Study On Effects Of Chinese Herbal Medicine Modified Maxingshigantang On Avian Infectious Bronchitis

The study was carried out to evaluate the therapeutic effects of Chinese herbal medicine modified maxingshigantang on Infectious Bronchitis Virus (IBV) infection, and its possible mechanisms. The results of this study will provide a novel thought and method for studying Chinese herbal medicine in treatment of avian Infectious BronchitisMethods: The EID50 of the infectious bronchitis virus strain M41 (IBV-M41) was calculated after rejuvenation on embryo for 5 generations. Then 15-day-old chicks were inoculated intranasally with IBV-M41 at 100 EID50. The clinical symptoms were observed and chicks were diagnosed by empirical method at 24h post challenge. Two hundred 15-day-old chicks were randomly divided into five groups, group I as negative control group; groupⅡas positive control group, and groupsⅢ,Ⅳ,Ⅴas the high, middle and low dose groups. Except for groupⅠ, chickens in other groups were inoculated intranasally with 0.2 mL of IBV-M41, respectively. Birds in herbal therapeutic groups were intervened with 0.6%, 0.4%, 0.2% dose of herbs respectively at 48h post challenge. Clinical signs were recorded daily before or after herbal usage and serum was collected at 18, 21, 24, 27, 30 days of age with six chicks in each group randomly. The SOD&GSH-Px activity and MDA contents in sera of each group were detected by spectrophotography. Antibody, IL-4 and IFN-γcontents were detected by ELISA. Then chickens were dissected and the quantities of IBV-M41 N gene in the lung and bronchus tissues were assayed by reverse transcriptase polymerase chain reaction (RT-PCR), and the pathological changes of lung and bronchus in all groups were observed under microscope.Results: (1) IBV infected model could be replicated successfully by inoculating with 0.2 mL inoculum containing 10-5.68 EID50/0.1mL of IBV-M41 and under the physical environment of low temperature and high moisturization. It could be confirmed by the clinical symptoms, the pathological appearances of lung and bronchus tissues, and the results of the experiments involving dwarfing of chicken embryo and RT-PCR for IBV-M41 in the allantoic fluids. (2)The total efficiency of maxingshigantang on IBV infection was 90%~95%, the cure rate was 82%~88.5%, it was confirmed that the therapeutic effect of Jiaweimaxingshigan on IBV infection was significantly and the optimum therapeutic concentration was 0.4%~0.6%. (3)Compared with positive control group, maxingshigantang could rapidly induce tissue regeneration through promotion of cell activation, and improve the pathological changes of the bronchus and lung tissues of the IBV infected model and there was no effect on IBV N gene's expression. (4) SOD & GSH-Px activity in sera of positive control group decreased apparently compared with those in blank control group, MDA content increased apparently. Compared with positive control group, SOD&GSH-Px activity in sera of drug intervened groups increased obviously and MDA contents decreased significantly. The SOD & GSH-Px activity in sera of high & middle dose group were higher than that of low dose group, and MDA contents were lower than that of low dose group. (5) After IBV infection, the serum level of IBV antibody was relatively lower, and sera IFN-γcontents were significantly decreased, IL-4 contents increased, there had an imbalance of Th1/Th2 function after IBV infection, Th1 and Th2 cytokines expression was in Th2 migration status. Maxingshigantang could significantly promote serum titer of IBV antibody, and decrease IL-4 contents, increase IFN-γcontents, therefore retrieve Th1/Th2 imbalance induced by IBV infection.Conclusion: Maxingshigantang had significant therapeutic effect on IBV infection, meanwhile reparation effect on pathological injury caused by IBV infection, and immune regulation. It could increase serum antibody against IBV, retrieve Th1/Th2 imbalance induced by IBV infection, improve the cellular immunity and humoral immunity, which would eventually kill the pathogenic microorganism and speed up the chick's recovery from IBV infection. Furthermore, Jiaweimaxingshigan could antagonize the oxidant injury through improving the level of SOD & GSH-Px activity and decreasing MDA contents, and adjust the imbalance of oxidant-antioxidant system caused by IBV, thereby protect the chickens with IBV infection.