Effcacy of experimental inactivated and live Rhodococcus equi vaccines for thoroughbred Arabian mares in mice

The aim of this study was to determine the effcacy of inactive Rhodococcus equi vaccine candidates included thatbacterin+aluminum hydroxide (Al(OH)3), bacterin+VapA+(Al(OH)3), bacterin+Montanide IMS 3012 (IMS), bacterin+VapA+IMS,and live vaccine using mice as a model. Te efcacy of vaccine was evaluated according to clinical fndings, humoral and cellularimmunity (levels of INF-g and IL-4), and results of microbiological culture from internal organs in dead or sacrifced mice. Inactive R.equi vaccines were subcutaneously administered to mice three times at 15-day intervals and live vaccine was intraperitoneally injectedonce. Fifeen days afer the last vaccination, aerosol challenges were carried out with the pathogenic R. equi VapA+K2002 strain in allgroups. Two mice were sacrifced from each challenge groups on days 1, 3, 5, and 7. The antibody titers of vaccinated mice were found tobe signifcantly higher than those of the controls. The largest number of INF-g positive samples were detected in the bacterin+VapA+IMSand bacterin+IMS groups. IL-4 positivity was determined only in live vaccine groups. The lowest reisolation rate of R. equi from internalorgans was observed in the bacterin+VapA+IMS group. It was concluded that R. equi vaccines, and especially bacterin+VapA+IMS, areuseful to protect mice against R. equi infection.

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