Transmission of infectious bronchitis virus within vaccinated and unvaccinated groups of chickens.
The aim of this study was to determine whether vaccination against infectious bronchitis virus (IBV) reduces virus transmission, i.e. to test whether IBV transmission among vaccinated chickens is significantly reduced compared to that among unvaccinated chickens. In two vaccinated and two unvaccinated groups of SPF chickens, a standard measure for virus transmission, the reproduction ratio (R) was determined. R is defined as the average number of new infections caused by one typical infectious individual during its entire infectious period. A single vaccination by eye-drop with IBV H120 reduced the transmission of the IBV challenge virus among the vaccinated chickens (estimated R = 0.69, s.e. = 0.33) significantly (P < 0.05) compared to the transmission among the unvaccinated chickens (estimated R = 19.95, s.e. = 12.41). The possible implications for further study, including selection or development of vaccines are discussed.
Molecular Characterization and Pathogenicity of Infectious Bronchitis Coronaviruses: Complicated Evolution and Epidemiology in China Caused by Cocirculation of Multiple Types of Infectious Bronchitis Coronaviruses
Objective: To monitor and study the molecular epidemiology, evolution and pathogenicity of infectious bronchitis viruses (IBVs) in China in recent years and further our knowledge of the evolution of IBVs. Methods: Thirty-seven IBV isolates were isolated from commercial chickens in China. The isolates were characterized by RT-PCR, sequencing, typing and analyzing the entire S1 gene. In addition, 4 selected IBV isolates were used to experimentally infect the specific pathogen-free chickens to study their pathogenicity. Results: Three types of IBV have been cocirculating in chicken flocks in China in recent years. Unique insertions and deletions in S1 protein regions were identified among different types of IBV. Moreover, a new IBV strain was isolated and identified in a layer hen. S1 gene analysis showed that a recombination event had occurred in the virus’s evolutionary process. In addition, experimental infection has shown that IBV isolates have been nephropathogenic in China in recent years. Conclusion: Mutations, insertions, deletions and recombination of the S1 protein gene contribute to the genetic diversity of IBV in China. Cocirculation of multiple types of IBV in field conditions in China renders its epidemiology and evolution very complicated, indicating the necessity for development of new vaccines or vaccine strategies.
Serologic and cross-protection studies with several infectious bronchitis virus isolates from Delmarva-reared broiler chickens.
Five isolates, from broiler-type chickens, capable of causing acute respiratory disease were identified as infectious bronchitis virus (IBV). The agar-gel precipitin (AGP) test was effective in identifying the isolates as IBV. Virus-neutralization (VN) and cross-challenge tests indicated two of the isolates to be Massachusetts types and one to be a JMK type. The remaining isolates were different from strains normally encountered in chickens reared on the Delmarva Peninsula. One isolate, although serologically similar to the Connecticut strain, was able to infect Connecticut-virus-immune chickens. Another isolate was similar to Arkansas 99, a strain not previously reported in Delmarva.