- An acute, febrile, infectious, rash-producing disease.

Causes and Incidence The cause is the Rickettsia rickettsii organism, which is transmitted through the bite of an adult Ixodes tick. The disease is seen most often from May to September, when adult ticks are active and humans are likely to be outdoors in tick-infested areas. The incidence is highest in children under age 15 and in those who frequent tick-infected areas for work or recreation.

Disease Process The organism enters humans through a prolonged bite (4 to 6 hours) by an adult tick. R. rickettsii then localizes and proliferates in the vascular endothelium of small and medium blood vessels, producing widespread swelling and degeneration that result in thrombi and vasculitis and affect the skin, subcutaneous tissues, heart, lungs, kidneys, liver, spleen, and central nervous system.

Symptoms The incubation time between bite and symptoms ranges from 3 to 12 days. The shorter the incubation period, the more severe the manifestations. The onset is abrupt and is marked by a severe headache; intermittent fever; chills; pain and aching in the back, bones, muscles, and joints; anorexia; nausea; vomiting; a thick white covering on the tongue; and a nonproductive cough. Skin eruptions develop on the wrists, ankles, and forehead within 2 to 5 days of symptom onset, and the rash spreads to the entire body, including the palms, soles, and scalp, within 2 days. The lesions become petechial and coalesce into hemorrhagic areas that ulcerate and peel; restlessness, insomnia, delirium, and coma may ensue.

Potential Complications Untreated cases lead to complications such as pneumonia; tissue necrosis, with gangrene of the digits; disseminated intravascular coagulation; circulatory failure; renal failure; and cardiac arrest with sudden death.

Diagnostic Tests The diagnosis is made through a history of a tick bite, a pattern of symptoms, and blood cultures that isolate the causative agent. Immunofluorescent tests that detect the organism in a punch biopsy of affected cutaneous tissue are also used.

Treatments

Surgery
None.

Drugs
Antiinfective, rickettsiostatic drugs until individual is afebrile; antiinfective drugs in combination with corticosteroids if treatment is started later in the disease process; analgesics for pain; antipyretics for fever; aspirin is avoided because it can cause hemorrhage.

General
Rest; fluid and electrolyte replacement; meticulous mouth and skin care; monitoring for complications.

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