‫بسم هللا الرحمن الرحيم‬
RICKETTSIA
AND
COXIELLA
Prof. Khalifa Sifaw Ghenghesh
Rickettsia species
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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
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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
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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
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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
Laboratory Diagnosis
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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:
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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
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Detection of the organism in
tissue
• Specimen: Skin biopsies from
petechial lesions
• Examined by:
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Immuno-fluorescence or
immuno-enzyme methods
Treatment
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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
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Gram-negative, Pleomorphic,
coccobacillary bacteria
Obligatory intracellular
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Q fever
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Typhoid-like illness
Almost worldwide distribution
Reservoirs: wild and domestic animals
Infection results from inhalation of
aerosols containing the organism
Coxiella burnetii
Coxiella burnetii
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Laboratory Diagnosis
• Demonstration of specific Abs
Complement fixation test
 Indirect immunofluorescence
assay
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• Isolation of organism
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Not recommended
Treatment
• Doxycycline
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Control