Medical Microbiology

OpportunisticEnterobacteriaceae 299

oftheproximalsmallintestinewiththehelpofTCP(seeabove)andsecrete

choleratoxin(seeFig.4. 20 ).Thepathogendoesnotinvadethemucosa.

Theincubationperiodofcholeraistwotofivedays.Theclinicalpictureis

characterizedbyvoluminous,waterydiarrheaandvomiting.Theamountof

fluidslostperdaycanbeashighas 20 l.Furthersymptomsderivefromthe

resultingexsiccosis:hypotension,tachycardia,anuria,andhypothermia.

Lethalitycanbeashighas 50 %inuntreatedcases.

Diagnosisrequiresidentificationofthepathogeninstoolorvomit.Some-

times a rapid microscopical diagnosis succeeds in finding numerous

Gram-negative,bentrodsinswarmpatterns.Culturingisdoneonliquid

orsolidselectivemediums,e.g.,alkalinepeptonewaterortaurocholatege-

latinagar.Suspectedcoloniesareidentifiedbybiochemicalmeansorbyde-

tectionoftheO:1antigeninanagglutinationreaction.

Therapy.Themostimportantmeasureisrestorationofthedisturbedwater

andelectrolytebalanceinthebody.Secondly,tetracyclinesandcotrimoxa-

zolecanbeused,abovealltoreducefecaleliminationlevelsandshorten

theperiodofpathogensecretion.

Epidemiologyandprevention.Nineteenth-centuryEuropeexperiencedsev-

eralcholerapandemics,allofwhichwerecausedbytheclassiccholeraebio-

var.Anincreasingnumberofcasescausedbythebiovareltor,whichischar-

acterizedbyalowerlevelofvirulence,havebeenobservedsince 1961 .With

theexceptionofminorepidemicsinItalyandSpain,Europe,andtheUSA

havebeensparedmajoroutbreaksofcholerainmorerecenttimes.South

Americahasforanumberofyearsbeenthevenueofepidemicsofthedisease.

Humansaretheonlysourceofinfection.Infectedpersonsinparticular

eliminatelargenumbersofpathogens.ConvalescentsmayalsoshedV.cho-

leraeforweeksorevenmonthsaftertheinfectionhasabated.Chroniccar-

riersaswithtyphoidfeverareveryrare.Transmissionofthediseaseisusual-

lyviafoods,andinparticulardrinkingwater.Thisexplainswhycholeracan

readilyspreadtoepidemicproportionsincountrieswithpoorhygienestan-

dards.

Protectionfromexposuretothepathogenisthemainthrustoftherele-

vantpreventivemeasures.Ingeneral,controlofcholerameansensuring

adequatefoodandwaterhygieneandpropereliminationofsewage.In

caseofanoutbreak,infectedpersonsmustbeisolated.Infectiousexcreta

andcontaminatedobjectsmustbedisinfected.Evensuspectedcasesof

choleramustbereportedtohealthauthoritieswithoutdelay.Theincubation

periodofthecholeravibrioisreportedininternationalhealthregulationsto

befivedays.Avaccinecontainingkilledcellsaswellanattenuatedlive

vaccineareavailable.Thelevelofimmunizationprotectionis,however,in-

completeandlastsforonlysixmonths.

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Kayser, Medical Microbiology © 2005 Thieme