Medical Microbiology

408 7 GeneralVirology

Selectionofahostsystem.Thehostsystemtobeusedischosenbasedonthe

suspected(andrelevant)virusinfectors.Observationandincubationtimes,

andthushowlongalaboratorydiagnosiswilltake,alsodependontheviral

speciesunderinvestigation.

Identificationofthevirusesisbasedfirstontheobservedcellchanges,then

determinedserologicallyusingknownantibodiesandappropriatemethods

suchasimmunoelectronmicroscopy,EIA,ortheneutralizationtest(seep.

402 fortheneutralizationmechanism).Methodsthatdetecttheviralgenome

bymeansofin-situorfilterhybridizationarenowseeingincreasinguse.

Significanceofresults.Theimportanceofvirusisolationdependsonthe

virustype.Inmostcases,isolationwillbeindicativeoftheetiologyofthe

patient’sdisease.Insomecases,(inparticulartheherpesvirusandadenovirus

group,seeChapter8),latentvirusesmayhavebeenactivatedbyacompletely

differentdisease.Insuchcases,theymayofcoursebeisolated,buthaveno

causalconnectionwiththeobservedillness.

Isolationisthemostsensitivemethodofviraldiagnosticdetection,butit

cannotdetectallvirusesinallsituations.Thismeansthatanegativeresult

doesnotentirelyexcludeaviralinfection.Anotheraspectisthatthemethods

ofvirusisolation,withfewexceptions,detectonlymature,infectiousvirions

andnotthelatentvirusesintegratedinthecells.Thisrendersdiagnosticiso-

lationuselessduringlatency(e.g.,herpessimplexbetweenrecidivations).

Amplificationculture.Inthismethod,thevirusisgrownforabriefperiodin

acellculture.BeforetheCPEisobserved,thecultureistestedusingtheanti-

genandgenomicmethodsdescribed.Thisisalsoknownasa“shellvialassay”

becausethecellsaregrownoncoverslipsinshellvials(testtubeswithscrew

caps).Usingthisarrangement,methodsensitivitycanbeincreasedbycen-

trifugingthediagnosticmaterialontothecell monolayer.Thegreatest

amountoftimeissavedbydetectingthevirus-specificproteinsproduced

earlyintheinfectioncycle,whichiswhythesearchconcentratesonsuch

so-called“earlyantigens”(seep.388).Usingthismethod,thetimerequired

toconfirmacytomegalyvirus,forinstance,canbeshortenedfromfourtosix

weekstoonlytwotofivedayswithpracticallynolossofsensitivitycompared

toclassicisolationmethods.

DirectVirusDetection

Inthisdiagnosticapproach,thevirusesarenotidentifiedasinfectiousunits

perse,butratherasviralparticlesorpartsofthem.Theideaistofindthe

virusesdirectlyinthepatientmaterialwithoutpriorculturingorreplication.

Virusesinserousfluidssuchasthecontentsofherpessimplexorvaricella-

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Kayser, Medical Microbiology © 2005 Thieme