Astroviruses are small, round, non-enveloped particles, typically 28-30 nm in diameter, having a star-like appearance in electron microscopy. AstV has a 6.8-7.9-kb positive-sense single-stranded RNA genome, which encodes three open reading frames (ORF1a and ORF1b, which are linked by a translational frameshift, and ORF2). ORF1b encodes the RNA-dependent RNA polymerase, and ORF2 encodes the capsid protein [3, 7, 11] . The ORF1b region is the most conserved gene in mammalian and avian astroviruses as well as in avian astroviruses [13] . On the other hand, ORF2 is the most variable region of the astrovirus genome and is possibly responsible for the antigenic and pathogenic diversity of astrovirus strains [23] . The family Astroviridae is divided into two genera: Mamastrovirus (mammalian astrovirus) and Avastrovirus (avian astrovirus). Recently, the Astroviridae Study Group of the International Committee for Taxonomy of Viruses (ICTV) has proposed a classification system based on genetic criteria instead of the host of origin. The genus Mamastrovirus includes19 astrovirus genotypes, and the genus Avastrovirus includes three genotypes that are distinguished based on the amino acid sequence of full-length ORF2 (http:// talk.ictvonline.org/files/proposals/taxonomy_proposals_ vertebrate1/m/vert01/2358.aspx).