EVALUATING THE EFFICACY OF A POLYVALENT INFECTIOUS CORYZA VACCINE AGAINST EMERGING AVIBACTERIUM PARAGALLINARUM SEROTYPES IN EGYPT
Infectious coryza (IC), an acute respiratory disease of chickens, is caused by Avibacterium paragallinarum (A. paragallinarum). Herein, we evaluated the efficacy of a polyvalent oil adjuvant IC vaccine against the circulating A. paragallinarum field isolates recovered from chickens in Egypt. Thirty two A. paragallinarum isolates were recovered from 165 chicken samples (19.39%) then identified by phenotypic and polymerase chain reaction (PCR) assays. Serotyping by hemagglutination inhibition (HI) test revealed the identification of both serotypes A and C. The results of antimicrobial susceptibility testing affirmed that all A. paragallinarum isolates were multidrug-resistant (MDR) with multiple antimicrobial resistance (MAR) indices ranged from 0.6 to 0.8. Protection of chickens against A. paragallinarum field isolates of serotypes A and C using polyvalent inactivated oil adjuvant vaccine was evaluated followed by bacterial challenge. An experimental study of 90 specific-pathogen-free (SPF) White Leghorn chickens (8-weeks-old) was divided into nine groups; three groups served as non-vaccinated challenged, five groups were used for vaccine evaluation, and the last one was non-vaccinated and non-challenged group. Serum samples were collected regularly during 91 days post 1st vaccination to evaluate the immune response based on the HI antibody titer. The effective protection of the polyvalent inactivated vaccine against the drug resistant field isolates was indicated by the antibody titers that reached the maximum levels at the 5th week post vaccination. Moreover, 80 to 90% survivability percentages were recorded for A. paragallinarum serotypes C, and A field isolates, respectively. A strong positive correlation (R = 0.9628, P < 0.001) was found between the mean HI titer and the level of protection against the challenge. Furthermore, low level of bacterial shedding post-vaccination along with bacterial counts below the infectious dose (2x102 - 6x103 CFU/mL) implying the role of vaccine in decreasing the chance of infection. Evidence from this study confirmed the effective protection of IC vaccine as a proper prophylactic tool against MDR A. paragallinarum field isolates of serotypes A and C.
Key words: A. paragallinarium, Infectious coryza, Vaccine, Hemagglutination inhibition.