Medical Microbiology

Yersinia(Plague,Enteritis) 289

abated.Transmissionisbydirectcontact(smearinfection)orindirectuptake

viafood,surfacewater,orflies.Controlofdysenteryincludesexposurepro-

phylaxismeasuresgearedtopreventsusceptiblepersonsfromcominginto

contactwiththepathogen.

Yersinia(Plague,Enteritis).........................................

&Y.pestisisthecausativepathogenofplague(blackdeath,bubonicplague).

Plagueisaclassicrodentzoonosis.Itoccurredinepidemicproportionsinthe

MiddleAges,butisseentodayonlysporadicallyinpersonswhohavehad

directcontactwithdiseasedwildrodents.Thepathogenspenetrateinto

theskinthroughmicrotraumata,fromwheretheyreachregionallymph

nodesinwhichtheyproliferate,resultinginthecharacteristicbuboes.In

thenextstage,thepathogensmayenterthebloodstreamortheinfection

maygeneralizetoaffectotherorgans.Laboratorydiagnosisinvolvesisolation

andidentificationoftheorganisminpus,blood,orothermaterial.Therapy

requiresuseofantibiotics.

Y.enterocoliticaandY.pseudotuberculosiscausegeneralizedzoonosesinwild

animalsandlivestock.Diseasedanimalscontaminatetheirsurroundings.Hu-

mansthentakeupthepathogensorallyinwaterorfood.Theorganisms

penetratethemucosaofthelowerintestinaltract,causingenteritisaccom-

paniedbymesentericlymphadenitis.

Extramesentericformsareobservedin 20 %ofinfectedpersons(sepsis,

lymphadenopathies,variousfocalinfections).Secondaryimmunopathologi-

calcomplicationsincludearthritisanderythemanodosum.Diagnosisin-

volvesidentificationofthepathogenbymeansofselectiveculturing. &

Todate, 10 differentspecieshavebeenclassifiedinthegenusYersinia.The

speciesmostfrequentlyisolatedisY.enterocolitica.Y.pestis,the“blackdeath”

pathogenresponsibleforepidemicsintheMiddleAges,todaynolongerpre-

sentsasignificantthreat.

Yersiniapestis.........................................

Morphologyandculture.Y.pestisisanonflagellated,short,encapsulated,

Gram-negativerodbacteriathatoftenshowsbipolarstaining.Thisbacterium

isreadilyculturedonstandardnutrientmediumsat 308 C.

Pathogenesisandclinicalpicture.Theplagueisprimarilyadiseaseofro-

dents(rats).Itspreadsamongthembydirectcontactorviatheratflea.Earlier

4

Kayser, Medical Microbiology © 2005 Thieme