSE) atypical Bovine Spongiform encephalopathy (BSE) were identified in 2003 in Italy and France respectively before being identified in other countries worldwide. As of December 2011, around 60 atypical BSE cases have currently been reported in 13 countries, with over one third in France. While the epidemiology of classical BSE (C-BSE) has been widely described, atypical BSEs are still poorly documented, but appear to differ from C-BSE. We analysed the epidemiological characteristics of the 12 cases of L-BSE and 11 cases of H-BSE detected in France from January 2001 to late 2009 and looked for individual risk factors. As L-BSE cases did not appear to be homogeneously distributed throughout the country, two complementary methods were used: spatial analysis and regression modelling. L-BSE and H-BSE were studied separately as both the biochemical properties of their pathological prion protein and their features differ in animal models.

RESULTS

The median age at detection for L-BSE and H-BSE cases was 12.4 (range 8.4-18.7) and 12.5 (8.3-18.2) years respectively, with no significant difference between the two distributions. However, this median age differed significantly from that of classical BSE (7.0 (range 3.5-15.4) years). A significant geographical cluster was detected for L-BSE. Among animals over eight years of age, we showed that the risk of being detected as a L-BSE case increased with age at death. This was not the case for H-BSE.

CONCLUSION

To the best of our knowledge this is the first study to describe the epidemiology of the two types of atypical BSE. The geographical cluster detected for L-BSE could be partly due to the age structure of the background-tested bovine population. Our regression analyses, which adjusted for the effect of age and birth cohort showed an age effect for L-BSE and the descriptive analysis showed a particular age structure in the area where the cluster was detected. No birth cohort effect was evident. The relatively small number of cases of atypical BSE and the few individual data available for the tested population limited our analysis to the investigation of age and cohort effect only. We conclude that it is essential to maintain BSE surveillance to further elucidate our findings.