The Establishment Of Infection With Streptococcus Suis Serotype 2 In Mini-Swine Model And Study On Immunological Detection In Blood

Streptococcus suis is one of the fatal bacteria of swine, it may cause various diseases of swine. Streptococcus suis serotype 2 (SS2), in particular, is an important zoonosis as well, infecting the persons who are close to the contaminated porcine products. The virulence factors of streptococcus suis have been widely researched, but lots of uncertainty still remained. Capsular polysaccharide is the only admitted virulence factor.The mechanism of SS2 infections still remained indefinitely. Arguments were focused on the progress of meningitis caused by SS2. So far, some other pathogenic agents, which may cause meningitis as well, were considered references for SS2 infection research, the results of research of virulent meningitis, in particular, were the most concerned among them. The results of SS2 infection research were varied because of the different virulence from different strains, different animals and experimental conditions and lack of standard protocols. Therefore, standard modeling protocol is of significance in research of infectious mechanism and immunological status of swine.To investigate the effect of infection of different strains (HA9801, ZY05719) of Streptococcus suis on the blood biochemical indices and immunological state of Bama miniature pigs, in this study we used 30 healthy Bama miniature pigs which were enrolled in the experiment and divided into 3 groups randomly, 10 for each group. Group 1 and group 2 were treated with ZY05719 and HA9801 by intramuscular injection respectively, group3 was control group. Bacterial content and leucocyte of blood were determined after infection, changes of IL-1,IL-8 ,TNF-α,IFN-γwere determined by ELISA, phagocytosis ability of neutrophil was determined by NBT reduction test. Acute death, subacute infection and chronic infection were found after intramuscular injection of streptococcus suis, the bacterial content of dead pigs reached 106CFU/ml. Hypersecretion of IL-1,IL-8,TNF-α,IFN-γwere found 12 hours after infection, the amount of TNF-a, in particular, increased significantly in all pigs. The numbers of blood neutrophil and leucocyte increased immediately in the subacute infectious pigs, and then increasd and reach the peak 5 days after infection, accompany with reduction of phagocytic ability of neutrophil. The number of blood neutrophil, neutrophil phagocytic ability and lymphocyte transformation ability varied with different prognosis. We concluded that differences of pathogenicity between ZY0571 and HA9801 exists, secretion of the cytokines involved and changes of the amount of T cell subset have a association with the infection progression of SS2.