In vitro propagation of Cytoecetes phagocytophila, the causative agent of tick-borne fever.

Cytoecetes phagocytophila, a neutrophilic rickettsia which parasitizes sheep and cattle, was propagated transiently at 37 degrees C in cultures of heparinized whole blood of sheep supplemented with Medium 199 containing HEPES buffer. Significant increases in the number of infected cells and the number of rickettsias per infected cell were observed within 24 h. Back-passage into sheep produced typical tick-borne fever.