Isolation and Characteristics of the Arkansas-Type Infectious Bronchitis Virus in China

Two infectious bronchitis virus (IBV) strains, designated as γCoV/ck/China/I0712/11 (I0712/11) and γCoV/ck/China/I0108/17 (I0108/17), were isolated from diseased chicken flocks in different provinces in China and genotyped as Arkansas (Ark)-type viruses with three other Chinese Ark field strains, the Jilin vaccine strain, and the American Ark- and Ark DPI-like viruses. Complete genomic sequence analysis and pairwise comparison of nucleotide sequences encoding the S1 subunit of the spike protein and other structural and accessory proteins revealed that Chinese Ark field isolates were genetically closely related to the Jilin vaccine and American ArkDPI11 strains, although extensive nucleotide changes were found across the genomes of Chinese Ark field isolates. This suggests that Chinese Ark-type isolates are derived from the Jilin vaccine, and have diverged and evolved independently by point mutations since introduction into China. It is also possible that the Chinese Ark viruses have arisen as a result of different introductions of American ArkDPI11-like strains from the United States; this hypothesis requires further investigation. Pathogenicity testing showed that Chinese Ark viruses had comparable virulence to that of the Massachusetts-type M41 strain, although they had lower affinity for the kidneys of chickens than the M41 strain had. Although Ark-type viruses are not widespread in China, surveillance and updating the currently applied vaccination strategy for sound protection against IBV disease are important because this type of virus has caused heavy economic losses in the United States.