Origin and evolution of Georgia 98 (GA98), a new serotype of avian infectious bronchitis virus

We previously identified GA98. a new serotype of infectious bronchitis viru s (IBV). which is closely related to the DE072 serotype of IBV genetically, but not antigenically. Herein. we analyzed the 421bp sequence of a hyperva riable region (HVR) (position 114-534, counting from the ATG start site) of the S1 subunit of GA98 IBVs to further examine the evolution of these viru ses. These viruses were isolated between the years 1997 and 2000. Phylogene tic analysis of the deduced amino acid sequence on that region indicated th at GA98 isolates from different regions of Georgia were the result of a sin gle introduction of the Sl gene of the DE072 serotype progenitor, Most of t he mutations were nonsynonymous and had become fixed in a progressive manne r. The evolutionary and mutation rates in the HVR was calculated as 2.5 and 1.5% per year, respectively. This new serotype of IBV appears to be evolvi ng very fast compared with other serotypes of IBV. We further determined th e complete coding sequence of the S1 gene of seven isolates obtained from o ne selected region in North Georgia. Together with virus neutralization dat a. it appears that GA98 arose from immune selection caused by DE072 vaccine use. Reasons for this conclusion are discussed. (C) 2001 Elsevier Science B.V. All rights reserved.