Group XII – Rickettsias
Important genera of this group include:
• Richettsia
• Wolbachia
• Coxiella
These are small (0.3-0.7 m x 1-2 m) rods that may at time appear as cocci. They are obligate intracellular parasites. They cause typhus, Rocky Mountain Spotted fever, Q fever.
Most often they organisms are transmitted to humans by lice. One organism, Coxiella burnetti, can be transmitted through aerosols. This is possible since it is able to form spores.