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.
Genetic Diversity of Avian Infectious Bronchitis Coronavirus in Recent Years in China
SUMMARY. Fifty-six isolates of avian infectious bronchitis virus (IBV) were obtained from different field outbreaks in China in 2010, and they were genotyped by comparison with 19 reference strains in the present study. The results showed that LX4-type isolates are still the predominant IBVs circulating in chicken flocks in China, and these isolates could be grouped further into two clusters. Viruses in each cluster had favored amino acid residues at different positions in the S1 subunit of the spike protein. In addition, a recombination event was observed to have occurred between LX4- and tl/CH/LDT3/03I-type strains, which contributed to the emergence of a new strain. The most important finding of the study is the isolation and identification of Taiwan II–type (TW II–type) strains of IBV in mainland China in recent years. The genome of TW II–type IBV strains isolated in mainland China has experienced mutations and deletions, as demonstrated by comparison of the entire genome sequence with those of IBV strains isolated in Taiwan. Pathogenicity testing and sequence analysis of the 3′ terminal untranslated region revealed that TW II–type IBV strains isolated in mainland China have a close relationship with the embryo-passaged, attenuated TW2296/95.
Serological comparisons of strains of infectious bronchitis virus using plaque-purified isolants.
SUMMARY Nineteen isolants of infectious bronchitis virus (IBV), including most of the recently reported new isolants, were adapted to chick kidney cell cultures. After plaque purification and the preparation of antiserums against purified strains, antigen interrelatedness was evaluated with cross-neutralization tests by the plaque-reduction technique. The results indicated that there are 7 serotypes current in the United States and that the Australian "T" strain is distinct from each of these. Antigenic variants occurred within some of these serotypes.