Tissue Culture and Attenuation of Avian Infectious Bronchitis Virus

II. Safety and Immunogenicity of Attenuated Virus

Abstract

The Nerima strain is infectious bronchitis virus attenuated by passage in chicken kidney cells. It was proved to be high in safety, since it produced no reaction to 3-day-old chicks showing an antibody titer of 0.5≥or 30-to 70-day-old chicks with no antibody.
The amount of virus required for immunization was 10^4.0 TCID50≤per capita. Neutralizing antibody began to increase 12 days after administration and reached a maximum 18 days. It was maintainedat a high level for 172 days or more. Contact infection by cohabitation was established up to 10 days after administration.
Attenuated virus was recovered from the trachea, lung, and an emulsion of liver, spleen, and kidney, although it was small in amount.
Attenuated virus was examined for recurrence of pathogenicity. The virus was successfully subjected to five passages in chickens. The resultant virus showed no enhancement in pathogenicity for chicks. Therefore, this virus is assumed to be available as strain for the preparation of live virus vaccine.