Evaluation Of Immune Protection Of Mycoplasma Bovis And Pasteurella Type A Inactivated Vaccine Model Animals

Bovine respiratory diseases syndrome(BRD)is an important disease endangering beef cattle industry.The main pathogens of BRD are Mycoplasma bovis,M.bovis,P.multocida,etc.Among them,BRD caused by mixed infection of M.bovis and P.multocida has higher morbidity and mortality,which has caused huge economic losses to beef cattle industry and "government-bank guarantee alliance".At present,the diseases caused by M.bovis and P.multocida are mainly treated with antibacterial drugs.However,with the unreasonable use of drugs,these two pathogenic bacteria have developed drug resistance to commonly used drugs,and it is not uncommon for them to fail to resist infection due to drug resistance.Screening vaccine candidate strains with good immunogenicity and developing inactivated binary vaccine of M.bovis and P.multicida are important strategies to effectively prevent mixed infection of M.bovis and P.multicida.In this study,the strains screened by the research group for production and testing were verified,and the original,basic and production seed batches of the binary vaccine were established to prepare the binary inactivated vaccine of M.bovis and P.multicida,and the immune protection of the binary inactivated vaccine was determined by using model animals.The main experimental contents are as follows:(1)Rabbit infection models were established based on M.bovis CC200910 strain,Mb1 strain and P.multicida YT150616 strain which were screened by the research group.The rabbit infection models were divided into M.bovis CC200910 strain infection group,M.bovis Mb1 pig infection group,P.multicida YT150616 strain infection group and blank control group respectively.Through clinical observation,diet,lung score and lethal rate determination,it was proved that M.bovis CC200910 strain(4.04 score)and P.multocida YT150616 strain(lethal rate up to 75%)had strong virulence and could be used as strains for double vaccine test.(2)Based on the vaccine strains M.bovis TL140428 and P.multicida YT150616 screened by the research group.In this study,the original,basic and production seed batches of two vaccine strains were established by freeze-drying technique,and the purity,safety and immunogenicity of the seed batches of M.bovis TL140428 and P.multicida YT150616 were determined.The results showed that the seed batches all met the standards,which provided guarantee for the preparation of M.bovis and P.multicida binary inactivated vaccine.(3)The two inactivated vaccines were prepared from the seeds of M.bovis TL140428 and P.multicida YT150616.The immune protection of the two inactivated vaccines was evaluated by the rabbit infection model established by the seeds of M.bovis CC200910 and P.multicida YT150616.The degree of lung lesions of M.bovis infection was scored by 5.5 points,and the mortality of P.multicida infection rabbit model was counted.The results showed that the protective rates of M.bovis CC200910 strain and P.multicida YT150616 strain were 73.4% and87.5%,respectively,which indicated that the inactivated vaccine had good immune protection and laid a solid foundation for later target animal experiments.