IMMUNITY TO RHODOCOCUS EQUI INFECTION IN HORSES

Abstract

Rhodococcus equi is an opportunistic bacterium that commonly infects foals and immunocompromised patients. Due to the large economic losses
that it can cause in the fi eld of horse breeding, the microorganism has been studied in details, including its immunological aspect. Within the humoral immunity, the most important immunoglobulins are those of the class G (IgG), produced as a response to the surface antigen associated with virulence (virulence associated protein A, VapA). IgG antibodies provide resistance to pneumonia in foals and have a dose dependent protective effect. In addition to them, the protective role of plasma is achieved through various cytokines. Cellular mechanisms are important for killing bacteria within the macrophage. Virulent strains which carry a plasmid with the gene for VapA stimulate the production of interferon gamma (IFN-γ), a key cytokine to kill these bacteria. Th e presence of IFN-γ is crucial for the removal of microorganisms from the lungs and prevention of formation of pulmonary granulomas. For the complete removal of bacteria cooperation of the humoral and cellular immunity is necessary. Particularly signifi cant is opsonization, which increases phagolysosomal fusion. Vaccination and application of hyperimmune plasma play a vital role in the treatment of disease. Only alive and virulent bacterium is capable of producing protective immunity in horses. Th e use of hyperimmune plasma in foals results in a lower percentage of sick animals and less severe clinical progression of the disease. Further research is needed in order to create a safe and effective vaccine.