Replication and adaptation of avian infectious bronchitis viruses in pheasants (Phasianus colchicus)

Infectious bronchitis virus (IBV) does not only cause disease in millions of chickens worldwide, but IBV-like viruses have also been detected or isolated from other domestic birds. We propose that the pheasant coronavirus (PhCoV) originates from IBV. Indeed, the IBV strains H120 and M41 can replicate but do not cause disease in pheasants. In this study, we found that three chicken nephropathogenic IBV strains, including ck/CH/LDL/091,021, ck/CH/LDL/140,520, and I0305/19, and the viruses recovered from the tissues of pheasants challenged with each IBV strain could replicate in some challenged pheasants with different capacities but could not cause disease. Overall, these viruses showed different capacities of replication and adaptation in pheasants, and the neutralizing antibody against each IBV strain could be detected in different numbers of pheasants challenged with each of the viruses, although the titers were generally low with large variation. Comparatively, ck/CH/LDL/140,520 and 20/P1-D5/Tr1 showed higher adaptation capacities in pheasants. Furthermore, the three IBV strains gained an increased capacity for adaptation when they passed in pheasants once, especially strain ck/CH/LDL/140,520, which gained an increased capacity for adaptation and extended tissue tropism when it was passaged in pheasants. Similar to IBV in chicken, the subpopulations within the virus were selected when the virus replicated and was passaged in pheasants, and the accumulation of mutations and deletions in the genome of each virus subpopulation accounted for the independent evolution of the virus in different tissues of pheasants. Taken together, we suggest that the phCoVs might originate from IBV through interspecies transmission from chickens to pheasants, before gaining increased tissue tropism, adaptation capacities, and disease-causing behaviors in pheasants during intraspecies transmission.