The typhus group and ‘spotted’ fevers are caused by bacteria of the family Rickettsiaceae,^[1] which are obligate, intracellular, Gram-negative, non-flagellate small pleomorphic coccobacilli (0.3–0.6 × 0.8–2.0 μm). Rickettsiae are often carried to humans by insects from animal reservoirs or by the insects themselves, in which the bacteria may be maintained transovarially.

The species of the genus Rickettsia are divided into:

	•	The typhus group, containing R. prowazekii, the agent of classical epidemic typhus transmitted by the human body louse, and R. typhi (mooseri), the cause of endemic murine typhus carried by the rat and rat fleas.
	•	The ‘spotted fever’ group (SFGR), containing a large number of species (R. rickettsii, R. conorii, R. africae, etc.) transmitted from rodents and other animals by ticks (except R. akari, which is transmitted by mouse mites).
	•	Scrub typhus, caused by Orientia …