Gram stain: negative Cell shape: rod-shaped or coccobacilli; highly pleomorphic Arrangement: Oxygen requirements: Other: Very small organisms -- 0.8 - 2.0 micrometers; these organisms are obligate intracellular parasites (they can only reproduce within a host cell). These organisms are transmitted to humans by insects and ticks. In humans they damage the permeability of capillaries; severe infections can cause the cardiovascular system to collapse. Patients exhibit a characteristic rash: progresses from small pink spots called macules to pink red pimple-like spots called papules which fuse together to form a maculopapular rash. Usually cultivated in lab only within living cultures such as fertilized eggs or animals.
Habitat:
Pathogenicity: causative agent of epidemic typhus (typhus fever); among the most notorious of all bacterial diseases; helped destroy the Aztec population in the 1500's and Napoleon's army during his battle against Russia in 1812.
Transmission: head and body lice (Pediculus)
Treatment: tetracycline and chloramphenicol.
* This genus is named after its discoverer in 1909, Howard Taylor Ricketts. Ricketts died from endemic typhus during his studies of this organism!
Rickettsia prowazekii
