Rocky Mountain spotted fever

A hemorrhagic rash that extends over the entire body, including the palms of the hands and soles of the feet, is the hall-mark of RMSF. An eschar at the site of the tick bite is uncommon with RMSF but is common with R. akari, R. africae, and R. conorii infection.

The vascular lesions that underlie the rash often lead to acute necrosis, fibrin extravasation, and occasionally thrombosis of the small blood vessels, including arterioles.

In severe RMSF, foci of necrotic skin are thus induced, particularly on the fingers, toes, elbows, ears, and scrotum. The perivascular inflammatory response is similar to that of typhus, particularly in the brain, skeletal muscle, lungs, kidneys, testes, and heart muscle.

The vascular necroses in the brain may involve larger vessels and produce microinfarcts. A noncardiogenic pulmonary edema causing adult respiratory distress syndrome is the major cause of death with RMSF.