Rocky Mountain spotted fever (RMSF), the most severe of the rickettsial
infections, is characterized by sudden onset of fever, severe headache,
myalgia, and a characteristic acral exanthem; it is associated with
Etiology Caused by Rickettsia rickettsii
gram-negative obligate intracellular bacteria.
Season April to September in the
United States (95% of patients).
Geography Endemic in Virginia,
North Carolina, South Carolina, Georgia, Kansas, Oklahoma, Texas,
New York, northern Mexico, central, and South America.
Occurs through bite of an infected tick or inoculation through
abrasions contaminated with tick feces or tissue juices. The reservoirs
and vectors are the wood tick (Dermacentor andersoni) in the western
United States, the dog tick (D. variabilis) in the eastern United
States, and the lone star tick (Amblyomma americanum) in the southern
United States. Patient either lives in or has recently visited an
endemic area; however, only 62% have knowledge of a recent
tick bite. Following inoculation, there is an initial local replication
of the organism in endothelial cells followed by hematogenous dissemination.
Focal infection of vascular smooth muscle causes a generalized vasculitis.
Hypotension, local necrosis, gangrene, and DIC may follow. The petechial rash
results from extravasated blood after vascular necrosis.
The incubation period for RMSF after tick exposure ranges from
5 to 7 days. The rash, present in 90% of cases, begins
on day 3 or 4 on the extremities and spreads proximally. By day
6 or 7, the rash is generalized. Systemic symptoms include abrupt
onset of fever (94%); severe headache (94%); generalized
myalgia, especially the back and leg muscles (87%); a sudden
shaking rigor; photophobia; prostration; and nausea with occasional
Type Macule, papule, eschar, infarcts,
Color Pink, deep red, violaceous
Rocky Mountain spotted feverA. Scattered pink, red, and purpuric
macules and papules on the forearm of a child. B. Later
face involvement of the rash is seen in the same child.
Distribution Distal extremities,
palms, soles to arms, thighs, trunk, face (Fig. 22-1B). Gangrene
(4%) occurs in acral digits, extremities, ears, and prepuce.
Pulmonary Cough, pneumonitis, lung
infections, pulmonary edema, ARDS.
GI Nausea, abdominal pain, hepatosplenomegaly,