Chitosan/alginate microparticles for the oral delivery of fowl typhoid vaccine: Innate and acquired immunity.

Oral fowl typhoid (FT) vaccine is necessary for improved flock vaccinations and economic growth. This study was undertaken to evaluate the immune responses of birds given oral fowl typhoid vaccine coated with chitosan/alginate microparticles and comparing it with the conventional subcutaneous route of administration. Preliminary studies were done to evaluate the particle size, encapsulation efficiency and agglutination. Sixty day-old chicks were divided into three groups of twenty birds each. This comprised a negative control group NEG 451 (non-vaccinated and non-challenged used as control for cytokine quantification), SC 634 (live 9R vaccine by the injection route) and OCV 567 (live 9R vaccine coated with chitosan/alginate microparticles). Vaccination was done at 10 weeks and 14 weeks of age followed by challenge at 16 weeks of age. IgG was measured using ELISA. mRNA fold expression of IFN-γ in spleen was calculated using qRT-PCR. Particle sizes ranged between 0.55 µm and 10 µm. Encapsulation efficiency was above 60%. ELISA showed E-values of 0.10 ± 0.14, 0.07 ± 0.01 and 0.02 ± 0.01 for OCV 567, SC 634 and NEG 451 respectively after primary vaccination. Also E-values were 0.25 ± 0.16, 0.19 ± 0.04 and 0.0008 ± 0.005 for SC 634, OCV 567 and NEG451 respectively after boost vaccination. The expression of IFN-γin spleen using 2-ΔΔ CT calculation was upregulated with values of 1.97 and 0.75 for OCV 567 and SC 634 respectively. After challenge with the 85-kb virulence plasmid SG9, there was 100% protection of the birds in both OCV 567 and SC 634 groups with no mortality. In conclusion, there was no significant difference at p < 0.05 of the means ± SD in immune responses between the oral fowl typhoid vaccine coated with chitosan/alginate microparticles and the subcutaneous route of administration. However, it is noteworthy to mention that the protective efficacy of the oral route is due to the chitosan/alginate biopolymers which coated the vaccine preventing destruction in the gastrointestinal tract.