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Rocky Mountain spotted fever is a potentially fatal tick-borne disease transmitted by infected ticks such as Dermacentor variabilis and Dermacentor andersoni.

It is caused by Rickettsia rickettsii, a gram-negative, coccobacillary, obligate intracellular bacterium.

After entering the bloodstream, the pathogen uses host cell surface proteins to invade vascular endothelial cells.

Once inside, the bacteria escape the phagosome, replicate in the cytoplasm, and spread between cells using host actin filaments.

This damages endothelial cells, increases vascular permeability and causes capillary leak with extravasation of leukocytes and plasma.

This leads to edema, reduced tissue perfusion, and hypotension.

Early symptoms appear within 2 to 14 days, and include high fever, headache, muscle aches, or nausea.

These symptoms are followed by a maculopapular or flat red rash on the wrists and ankles, which may progress to a petechial rash with pinpoint red or purple spots.

If left untreated, the illness can cause fatal complications like multiorgan failure.