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RICKETTSIOSESBy Martin Osodo(MBChB Y3)
Rickettsiosesare a group of diseases generally caused by speciesofRickettsia.Genera;RickettsiaOrientiaCoxiellaEhrlichiaRochalimaeaAnaplasma,NeorickettsiaThey are small, Gram-negative, aerobic, coccobacilli that are obligateintracellular parasites of eucaryotic cells (residing in the cytoplasm orwithin the nucleus).
mammals and arthropods are natural hosts,but humans are incidental hosts(i.etransmitted to humans by arthropods).3 major groupsbased on clinicalcharacteristics of disease:1. spotted fever group;2. typhus group;3. scrub typhus group.
Spotted fever groupRocky Mountain spotted feverRickettsialpoxBoutonneuse feverTyphus groupLouse-borne (epidemic) typhusBrill-Zinsser disease (relapsing louse-borne typhus)Murine (endemic or flea-borne) typhusScrub typhus group (Tsutsugamushi disease).
PathogenesisArthropod biteInvade endothelial cells, destroy endothelial cellsInflammatory cells accumulate/ blood leakagehence red spots and rashes.Release organisms reinfection
Increased vascular permeabilty>>edema(lifethreatenind in brain amd lungs)>>>low bloodvolume>>>hypotension>>>decreasedperfusion of organs>>> organ dysfunction(e.gacute renal failure, prerenal azotemia)
Spotted fever groupRocky Mountain spotted feverAgent: R. rickettsiiVector: ticksDistribution:Western Hemisphere, including mostof the US (except Maine, Hawaii, and Alaska);Central and South AmericaClinical features: rash>>>petechial;vasculitis (skin,subcutaneous tissues, CNS, lungs, heart, kidneys,liver, or spleen).

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Term
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Rickettsia

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