Rickettsialpox is an acute febrile illness caused by Rickettsia akari transmitted by mite bites; it produces a black eschar at the bite site followed by a vesicular rash resembling mild chickenpox.
Etiology and Pathogenesis
Rickettsialpox results from infection by Rickettsia akari, a member of the spotted fever group of rickettsiae. The bacterium is maintained in a cycle involving the house mouse (Mus musculus) and its mite parasite, Liponyssoides sanguineus. Humans are incidental hosts who become infected when bitten by an infected mite. After entering the skin, the organism invades endothelial cells and multiplies intracellularly, leading to local necrosis and the formation of a dark eschar at the bite site. The bacteria disseminate through the bloodstream, causing vasculitis and the characteristic febrile illness. Because R. akari relies on host cells for energy and biosynthetic precursors, it cannot be cultured on standard media; diagnosis often relies on serology or polymerase chain reaction.
Epidemiology and Clinical Features
Rickettsialpox was first recognized in New York City in the 1940s but has since been reported in urban centers and rural settings worldwide where rodent–mite cycles exist. After an incubation period of about one week, patients develop fever, chills, headache and myalgia. A papulovesicular rash appears a few days later, often accompanied by regional lymphadenopathy. The rash resembles varicella but lacks lesions at different stages, and a single eschar is typically present at the mite bite site. The illness is generally self‑limited, resolving within two to three weeks, but doxycycline hastens recovery and is recommended for treatment. Preventive measures focus on rodent control and reducing exposure to mites in infested buildings. There is no evidence of human‑to‑human transmission.
Rickettsialpox is a mild spotted fever that illustrates the diversity of rickettsial diseases and the importance of vector control in urban environments.
Related Terms: Rickettsial, Rickettsia akari, Eschar, Vesicular rash, Doxycycline