LONG-TERM STUDY OF PATHOGENESIS OF INFECTION OF FOWLS WITH 3 STRAINS OF AVIAN INFECTIOUS-BRONCHITIS VIRUS

Groups of 3 wk old Rhode Island Red chicks were infected with T, H52 and H120 strains of avian infectious bronchitis virus (IBV) by either drinking water (DW) administration or i.v. injection. From 17-94 days after infection all birds appeared normal but between 94-227 days, when the experiment was terminated, 15/27 T strain, 2/23 H52 and 4/23 H120 infected birds died. Post mortem examination revealed gross kidney lesions in all but 1 of the birds which died and in 2 of the surviving birds killed at the end of the experiment. Virus was recovered from the feces or cecal tonsils of all but 2 of the dead birds tested. No virus was isolated from the 12 T strain infected birds alive 227 days after infection but 7/20 H52-infected and 5/19 H120-infected survivors had virus in the feces. The immune response (hemagglutination inhibition (HI) titer) of individual birds, was similar in pattern for all 3 viruses, with an early peak at 28 days after infection followed by a gradual rise to a titer which was maintained throughout the rest of the 227 days observation period. One hundred and fourteen days after infection, T strain infected birds which died, or showed kidney lesions at 227 days, had significantly higher HI titers than those that remained normal until 227 days after infection. The route of infection had little effect on the incidence of deaths or virus isolation and differences in the immune response were only seen in the H120 infected birds where the IV infected birds had higher HI titers than the DW infected birds.