Medical Microbiology

DNAViruses 429

Diagnosis.Thepoxvirusesgrouparerelativelyeasytorecognizeunderan

electronmicroscopeinpustulecontents,providedthepustuleshavenot

yetdriedoutorbeensuperinfectedwithbacteria.Orthopoxvirusesandpara-

poxvirusescanbedifferentiatedmorphologically,buttheviruseswithineach

genussharethesamemorphology.Molluscumcontagiosumisdiagnosedhis-

tologically.

Epidemiologyandprevention.Diseasedhumanswerethesoleviralreser-

voirofvariolaandalastrim.Transmissionwasdirectandaerogenicand,

althoughthevirusishighlyresistantevenwhendesiccated,lessfrequent

viacontaminatedobjects(bedlinens).Thevacciniavirusdoesnotoccurin

natureandanyhumaninfectionsarenowaccidental(laboratoryinfections).

Thezootropicpoxvirusesaretransmittedsolelybymeansofcontactwith

infectedanimals.Molluscumcontagiosumistransmittedbyinterhuman

contact.

Hepadnaviruses:HepatitisBVirusand

HepatitisDVirus

&AhepatitisBvirus(HBV)infection(seep.385ff.,replication)oftheliver

cellsresultsinexpressionofviralantigenonthecellsurface,followedbyim-

munologicalcelldamagewithacute,possiblyfulminant,chronicpersistentor

chronicaggressivehepatitis.Thefinalstagescanbelivercirrhosisorhepa-

tocellularcarcinoma.Aconcurrentorlatersuperinfectionbyadefective,

RNA-containingandHBV-dependenthepatitisDvirus(HDV,deltaagent)

normallyexacerbatestheclinicalcourse.Bothvirusesaretransmittedin

bloodorbodyfluids,wherebyevenatinyamountofbloodmaybeenough

tocauseaninfection.

Diagnosis:immunologicalantigenorantibodyassayinpatientserum.The

antigenorantibodypatternsobservedprovideinsightsonthestageand

courseofthedisease.

Prevention:activeimmunizationwithHBVsurface(HBs)antigen;concur-

rentpostexposurepassiveimmunization. &

HepatitisBpathogen.ThehepatitisBvirus(HBV)isthemainrepresentative

ofthefamilyofhepadnaviruses,Hepadnaviridae.Thenameofthefamilyisan

acronymofthediseasecausedbythevirusanditsgenomictype.Itcausesa

sometimeschronicformofliverinflammation(hepatitis)anditsgenome

consistsofpartiallydouble-strandedDNA(hepadnavirus=hepatitisDNA

virus).ThereplicationcycleoftheHBVincludesatransientRNAphase

(fordetailsseeChapter 7 ,p.385).TheHBVpossessanenvelopemadeup

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Kayser, Medical Microbiology © 2005 Thieme