Contributor: Gordon K. Klintworth
Rickettsial diseases (epidemic typhus [typhus - epidemic], endemic typhus [typhus - endemic], scrub typhus [typhus - scrub], Q fever, Rocky Mountain spotted fever, Boutonneuse fever, Trench fever, Ehrlichiosis) are infections due to Rickettsiae. The organisms are transmitted by blood-sucking arthropods (ticks, lice, fleas, and mites). Rickettsiae replicate in the salivary glands and alimentary canal of these arthropods and when introduced into human tissue they replicate mainly within vascular endothelial cells causing the infected cells to proliferate and degenerate and resulting in vascular occlusion. This induces a focal ulcer and it is followed by the hematogenous dissemination of the organisms to distant sites. After ~4 weeks clinical disease abruptly ensues, with headache, fever, and often a hemorrhagic rash. Ocular lesions sometimes occur in all of the diseases produced by Rickettsiae. Rickettsiae can be identified in the affected tissues using specific stains.