Analysis of the S1 gene of the avian infectious bronchitis virus (IBV) reveals changes in the IBV genetic groups circulating in southern Thailand

Abstract

The new variants of the avian infectious bronchitis virus (IBV) produce a range of symptoms and cause global economic losses to the poultry industry. We investigated the S1 glycoprotein of 24 recent IBV isolates from chickens and demonstrated that two predominant genetic groups were circulating in southern Thailand between 2008 and 2013. Seven IBV variants, isolated from 2008 to 2009, were clustered in the Thailand THA001 group I while 15 IBV variants, isolated from 2009 to 2013, were classified into the QX-like group II. Moreover, a single isolate from a broiler was categorized into the Massachusetts-type, and an isolate from a layer belonged to the 4/91 type virus. Interestingly, both the IBV groups I and II were isolated from native chickens (62.5%) and caused a range of symptoms. Our results indicate that the QX-like viruses were predominant after 2009, replacing the THA001 type viruses. Furthermore, native chickens may contribute to the epidemiology of IB.

Keywords: Infectious bronchitis virus; Native chickens; Phylogenetic analysis; S1 glycoprotein; Southern Thailand.

Fig. 1

Phylogenetic relationship of local isolates, vaccine and global IBV strains. Analysis was based on partial S1 nucleotide sequences determined using MEGA 6.0 with the Clustal W method. The isolates sequenced in this study are illustrated with black triangles, black squares, black diamonds and black circles.

Fig. 2

Geographic distribution of field isolates of IBV in southern Thailand between 2008 and 2013. (A) Group I, the THA001 isolates clustered between 2008 and 2009. (B) Group II, the QX-like field isolates circulated from 2009 to 2013, (C) the Mass-like isolated in 2012, and (D) the 4/91-like recovered in 2013.