3.3 Astroviridae
The family Astroviridae contains two genera Avastrovirusand Mamastrovirus that infect birds and mammals, respectively. Astroviruses are commonly associated with acute gastroenteritis in humans (Vu et al., 2017; Walter et al., 2001). The recognised feline astrovirus species is Mamastrovirus 2, although several novel feline astroviruses have been identified (Brussel et al., 2020; Zhang et al., 2014). Recently, we proposed two novel feline astroviruses,Feline astrovirus 3 and Feline astrovirus 4 , identified in a pilot study of four cats included here, one with FPV and diarrhoea and three healthy control cats (Brussel et al., 2020). Further analysis on this larger data set showed the presence of astrovirus contigs at a higher frequency in FPV-cases (19/23, 82.6%) compared to healthy controls (18/36, 50%) (p = 0.0142) (Figure 2). Two FPV-case libraries had contigs with 96-99% nucleotide similarity to Feline astrovirus 4 and one contig, identified in an FPV-case library (cat #FPV166), contained the full ORF1a with 99% nucleotide similarity. TheMamastrovirus 2 sequence infecting two healthy controls is identical to the Mamastrovirus 2 sequence AUS/AWL isolated in our pilot study, with read abundance counts of 932,723 and 312,958 RPM for the two metatranscriptomic libraries and 896,065 and 862,160 RPM for the two metagenomic libraries. The capsid protein phylogeny revealed two groupings of Mamastrovirus 2 sequences (Figure 4). Interestingly, two Mamastrovirus 2 sequences - FPV-2 and FPV-8 - formed a basal group to the human astroviruses in the capsid phylogeny although not in the ORF1b phylogeny (Figure 4). RDP4 and Simplot analysis detected a possible recombination event in theMamastrovirus 2 sequence FPV-1 and sequence FPV-10 in the ORF1b and capsid overlap (Supplementary Data S4). However, no recombination events were detected in Mamastrovirus 2 sequence FPV-2 and FPV-8, contrary to the positioning of both sequence in the ORF1b and capsid phylogenies. It is likely that the currently limited number of completeMamastrovirus 2 genomes available on GenBank precludes identification of recombination events.