Determination of Mycoplasma Mycoides Subsp. Mycoides Components That Confer Protection Against Contagious Bovine Pleuropneumonia and Understanding of Immunological Responses
Contagious Bovine Pleuropneumonia (CBPP) is a severe respiratory disease caused by Mycoplasma mycoides subsp. mycoides (Mmm) which is widespread in Africa. The main control option is a live vaccine, with low efficacy and a short duration of immunity. Development of an efficacious CBPP vaccine requires understanding immunogenicity of the antigens and protective immune responses. A series of experiments were undertaken to establish whether components of the Mmm, including whole cell lysate, membrane proteins and capsular polysaccharide can induce protection. Three separate experiments were conducted to evaluate the capacities to protect and detect possible correlations with immunological responses. The first experiment examined the efficacy of inactivated vaccine formulations: heat inactivated and formalin inactivated Mmm were compared with the live attenuated vaccine. Second experiment involved evaluation of a vaccine formulation generated from the Mmm membrane protein components. The third experiment entailed vaccination of cattle with a conjugated Capsular Polysaccharide and subsequent experimental challenge with the infective Afadé strain. Disease outcome was analysed through clinical, pathological observations and immunological parameters. The protection levels were 31%, 80.8% and 74.1% for the formalin-inactivated, heatinactivated and live attenuated preparations, respectively. Conjugated capsular polysaccharide produced a protection rate of 57%. The vaccine also elicited CPS-specific antibody responses with the same or a higher titer than animals vaccinated with the live vaccine. Interestingly, the animals immunised with membrane proteins had enhanced disease. These findings indicate that; i) low doses of heat-inactivated Mmm can offer protection to a level similar to the current live attenuated (T1/44) vaccine formulation, ii) vaccination with membrane proteins revealed enhanced inflammatory reactions after xvii challenge iii) capsular polysaccharide antigens conjugated to a protein is immunogenic and induces protective immunity in cattle and iv) high immunoglobulin (IgG and IgM) responses can be raised against the carbohydrate component of the CPS-based glycoconjugate. Future development for a vaccine against CBPP needs to focus on understanding of immunological reactions that leads to pathological conditions and those that lead to protection especially the innate immune response.
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