Kinetics of experimental infection of sheep with Ehrlichia ruminantium cultivated in tick and mammalian cell lines

Inoculation of sheep with Ehrlichia (previously Cowdria) ruminantium which has been cultivated in mammalian endothelial cell cultures is almost always followed by a severe clinical reaction, whereas inoculation of the agent cultivated in tick cell lines usually does not provoke a clinical response, but may result in seroconversion and/or protection against subsequent challenge with virulent stabilates. A quantitative, real-time PCR assay was developed to determine the kinetics of infection (rickettsaemia) in sheep inoculated with tick cell- and mammalian cell- derived E. ruminantium (Gardel isolate). The method and initial results are described, and the significance of the findings is discussed in relation to the clinical responses of the sheep.