Immunogenicity of Infectious Coryza vaccine against a native isolate of Avibacterium paragallinarum from Iran

Infectious Coryza (IC) an acute respiratory disease of chicken that caused by Avibacterium paragallinarum( Av.P). Immunity offered by a commercial IC killed oil vaccine against a native field isolate of Av. P serogroup A of Iran was studied by designing a vaccination / challenge experiment. 36 SPF birds of 14 weeks old were randomly divided into three separate groups. One group was vaccinated by two doses within 2 weeks by a commercial vaccine. After two weeks of last vaccination this group and the second one were challenged with 1×10 8 CFU/ml bacterial suspension prepared from fresh 24 hours cultured of Av. p through infra orbital sinus. The third group kept as control only received phosphate buffer saline. Three birds from each group were bled for serum sample collection on days of 2, 4, 6 and 8 after challenge. On Clinical observation of first group, mild swelling on inoculation site was developed on second day of experiment that gradually disappeared on days after. In second group on post infection day (PID) of 2, nasal discharge and facial swelling that extended to become bilateral beside tracheal rales were noticed in all bird throughout the experiments days. For all birds Sero-conversions monitored by serum plate agglutination (SPA) and agar gel precipitation (AGP) test using antigen prepared from 24 hours culture of bacterium. While birds of control remained negative, All bird of first group shown positive serum reaction by SPA and AGP tests while in second group, only SPA becomes positive after 6 PID. In conclusion, this native isolate have an antigenic relationship with vaccine contained strains and the commercial vaccine can prevent must clinical sign in infected birds. However, more studies needed to verify serovar identity of isolate and reach a conclusive outcomes about efficacy of currently used vaccine in country.