Protection from infectious bursal disease virus (IBDV)-induced immunosuppression by immunization with a fowlpox recombinant containing IBDV-VP2

Immunosuppression resulting from infectious bursal disease virus ( IBDV) infection has critical health and welfare implications for birds, yet it is incompletely understood and largely overlooked as a measure of vaccine efficacy. The ability of a fowlpoxvirus recombinant (fpIBD1) containing the VP2 protein of IBDV to protect against IBDV-induced immunosuppression was investigated by measuring the convalescent chicken's ability to mount antibody responses to IBDV infection, and to inactivated IBDV and salmonella vaccines. An immunoglobulin (Ig) M response, but no IgG response, occurred after IBDV infection. Uninfected chickens produced a sustained IgM response and some IgG response to inactivated IBDV vaccine, while in previously infected birds only a transient IgM response was detected. A moderate suppression of the response to a commercial salmonella vaccine was evident after IBDV infection, which was largely prevented by immunization with fpIBD1. These results indicate that measurement of immunosuppression could be a useful strategy for assessing the efficacy of vaccines to protect against the consequences of IBDV infection.