Genotypic characterization of infectious bronchitis viruses from India

Infectious bronchitis (IB) is an acute, highly contagious and economically important disease of chickens. In India, IB vaccinations are carried out using vaccines belonging only to the Massachusetts 41 (Ma41) serotype. However, the vaccine strain used may not always be protective and it becomes necessary to continuously monitor the viruses causing disease. There has been anecdotal evidence of IB outbreaks even in vaccinated flocks in India. Tissue suspensions were inoculated intra-allantoically into 11-day-old embryonated chicken eggs. The allanotic fluids collected at 48 h post-inoculation (PI) were used in reverse transcription-polymerase chain reaction (RT-PCR) to amplify a part of S1 gene. The partial S1 gene products obtained were sequenced. All the seven isolates had sequences with 94.8-98.8% homology with the vaccine strain, H120. The cross-neutralization tests were used to identify the serotype of the field isolates. All the four isolates showed greater than 50% antigenic relatedness value indicating their classification in Massachusetts’s serogroup. The commercial vaccines conferred protection to the viruses isolated.