The observed increase in cytokines, including monokine induced by IFN-γ (MIG), IP10 (IFN-γ-inducible 10-kDa protein), and IL-18 (also known as IFN-γ-inducing factor), indicate that an IFN-γ-related mechanism is contributing to the pathogenesis of severe rickettsioses. The gene discussed is IL18; the disease is Rickettsiosis.