lecture 30 rickettsia and coxiella
TRANSCRIPT
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بسم الله الرحمن الرحيم
RICKETTSIA AND
COXIELLAProf. 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 >> endothelial cells by induced phagocytosis >> escape from phagosome >> multiply intra-cellularly >> 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 >> 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 ticksRemoving 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