RICKETTSIA

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• RICKETTSIA
• AND
• COXIELLA
• Prof. Khalifa Sifaw Ghenghesh

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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

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Pathogenesis

• The organisms enter the body through the bite or
  faeces of an infected arthropod vector
• Disseminate through bloodstream gtgt endothelial
  cells by induced phagocytosis gtgt escape from
  phagosome gtgt multiply intra-cellularly gtgt destroy
  host cell

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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

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• 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)

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• Scrub typhus
• Orientia tsutsugamushi (previously R.
  tsutsugamushi )
• Larval stages (chiggers) of mites
  (Leptotrombidium)
• Hosts Rats or other small mammals

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Laboratory Diagnosis

• Serological Methods
• Weil-Felix test (Agglutination test)
• Somatic Ags of non-motile Proteus species
• Not reliable gtgt 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

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• 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

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Treatment

• Rickettsiostatic antibiotics
• Tetracyclines
• Chloramphenicol
• Intensive nursing care and management of fluids
  and electrolytes

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Child's right hand and wrist displaying the
characteristic spotted rash of Rocky Mountain
spotted fever caused by Rickettsia rickettsii
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Rickettsia tsutsugamushi free within the
cytoplasm of a mouse brain capillary endothelial
cell. Capillary wall appears in cross section
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Dorsal view of an American Dog Tick, Dermacentor
variabilis, a known carrier of Rocky Mountain
Spotted Fever caused by the bacterium Rickettsia
rickettsii.
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IFA reaction of a positive human serum on
Rickettsia rickettsii grown in chicken yolk sacs,
400X
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Red structures indicate immunohistological
staining of Rickettsia rickettsii in endothelial
cells of a blood vessel from a patient with fatal
RMSF
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Removing attached ticks
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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

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Coxiella burnetii
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Coxiella burnetii
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• Laboratory Diagnosis
• Demonstration of specific Abs
• Complement fixation test
• Indirect immunofluorescence assay
• Isolation of organism
• Not recommended
• Treatment
• Doxycycline
• Control