Abstract

Aim/Background: Live attenuated infectious bursal disease (IBD) vaccines are widely used to prevent and control IBD in poultry. However, increasing reports of IBD outbreaks in vaccinated flocks raise concerns about the efficacy of commercially available conventional vaccines. A comprehensive understanding of vaccine failure mechanisms is essential for establishing quality standards for IBD vaccine immunogenicity. This study therefore evaluated the sterility, identity, potency of six live attenuated commercially available IBD vaccines and their immunogenicity in naive Leghorn chicks.

Methods: The vaccine infectious titre was determined using a simplified median tissue culture infectious dose (TCID50) assay in chicken embryo fibroblast cultures. Vaccine sterility was performed by inoculating 500ul of reconstituted vaccine in thioglycolate broth and tryptose Soy broth and incubating at 25 oC and 37 oC for 14 days and observed daily for presence of turbidity. Identity test was determined using a commercial real-time polymerase chain reaction kit (kylt IBDV screening), while a quantitative indirect enzyme linked immunosorbent assay (ELISA) kit (IDVet, Germany) was employed according to manufacturer’s protocol to determine the immunogenicity of the vaccines.

Results: Viral content assays from chicken embryo fibroblast revealed that only two vaccines contained a minimum viral titre of >102.5 TCID50/dose, the threshold to elicit an immune response. At 14 days post vaccination (dpv) only chickens in group C developed detectable IBD antibodies. However, by 28dpv (14 days after the second vaccination) all groups exhibited sufficient protective antibody titres compared to chickens in the control group. However, antibody levels waned in group A by 42 dpv highlighting variability in vaccine efficacy.

Conclusion: These findings underscore the importance of routine antibody profiling in chickens before, during and after vaccination of poultry as well as stringent quality testing of commercially available vaccines in Nigeria to ensure effective disease prevention.

Key words: Live attenuated IBD, Sterility, Potency, Quality Assessment, Immunogenicity