Experimental infection with Ehrlichia phagocytophila in cattle.

Twenty Norwegian Red cattle, aged 8-10 months were used. Ten animals were inoculated intravenously with 3 ml of a whole blood dimethyl sulphoxide stabilate of a bovine strain of Ehrlichia (Cytoecetes) phagocytophila. The animals were observed on a daily basis for clinical symptoms and rectal temperatures were recorded daily for 36 days post inoculation. Blood and serum samples were collected regularly during the observation period. All infected animals developed fever of 2-4 days duration within a week. Six out of 10 animals had secondary temperature rises of 1-2 days duration. Three animals showed swellings in the hind limbs and a stiff gait. Compared with the control group, there was a 10% decrease in the mean haematocrit and a leukopenia that initially was due to a lymphopenia and later to a neutropenia. A monocytosis occurred after the subsidence of the primary fever period. A thrombocytopenia occurred during the early phase of infection. Granulocytic inclusions were detected for 18-32 days. All infected animals developed antibodies > or = 1:4096 to E. phagocytophila within 14 days post infection.