Rickettsia
Summary
Rickettsia are obligate intracellular gram-negative coccobacilli transmitted by arthropod vectors that infect vascular endothelium, producing vasculitis, rash, fever, and headache. Doxycycline is the treatment for all rickettsial disease at any age.
Detail
Rickettsiae cannot be cultured on artificial media because they depend on host ATP and CoA. They invade endothelial cells, and the resulting widespread small-vessel vasculitis explains the rash, increased vascular permeability, oedema, hypotension, and end-organ damage. The spotted fever group includes R. rickettsii, the cause of Rocky Mountain spotted fever, transmitted by Dermacentor ticks; its rash begins on wrists and ankles, including palms and soles, and spreads centripetally to the trunk, and it is most common in the south-eastern and south-central United States despite the name. The typhus group includes R. prowazekii, causing epidemic typhus spread by the human body louse in conditions of crowding and poor hygiene, with a rash that starts centrally and spreads outward sparing palms and soles, and R. typhi, causing endemic murine typhus via fleas from rats. Brill-Zinsser disease is a later recrudescence of epidemic typhus. Rash on the palms and soles should also raise secondary syphilis and coxsackievirus hand-foot-and-mouth disease.
Sources
- Levinson Medical Microbiology and Immunology
- First Aid for the USMLE Step 1
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