Epidemiology Studies On Hemophilus Parasuis And Screening Of The Vaccine Candidate Strains

Haemophilus parasuis (HPS), a member of the family Pasteurellaceae, is the causative agent of Gl?sser's disease which characterized by polyserositis, arthritis, and meningitis. It has been one of important diseases which lead to significant economic losses in the swine industry in recent years.From 2007 to 2009, a total of 52 strains of HPS were isolated from clinically diseased pigs in 7 different provinces of China. All were identified as HPS based on morphology, biochemical tests and polymerase chain reaction (PCR). Serotyping for these isolates were conducted by gel diffusion test (GD) and indirect haemagglutination (IHA) based on the heat stable antigen. By combining the GD and IHA results, serovar 5 (13 strains), serovar 4(11 strains), serovar 12 (9 strains), and serovar 13 (8 strains) were the most prevalent serovars in the provinces above-mentioned, followed by serovar 14 (3 strains), serovar 3(3 strains) and serovar 10 (1 strains), while 4 strains were nontypable.A PCR-RFLP method on the basis of gene tbpA was employed to study epidemiology on HPS strains in molecular level. 13 different genotypes for the reference strains of the 15 known HPS serovars and 13 RFLP patterns for 52 HPS clinical isolates tested were produced, respectively. Different RFLP patterns could be found in the strains presenting uniform serotype. Genotypes DBN (34.6%) and ABN (23.1%) were the most prevalent in these strains from different provinces in recent 2 years. The results suggested that the PCR-RFLP for HPS based on tbpA gene has better sensitivity and typeability than that of serotyping method, also suggested that there are a high heterogeneity among HPS strains.High virulent strains of hps0910 (serovar 4), hps0814 (serovar 5) and hps0709 (serovar 12) among those predominant serovars of HPS in parts of China were selected by experiment infection to guinea pig and swine. Immunization experiments were conducted to further evaluate their immunogenicity. 3 groups of pigs immunized with different vaccines containing HPS strain hps0910 or hps0814 or hps0709 were respectively challenged intraperitoneal with source strains. 5 in 6 pigs of groups hps0910 and hps0814, all pigs of group hps0709 were protected, respectively. The results suggested that the strains of hps0910, hps0814and hps0709 can be candidates for development of an inactivated trivalent vaccine against Gl?sser's disease.