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RICKETTSIA

AND

COXIELLAProf. Khalifa Sifaw Ghenghesh

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Rickettsia species

Gram-negative bacilli

Obligateintracellularparasites

Allassociated withanarthropodvector

Pathogenicspeciesparasitizeendothelialcellsalmostexclusively

2antigenicallydistinctgroups Typhusgroup

Spotted fevergroup

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Pathogenesis

Theorganismsenterthe bodythroughthe biteor faecesofan

infectedarthropodvector Disseminatethrough bloodstream

>> endothelialcells byinducedphagocytosis >> escape from

phagosome >> multiplyintra-cellularly >> destroyhostcell

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Flea-borne fevers (Murinetyphus) R. typhi

Ratsandtheirinfected fleas

Tropicalandsubtropicalcoastalregions

Ports withlargenumberofrats

Disease:similartoepidemictyphusbutmilder

Tick-bornespotted fever (group)

Example:R. rickettsii Can belife-threatening

Maintainedinenzooticcycle (ticksandtheir wildanimalhosts)

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Scrub typhus

Orientia tsutsugamushi(previouslyR. tsutsugamushi)

Larvalstages (chiggers) ofmites(Leptotrombidium)

Hosts:Ratsorothersmallmammals

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Laboratory Diagnosis

SerologicalMethods

Weil-Felixtest (Agglutinationtest)

Somatic Agsofnon-motileProteus

species

Notreliable >> low levelsofsensitivityandspecificity

Detectionof AbstoRickettsia species by:

Immunofluorescence Latexagglutination

Enzymeimmuno-assay

Deathmayoccur beforedetectablelevelsof Abarepresent

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IsolationoftheOrganism

Incellculture Insusceptiblelaboratoryanimal

Notpracticle

Detectionoftheorganismintissue Specimen:Skin biopsies from

petechiallesions Examined by:

Immuno-fluorescenceor

immuno-enzymemethods

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Treatment

Rickettsiostaticantibiotics

Tetracyclines

Chloramphenicol Intensivenursingcareandmanagementof fluidsand

electrolytes

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Child'srighthandand wristdisplayingthecharacteristicspottedrashofRockyMountain

spotted fevercaused byRickettsia rickettsii

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Rickettsia tsutsugamushifree withinthecytoplasmofamouse braincapillary

endothelialcell.Capillary wallappearsincrosssection

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Dorsalview ofanAmerican Dog Tick,Dermacentor variabilis, aknowncarrierof

RockyMountainSpotted

Fevercaused bythebacteriumRickettsia rickettsii.

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IFA reactionofapositivehumanserumonRickettsia rickettsiigrowninchicken

yolksacs, 400X

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RedstructuresindicateimmunohistologicalstainingofRickettsia rickettsiiinendothelialcellsofa bloodvessel fromapatient with

fatalRMSF

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Removing attached ticksRemoving attached ticks

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Coxeilla burnetii

Gram-negative, Pleomorphic,coccobacillary bacteria

Obligatoryintracellular

Q fever Typhoid-likeillness

Almost worldwidedistribution

Reservoirs: wildanddomesticanimals Infectionresults frominhalationofaerosolscontainingtheorganism

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Coxiella burnetii

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Coxiella burnetii

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Laboratory Diagnosis

Demonstrationofspecific AbsComplement fixationtest

Indirectimmunofluorescenceassay

Isolationoforganism

Notrecommended

Treatment

Doxycycline

Control