Immune Response in Chickens to Infectious Bronchitis Virus, Strain 33 I. Response to Beta-Propiolactone-Inactivated Virus

Abstract

Immune response in susceptible White Leghorn chickens was studied following vaccination with avian infectious bronchitis virus, strain 33 (IBV-33), inactivated by beta-propiolactone (BPL). Criteria for the immune response were plaque-reduction neutralization-index (PR-NI) titers of 1.5 or greater, absence of respiratory signs, and failure to isolate virus from selected tissues following challenge. Three groups of chickens were given 2 doses at a 4-week interval of BPL-inactivated IBV-33 by the following methods: 1) aerosol exposure; 2) subcutaneous (SC) inoculation; and 3) aerosol exposure and SC inoculation concurrently. Significant levels of virus-neutralizing antibodies to 3 strains of the Massachusetts type of IBV were detected 2 weeks following the second dose in birds vaccinated by methods 2 or 3. Respiratory signs were observed in all birds following challenge by contact with infected birds. Virus isolation attempts were successful from trachea, lung, and kidney tissue of the controls and the aerosol vaccinates. Kidney tissue of SC-inoculated birds yielded no virus, while tissues from half of the birds vaccinated by method 3 yielded no virus. No correlation existed between virus isolation attempts, virus-neutralizing antibody titers, or intracellular IBV antigens. The best immune response was induced by aerosol exposure and concurrent SC inoculation of BPL-inactivated IBV-33.