| About 18 Haemophilus paragallinarum (Hpg) strains were isolated and identified in different sites, there are 3 B serovar strains in them, indicating the new epidemiological characteristics of infectious coryza in China. In order to resolve the field problems, analysis the reasons for immunity failure, the protection ability against B serovar of chickens immunized with different A+C vaccine were studied by challenging and antibody test, the results showed that, vaccines from different producer got different efficacy, 3 products in 5 gave good protection to challenge with A or C Hpg, but failed to gave good protection against challenge with B strain, and there is no obvious correlation between A or C antibody titer and protection rate for serovar B. Strain SD-1 is a A serovar variant with enhanced pathogenicity.Regarding the infection of serovar B and the virulent variety of A serovar, also to analysis the molecular mechanism of the variations among isolates, the genes encoded Hpg hemagglutinin antigen were coloned, sequenced and compared with the published sequences for reference strains, the results demonstrated that, except for the similarity between Hp8 and 0221, SD-1, DL-1 and TJ-1 containing 3 accessorial bp, the homogencity between the reference strains and native isolates was also decreased, the phylogenetic tree indicated these 3 isolates belonged to the same branch and there were some new molecular characteristics in the strain prevalent in China, the accessorial 3 bp was most likely the reason to the alteration for antigenicity and pathogenicity.In order to prevent the infection of serovar B and get reference for the development of trivaluent vaccine, the antigenicities of the B serovars were compared with challenging and antibody test, the results showed that there are some different among the strains from different sites. TJ-1 immunized chicken achieved an 90%, 91.4% and 63.6% protective rates for the challenge against TJ-1, SD-1 and BJ-1 respectively, so TJ-1 could be the most suitable vaccine strain at this time. According to results for antigenic comparation, 3 lots of trivaluent vaccine were prepared (TJ-1 strain was used as B serovar vaccine strain) and their safety and efficacy were also tested. There is no obvious change in appetite and spirit of the chickens injected with 2.0 ml vaccine, there is also no significant pathological damage being observed in vitro after 2 weeks postinjection, the vaccinated chickens achieved 100%, 94.4% and 93.3% protective rates to the challenge against A, B, C high virulent strain. We also detected high level of antibodies to B-ELISA, SPA and HI in the sera from vaccinated chickens, all the results demonstrated the good safety and efficacy of the the developed trivaluent vaccine.
|
PDF Full Text Request