Medical Microbiology

448 8 VirusesasHumanPathogen

withpossiblyotherroutesoftransmissionseemsimportant.Theonlypre-

ventivemeasuretodateisexposureprevention.Undertherapywithribavirin

andintensivecare,mortalityofSARSisaround 10 %.

Retroviruses

&Retrovirusespossessanenzyme,reversetranscriptase,thatcantranscribe

ssRNAintodouble-strandedDNA.Thisactivityisreflectedinthedesignation

“retroviruses.”IntegrationoftheDNAthusderivedfromtheviralgenomein

thehost-cellgenomeisapreconditionforviralreplication.Certainretro-

virusesarealsocapableofoncogeniccelltransformation.Duetothispoten-

tialandtheirRNAgenome,thesevirusesarealsocalledoncornaviruses(see

Chapter7).

HumanpathogenretrovirusesknowntodateincludethetypesHTLV(human

T-cellleukemiavirus)IandIIandHIV(humanimmunodeficiencyvirus) 1 and

2.TheformerareT-cellmalignancy-causingpathogens,thelattercauseac-

quiredimmunedeficiencysyndrome—AIDS.

AIDSmanifestsasareductionofThelpercellsafteranaverageincubation

timeof 10 years.Thecollapseofcellularimmunityresultsinoccurrence

oftypicalopportunisticinfections(Pneumocystiscariniipneumonia,fungal

andmycobacterialinfections,CMV,andotherviralinfections)aswellaslym-

phomasandKaposisarcoma.Transmissionisbysexualintercourse,blood

andbloodproducts,aswellasprenatalandperinatalinfections.

Diagnosis:HIVinfectionsareroutinelydetectedbyserology(antibodiesor

viralantigen).Thecirculatingviruscount(viralload)isdeterminedbymeans

ofquantitativeRT-PCR.TheAIDSdiagnosisisaclinicalprocedurethatpre-

supposespositiveconfirmationofHIVinfection.

Therapy:inhibitorsofreversetranscriptaseandprotease.

Prevention:exposureprophylaxiswhencontactwithbloodisinvolved(drug

addicts,healthcarestaff)andsexualintercourse.Postexposureprophylaxis

andprophylaxisinpregnancywithchemotherapeutics. &

Pathogen.TheRetroviridaefamilyistheclassificationgroupforallRNA

viruseswithreversetranscriptionofRNAtoDNAintheirreproductivecycles

(RNA-dependentDNAsynthesis)(p.385).Onlyzoopathicretroviruseswere

knownformanyyears.Thesevirusescausevariouskindsoftumorsin

animals.In 198 0,retroviruseswerealsodiscoveredinhumans.Thisvirus

familyincludessevengenera,threeofwhichplaysignificantrolesinhuman

medicine:

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Kayser, Medical Microbiology © 2005 Thieme