Comparison of vaccines against infectious bursal disease

Abstract

A comparative study was undertaken of 9 products from 7 different sources intended for use as vaccines against infectious bursal disease of chickens (IBD). A range of properties was found in laboratory tests for safety, efficacy and immunosuppressive effect. No vaccine caused clinical disease after administration to chicks at 7 days of age, but one caused a significant impairment of weight gain, and when given to day-old chicks caused some morbidity and deaths. Most vaccines affected the bursa of Fabricius and histological examination of this organ revealed varying degrees of tissue damage which correlated with the reduction in size of this organ. The effects with the different products ranged from no damage to damage almost as rapid and severe as that produced by a fully virulent field strain of the agent. Selected products which differed in their effect on the bursa were tested for their immunosuppressive properties by assessing the response to live Newcastle disease vaccine administered after the IBD vaccine. The effect on the response to Newcastle disease vaccine was found to be correlated with the degree of tissue damage. Variations in the ability of the vaccines to protect against IBD challenge were also found, but these did not depend on the degree of damage to the bursa. These studies enable proposals for standard tests for IBD vaccines to be formulated in respect of safety, potency and lack of immunosuppressive effect. Only 2 of the 9 vaccines tested satisfied these standards.