Immunogenicity of a single intranasal dose of IBD vaccine based on Poly-Lactide-Co-Glycolide (PLG) microparticles in broiler chickens

In this study, immunogenicity of the microencapsulated IBD virus (intermediate strain) was investigated after intranasal delivery of the viral antigens incorporated in PLG microparticles. Although the size of virus entrapped microparticles ranged from 1–10 µm, majority were of less than 2 µm and they contained viral antigens to the extent of 1.4 to 1.7% by weight of microspheres. A single intranasal dose (75 µg) of the experimental microsphere vaccine was able to induce both mucosal and systemic immunity in poultry. The immunized chicks showed significantly higher levels of virus specific IgG with the peak titre of (log₁₀) 3.77 at the 3rd wk post-immunization (PI) and also protective levels of neutralizing antibodies (log₁₀ NI  2) up to 6-week PI, which were comparable to that of the conventionally vaccinated chicks. In the tracheal washings, considerably higher levels of virus specific IgA were detected with the peak titre 40 at the 3rd wk PI, which gradually decreased to 24 at 6th wk PI. Intranasal delivery of microspheres induced lymphocyte blastogenic response with peak stimulation index of (1.360±0.031) at the 3rd wk PI, which was significantly (p<0.05) higher than that of the unvaccinated control group. The immunized chicks also afforded resistance against challenge infection with virulent IBD virus, which was comparable to the conventional vaccine.