The Rickettsia rickettsii organism causes Rocky Mountain spotted fever. Transmitted by the wood tick (Dermacentor andersoni) in the western United States and by the dog tick (D. variabilis) in the eastern United States, this rickettsial organism enters humans or small animals with the prolonged bite (4to 6 hours) of an adult tick. This disease occasionally is acquired through inhalation or through contact of abraded skin with tick excreta or tissue juices. (This explains why people shouldn’t crush ticks between their fingers when removing them from others.) In most tick-infested areas, 1% to 5% of the ticks harbor R. rickettsii.

Complications can include lobar pneumonia, pneumonitis, otitis media, parotitis, disseminated intravascular coagulation, and shock. Systemic and pulmonary microcirculation are compromised; renal failure, meningoencephalitis, and hepatic injury can also occur. Death can occur from severe visceral lesions. Death can occur in 2 weeks after onset in untreated cases and in 5 days with fulminant Rocky Mountain spotted fever.

The patient’s history may show recent exposure to ticks or tick-infested areas, or a known tick bite.

The patient typically complains of signs and symptoms that began abruptly, including a persistent fever with temperature ranging between 102° and 104° F (38.9° to 40° C); generalized, excruciating headache; and aching in the bones, muscles, joints, and back. He also may report anorexia, nausea, vomiting, constipation, and abdominal pain.

A rash is evident in 14% of patients on the first day and in 49% by the 3rd day. In 2 to 5 days, eruptions begin at the wrists, ankles, or forehead and spread centrally. Within 2 days, the rash covers the entire body (including the scalp, palms, and soles). It consists of erythematous macules 1 to 5 mm in diameter. The pink foci of vasodilation are leaky with local edema. The lesions become maculopapules that blanch on pressure. As more severe vascular damage occurs, frank hemorrhage occurs at the center of the maculopapule, creating a petechia that doesn’t blanch on pressure.

The patient may have a bronchial cough, a rapid respiratory rate (up to 60breaths/minute), insomnia, restlessness and, in extreme cases, delirium and circulatory collapse. Urine output decreases considerably, and the urine, which appears dark, contains albumin.