Diagnosis
The association of a tick bite and proper geographical distribution is of prime importance. The more sudden onset, joint pains and negative Widal differentiate it from typhoid fever.
Typhus fever shows more marked abruptness of onset and decline of fever than does Rocky Mountain fever. The guinea pig, while susceptible to both infections, is more easily infected with this disease than with typhus fever.
As a matter of fact there are marked clinical resemblances between typhus fever and Rocky Mountain fever. Tsutsugamushi and trench fever also have points of resemblance.
Fig. 140.—Generalized eruption of spotted fever of the Rocky Mountains. (Kindness of Doctor Frick.)
Prognosis
It is very remarkable that the disease should rather constantly give a mortality approximating 75 to 90% in western Montana and only about 5% for Idaho.
Where the nervous manifestations are marked the prognosis is more unfavorable. Death tends to occur in the second week and patients living through this week have a good chance for recovery. The death rate is greatest in old people and least in young children.