Lecture 30 Rickettsia and Coxiella
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Lecture 30 Rickettsia and Coxiella






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Lecture 30 Rickettsia and Coxiella Lecture 30 Rickettsia and Coxiella Presentation Transcript

  • ‫بسم ا الرحمن الرحيم‬ RICKETTSIA AND COXIELLA Prof. Khalifa Sifaw Ghenghesh
  • Rickettsia species      Gram-negative bacilli Obligate intracellular parasites All associated with an arthropod vector Pathogenic species parasitize endothelial cells almost exclusively 2 antigenically distinct groups • Typhus group • Spotted fever group
  • Pathogenesis   The organisms enter the body through the bite or faeces of an infected arthropod vector Disseminate through bloodstream >> endothelial cells by induced phagocytosis >> escape from phagosome >> multiply intracellularly >> destroy host cell
  • Rickettsial Diseases  Epidemic typhus • Transmitted from human to human by R. prowazekii • Vector: body louse (Pediculus humanus) • Incubation period: 5-15 days • Macular rash: 4-7 days after illness and begin to fade after 1-2 days • In severe: rash may last longer and become haemorrhagic
  •  Flea-borne fevers (Murine typhus) • R. typhi • Rats and their infected fleas • Tropical and subtropical coastal regions • Ports with large number of rats • Disease: similar to epidemic typhus but milder  Tick-borne spotted fever (group) • Example: R. rickettsii • Can be life-threatening • Maintained in enzootic cycle (ticks and their wild animal hosts)
  •  Scrub typhus • Orientia tsutsugamushi (previously R. tsutsugamushi ) • Larval stages (chiggers) of mites (Leptotrombidium) • Hosts: Rats or other small mammals
  • Laboratory Diagnosis  Serological Methods • Weil-Felix test (Agglutination test) Somatic Ags of non-motile Proteus species  Not reliable >> low levels of sensitivity and specificity • Detection of Abs to Rickettsia species by:     Immunofluorescence Latex agglutination Enzyme immuno-assay • Death may occur before detectable levels of Ab are present
  •  Isolation of the Organism • In cell culture • In susceptible laboratory animal • Not practicle  Detection of the organism in tissue • Specimen: Skin biopsies from petechial lesions • Examined by: Immuno-fluorescence or  immuno-enzyme methods 
  • Treatment  Rickettsiostatic antibiotics  • Tetracyclines • Chloramphenicol Intensive nursing care and management of fluids and electrolytes
  • Child's right hand and wrist displaying the characteristic spotted rash of Rocky Mountain spotted fever caused by Rickettsia rickettsii
  • Rickettsia tsutsugamushi free within the cytoplasm of a mouse brain capillary endothelial cell. Capillary wall appears in cross section
  • Dorsal view of an American Dog Tick, Dermacentor variabilis, a known carrier of Rocky Mountain Spotted Fever caused by the bacterium Rickettsia rickettsii.
  • IFA reaction of a positive human serum on Rickettsia rickettsii grown in chicken yolk sacs, 400X
  • Red structures indicate immunohistological staining of Rickettsia rickettsii in endothelial cells of a blood vessel from a patient with fatal RMSF
  • Removing attached ticks
  • Coxeilla burnetii    Gram-negative, Pleomorphic, coccobacillary bacteria Obligatory intracellular Q fever • • • • Typhoid-like illness Almost worldwide distribution Reservoirs: wild and domestic animals Infection results from inhalation of aerosols containing the organism
  • Coxiella burnetii
  • Coxiella burnetii
  •  Laboratory Diagnosis • Demonstration of specific Abs Complement fixation test  Indirect immunofluorescence assay  • Isolation of organism   Not recommended Treatment • Doxycycline  Control