Experimental iron-inactivated Pasteurella multocida A: 1 vaccine adjuvanted with bacterial DNA is safe and protects chickens from fowl cholera

Fowl cholera is a serious problem in large and small scale poultry production. The present study describes the development and testing of an inactivated whole-cell, low-cost, safe, and effective vaccine for fowl cholera based on a previous work (Vaccine 23:5590–5598). Pasteurella multocida A: 1 grown in the presence of low FeCl₃ concentrations, inactivated with higher concentrations of FeCl₃, and adjuvanted with bacterial DNA from P. multocida B: 2 containing immunostimulatory CpG motifs protect chickens with a lethal P. multocida A: 1 challenge. Chickens were immunized with two whole-cell inactivated vaccine doses at 4 weeks apart and challenged 4 weeks after booster immunization. Experimental vaccines were pure, easy injectable, and caused very little distress in chickens due to their aqueous consistency. Vaccines and bacterial DNA (bDNA) posed no safety problems when chickens were injected subcutaneously (s.c.) with a single, double, and overdose of these preparations. Immunized chickens produced systemic IgY antibodies (Ab) responses and vaccine adjuvanted with bDNA protected 100% chickens from lethal intrapertoneal (i.p.) P. multocida A: 1 challenge. This work suggests that use of bDNA as an adjuvant can improve the cost-effectiveness of inactivated veterinary vaccines for their use in developing countries. Our future studies will focus on safety and potency evaluation of experimental and current vaccines using bDNA as an adjuvant.