DISTINCTIVE PROPERTI14 - • Replication of the bacteria...

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DISTINCTIVE PROPERTIES: These organisms are small, pleomorphic coccobacilli about 2 µm in length. Their structure is typical of Gram-negative bacteria. Rickettsia replicate in the cytoplasm and nucleus of their host cell; Coxiella replicate only in the phagolysosome. PATHOGENESIS: Typhus, spotted fever and trench fever are transmitted via arthropod vectors; Q fever is acquired via inhalation or ingestion of contaminated milk or food. Within minutes, the bacteria enter host endothelial cells via an induced phagocytosis. The enzyme phospholipase A may help penetration.
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Unformatted text preview: • Replication of the bacteria causes lysis of the host cell and consequent spread to other cells. • Initial replication occurs at the site of entry producing a local lesion. This is followed by dissemination via the vascular system producing vasculitis and a skin rash . These lesions may become necrotic. • Virulence is probably due to many factors including release of endotoxin, the production of immune complexes and hypersensitivity reactions. • A characteristic triad of symptoms include fever, headache and rash (no rash with Q fever)....
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