Genetic diversity and evolutionary relationships of porcine astroviruses from wild boars and domestic pigs in Japan

Porcine astrovirus (PoAstV) is a viral pathogen associated with diarrhea and neurological disorders in piglets. In this study, we performed metatranscriptome analysis of fecal samples, and compared the full-length genomes of PoAstVs detected in Japanese wild boars and domestic pigs collected between 2017 and 2023 with astrovirus sequences from the GenBank database. Phylogenetic analyses of near-complete genomes from 12 wild boar and 67 pig PoAstVs, together with sequences from our previous study and the GenBank database, revealed that six, four, and two wild boar PoAstV sequences clustered with PoAstV-2, PoAstV-4, and PoAstV-5, respectively. Pig-derived PoAstVs comprised all five known genotypes, with PoAstV-2 (31/67) being predominant, followed by PoAstV-4 (18/67) and PoAstV-5 (12/67), similar to the pattern observed in wild boars. Some wild boar PoAstV strains showed high nucleotide identity with domestic Japanese strains, whereas others exhibited greater similarity to foreign porcine strains. Notably, two wild boar PoAstV-4 strains showed high identity with Chinese and Vietnamese PoAstV-4 in ORF1a and ORF1b, forming a distinct cluster, while no clustering was observed in ORF2, indicating possible recombination events. Intragenotype recombination was also detected among wild boar and domestic pig strains of PoAstV-2, -4, and - 5, implying wildlife-domestic interface. These findings suggest that PoAstVs are exchanged between wild boars and domestic pigs in Japan, promoting genetic diversification within each genotype through recombination. To our knowledge, this is the first detection and genomic characterization of PoAstV in Japanese wild boars.