Medical Microbiology

8 VirusesasHumanPathogen

K.A.Bienz

DNAViruses

ViruseswithSingle-StrandedDNAGenomes

Thegroupsofviruseswithsingle-strandedDNAgenomesarecontainedin

onlyonefamily,theparvoviruses,withonlyasinglehumanpathogen

type.TheGeminiviridae,Circoviridae,andmanyotherfamilieshavecircular

single-strandedDNA,butinfectonlyplantsand,morerarely,animals.

Parvoviruses

&Thisgroup’sonlyhumanpathogen,parvovirusB19,isthecausativevirus

inerythemainfectiosum(alsoknownas“slappedcheeksyndrome”orthe

“fifthdisease”)inchildrenandcausesaplasticcrisisinanemicpatients.

Thevirusalsocontributestojointdiseases,embryopathies,andtissuerejec-

tionfollowingrenaltransplants.Diagnosis:serological(IgGandIgM)and

PCR. &

Pathogen.Theparvovirusesareamongthesmallestviruseswithadiameter

of 19 – 25 mm.Theyareicosahedral,nonenveloped,andtheirgenomeisinthe

formofsingle-strandedDNA(ssDNA).Someparvovirusescanonlyreplicate

inthepresenceofahelpervirus(adenovirusorherpesvirus).ParvovirusB19,

theonlyhumanpathogenicparvovirusidentifiedtodate,iscapableofauto-

nomicreplication,i.e.,itrequiresnohelpervirus.Somezoopathicstrainsalso

showthiscapabilityinrodents,dogs,andpigs.

Pathogenesisandclinicalpicture.ParvovirusB1 9 replicatesinthebone

marrowinerythrocyteprecursorcells,whicharedestroyedintheprocess.

Inpatientsalreadysufferingfromanemia(sickle-cellanemia,chronichemo-

lyticanemia),suchinfectionsresultinso-calledaplasticcrisesinwhichthe

lackoferythrocyteresupplyleadstoacriticalshortage.Inotherwisehealthy

persons,theseinfectionsusuallyrunanasymptomaticcourse.Theycan,how-

ever,alsocauseaharmlessepidemicinfectioninchildren,erythemainfec-

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Kayser, Medical Microbiology © 2005 Thieme