Tick typhus of the new world is widely distributed in North America, and occurs in people exposed to ticks. The infective agent is R. rickettsi.
After a variable incubation period, averaging one week, there is an onset of disease similar to epidemic typhus.
Features include a fever which is moderately high which lasts for ten or twelve days, accompanied by a severe headache, myalgia and arthralgia. The rash appears on the about the fourth day of the disease, starting on the periphery, spreading inwards as pink macules becoming papular after about a day. The lesions may become petechial and may ulcerate. Neurological features are common.
Mortality is dependent on age, and averages at 6%.
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