e 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.

The association between PRNP variation and scrapie incidence was investigated in a highly affected Greek goat herd. Four mutations were identified at codons 171Q/R, 211R/Q, 222Q/K and 240P/S. Lysine at codon 222 was found to be associated with the protection from natural scrapie (P50.0111). Glutamine at codon 211 was observed in eight animals, all of them being scrapie-negative, indicating a possible protective role of this polymorphism although statistical analysis failed to support it (P50.1074). A positive association (P50.0457) between scrapieaffected goats and the wild-type Q 171 R 211 Q 222 S 240 allele is presented for the first time. In addition, a novel R 171 RQS allele, which is identical to the A 136 R 154 R 171 allele that has been associated with resistance to classical scrapie in sheep, was observed in low frequency. Resistant alleles that include K 222 and Q 211 are absent or rare in sheep and can provide the basis for the development of a feasible breeding programme for scrapie eradication in goats.

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.

Therapeutic vaccination offers great promise as an intervention for a diversity of infectious and non‐infectious conditions. Given that most chronic health conditions are thought to have an immune component, vaccination can at least in principle be proposed as a therapeutic strategy. Understanding the nature of protective immunity is of vital importance, and the progress made in recent years in defining the nature of pathological and protective immunity for a range of diseases has provided an impetus to devise strategies to promote such responses in a targeted manner. However, in many cases, limited progress has been made in clinical adoption of such approaches. This in part results from a lack of safe and effective vaccine adjuvants that can be used to promote protective immunity and/or reduce deleterious immune responses. Although somewhat simplistic, it is possible to divide therapeutic vaccine approaches into those targeting conditions where antibody responses can mediate protection and those where the principal focus is the promotion of effector and memory cellular immunity or the reduction of damaging cellular immune responses as in the case of autoimmune diseases. Clearly, in all cases of antigen‐specific immunotherapy, the identification of protective antigens is a vital first step. There are many challenges to developing therapeutic vaccines beyond those associated with prophylactic diseases including the ongoing immune responses in patients, patient heterogeneity, and diversity in the type and stage of disease. If reproducible biomarkers can be defined, these could allow earlier diagnosis and intervention and likely increase therapeutic vaccine efficacy. Current immunomodulatory approaches related to adoptive cell transfers or passive antibody therapy are showing great promise, but these are outside the scope of this review which will focus on the potential for adjuvanted therapeutic active vaccination strategies.

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.