Sequence and phylogenetic analysis of the sigmaA-encoding gene of avian reovirus.

The full-length sigmaA-encoding gene nucleotide sequences (1251 bp) of ten avian reovirus (ARV) field-isolates and three vaccine strains were determined and analyzed to study the degree of genetic divergence and evolution. Strains were isolated over a 23-year period from different hosts, pathotypes, and geographic locations. A phylogenetic tree constructed from variation in the sigmaA nucleotide sequences among ARV isolates showed that Taiwanese isolates from different dates of isolation were grouped into two distant groups, indicating that they have evolved in nature. In paired identity analysis, there was over 97.3% nucleotide sequence identity in the sigmaA-encoding genes between group I Taiwanese isolates (T6, 750505, 919, and 918) and Japanese isolate OS161 as well as three US vaccine strains, suggesting that they might have descended from a common ancestor. However, the nucleotide sequences of these sigmaA-encoding genes varied extensively from those of group II Taiwanese isolates (601SI, R2/TW, 1017-1, 916, and 601G), displaying only 86% identity. These results revealed that the genetic diversity in the sigmaA-encoding gene of ARV correlated with the date of isolation and geographic locations.