Abstract
In mammals, the small, positive-sense single-stranded RNA astroviruses are known as being mostly enterotropic and host-specific. Over the past years, however, they were identified several times in central nervous system tissues of humans, minks, cattle, sheep, and pigs with nonsuppurative inflammatory disease of that organ system. We recently reported such neurotropic astroviruses, amongst which bovine astrovirus CH15 (BoAstV-CH15) in two cows, and ovine astrovirus CH16 (OvAstV-CH16) in a sheep, which were genetically almost identical to one another. In order to investigate the occurrence of this virus species in Switzerland over time, we selected formalin-fixed, paraffin-embedded (FFPE) brain tissues of small ruminants diagnosed with severe encephalitis between 1969 and 2012 and screened those by immunohistochemistry for the capsid protein of BoAstV-CH15/OvAstV-CH16. We found one sheep, which died in 1992, that displayed positive immunostaining in various brain regions, and observed that immunostained cells were generally co-localized with the strongest histopathological lesions. We confirmed the virus presence with a second immunohistochemical protocol and demonstrated its close genetic relationship to other BoAstV-CH15/ OvAstV-CH16 strains by next-generation sequencing of an RNA extract from FFPE brain material. Our findings demonstrate that astrovirus BoAstV-CH15/OvAstV-CH16 existed in Switzerland already more than 2 decades ago and underline again the close relationship of the bovine and ovine strains of this virus.
Highlights
Astroviridae, which are positive-sense, single-stranded RNA viruses, were described in a huge variety of birds and mammals [1]
A second IHC protocol detecting another part of the capsid protein of BoAstV-CH15/OvAstV-CH16 was performed on all brain regions of animal 21979 in order to confirm the virus presence, and was positive (Figure 1E)
Astroviruses were reported in three sheep with different nonsuppurative inflammatory patterns of the central nervous system: one ewe and one lamb belonging to the same herd in Wales [16], as well as a single case from Switzerland [17]
Summary
Astroviridae, which are positive-sense, single-stranded RNA viruses, were described in a huge variety of birds and mammals [1]. The genus Avastrovirus is known to infect birds, while mamastroviruses are to be found in mammalian hosts, in which they were identified mostly in fecal samples. 7 kb long genome of astroviruses displays three open reading frames (ORF): ORF1a and ORF1b (which is translated through a ribosomal frameshift mechanism together with ORF1a) encode nonstructural proteins, whereas capsid proteins are derived from ORF2 [1]. The taxonomy of astroviruses is based on the host species from which they were isolated, as well as the amino acid sequence of the capsid protein precursor [2]. Within the Mamastrovirus genus, astroviruses are classified within the same genotype species when the amino acid genetic distance of their capsid protein precursor sequence is
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