Rickettsialpox

Key Features

• An acute, self-limiting, febrile illness

• Caused by Rickettsia akari, a parasite of mice, transmitted by the mite Liponyssoides sanguineus

• Infections are reported globally

• Crowded conditions and mouse-infested housing allow transmission of the pathogen to humans

• Has also been found in farming communities

Clinical Findings

• Primary lesion is a painless red papule that vesiculates and forms a black eschar followed by an incubation period of 7–12 days

• Onset of symptoms is sudden, with chills, fever, headache, photophobia, and disseminated aches and pains

• Widespread papular eruption appears 2–4 days later

• Rash becomes vesicular and forms crusts that are shed in about 10 days

• Early lesions may resemble those of chickenpox (typically vesicular versus papulovesicular in rickettsialpox)

• Lesions of African tick bite fever caused by Rickettsia africae may resemble those of rickettsialpox

• Pathologic findings include dermal edema, subepidermal vesicles, and a lymphocytic and granulocytic vasculitis that seems to be the essential feature of the disease

Diagnosis

• Transient leukopenia and thrombocytopenia and acute hepatitis can occur

• A fourfold rise in serum antibody titers to rickettsial antigen, detected by complement fixation or indirect fluorescent assays

• Conjugated antirickettsial globulin can identify antigen in punch biopsies of skin lesions

• Polymerase chain reaction (PCR) detection of rickettsial DNA in fresh tissue

• R akari can also be isolated from eschar biopsy specimens

Treatment

• Oral doxycycline (200 mg loading dose followed by 100 mg twice daily) for 2–5 days until defervescence

• Severe symptoms may require hospitalization

• Control requires the elimination of mice from human habitations and insecticide applications