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Rickettsialpox, Scrub Typhus, and Tick Typhus

Rickettsialpox is an uncommon condition caused by Rickettsia akari, transmitted to humans by the mouse mite. Cases have been described primarily in New York City, Pittsburgh, Cleveland, and Boston and in Arizona and Utah. One to two days following the mite bite, a red papule forms at the site of inoculation, and enlarges to 1 to 1.5 cm. A vesicle then forms in the center of the papule, producing a red halo. The vesicles dries, and a black eschar forms, followed by the abrupt onset of fever and proximal lymphadenopathy. The fever lasts about a week and is associated with a generalized macular-papular-vesicular eruption, often mimicking chickenpox. The rash is sparse, usually located on the face, trunk, and extremities, but may involve the palms, soles, and oral mucosa.

Scrub typhus, caused by Orientia tsutsugamushi, is transmitted by the bite of a larval mite, also known as a "chigger". It produces disease in India, Southeast Asia, and Australia. A red papule forms, followed by a vesicle or black eschar on the papular base. Systemic symptoms include fever, chills, and headache. On the fifth day of fever, a generalized macular and papular, or occasionally papular-vesicular rash develops on the abdomen, progressing to the extremities. This stage of the illness is frequently associated with generalized lymphadenopathy.

Tick typhus can be produced by a number of different but closely related rickettsiae found in the eastern hemisphere. Five to 7 days following inoculation, the illness begins suddenly with fever and headache. The primary lesion begins as a red papule, which ulcerates and is then covered by an eschar, surrounded by a red halo. The primary lesion associated with regional and then generalized lymphadenopathy. After about four days of fever, a generalized, red, macular and papular rash develops.

Differential Diagnosis: Rickettsialpox, and scrub and tick typhus can be distinguished from cutaneous anthrax in the following manner.

Rickettsialpox, scrub typhus, tick typhus

 

Cutaneous anthrax

*Disease is associated with a generalized macular-papular or papular-vesicular rash

*Papular base is discernible under the vesicle or eschar

* Patient resides in or has traveled to endemic areas (scrub typhus and tick typhus)

 

* Ulcer and eschar are surrounded by characteristic non-pitting edema

*No other cutaneous manifestations are present

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