Development Of A Bivalent Oil-emulsion Inactivated Vaccine Against Newcastle Disease And Chronic Respiratory Disease In Chickens

Mycoplasma gallisepticum(MG) is an important pathogen of poultry,causing chronic respiratory disease in chickens and infectious sinusitis in turkeys.Newcastle disease(ND) is a most important infectious agent in chickens.Respiratory disease syndrome caused by MG and NDV is very difficult to be controlled,having a high prevalence throughout the world with significant economic impacts on the poultry industries.For the big problems,bivalent vaccine is urgent to be used in farms.In the present study,we try to prepare a bivalent oil-emulsion inactivated vaccine against ND and chronic respiratory disease caused by MG in chickens.The introduced strains were for antigenic materials of the vaccine,strain La Sota and MG strain S6.La Sota strain was amplified as the seeds in SPF embryos and MG S6 was cultured in the special cell-free medium less than 5 passages.The titer of the virus must be higher than 10^9.5 EID₅₀.And the indexes of MDT,ICPI and others were followed with the standard's measures.The results showed that the strain had full-immunological antigencity,and the virulence is very low.For MG S6,in PPLO complete medium,it could be proliferated over at a number of 5×10⁹ CFU.By cultured in plates,the shape of the bacteria is the classical MG.And then by the agglutination assay,hemagglutination test,Immunofluorescence assay, transmission electron microscope detection,and immunogenic characterization,the strains is a medial virulent one,fit for MG vaccine seed.Harvested the virus or MG strain multiplicated by SPF embryos or by PPLO complete medium, respectively,and then completely inactivated by 0.1%or 0.2%formaldehyde for 24h,the antigens were mixed with emulsifying agents as a proper proportion.The prepared vaccine was used in SPF chickens.In 2 months after vaccination,the groups were healthy with a higher weight and a higher antibody titer than those in the control groups.Infected by F₄₈E₈ and R_low strains,the air sacs protective ratio of the chickens with the ND-MG bivalent inactivated vaccine is significantly higher than the unvaccinated groups,which was 98%.What's more,full prevention was got in vaccinated groups even though NDV virulent strain F₄₈E₈ attacking.