Abstract
Astroviruses (AstV) are single-stranded, positive-sense RNA viruses, best known for causing diarrhea in humans and are also found in many other mammals; in those, the relevance in gastroenteritis remains unclear. Recently described neurotropic AstV showed associations with encephalitis in humans as well as in other mammals. In Switzerland, two different neurotropic AstV were identified in cattle, as well as one in a sheep. The high genetic similarity between the ovine and one of the bovine AstV strengthens the hypothesis of an interspecies transmission. In humans, AstV associated with encephalitis were found also in human stool samples, suggesting that in these patients the infection spreads from the gastrointestinal tract to the brain under certain conditions, such as immunosuppression. Whether a similar pathogenesis occurs in ruminants remains unknown. The aims of this study were (1) the investigation of the potential occurrence of neurotropic AstV in feces samples, (2) the discovery and analysis of so far unknown AstV in small ruminants and other ruminant species’ fecal samples and (3) the examination of a potential interspecies transmission of AstV. To achieve these aims, RNA extraction out of 164 fecal samples from different ruminant species was performed and all samples were screened for known neurotropic AstV occurring in Switzerland, as well as for various AstV using RT-PCR. Positive tested samples were submitted to next generation sequencing. The generated sequences were compared to nucleotide- and amino acid databases, virus properties were identified, and phylogenetic analyses as well as recombination analysis were performed. The excretion of neurotropic AstV in small ruminants’ feces could not be demonstrated, but this work suggests the first identification of AstV in goats as well as the discovery of multiple and highly diverse new genetic variants in small ruminants, which lead to a classification into novel genotype-species. Additionally, the prediction of multiple recombination events in four of five newly discovered full or almost full-length genome sequences suggests a plausible interspecies transmission. The findings point out the occurrence and fecal shedding of previously unknown AstV in sheep and goats and pave the way towards a better understanding of the diversity and transmission of AstV in small ruminants.
Highlights
Astroviruses (AstV) are non-enveloped, single-stranded positive-sense RNA viruses with an icosahedral virion structure, appearing as a star-like shape in electron microscopy (Caul & Appleton, 1982)
The AstV genome is 6.2–7.8 kb in size and polyadenylated at the 3′ end. It presents at least three open reading frames (ORF): ORF1a, ORF1ab, and ORF2
Detection of various astroviruses using Pan-astrovirus RT-PCR To ensure the effective implementation and to establish positive controls, the protocol was first applied to brain-extracts of BoAstV-CH13 and ovine astroviruses (OvAstV)-CH16 positive animals
Summary
Astroviruses (AstV) are non-enveloped, single-stranded positive-sense RNA viruses with an icosahedral virion structure, appearing as a star-like shape in electron microscopy (Caul & Appleton, 1982). The AstV genome is 6.2–7.8 kb in size and polyadenylated at the 3′ end. It presents at least three open reading frames (ORF): ORF1a, ORF1ab, and ORF2. ORF1a and ORF1ab encode nonstructural precursor proteins, nsp1a, and nsp1ab. The latter is translated via a ribosomal frameshift mechanism, where ORF1b is translated together with ORF1a (Marczinke et al, 1994). ORF2 encodes the capsid precursor protein, which is intra- and extracellularly further processed to mature structural proteins (Willcocks et al, 1994)
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