Certain authors, while proving the measurable growth of R. burneti in vitro, noticed a light weakening of its pathogenic power. An attempt was made to verify this in the course of some passages on KB cells, controlling each time the guinea pigs, the embryonate eggs, and the KB cells. It was found that R. burneti retained its pathogenicity after many weeks of culture on KB cells or on chick fibroblasts.
Trans. of Societe de Pathologie Exotique. Bulletin (France) v56 n1 p8-12 1963.