Rocky Mountain spotted fever (RMSF), the most severe of the rickettsial spotted fevers, is characterized by sudden onset of fever, severe headache, myalgia, and a characteristic acral exanthem; it is associated with significant morbidity and mortality rates.
RMSF is caused by an infection with the bacteria Rickettsia rickettsii. Feeding by ticks usually takes place for ≥6 h, after which rickettsiae are released from the salivary glands. After inoculation of rickettsiae into the pool of blood in the dermis, initial local replication of rickettsiae occurs in endothelial cells, which is followed by hematogenous and lymphatic dissemination. Organisms spread throughout the body and attach to the vascular endothelial cells, the principal target. Foci infected by R.rickettsii enlarge as rickettsiae spread from cell to cell, forming a network of contiguously infected endothelial cells in the microcirculation of the dermis, brain, lungs, heart, kidneys, stomach, large and small intestines, pancreas, liver, testes, skeletal muscle, and other organs and tissues. Focal infection of vascular smooth muscle causes a generalized vasculitis. Patients with severe infection of brain and lungs have a high mortality rate. Hypotension, local necrosis, gangrene, and DIC may follow. Rash results from extravasation of blood after vascular necrosis.
Symptoms of RMSF begin within two weeks of the bite of the infected tick. he most common symptoms of Rocky Mountain spotted fever are the abrupt onset of fever, severe headache, muscle aches, and vomiting. Other symptoms that are less common are abdominal pain, swollen lymph nodes, cough, stiff neck, confusion, and coma.
The Rocky Mountain Spotted Fever Rash
The rash that makes RMSF a "spotted" fever may begin anytime between 1 to 10 days after the fever and headache start, but it most often appears on the third to fifth day. The rash looks like small red spots or blotches that begin on the wrists, ankles, palms, and soles. It spreads up the arms and legs toward the trunk, but often spares the face.
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