Isolation and characterization of a novel antigenic subtype of infectious bronchitis virus serotype DE072

Three infectious bronchitis virus (IBV) isolates, CU82792, CU82805, and CU82808, were recovered from sentinel chickens placed with three different layer flocks of a large commercial poultry farm in New York State. The three isolates were classified as members of the DE072 serotype on the basis of 1) their S1 genes could be amplified with only a modified primer designed for the DE072 serotype and 2) their restriction fragment length polymorphism patterns, after digestion with endonucleases HaeIII, BstyI and XcmI, were indistinguishable from that of DE072 virus. Additional characterization of one of the isolates, CU82805, revealed that its S1 gene bears approximately 96% identity at the nucleotide level and 94% identity at the amino acid level with DE072. Yet, in an in vitro reciprocal virus neutralization test, only a one-way neutralization was observed, i.e., antiserum to CU82805 neutralized DE072, whereas CU82805 was not neutralized by DE072 antiserum. Implications of these findings with regard to IBV diagnosis and immunization are discussed.