•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.
•Pathogenesis–Arthropod bite–Invade endothelial cells, destroy endothelial cells–Inflammatory 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 group•Rocky Mountain spotted fever–Agent: R. rickettsii–Vector: ticks–Distribution:Western Hemisphere, including mostof the US (except Maine, Hawaii, and Alaska);Central and South America–Clinical features: rash>>>petechial;vasculitis (skin,subcutaneous tissues, CNS, lungs, heart, kidneys,liver, or spleen).