A long‐term study of Australian infectious bronchitis viruses indicates a major antigenic change in recently isolated strains

Abstract

The antigenic relationship among 36 IBV strains isolated between 1961 and 1994 from vaccinated and non-vaccinated chicken flocks was determined. Based on the reaction with nine monoclonal antibodies (MAbs) in ELISA and polyclonal chicken sera in western blotting, IBV strains clearly fell into two distinct antigenic groups. Nineteen IBV strains isolated between 1961 and 1994 from various locations were antigenically related, having common cross-reactive epitopes on the peplomer S, the nucleocapsid N and the membrane M proteins. IBV strains within this classical group could be antigenically differentiated further by serotyping and by their reaction with MAbs. Seventeen IBV strains isolated between 1988 and 1994, shared only a minor degree of antigenic similarity with strains in the classical group. Strains in this novel group were antigenically related to each other and shared cross-reactive epitopes particularly on the N and M proteins. The novel IBV strains were not detected before 1988 and their origin is unknown. They appeared suddenly and almost simultaneously at two distant commercial sites, Redland Bay and Appin, and were also isolated at a third location in Victoria 3 years later. The Appin strains persisted on the site for 3 years without changes in antigenicity, including the serotype; however, following introduction of vaccination with novel strains a variant of new serotype was isolated. Variants isolated in Victoria on the other hand showed greater antigenic diversity and tendency for change. Novel strains have not displaced classical strains which continued to be isolated frequently.

Complete Nucleotide Sequences of S1 and N Genes of Infectious Bronchitis Virus Isolated in Japan and Taiwan

“…The S1 protein of IBV plays a key role in the induction of protective immune response against IBV and the variation in the S1 sequence is the major mechanism by which a new serotype emerges [2,12]. Phylogenetic analysis showed that the S1 sequences of JP8127, JP8443 and JP9758 are closely related to those of Australian viruses, which have a serotype distinct from the Massachusetts and Connecticut serotypes that have been commonly used as the vaccine [4,8]. Similarly, the S1 protein of strain TW/97-4 was very similar to that of strains A1211, which belonged to the TW-I serotype that was different from the Massachusetts and Connecticut serotypes [11].…”

“…The S protein is processed into S1 and S2 subunits; the S1 forms the receptor-binding site whereas the S2 anchors the S1 to the viral membrane. Both S1 and N proteins play a critical role in the induction of immune response against IBV and understanding of the S1 and N sequences are important for selection of useful vaccines [2,4,9,12]. However, little information is available on the sequences of the S1 and N genes of Japanese and Taiwanese field strains of IBV [10,11].…”

Evaluation of a novel strain of infectious bronchitis virus emerged as a result of spike gene recombination between two highly diverged parent strains

“…In contrast, subgroup 2 strains, such as N1/88, cause only mild lesions in the trachea and are associated with minimal signs of respiratory disease (Ignjatovic et al, 1997). Experimental infection of chickens with N1/08 in this study appeared to indicate that the pathogenicity of N1/08 was more similar to that of subgroup 2 strains than subgroup 3 strains.…”

“…Historically these strains have been the most prevalent and are associated with lesions in both tracheal and kidney tissues (Ignjatovic et al, 2002;Mardani et al, 2008). Australian subgroup 2 strains were detected between the mid 1980s and early 1990s (Ignjatovic et al, 1997) and have not been reported since, and appear to have emerged from a very different origin and adapted to growth in chickens. Australian Subgroup 2 strains are known to replicate only in the trachea of infected chickens (Ignjatovic et al, 2002;Mardani et al, 2008).…”

“…Australian Subgroup 2 strains are known to replicate only in the trachea of infected chickens (Ignjatovic et al, 2002;Mardani et al, 2008). Based on the nucleotide sequence of the structural protein gene region at the 3′ end of their genome, subgroup 2 viruses belong to a different lineage of the Australian subgroup 1 IBV strains (Ignjatovic et al, 1997;Mardani et al, 2008). Australian subgroup 3 strains, first detected in 2002, emerged as a result of recombination and have a high sequence identity over the entire structural protein gene region, except for the S1 gene, with subgroup 1 strains.…”