Comparative tests on safety and potency of IBA vaccines.

During a comparative test on the pathogenicity and immunogenicity of a non-adapted and an embryo-adapted IDA virus, following observations were made: 1) the non-adapted virus remained pathogenic as determined by weight loss and bursal lesions. Clinical signs and mortality did not occur. A change in the virulence did not occur during back passages; 2) the immunosuppressive effect of the non-adapted virus was diminished by maternal antibodies; 3) the embryo-adapted virus produced little pathogenicity as demonstrated by minor weight depressions. The vaccinated birds had no recognizable pathological lesions in the bursae. Immunosuppression with this virus was not observed; 4) the embryo-adapted strain was able to induce neutralizing antibodies in birds with or without maternal antibodies. However, precipitins were not detected; 5) immunization with the embryo-adapted strain after 8 days of age was protective whereas prior to that age it was not confirming the age susceptibility factor reported by Hitchner (1971); 6) no change in virulence occurred during back passages with both test materials.