Isolation, pathogenicity, and H120 protection efficacy of infectious bronchitis viruses isolated in Taiwan.

Seven isolates of infectious bronchitis (IB) virus (IBV) were isolated from two breeder farms and five broiler farms in Taiwan in 1992. The cardinal signs of disease in breeders were egg production drops and watery albumen, and those in broilers were respiratory distress and renal urate deposition or death. All diseased chickens had been vaccinated with IB vaccines (mostly H120). The viruses were isolated and identified by chicken embryo inoculation and electron microscopy. The genomes of the isolates were extracted and amplified by polymerase chain reaction; the restriction fragment length polymorphism analysis suggested that the genotypes of the present IBV isolates were different from the eight reference strains. One-day-old specific-pathogen-free chicks were inoculated with the field isolates in order to test the virulence of those isolates. Respiratory distress and depression commenced at 24 hours after inoculation. Two of the seven isolates were found to be highly virulent, causing 50% or more mortality in inoculated chicks. Vaccine protection tests showed that H120 could protect chickens against challenges with four of six field isolates.