Rickettsial infections (typhus group and spotted fever)

What it is

Rickettsia, written on the slide as Rickettsia (typhus), are parasitic bacteria and are arthropod-borne: transmitted by, and dependent on, parasitic arthropod vectors, which are lice, fleas and ticks. The treatment is given with the name, on the same slide: Tx doxycycline.

The three set side by side

Three are named, each with its disease and its vector:

• R. prowazekii: epidemic typhus, human louse
• R. typhi: murine typhus, flea
• Rickettsia rickettsiae: RMSF, that is Rocky Mountain spotted fever, tick

How it presents

Two signs are given. Rash is the first. The eschar is the second: a dark, crusty ulcer at the site of the bite, going on to necrosis. In Rocky Mountain spotted fever, caused by R. rickettsii, the rash is petechial, and the slide carries a view of petechial rash on the arm.