Comparison of Ciliary Activity and Virus Recovery from Tracheas of Chickens and Humoral Immunity after Inoculation with Serotypes of Avian Infectious Bronchitis Virus

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Abstract
Cross-protection tests with homologous and heterologous serotypes of infectious bronchitis virus (IBV) were used to compare ciliary activity and virus recovery from tracheas of chickens. Validation of this technique included correlating the neutralization indices of antiserum obtained from some infected birds. Chickens were inoculated intratracheally with the JMK or Connecticut (Conn) IBV serotype. Infected and uninfected groups were challenged 3 wk later by the same route with homologous and heterologous virus. The JMK strain provided immunity against homologous challenge and the Conn strain, as indicated by good ciliary activity and lack of challenge virus recovery. The Conn strain provided only homologous protection as ciliostasis occurred and virus was recovered after challenge with the JMK strain. In each case, antiserum to immunizing virus neutralized only the homologous virus. Controls were uniformly susceptible and lacked neutralizing antibody. A similar experiment with the Ark 99 serotype and a recent isolate (397) of IBV revealed complete cross-protection of the tracheas. Antiserum to each virus neutralized the homologous and heterologous virus in each case in reciprocal tests. Thus, these 2 viruses are closely related. Complete agreement between ciliary activity and virus isolation indicates that ciliary activity is a reliable, objective criterion for judging tracheal immunity in cross-protection tests.