Duck
plague (DP) is a severe disease caused by DP virus (DPV). Control of the disease is recognized as one of the biggest challenges in avian medicine. Vaccination is an efficient way to control DPV, and an
attenuated vaccine is the main routine
vaccine. The attenuated DPV
vaccine strain CHa is a modified live
vaccine, but the systemic and mucosal immune responses induced by this
vaccine have been poorly understood. In this study, the immunogenicity and efficacy of the
vaccine were evaluated after subcutaneous immunization of ducks. CD4(+) and CD8(+) T cells were counted by flow cytometry, and humoral and mucosal Ig
antibodies were analyzed by
enzyme-linked
immunosorbent assay (ELISA). The results showed that high levels of T cells and Ig
antibodies were present postimmunization and that there were more CD4(+) T cells than CD8(+) T cells. Titers of humoral
IgG were higher than those of humoral
IgA. Local
IgA was found in each sample, whereas local
IgG was found only in the spleen, thymus, bursa of Fabricius, harderian gland, liver, bile, and lung. In a protection assay, the attenuated DPV
vaccine completely protected ducks against 1,000 50% lethal doses (LD50) of the lethal DPV strain CHv via oral
infection. These data suggest that this subcutaneous
vaccine elicits sufficient systemic and mucosal immune responses against lethal DPV challenge to be protective in ducks. This study provides broad insights into understanding the immune responses to the attenuated DPV
vaccine strain CHa through subcutaneous immunization in ducks.