In contrast to C. trachomatis, mice are significantly more susceptible to infection and disease mediated by the rodent-adapted pathogen C. muridarum, presumably because C. muridarum encodes host-tailored virulence factors that help it counter the relevant IFN-γ-regulated cell-autonomous defenses of its definitive murine host (5, 16). The gene discussed is IFNG; the disease is infection.