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.
Evaluation of ciliary movement in tracheal rings to assess immunity against infectious bronchitis virus.
Chickens vaccinated at one and 14 days of age with a live vaccine containing the Massachusetts and Connecticut strains of infectious bronchitis virus were protected against challenge with a Massachusetts strain administered at 5 weeks of age. The virus recovery method in which tracheal swabs taken 4 days post-challenge were used to inoculate chicken embryos was compared with the method based on ciliary activity in tracheal explants. The results showed that evaluation of ciliary activity effectively measured immunity to infectious bronchitis virus. Serological results obtained in a microneutralization test using chicken embryo kidney cells correlated with the immune status of the birds as well as with the alpha neutralization results obtained using chicken embryos.
Cross-immunity in chickens using seven isolates of avian infectious bronchitis virus.
Groups of 75 chickens were each infected with one of 7 isolates of infectious bronchitis virus (Mass 41, Holland 52, SE 17, Ark 99, Clark 333, JMK, and Florida). Following recovery, they were challenged along with susceptible controls to the homologous and 6 heterologous isolates. Cross-immunity was determined by virus recovery 4 or 5 days post-challenge. Challenge with the homologous isolate resulted in 90-100% protection. Challenge with heterologous isolates gave variable results and an overall average resistance of 38%. The SE-17-recovered chickens had a 50% protection, whereas the Holland-52-recovered chickens ahd a 13.3% protection.