Efficacy of a recombinant vaccine against pasteurellosis in chickens and ducks

Pasteurellosis or fowl cholera (FC), is an economically-important poultry disease caused by Pasteurella multocida serotype A. In ducks, it is caused by Riemerella anatipestifer. Outbreaks of FC is frequently reported, suggestive of inefficacious vaccine. In this study, recombinant cells carrying OMP36 gene of Pasteurella multocida A:1 was prepared as a killed vaccine to test against pasteurellosis in chickens and ducks. A total of 325 chickens and 125 ducks were selected and divided to 4 groups based on the types of immunization. Groups 1, 2, 3, and 4 were administered with the recombinant vaccine, control E. coli without insert, commercial FC vaccine, and sterile PBS, respectively. A booster dose was administered after 2 weeks. Each group were then further divided to 4 subgroups based on birds and challenge strain. A challenge trial was conducted against P. multocida A:1, A:3, or A:1,3 for the chickens; and P. multocida A:1 and R. anatipestifer for the ducks. Clinical signs were observed and serum samples were collected weekly for determination of IgG antibody levels. Birds with severe clinical signs were euthanized for necropsy. Following immunization of chickens, IgG increased at week 1 and continued to increase after booster vaccination at week 2, and peaked at week 4 for both recombinant and commercial vaccines. The recombinant vaccine stimulated higher level of antibody in chickens. Following challenge, the recombinant vaccine provided excellent homologous (21/25; 84%) and crossprotection against P. multocida serotype A:1,3 (23/25; 92%) but provided low cross-protection against P. multocida serotype A:3 (11/25; 44%). In ducks, the recombinant vaccine provided moderate protection (14/25; 56%) compared to the excellent protection provided by the commercial vaccine (23/25; 92%). All euthanized birds showed typical clinical signs and gross pathology of FC. In conclusion, the recombinant vaccine is suitable against pasteurellosis in chicken, being more superior compared to the commercial vaccine. However, it provides poor protection against R. anatipestifer infection in ducks.