Comparison of capsid gene sequences of turkey astrovirus-2 from poult-enteritis-syndrome-affected and apparently healthy turkeys

This study was conducted to determine genetic variations in the capsid gene of turkey astrovirus-2 (TAstV-2) detected in apparently healthy and poult enteritis syndrome (PES)-affected turkeys. Capsid genes of astroviruses obtained from 30 PES-affected and 45 apparently healthy turkey flocks had sequence homologies of 73.4-100% and 72.4-100% at the nucleotide levels, respectively. The analysis of deduced amino acid sequences revealed one amino acid deletion at position 552 in 28 (93.3%) of 30 PES-affected cases. However, there were two deletions (at positions 551 and 552) in 31 (68.9%) of 45 TAstV-2 from apparently healthy flocks. The TAstV-2 (6.7%) from two PES-affected cases had two amino acid insertions each between positions 552 and 553, while TAstV-2 from 14 (31.1%) of 45 healthy flocks had two insertions at the same position. Phylogenetic analysis based on nucleotide sequences revealed that the astroviruses in this study were closely related to most of the previously published TAstV-2 isolates. The sequence homology of TAstV-2 in this study ranged from 70.4% to 99.4% at the nucleotide level with those of previously published TAstV-2 isolates. The variations at the amino acid level in the capsid gene suggest the possibility of the existence of different serotypes of turkey astrovirus. The close relationship of turkey astroviruses from apparently healthy flocks to those from PES-affected cases in capsid gene phylogeny necessitates further studies to compare complete capsid gene sequences from both types of flocks from different geographic areas for better understanding of TAstV circulating in turkeys.