Rocky Mountain Spotted Fever Causes

RMSF is caused by R. rickettsii, which are bacteria that are Gram stain negative, aerobic coccobacilli (round and rod shaped) that must live within eukaryotic cells (cells, such as human cells, that have a nucleus bound by a membrane). The organisms only proliferate if they are inside of a eukaryotic cell. In most cases in humans, the endothelial cells that line blood vessels are the cells that are parasitized. These cells can be disrupted by the organisms, thus producing vascular permeability (leaky blood vessels) that results in macules (flat areas of skin color change) and eventually a petechial rash (red or purple spots about 1 mm-2 mm in diameter usually caused by a broken blood vessels). This vascular permeability can occur throughout the body and eventually cause death.

Although RMSF is caused by R. rickettsii, the bacteria need to be transmitted to humans by a tick vector (carrier) infected with R. rickettsii. RMSF will not occur in people bitten by uninfected ticks. The following ticks have been shown to be vectors for RMSF: the mountain wood tick (Dermacentor andersoni), the American dog tick (Dermacentor variabilis), and the brown dog tick (Rhipicephalus sanguineus), with the first two as the primary vectors. Other ticks can be responsible as vectors in various worldwide regions.