Overview of rickettsial and related infections

[Britney]

Rickettsial diseases (rickettsioses) and related diseases (anaplasmosis, ehrlichiosis, Q fever, scrub typhus) are caused by a group of gram-negative, obligately intracellular coccobacilli. All, except for Coxiella burnetii, have an arthropod vector. Symptoms usually include sudden-onset fever with severe headache, malaise, prostration, and, in most cases, a characteristic rash. Diagnosis is clinical, confirmed by immunofluorescence assay or polymerase chain reaction (PCR). Treatment is with tetracyclines or, except for anaplasmosis and ehrlichiosis, chloramphenicol .
Rickettsia, Orientia, Ehrlichia, Anaplasma, and Coxiella species were once thought to belong to the same family but now, based on genetic analysis, are considered distinct entities. Although this group of organisms require living cells for growth, they are true bacteria because they have metabolic enzymes and cell walls, use oxygen, and are susceptible to antibiotics.
These organisms typically have an animal reservoir and an arthropod vector; exceptions are R. prowazekii, for which humans are the primary reservoir, and C. burnetii, which does not require an arthropod vector. Specific vectors, reservoirs, and endemic regions differ widely (see table).
There are many rickettsial species, but 3 cause most human rickettsial infections:

R. rickettsii
R. prowazekii
R. typhi