Ehrlichial proliferation and acute hepatocellular necrosis in immunocompetent mice experimentally infected with the HF strain of Ehrlichia, closely related to Ehrlichia chaffeensis.

Ehrlichia chaffeensis, the agent of human monocytic ehrlichiosis, is closely related to the HF strain of Ehrlichia isolated from ticks in Japan. In this study, BALB/c mice inoculated intraperitoneally with the HF strain developed severe illness and died at about day 9 post-inoculation. At necropsy, diffuse liver necrosis was evident. Ehrlichial microcolonies were observed in endothelial cells, monocytes and macrophages of the liver, bone marrow, spleen, thymus, and large and small intestine. Immunocompetent mice infected with the HF strain would provide a useful model for studying pathogenesis and immunity in acute and severe ehrlichiosis caused by E. chaffeensis and related Ehrlichia spp.