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Lecture 30 Rickettsia and Coxiella
1. بسم ا الرحمن الرحيم
RICKETTSIA
AND
COXIELLA
Prof. Khalifa Sifaw Ghenghesh
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. 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. 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.
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.
Scrub typhus
• Orientia tsutsugamushi (previously
R. tsutsugamushi )
• Larval stages (chiggers) of mites
(Leptotrombidium)
• Hosts: Rats or other small mammals
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.
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
10. Child's right hand and wrist displaying the
characteristic spotted rash of Rocky Mountain
spotted fever caused by Rickettsia rickettsii
11. Rickettsia tsutsugamushi free within the
cytoplasm of a mouse brain capillary
endothelial cell. Capillary wall appears in cross
section
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. IFA reaction of a positive human serum
on Rickettsia rickettsii grown in chicken
yolk sacs, 400X
14. Red structures indicate immunohistological
staining of Rickettsia rickettsii in endothelial
cells of a blood vessel from a patient with fatal
RMSF
20.
Laboratory Diagnosis
• Demonstration of specific Abs
Complement fixation test
Indirect immunofluorescence
assay
• Isolation of organism
Not recommended
Treatment
• Doxycycline
Control