Molecular epidemiology of infectious bronchitis virus in The Netherlands.

Twelve Dutch isolates and the M41 strain of infectious bronchitis virus (IBV), a coronavirus of chickens, were characterized by cross-neutralization and T1 finger-printing to elucidate their evolutionary relationship. The T1 fingerprinting showed that the Dutch isolates formed two clusters. The first cluster contained strains H52, H120, D387, V1259, V1385 and V1397; the estimated sequence homology is 99%. Cluster two comprised strains D207, D274, D212, D1466, D3128 and D3896, which have about 95% sequence homology. The M41 virus did not belong to either cluster. The four different serotypes which arose in the late 1970s belonged to cluster two and appeared to be different from the vaccine strains (H52 and H120) used at that time. This indicates that the strains were newly introduced and could have arisen from a common virus. On the other hand, three recently isolated field strains were genetically closely related to the vaccine strains H120 and H52 (cluster one), suggesting that these live vaccine strains themselves could have given rise to these serologically altered field isolates. The data are relevant to the development of new vaccine strategies.