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:
8
Kayser, Medical Microbiology © 2005 Thieme