Medical Microbiology

Shigella(BacterialDysentery) 287

Eliminatingtheinfectioninchronicstoolcarriersoftyphoidsalmonellae,

2 – 5 %ofcases,presentsaproblem.Chroniccarriersaredefinedasconvales-

centswhoarestilleliminatingpathogensthreemonthsaftertheendofthe

manifestillness.Theorganismsusuallypersistinthescarifiedwallofthe

gallbladder.Successissometimesachievedwithhigh-doseadministration

ofanti-infectiveagents,e.g.,4-quinolonesoraminopenicillins.Acholecystec-

tomyisrequiredinrefractorycases.

Epidemiology.Thecasesoftyphoidsalmonellosisseeninnorthernandcen-

tralEuropeareimportedbytravelers.Casesariseonlysporadicallyorinform

ofanepidemicbecauseofachainofunfortunatecircumstances.Humansare

theonlyprimarysourceofinfection.

Bycontrast,entericsalmonellosesoccurinthispopulationbothendemi-

callyandepidemically.Casecountsaresteadilyincreasing.Exactmorbidity

dataarehardtocomebyduetothelargenumbersofunreportedcases.Live-

stockrepresentsthemostimportantsourceofinfection.Thepathogensare

transmittedtohumansinfood.

Prevention.Themainmethodofeffectivepreventionistoavoidexposure:

thismeanscleandrinkingwater,preventionoffoodcontamination,avoid-

anceofuncookedfoodsincountrieswheresalmonellaeoccurfrequently,dis-

infectionofexcretacontainingsalmonellaeorfromchroniccarriers,etc.Itis

alsoimportanttoreportallcasestohealthauthoritiessothatappropriate

measurescanbetaken.

Typhoidfevervaccinationsfortravelerstoendemicareascanbestbedone

withtheoralattenuatedvaccineVirotifTy 2 1a.

Shigella(BacterialDysentery).....................................

&Shigellaisthecausativepathogeninbacterialdysentery.Thegenuscom-

prisesthespeciesS.dysenteriae,S.flexneri,S.boydii,andS.sonnei.Shigellae

arenonmotile.Thethreeprimaryspeciescanbeclassifiedinserovarsbased

onthefinestructureoftheirOantigens.Shigellaearecharacterizedbyin-

vasiveproperties.Theycanpenetratethecolonicmucosatocauselocalne-

croticinfections.Humansarethesolesourceofinfectionsinceshigellaeare

pathologicallyactiveinhumansonly.Thepathogensaretransmitteddirectly,

morefrequentlyindirectly,viafoodanddrinkingwater.Antibioticscanbe

usedtherapeutically. &

Classification.ThegenusShigellaincludesfourspecies:S.dysenteriae,S.flex-

neri,S.boydii,andS.sonnei.Thefirstthreearesubdividedinto 1 0,six,and

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Kayser, Medical Microbiology © 2005 Thieme