Imperfection of Commercial InactivatedVaccine AgainstInfantis During Induced Molting in Chickens and Proposed Evaluation Method.

Abstract

In the present study, we evaluated the continuance and efficacy of inactivated vaccine againstInfantis (SI) in chickens raised on a commercial farm. Chickens (88-days-old) were inoculated with 1 or 0.5 doses of commercially available trivalent inactivatedvaccine; anti-SI antibody titer was examined continuously for 11 mo thereafter. Molting was induced 11 mo after vaccination, and SI was administered orally. SI colony-forming units (CFUs) were measured in cecal feces, cecal contents, liver, and spleen samples. Anti-SI antibodies in the 1 dose vaccination group could be detected in at least 90% of cases until the end of testing. SI discharge was significantly reduced in birds treated with either dose of vaccine. However, SI CFUs were elevated in the induced molting group, regardless of vaccination dose, particularly in the cecal feces, cecal contents, and spleen. Thus, the vaccine provided remarkable protection against SI infection under ordinary rearing methods but not during induced molting. To achieve sufficient SI protective efficacy, we recommend inoculation with 1 dose of vaccine. Moreover, the efficacy of inactivatedvaccine is recommended to be evaluated by challenging chickens with livein addition toantibody titration.