Immunoprotective role of LaSota vaccine under immunosuppressive conditions in chicken challenged with velogenic avian avulavirus-1.

The first objective of the present study was to evaluate if the antibodies induced by the live LaSota and killed Newcastle disease (sub-genotype VIIi) vaccines protect the chickens against exposure with pathogenic avian avulavirus-1 (AAvV-1) of chicken and/or pigeon origins. The second objective was to study the effect of vaccines on stressed birds (dexamethasone, aflatoxin, and heat stressed) with respect to antibody production and protection against pathogenic AAvV-1 challenge. Sixty-one-day-old Hubbard chickens were divided into six groups (gA-gF) with ten animals each. All the groups received LaSota (105 EID50 , 0.1 ml per chick) on days 7 and 27 via eye drop and one intramuscular injection of a killed vaccine (sub-genotype VIIi) (107.5 EID50 , 1 ml) on day 18, except the control birds received the PBS only. Moreover, group gC-DEX received dexamethasone intramuscularly at a dose rate of 1-mg/kg body weight daily; gD-AFLA had received aflatoxin as oral gavage at a dose rate of 30 ppb daily, and gE-HEAT was kept under heat stressed (38 °C) till challenged. All the groups were challenged with AAvV-1 strain of chicken origin of sub-genotype VIIi, except the group gA-pigeon was challenged with pigeon-origin strain (sub-genotype VIm). The result showed that the gA-pigeon and gB-chicken vaccinate showed 100% and 80% protection. The immunosuppressive birds produced low pre-challenge HI titer, and protection was observed at 40%, 50%, and 70% in gC-DEX, gD-AFLA, and gE-HEAT, respectively. Our findings suggest the stress factors such as aflatoxin in the feed and dexamethasone are immunosuppressive in nature and suppress the immune response and its associated protective role during infection.