Medical Microbiology

LaboratoryDiagnosis 405

formationforproteinstobesynthesizedbythecell.Thiscloseassociation

betweenvirusesandtheirhostcellsisasourceofsomeessentialdifficulties

encounteredwhendevelopingvirus-specificchemotherapeutics,sinceany

interferencewithviralsynthesisislikelytoaffectphysiologicalcellularsyn-

theticfunctionsaswell.Specificinterventionisonlypossiblewithviruses

thatcodefortheirownenzymes(e.g.,polymerasesorproteases),whichen-

zymesalsoreactwithviralsubstrates.Anotherproblematicaspectisthene-

cessityofadministeringchemotherapeutics(Table 7. 4 )early,preferablybe-

foreclinicalsymptomsmanifest,sincethepeakofviralreplicationisthen

usuallyalreadypast(p.399).

Development of resistance to chemotherapeutics. Acyclovir-resistant

strainsofherpesviruses,inparticularherpessimplexviruses,areoccasionally

isolated.Lessfrequently,cytomegalyvirusesresistanttoganciclovirarealso

found.ThesevirusespossessathymidinekinaseorDNApolymerasealtered

bymutation.Infectionscausedbyresistantherpesvirusesarealsoobserved

inimmunodeficientpatients;thepathogensnolongerrespondtotherapy

afterlong-termtreatmentofdermalormucosalefflorescences.

Thereare,asyet,nostandardizedresistancetestsforchemotherapy-re-

sistantviruses,sothattheusefulnessofsuchtestresultsisofquestionable

valueinconfirmedcases.Also,theresultsobtainedinvitrounfortunatelydo

notcorrelatewellwiththecasesofresistantvirusesobservedinclinicalset-

tings.

LaboratoryDiagnosis

&Thefollowingmethodscanbeusedtoobtainavirologicallaboratorydi-

agnosis:

— Virusisolationbygrowingthepathogeninacompatiblehost;usually

doneincellcultures,rarelyinexperimentalanimalsorhenembryos.

— Directvirusdetection.Themethodsofserology,molecularbiology,and

electronmicroscopyareusedtoidentifyvirusesorviruscomponentsdi-

rectly,i.e.,withoutpreculturing,indiagnosticspecimens.

— SerodiagnosticsinvolvingassayofantiviralantibodiesoftheIgGorIgM

classesinpatientserum. &

Indicationandmethods.Laboratorydiagnosticproceduresforvirusinfec-

tionsarecostly,time-consuming,andrequireconsiderablestafftime.Itis

thereforeimportanttoconsidercarefullywhethersuchtestsareindicated

inaconfirmedcase.Thephysicianinchargeoftreatmentmustmakethis

decisionbasedondetailedconsiderations.Ingeneral,itcanbesaidthat

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Kayser, Medical Microbiology © 2005 Thieme