A NOVEL VARIANT OF AVIAN INFECTIOUS-BRONCHITIS VIRUS RESULTING FROM RECOMBINATION AMONG 3 DIFFERENT STRAINS

An antigenic variant of avian infectious bronchitis virus (IBV), a cor onavirus, was isolated and characterized. This strain, CU-T2, possesse s a number of unusual features, which have not been previously observe d in IBV. The S1 glycoprotein of CU-T2 carries virus-neutralizing and serotype-specific epitopes of two IBV serotypes, Arkansas (Ark) and Ma ssachusetts (Mass). Sequence analysis revealed that the virus, origina lly an Ark serotype, has acquired the Mass-specific epitope by mutatio n(s). This provides evidence that point mutations may lead to generati on of IBV antigenic variants in the field. It was further observed tha t two independent recombination events involving three different IBV s trains had occurred in the S2 glycoprotein gene and N protein gene of CU-T2, indicating that genomic RNA recombination in IBV may occur in m ultiple genes in nature. It was especially significant that a sequence of Holland 52 (a vaccine strain) had replaced half of the N gene of C U-T2. This proves that recombination among vaccine strains is contribu ting to the generation of IBV variants in the field. Based on these ob servations it is predicted that every IBV field isolate could have uni que genetic nature. Therefore, several recently reported diagnostic an d serotyping methods of IBV which are based on dot-blot hybridization, restriction fragment length polymorphism (RFLP), and polymerase chain reaction (PCR), may not reveal the true antigenic and/or genetic natu re of IBV isolates, and may in fact yield misleading information.