Neuropathological and aetiological studies of sporadic non-suppurative meningoencephalomyelitis of cattle

Bovine astrovirus and its role in lymphocytic encephalitis in cattle in Ontario, Canada, 1988-2019

Astroviruses have been found in cattle and other species with encephalitis. Our objective was to determine the frequency of neurotropic bovine astrovirus (BoAstV) in cases of encephalitis in cattle ≥ 4-mo-old. Of 56 cases of idiopathic lymphocytic encephalitis examined retrospectively (1988-2019), fixed brain from 11 cases (19%) tested positive by semi-quantitative RT-PCR for BoAstV CH13/NeuroS1. None of the control cases tested positive, including 32 with other forms of encephalitis and 40 with no neurologic disease. Most astrovirus-positive cases were 1-2-y-old, with a range of 7 mo to 7 y, and affected both beef and dairy breeds with wide geographic distribution. BoAstV-positive cases had acute onset of neurologic signs of 12 h to 7 d before death or euthanasia. Affected cattle had lymphocytic inflammation throughout the brain including cerebrum, thalamus, midbrain, cerebellum, medulla oblongata, and spinal cord, and affecting gray and white matter. Further PCR testing identified a possible cause in 9 of the 45 (20%) remaining idiopathic cases of lymphocytic encephalitis, including eastern equine encephalitis virus, Listeria monocytogenes, bovine viral diarrhea virus, bovine alphaherpesvirus 1, and ovine gammaherpesvirus 2 (malignant catarrhal fever); we found no cases of infection by West Nile virus, rabies virus, or Chlamydia spp. No cause was identified in 36 of 56 (64%) cases of lymphocytic encephalitis. We frequently identified neurotropic BoAstV in cases of lymphocytic encephalitis that had no previously identified cause. Neurotropic BoAstV infections had gone undetected for decades, but the frequency of BoAstV infections has not increased among contemporary cases.

A novel Betaretrovirus discovered in cattle with neurological disease and encephalitis

Background

The majority of emerging infectious diseases in humans are of animal origin, and many of them are caused by neuropathogenic viruses. Many cases of neurological disease and encephalitis in livestock remain etiologically unresolved, posing a constant threat to animal and human health. Thus, continuous extension of our knowledge of the repertoire of viruses prone to infect the central nervous system (CNS) is vital for pathogen monitoring and the early detection of emerging viruses. Using high-throughput sequencing (HTS) and bioinformatics, we discovered a new retrovirus, bovine retrovirus CH15 (BoRV CH15), in the CNS of a cow with non-suppurative encephalitis. Phylogenetic analysis revealed the affiliation of BoRV CH15 to the genus Betaretrovirus.

Results

BoRV CH15 genomes were identified prospectively and retrospectively by PCR, RT-PCR, and HTS, with targeting of viral RNA and proviral DNA, in six additional diseased cows investigated over a period of > 20 years and of different geographical origins. The virus was not found in brain samples from healthy slaughtered control animals (n = 130). We determined the full-length proviral genomes from six of the seven investigated animals and, using in situ hybridization, identified viral RNA in the cytoplasm of cells morphologically compatible with neurons in diseased brains.

Conclusions

Further screening of brain samples, virus isolation, and infection studies are needed to estimate the significance of these findings and the causative association of BoRV CH15 with neurological disease and encephalitis in cattle. However, with the full-length proviral sequences of BoRV CH15 genomes, we provide the basis for a molecular clone and further in vitro investigation.

Graphical Abstract

Supplementary Information

The online version contains supplementary material available at 10.1186/s12977-021-00585-x.

Astrovirus Infection in Cattle with Nonsuppurative Meningoencephalitis in South Korea

Neurological diseases in cattle can be caused by several infectious agents. Astroviruses are increasingly recognized as the causative agent of encephalitis in various animals, including humans. In this study, a neuroinvasive astrovirus (BoAstV 20B05) was discovered in the brain tissues of an 81-month-old Korean native cattle with neurological symptoms. Lymphocyte infiltration and multifocal perivascular cuffing were observed in the cerebrum and brain stem, and viral antigens were also detected in the meninges. In particular, the concentration of the astroviral genome was high in the brain tissues. Korean BoAstV 20B05 was classified into the CH13/NeuroS1 clade and was closely related to the Neuro-Uy and KagoshimaSR28-462 strains. Our evolutionary analysis showed that Korean BoAstV 20B05 belongs to the sub-lineage NeuroS1 and evolved independently of BoAstV KagoshimaSR28-462. These results suggest that neuroinvasive astroviruses were first introduced in Korea. However, analysis is limited by the lack of reference astrovirus sequences reported in various countries within Asia, and further analysis should be performed using more strains. In this study, we identified a neuroinvasive astrovirus infection with neurological symptoms for the first time in South Korea and confirmed that BoAstV 20B05 may have been introduced in South Korea a long time ago.

Neurotropic Astroviruses in Animals

Astrovirus infections are among the main causes of diarrhea in children, but their significance for animal health has remained underestimated and largely unknown. This is changing due to the increasing amount of newly identified neurotropic astroviruses in cases of nonsuppurative encephalitis and neurological disease in humans, pigs, ruminant species and minks. Neurological cases in ruminants and humans usually occur sporadically and as isolated cases. This contrasts with the situation in pigs and minks, in which diseases associated with neurotropic astroviruses are endemic and occur on the herd level. Affected animals show neurological signs such as mild ataxia to tetraplegia, loss of orientation or trembling, and the outcome is often fatal. Non-suppurative inflammation with perivascular cuffing, gliosis and neuronal necrosis are typical histological lesions of astrovirus encephalitis. Since astroviruses primarily target the gastrointestinal tract, it is assumed that they infect the brain through the circulatory system or retrograde following the nerves. The phylogenetic analysis of neurotropic astroviruses has revealed that they are genetically closely related, suggesting the presence of viral determinants for tissue tropism and neuroinvasion. In this review, we summarize the current knowledge on neurotropic astrovirus infections in animals and propose future research activities.

Parainfluenza Virus 5 Infection in Neurological Disease and Encephalitis of Cattle

The etiology of viral encephalitis in cattle often remains unresolved, posing a potential risk for animal and human health. In metagenomics studies of cattle with bovine non-suppurative encephalitis, parainfluenza virus 5 (PIV5) was identified in three brain samples. Interestingly, in two of these animals, bovine herpesvirus 6 and bovine astrovirus CH13 were additionally found. We investigated the role of PIV5 in bovine non-suppurative encephalitis and further characterized the three cases. With traditional sequencing methods, we completed the three PIV5 genomes, which were compared to one another. However, in comparison to already described PIV5 strains, unique features were revealed, like an 81 nucleotide longer open reading frame encoding the small hydrophobic (SH) protein. With in situ techniques, we demonstrated PIV5 antigen and RNA in one animal and found a broad cell tropism of PIV5 in the brain. Comparative quantitative analyses revealed a high viral load of PIV5 in the in situ positive animal and therefore, we propose that PIV5 was probably the cause of the disease. With this study, we clearly show that PIV5 is capable of naturally infecting different brain cell types in cattle in vivo and therefore it is a probable cause of encephalitis and neurological disease in cattle.

Central nervous system diseases of cattle in Georgia, 2001-2017

In a review of 159 archived bovine autopsy cases submitted to the Georgia Veterinary Diagnostic Laboratory System from 2001 to 2017, we evaluated histologic lesions and other laboratory test results in cases diagnosed with central nervous system (CNS) disease to determine the most common disorders and the rate of definitive morphologic and etiologic diagnosis within the population. The most common breed was Aberdeen Angus or Angus (31%), and female animals comprised 60% of the overall submissions. Gross anatomic changes were described in 33% of cases that had histologic lesions. Suppurative meningoencephalitis was the most common diagnosis (28% of cases overall) and was frequently associated with bacterial sepsis. Lymphocytic meningoencephalitis without an identified etiology was diagnosed in 17% of cases. Polioencephalomalacia was the most commonly identified noninfectious diagnosis (17%). Hydrocephalus was the most common CNS comorbidity and potential congenital defect. Identification of specific agents was sporadic, and infectious disease testing was largely dependent on fluorescent antibody testing, almost all of which were negative. Our findings indicate the common differential diagnoses for cattle with neurologic signs in the southeastern United States, as well the need for a well-defined, methodical diagnostic approach, including autopsy, histology, and appropriate additional laboratory testing.

Nonsuppurative (Aseptic) Meningoencephalomyelitis Associated with Neurovirulent Astrovirus Infections in Humans and Animals

Astroviruses are thought to be enteric pathogens. Since 2010, a certain group of astroviruses has increasingly been recognized, using up-to-date random amplification and high-throughput next-generation sequencing (NGS) methods, as potential neurovirulent (Ni) pathogens of severe central nervous system (CNS) infections, causing encephalitis, meningoencephalitis, and meningoencephalomyelitis. To date, neurovirulent astrovirus cases or epidemics have been reported for humans and domesticated mammals, including mink, bovines, ovines, and swine. This comprehensive review summarizes the virology, epidemiology, pathology, diagnosis, therapy, and future perspective related to neurovirulent astroviruses in humans and mammals, based on a total of 30 relevant articles available in PubMed (searched by use of the terms "astrovirus/encephalitis" and "astrovirus/meningitis" on 2 March 2018). A paradigm shift should be considered based on the increasing knowledge of the causality-effect association between neurotropic astroviruses and CNS infection, and attention should be drawn to the role of astroviruses in unknown CNS diseases.

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.

Neurologic Clinical Signs in Cattle With Astrovirus-Associated Encephalitis

Background

Evidence of neurotropic astroviruses has been established using novel genetic methods in cattle suffering from viral encephalitis of previously unknown origin.

Objectives

To describe the clinical signs observed in cattle with astrovirus‐associated encephalitis.

Animals

Eight cattle (4 cows, 3 heifers, and 1 bull of 4 different breeds) admitted to the Clinic for Ruminants for neurologic disease and 1 cow investigated in the field.

Methods

Cases were selected based on neuropathologic diagnosis of nonsuppurative encephalitis, positive in situ hybridization result for astrovirus, and availability of the results of physical and neurologic evaluations. Laboratory results were evaluated if available.

Results

The most frequently observed clinical signs were decreased awareness of surroundings (7), cranial nerve dysfunction (5), and recumbency (5). The cow seen in the field was the only animal that had severe behavioral changes. Cell counts in cerebrospinal fluid (CSF) were increased in 4 animals, and protein concentration was increased in 3 of 5 specimens. In 1 case, the presence of astrovirus could be identified in a CSF sample by reverse transcriptase polymerase chain reaction. Other laboratory abnormalities were nonspecific.

Conclusions and Clinical Importance

Astrovirus infection may be an important differential diagnosis in cattle with clinical signs of brain disease and should be considered after exclusion of other causes. The clinical and epidemiological relevance of encephalitis associated with astrovirus infection should be further investigated.

Detection of a novel sapelovirus in central nervous tissue of pigs with polioencephalomyelitis in the USA

An approximately 3,000 finishing swine operation in the United States experienced an outbreak of an atypical neurologic disease in 11-weeks-old pigs with an overall morbidity of 20% and case fatality rate of 30%. The clinical onset and progression of signs in affected pigs varied but included inappetence, compromised ambulation, ataxia, incoordination, mental dullness, paresis, paralysis and decreased response to environmental stimuli. Tissues from affected pigs were submitted for diagnostic investigation. Histopathologic examination of the cerebrum, cerebellum and spinal cord revealed severe lymphoplasmacytic and necrotizing polioencephalomyelitis with multifocal areas of gliosis and neuron satellitosis, suggestive of a neurotropic viral infection. Bacterial pathogens were not isolated by culture of neurologic tissue from affected pigs. Samples tested by polymerase chain reaction (PCR) were negative for pseudorabies virus and atypical porcine pestivirus. Immunohistochemistry for porcine reproductive and respiratory syndrome virus, porcine circovirus and Listeria was negative. Porcine sapelovirus (PSV) was identified in spinal cord by a nested PCR used to detect porcine enterovirus, porcine teschovirus and PSV. Next-generation sequencing of brainstem and spinal cord samples identified PSV and the absence of other or novel pathogens. In addition, Sapelovirus A mRNA was detected in neurons and nerve roots of the spinal cord by in situ hybridization. The PSV is genetically novel with an overall 94% amino acid identity and 86% nucleotide identity to a recently reported sapelovirus from Korea. This is the first case report in the United States associating sapelovirus with severe polioencephalomyelitis in pigs.

Frequency and Pathological Phenotype of Bovine Astrovirus CH13/NeuroS1 Infection in Neurologically-Diseased Cattle: Towards Assessment of Causality

Next-generation sequencing (NGS) has opened up the possibility of detecting new viruses in unresolved diseases. Recently, astrovirus brain infections have been identified in neurologically diseased humans and animals by NGS, among them bovine astrovirus (BoAstV) CH13/NeuroS1, which has been found in brain tissues of cattle with non-suppurative encephalitis. Only a few studies are available on neurotropic astroviruses and a causal relationship between BoAstV CH13/NeuroS1 infections and neurological disease has been postulated, but remains unproven. Aiming at making a step forward towards assessing the causality, we collected brain samples of 97 cases of cattle diagnosed with unresolved non-suppurative encephalitis, and analyzed them by in situ hybridization and immunohistochemistry, to determine the frequency and neuropathological distribution of the BoAstV CH13/NeuroS1 and its topographical correlation to the pathology. We detected BoAstV CH13/NeuroS1 RNA or proteins in neurons throughout all parts of the central nervous system (CNS) in 34% of all cases, but none were detected in cattle of the control group. In general, brain lesions had a high correlation with the presence of the virus. These findings show that a substantial proportion of cattle with non-suppurative encephalitis are infected with BoAstV CH13/NeuroS1 and further substantiate the causal relationship between neurological disease and astrovirus infections.

Enhanced immunosurveillance for animal morbilliviruses using vesicular stomatitis virus (VSV) pseudotypes

The measurement of virus-specific neutralising antibodies represents the “gold-standard” for diagnostic serology. For animal morbilliviruses, such as peste des petits ruminants (PPRV) or rinderpest virus (RPV), live virus-based neutralisation tests require high-level biocontainment to prevent the accidental escape of the infectious agents. In this study, we describe the adaptation of a replication-defective vesicular stomatitis virus (VSVΔG) based pseudotyping system for the measurement of neutralising antibodies against animal morbilliviruses. By expressing the haemagglutinin (H) and fusion (F) proteins of PPRV on VSVΔG pseudotypes bearing a luciferase marker gene, neutralising antibody titres could be measured rapidly and with high sensitivity. Serological responses against the four distinct lineages of PPRV could be measured simultaneously and cross-neutralising responses against other morbilliviruses compared. Using this approach, we observed that titres of neutralising antibodies induced by vaccination with live attenuated PPRV were lower than those induced by wild type virus infection and the level of cross-lineage neutralisation varied between vaccinates. By comparing neutralising responses from animals infected with either PPRV or RPV, we found that responses were highest against the homologous virus, indicating that retrospective analyses of serum samples could be used to confirm the nature of the original pathogen to which an animal had been exposed. Accordingly, when screening sera from domestic livestock and wild ruminants in Tanzania, we detected evidence of cross-species infection with PPRV, canine distemper virus (CDV) and a RPV-related bovine morbillivirus, suggesting that exposure to animal morbilliviruses may be more widespread than indicated previously using existing diagnostic techniques.

Detection of Astrovirus in Historical Cases of European Sporadic Bovine Encephalitis, Switzerland 1958-1976

European sporadic bovine encephalitis is a frequent diagnosis in neurologically diseased cattle, but its etiology remained unresolved. Using in situ hybridization, we have detected a recently discovered neurotropic bovine astrovirus in historical tissues in a high proportion of brain samples of affected cattle. Our results suggest that astroviruses were already involved in the pathogenesis of the disease several decades ago, but have gone undetected.

Screening red foxes (Vulpes vulpes) for possible viral causes of encephalitis

Background

Next to various known infectious and non-infectious causes, the aetiology of non-suppurative encephalitis in red foxes (Vulpes vulpes) often remains unclear. Known causes in foxes imply rabies, canine distemper, toxoplasmosis, Aujeszky’s disease, as well as parvovirus, adenovirus, circovirus and flavivirus infections. In this study, particular attention was paid on bornaviruses, since red foxes are predators of bicoloured white-toothed shrews, a reservoir of Borna disease virus 1 (BoDV-1). In addition, foxes are known to be highly susceptible for viruses of the order Mononegavirales.

Methods

Analyses for the presence of anti-BoDV-1 antibodies, BoDV-1-RNA and antigen were performed on 225 blood and 59 brain samples, from a total of 232 red foxes. Foxes originated from BoDV-1 endemic and non-endemic German areas. Additional investigations for the presence of rabies, canine distemper, toxoplasmosis, Aujeszky’s disease, parvovirus, adenovirus and flavivirus infections were carried out on 16 red foxes with non-suppurative (meningo-) encephalitis. A metagenomic analysis was used on three representative brain samples displaying encephalitis.

Results

Among 225 foxes, 37 displayed anti-BoDV-1 antibodies with titres ranging between 1:40 and 1:2560, regardless of geographic origin. In 6 out of 16 foxes with encephalitis, canine distemper virus was detected. No evidence of any of the other investigated agents was found in the 16 fox brains with encephalitis. Metagenomics revealed no infectious agents, except for one already known canine distemper case.

Conclusion

Red foxes can exhibit BoDV-1 specific antibodies without association with geographic origin or encephalitis due to bornavirus infection. The encephalitis pattern was highly conspicuous for a viral infection, but remained unclear in 10 out of 16 foxes. Thus, presently unknown infectious and non-infectious causes need to be considered and further investigated, especially since foxes also tend to occur in human proximity.

Full-genome based molecular characterization of encephalitis-associated bovine astroviruses

Novel types of astrovirus have been identified recently in association with neurological disease in cattle. Among those viruses is bovine astrovirus CH13 (BoAstV CH13) that has been identified in Switzerland in a cow with encephalitis. Molecular testing by a combination of reverse transcription (RT-) PCR and in situ hybridization (ISH) indicated that astrovirus infection accounts for around one quarter of viral encephalitis cases of unknown etiology in cattle. Yet, it remained to be explored whether these animals were infected by BoAstV CH13 or other astrovirus species. In the present study we sequenced the entire astrovirus genome in brain tissues of eight RT-PCR and/or ISH positive cattle. Phylogenetic comparison of the genomic RNA and the encoded non-structural and structural proteins revealed that all these astrovirus strains were very similar to BoAstV CH13 as well as to a bovine encephalitis strain reported from the USA (BoAstV NeuroS1), and clearly distinct from other previously reported astroviruses. Conserved 5' and 3' untranslated regions (UTRs) were predicted to display distinct secondary RNA structures, which likely play a role in viral RNA replication and/or protein translation. Based on these data we propose that BoAstV CH13/NeuroS1 represents a new genotype species within the genus Mammastrovirus. The high degree of similarity between the strains and their relative distance to other genotype species suggest that during evolution some astroviruses acquired factors that specifically contribute to neuroinvasion.

Exploring the virome of cattle with non-suppurative encephalitis of unknown etiology by metagenomics

Non-suppurative encephalitis is one of the most frequent pathological diagnosis in cattle with neurological disease, but there is a gap in the knowledge on disease-associated pathogens. In order to identify viruses that are associated with non-suppurative encephalitis in cattle, we used a viral metagenomics approach on a sample set of 16 neurologically-diseased cows. We detected six virus candidates: parainfluenza virus 5 (PIV-5), bovine astrovirus CH13/NeuroS1 (BoAstV-CH13/NeuroS1), bovine polyomavirus 2 (BPyV-2 SF), ovine herpesvirus 2 (OvHV-2), bovine herpesvirus 6 (BHV-6) and a novel bovine betaretrovirus termed BoRV-CH15. In a case-control study using PCR, BoAstV-CH13 (p=0.046), BoPV-2 SF (p=0.005) and BoHV-6 (p=4.3E-05) were statistically associated with the disease. These data expand our knowledge on encephalitis-associated pathogens in cattle and point to the value of NGS in resolving complex infection scenarios in a clinical disease setting.

Neurotropic astrovirus in cattle with nonsuppurative encephalitis in Europe

Encephalitis is a frequently diagnosed condition in cattle with neurological diseases. Many affected animals present with a nonsuppurative inflammatory reaction pattern in the brain. While this pattern supports a viral etiology, the causative pathogen remains unknown in a large proportion of cases. Using viral metagenomics, we identified an astrovirus (bovine astrovirus [BoAstV]-CH13) in the brain of a cow with nonsuppurative encephalitis. Additionally, BoAstV RNA was detected with reverse transcription-PCR and in situ hybridization in about one fourth (5/22 animals) of cattle with nonsuppurative encephalitis of unknown etiology. Viral RNA was found primarily in neurons and at the site of pathology. These findings support the notion that BoAstV infection is a common cause of encephalitis in cattle. Phylogenetically, BoAstV-CH13 was closely related to rare astrovirus isolates from encephalitis cases in animals and a human patient. Future research needs to be directed toward the pathogenic mechanisms, epidemiology, and potential cross-species transmission of these neurotropic astroviruses.

Investigation into an outbreak of encephalomyelitis caused by a neuroinvasive porcine sapelovirus in the United Kingdom

An outbreak of neurological disease in grower pigs characterised by ataxia and paraparesis was investigated in this study. The outbreak occurred 3-4 weeks post weaning in grower pigs which displayed signs of spinal cord damage progressing to recumbency. Pathology in the affected spinal cords and to a lesser extent in the brainstem was characterised by pronounced inflammation and neuronophagia in the grey matter. Molecular investigation using a pan-virus microarray identified a virus related to porcine sapelovirus (PSV) in the spinal cord of the two affected pigs examined. Analysis of 802 nucleotides of the virus polymerase gene showed the highest homology with those of viruses in the genus Sapelovirus of Picornaviridae. This PSV, strain G5, shared 91-93%, 67-69% and 63% nucleotide homology with porcine, simian and avian sapeloviruses, respectively. The nucleotide homology to other members of the Picornaviridae ranged from 41% to 62%. Furthermore, viral antigen was detected and co-localised in the spinal cord lesions of affected animals by an antibody known to react with PSV. In conclusion, clinical and laboratory observations of the diseased pigs in this outbreak are consistent with PSV-G5 being the causative agent. To the best of the authors' knowledge, this is the first unequivocal report of polioencephalomyelitis in pigs by a neuroinvasive PSV in the United Kingdom.

Emerging Chlamydial Infections

Chlamydiae are important intracellular bacterial pathogens of vertebrates. In the last years, novel members of this group have been discovered: Parachlamydia acanthamoebae and Simkania negevensis seems to be emerging respiratory human pathogens, while Waddlia chondrophila might be a new agent of bovine abortion. Various species have been showed to infect also the herpetofauna and fishes, and some novel chlamydiae are endosymbionts of arthropods. In addition, molecular studies evidenced a huge diversity of chlamydiae from both environmental and clinical samples, most of such a diversity could be formed by novel lineages of chlamydiae. Experimental studies showed that free-living amoebae may support multiplication of various chlamydiae, then could play an important role as reservoir/vector of chlamydial infections. Here we reviewed literature data concerning chlamydial infections, with a particular emphasis on the novely described chlamydial organisms.

Neuropathological survey of fallen stock: active surveillance reveals high prevalence of encephalitic listeriosis in small ruminants

This paper describes the prevalence of brain lesions in the Swiss fallen stock population of small ruminants. 3075 whole brains (75% sheep, 25% goats) were collected as part of a year-long active survey of transmissible spongiform encephalopathies (TSEs) in small ruminants conducted by the Swiss authorities between July 2004 and July 2005. All fallen stock brains were systematically examined by histopathology to obtain reliable data on histologically identifiable brain lesions. Lesions were found in an unexpectedly high number of animals (8.1% of all examined brains). A wide spectrum of diseases was detected showing that this approach provides an excellent opportunity to screen for the prevalence of neurological diseases. Encephalitic listeriosis was by far the most frequent cause of CNS lesions in both species and its prevalence was unexpectedly high when compared to notified confirmed cases. In conclusion, the prevalence of listeriosis as estimated by passive surveillance based on the notification of clinical suspects has been underestimated in the past.

Greyhound meningoencephalitis: PCR-based detection methods highlight an absence of the most likely primary inducing agents

Greyhound meningoencephalitis is currently classified as a breed-associated idiopathic central nervous system inflammatory disorder. The non-suppurative inflammatory response can be distinguished from the other breed-associated disorders based on histopathology and lesion topography, however the nature of the response primarily suggests a viral infection. In the present study PCR and RT-PCR technologies were employed on frozen cerebral tissue from confirmed cases of meningoencephalitis to target specific viruses and protozoa likely to be implicated and to exclude the presence of bacterial 16SrRNA. Secondly, degenerate primers were used to detect viruses of the herpesvirus and flavivirus families. In addition cerebral tissues were probed for West Nile Virus. Viral nucleic acid sequences to Borna disease virus, to louping ill, tick borne encephalitis, West Nile and other flaviviruses were not detected. Canine distemper virus was detected in one animal with 97% homology to strain A75/15. Degenerate PCR for herpesviruses detected viral amplification products in one animal with 90% homology to canine herpesvirus DNA polymerase gene. Protozoal amplification products were only detected in a single dog with pathological confirmation of a combination of lesions of greyhound meningoencephalitis and a protozoal encephalomyelitis. Neospora was confirmed with sequence homology to Austrian strain 1. Bacterial 16SrRNA was not detected. The present study supports previous observations that many of the known microbial causes of canine meningoencephalitis are not involved. Findings could reflect that the causal agent was not specifically targeted for detection, or that the agent is at undetectable levels or has been eliminated from brain tissue. The potential roles of genetics and of molecular mimicry also cannot be discounted.

Epidemiological pattern of classical Borna disease and regional genetic clustering of Borna disease viruses point towards the existence of to-date unknown endemic reservoir host populations

Classical Borna disease (cBD), a non-purulent encephalitis of solipeds and sheep, is endemic in certain areas of central Europe. The etiologic agent is Borna disease virus (BDV), thus far the only member of the family Bornaviridae. Based on epidemiological patterns of cBD and recent phylogenetic findings this review hypothesizes the possible existence of yet unknown BDV reservoir host populations, and analyzes critically BDVs from outside endemic regions.

Viral diseases of the ruminant nervous system

This article presents the etiology, epidemiology, clinical features,and diagnosis of the primary viral neurologic diseases observed in ruminants. In general, these viral neurologic diseases are uncommon but often fatal. Rabies virus is perhaps the most important cause of encephalitis in cattle because of the public health implications. Other viral encephalitis diseases in ruminants include bovine herpesvirus encephalomyelitis, pseudorabies, malignant catarrhal fever, ovine and caprine lentiviral encephalitis, West Nile virus encephalitis, Borna disease, paramyxoviral sporadic bovine encephalomyelitis,and ovine encephalomyelitis (louping-ill).