Characterization of a small round virus associated with the poult enteritis and mortality syndrome

A small round virus (SRV) identified and isolated in our laboratory from intestinal samples of poults affected with the poult enteritis and mortality syndrome was further characterized. The SRV was propagated in turkey embryos and purified by differential and isopycnic ultracentrifugation. The size of the SRV was 30-32 nm in diameter. The buoyant density of the SRV in cesium chloride was between 1.34 and 1.36 g/cm3. It was resistant to chloroform treatment, stable at pH 3.0, and resistant to heat treatment. Attempts to propagate the SRV in turkey embryo kidney, turkey kidney, Caco-2, Vero, and BGM-70 cells were unsuccessful. Analysis of the SRV capsid proteins by sodium dodecyl sulfate-polyacrylamide gel electrophoresis revealed three polypeptides with molecular weights of 34.5, 31, and 28 kD. Genome analysis of the SRV showed that the SRV had a single-strand RNA genome about 7500 nucleotides in length. Reverse transcription-polymerase chain reactions (RT-PCRs) with primers specific to conserved sequences of enteroviruses yielded products with expected sizes. However, sequence analysis of the RT-PCR products showed that there was no similarity between the sequences and that of enteroviruses. RT-PCR with primers specific to the 3' end of a SRV RNA genome yielded products with expected sizes. These products were sequenced and found to contain 669 nucleotides, excluding the polyadenylated tail. Sequence analysis indicated that the SRV shared 38.18% amino acid identity in the C-terminal capsid precursor protein and 41.26% nucleotide identity of the 3' end of turkey astrovirus RNA genome (Genbank accession no. Y15936). We concluded that the SRV is a member of the astrovirus family.