Rocky Mountain Spotted Fever

Rocky Mountain spotted fever (RMSF) is an infectious disease caused by Rickettsia rickettsii which is transmitted by ticks. The prominent clinical manifestations of RMSF can be directly related to the primary pathologic lesion in the endothelial cells lining small blood vessels where the rickettsia multiply. Rash, headache, mental confusion, terminal heart failure, and shock are manifestations of the generalized vasculitis.

The incubation period is from 2 to 12 days with either a sudden or gradual onset of symptoms. Peak severity usually occurs within 1 to 2 weeks. Headache, fever, toxicity, rash, and myalgia are the major clinical features. The rash ( Fig 131-2), a pathognomonic feature of the disease, usually appears on the second or third day.

The initial lesions first appear on the wrist and ankles spreading rapidly to the extremities and trunk. These lesions also are found on the palms and soles of the patient. Initially, lesions are small, erythematous macules which blanch on pressure. They rapidly become maculopapular and petechial.

FIG. 131-2. Rocky Mountain spotted fever. [From Burnett JW, Crutcher WA: Viral and rickettsial infections, in Moschella SL, Hurley HJ (eds): Dermatology. Philadelphia, Saunders, 1985, vol 1, chap 12, pp 673-738, with permission.]

Laboratory diagnostic confirmation is difficult during the early phase of the disease, frequently mandating treatment based on clinical criteria. Serologic tests are used to confirm the diagnosis of RMSF. Some laboratory data may be helpful in establishing the presumptive diagnosis early, such as hyponatremia, leukopenia, and thrombocytopenia.

Specific therapy consists of tetracycline or chloramphenicol. In seriously ill children 100 mg/kg per 24 h of chloramphenicol up to 3 g total dose is advised. As improvement is noted, therapy can be changed to 50 mg/kg per 24 h in four divided doses orally. Treatment can be terminated 2 or 3 days after fever returns to normal for 24 h. The mortality of RMSF in the United States has held steady for a decade at 3 to 6 percent of identified cases despite treatment.

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