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 closel y related to the HF strain of Ehrlichia isolated from ticks in Japan. In th is study, BALB/c mice inoculated intraperitoneally with the HF strain devel oped 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 infecte d with the HF strain would provide a useful model for studying pathogenesis and immunity in acute and severe chrlichiosis caused by E. chaffeensis and related Ehrlichia spp. (C) 2001 Harcourt Publishers Ltd.