Medical Microbiology

Yersinia(Plague,Enteritis) 291

Morphology,culture,andantigenstructure.Thesearepleomorphic,short

rodswithperitrichousflagellation.Theycanbeculturedonallstandardme-

diums.TheseYersiniabacteriagrowbetterat 20 – 308 Cthanat 378 C.

Pathogenesisandclinicalpictures.Allofthestrainsisolatedashuman

pathogensbeara 70 kbvirulenceplasmidwithseveralvirdeterminants.

Theycodeforpolypeptidesthatdirectthefunctionscelladhesion,phago-

cytosisresistance,serumresistance,andcytotoxicity.Yersiniaealsohave

chromosomalvirulencegenes,forexamplemarkersforinvasins,entero-

toxins,andanironcapturingsystem.Exactlyhowthesevirulencefactorsin-

teracttoproducethediseaseistoocomplextobedescribedindetailhere.

Yersiniaeareusuallyingestedindirectlywithfood.Althoughmuchlessfre-

quent,infectionscanalsooccurbywayofdirectcontactwithdiseasedanimals

oranimalcarriers.Thebacteriaenterthelowerintestinaltract,penetratethe

mucosaandaretransportedwiththemacrophagesintothemesentericlymph

nodes.Asimplifiedoverviewoftheresultingclinicalpicturesfollows:

&Intestinalyersinioses.Theclinicallydominantsymptomisenteritisto-

getherwithmesentericlymphadenitis.Thisformisfrequentlyobservedin

youthsandchildren.Otherentericformsincludepseudoappendicitisin

youthsandchildren,ileitis(pseudoCrohndisease),andcolitisinadults.

&Extraintestinalyersinioses.Theseinfectionsaccountforabout 20 %of

cases,usuallyadults.Notablefeaturesoftheclinicalpictureincludesepsis,

lymphadenopathy,rarelyhepatitis,andvariouslocalinfections(pleuritis,en-

docarditis,osteomyelitis,cholecystitis,localizedabscesses).

&Othersequelae.The immunopathologicalcomplicationsobservedin

about 20 %ofacutelyinfectedpatientsonetosixweeksafteronsetofthe

intestinalsymptomsincludereactivearthritisanderythemanodosum.

Diagnosis.Aconfirmeddiagnosisisonlypossiblewithidentificationofthe

pathogeninaculturebasedonphysiologicalcharacteristics.Specialmediums

areusedtoisolatethepathogenfromstool.Theagglutinationreaction,an

ELISAorimmunoblotassaycanbeusedtodetecttheantibodies.

Therapy.Generally,favorablecoursesrequirenochemotherapy.Clinically

difficultcasescanbetreatedwithcotrimoxazole,second-orthird-generation

cephalosporins,orfluorinated4-quinolones.

Epidemiologyandprevention.PrevalenceofY.enterocoliticaandY.pseudo-

tuberculosisinanimalsiswidespread.Themostimportantreservoirsinepi-

demiologicaltermsaremammalsthatarediseasedorcarrylatentinfections.

Fromthesesources,vegetation,soil,andsurfacewaterarecontaminated.

Transmissionisbytheoralpathwayinfood.Contactzoonosisispossible,

butrare.Therearenospecificprophylacticmeasures.

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Kayser, Medical Microbiology © 2005 Thieme