Medical Microbiology

RNAviruses 445

observedforthefirsttimeintheUSA(NewYork)in 1 999,apparentlyintro-

ducedintotheareabymigratingbirds.Itisstillnotknownwhythegeo-

graphicdistributionofthevirusorinfectedbirdschanged.

Vaccinesareavailableagainstyellowfever(livevaccine)andEuropean

tickborneencephalitis(deadvaccine).

Hepaciviruses(HepatitisCandG)

Pathogen.Aseriesofhepatitisinfectionsfollowingbloodtransfusionswas

observedthatcouldnotbeidentifiedaseitherhepatitisA(p. 43 7)orhepatitis

B(p.429),andwerethereforedesignatedas“non-A-non-B(NANB)hepatitis.”

ThediscoveryofthehepatitisCvirus(HCV)bymolecularbiologicalmeansin

1988 wasanelegantpieceofwork:RNAwasextractedfromtheplasmaofan

infectedchimpanzee,fromwhichcDNAwasproducedusingreversetran-

scriptase.ThecDNAwasthenclonedandthecorrespondingproteinsex-

pressed.Aboutonemillioncloneswere testedforreactivitywithsera

frompatientssufferingfromchronicNANBhepatitis.Aproteinwasfound

bythismethodthatreactedwithantibodiestoNANB,whereuponthecorre-

spondingclonedDNAwasusedasaprobetoidentifyfurtheroverlapping

genesegments.Theybelongtoaflaviviruswithapproximately 10 kbsense

RNAandseveralgenotypes.Asimilarstrategyledtoidentificationofafurther

flavivirusthatalsocauseshepatitis,nowknownasthehepatitisGvirus

(HGV).

Pathogenesisandclinicalpicture.HepatitisCresembleshepatitisBinmany

respects.Onemajordifferenceisthatitmuchmorefrequentlyproducesa

persistentinfection(85%)and,in 70 %ofcases,developsintoachronichep-

atitis,resultingincirrhosisoftheliverwithin 20 yearsandahepatocellular

carcinoma(HCC)inafurther 10 years.Thereasonforthehighlevelofviral

persistenceisthoughttobeapronouncedmutabilityfacilitatingevasionof

theimmunedefenses(quasispeciesofRNAviruses,p. 39 1).

DiagnosisofhepatitisCisdonewithantibodyEIAusinggeneticallyengi-

neeredviralproteins.Westernblotcanbeusedtoconfirmtheresult.The

RNAcanbedetectedbymeansofRT-PCRandthecourseoftherapycan

bemonitoredwithquantitativePCR.

Epidemiologyandprevention.TheincidenceofHCVinEuropeisabout0.3%,

withadecreasingtendencyintheyoungersegmentofthepopulation.

About 50 %ofacutehepatitiscasesareHCVinfections.Transmissionisby

bloodandbloodproducts.High-riskpersonsincludedialysispatients,health-

carestaff,andneedle-sharingdrugconsumers.Perinataltransmissionispos-

sible,butsexualcontactdoesnotappeartobeariskfactor.Thetransmission

routeisnotapparentinmanycases,givingrisetotheexpression“commu-

nity-acquiredinfection.”Feasibleprotectivemeasuresarethesameasinhep-

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Kayser, Medical Microbiology © 2005 Thieme