Background: Haemophilus paragallinarum is a causative agent of avian infectious coryza and has been classified into serovars A, B, and C by Page scheme. HagA protein was identified among strains with slightly differences in their gene sequences. It suggested that HagA might be a potential candidate for vaccine development. Methods: The recombinant HagA derived from Taiwan isolates A9 (serovar C) was expressed by pET system. The compositions of vaccines are listed in Table1. All groups were immunized at 6 and 9 weeks of age. At 11 weeks of age, the chickens were challenged intranasally with 1010 CFU of live A9. The chickens were monitored for 1 week for clinical signs of infectious coryza. Results: All chickens vaccinated intramuscularly with 108 cells developed serum haemagglutination inhibition (HI) antibodies (1:10 to 1:160) and were protected against A9 infection. No unimmunized chickens developed serum HI antibodies, all showed clinical signs of coryza after challenge. Further, no difference was found in serum HI antibody titers between the chickens infected with 105 cells (1:5 to 1:20) and those inoculated with rHagA proteins (1:5 to 1:20). The chickens showed clinical sings of coryza developed the HI titer of 1:5 or less. The rHagA protein protected 71% of immunized chickens against 1010 cells of live A9. Among the groups immunized with the whole bacteria, 100% (vaccinated with 108 cells), 71%(vaccinated with 105 cells), 57% (vaccinated with 102 cells) were protected. Western blots of the chicken sera indicated that protected animals produced HagA specific antibodies, while the unprotected chickens did not. Conclusion: All chickens injected with vaccines developed serum HI antibodies and were protected against H. paragallinarum challenge with different rates. No chickens that developed HI titers of 1:10 or greater showed any clinical signs of coryza. High dosage of the whole cell killed H. paragallinarum vaccine (108 CFU/dose) still showed the best protection
關聯:
American Society for Microbiology 106th General Metting
