Oral immunization with EDS-76 virus encapsulated in biodegradable PLG microspheres elicits systemic immune responses in poultry

White Leghorn layer chicks were immunized orally with the egg drop syndrome-76 (EDS-76) virus encapsulated in poly (D, L-lactide-co-glycolide) PLG microspheres. The systemic antibody responses as well as cell-mediated immunity (CMI) were evaluated up to 4-wk post immunization (PI) after which the immunized chicks were challenged with virulent EDS-76 virus at the dose of 0.5×10⁷ ElD₅₀/chick. It was found that the microencapsulated EDS-76 virus could induce satisfactory levels of virus specific haemagglutination inhibition (HI) antibody with a mean titre of (log₂) 7.0 at 30 days PI (DPI) and also the circulating IgG showing the peak titre of (log₁₀) 3.77 (i.e, 6000) by indirect ELISA at 3^rd wk PI. The antibody levels induced by the microencapsulated EDS-76 virus were comparatively lower than that induced by the conventional killed oil adjuvanted EDS-76 vaccine, which was administered intramuscularly. However, the antibody levels in the immunized chicks were steadily maintained up to 4-wk PI and also after the challenge infection. The systemic CMI in terms of proliferation of the peripheral blood lymphocytes in the immunized chicks was also found to be significantly higher (p < 0.5) as compared to that of the unvaccinated control and was maintained up to 4-wk PI as well as 3 wk post challenge. Hence, it is concluded that microencapsulated EDS-76 virus can elicit humoral as well as systemic CMI response after oral delivery.