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Lecture 30 Rickettsia and Coxiella

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Lecture 30 Rickettsia and Coxiella

  1. 1. ‫بسم ا الرحمن الرحيم‬ RICKETTSIA AND COXIELLA Prof. Khalifa Sifaw Ghenghesh
  2. 2. 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
  3. 3. 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
  4. 4. 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
  5. 5.  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)
  6. 6.  Scrub typhus • Orientia tsutsugamushi (previously R. tsutsugamushi ) • Larval stages (chiggers) of mites (Leptotrombidium) • Hosts: Rats or other small mammals
  7. 7. 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
  8. 8.  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 
  9. 9. Treatment  Rickettsiostatic antibiotics  • Tetracyclines • Chloramphenicol Intensive nursing care and management of fluids and electrolytes
  10. 10. Child's right hand and wrist displaying the characteristic spotted rash of Rocky Mountain spotted fever caused by Rickettsia rickettsii
  11. 11. Rickettsia tsutsugamushi free within the cytoplasm of a mouse brain capillary endothelial cell. Capillary wall appears in cross section
  12. 12. Dorsal view of an American Dog Tick, Dermacentor variabilis, a known carrier of Rocky Mountain Spotted Fever caused by the bacterium Rickettsia rickettsii.
  13. 13. IFA reaction of a positive human serum on Rickettsia rickettsii grown in chicken yolk sacs, 400X
  14. 14. Red structures indicate immunohistological staining of Rickettsia rickettsii in endothelial cells of a blood vessel from a patient with fatal RMSF
  15. 15. Removing attached ticks
  16. 16. 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
  17. 17. Coxiella burnetii
  18. 18. Coxiella burnetii
  19. 19.  Laboratory Diagnosis • Demonstration of specific Abs Complement fixation test  Indirect immunofluorescence assay  • Isolation of organism   Not recommended Treatment • Doxycycline  Control

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