The primary site of multiplication of rickettsia! organisms is in the ?

Ans. is 'b' i.e., Endothelial cells of small vessels Pathogenicity On entry into the human body, the rickettsiae multiply locally and enter the blood. They become localized chiefly in vascular endothelial cells, which enlarge, degenerate and cause thrombus formation, with paial or complete occlusion of the vascular lumen. . The overall pathological features of the rickettsia! diseases are due to the damage of vascular endothelium.