RNAviruses 449— HTLV-BLVretroviruses,includingHTLvirusestypesIandIIandthebo-
vineleukemiavirus.
— Spumaviruses,whichonlyoccurinanimals,twoofwhichare(probably)
fromhumans.
— Lentiviruses,withthehumanpathogensHIV 1 and2,maedivirus(pneu-
monia),andvisnavirus(encephalomyelitis)insheep,virusesaffecting
goatsandhorses,andanimalimmunedeficiencyviruses.
Ahumanpathogenretroviruswasisolatedforthefirsttimein 1980 from
adultssufferingfromT-cellleukemias.ItwasdesignatedasHTLVI(human
T-cellleukemiavirus).Ashorttimelater,aviruswasisolatedfromhairycell
leukemiapatientsandnamedHTLVII.
HTLVIisfoundinadultswithT-cellmalignancyaswellasinpatients
withneurologicaldiseases(myelopathies).HTLVIIappearstobeassociated
withT-cellmalignancyandotherlymphoproliferativediseases.Itsownetio-
logicalroleisstillunderdiscussion.
HereisasummaryofthehumanpathogenicaspectsofHIVincludingits
relationtoacquiredimmunedeficiencysyndrome(AIDS).
TheviralRNAgenome,whichisintegratedinthegenomeofthehostcell,
containsthefollowinggenesandregulatorysequences(see.Fig.8. 14 ):
Genesessentialtoviralreplication:
— tatgene:“transactivetranscription,”enhancesthetranscriptionand
thustheexpressionofviralproteinsbybindingtotheTAR(transactivation
responsiveregion)intheLTR.
— revgene:posttranscriptionalactivatorforsplicingandtransportofviral
mRNA(productionofstructuralproteins).
— LTRsequence:promoterandenhancerelements.
Structuralgenes:
— gaggene:group-specificantigen.
— polgene:codesforthereversetranscriptase,aproteaseandtheintegrase.
— envgene:envelopeglycoprotein(gp).
Genesnotessentialtoviralreplication:
— Virusinfectionfactor(vif):makesthevirusmoreinfectious.
— “Negative”factor(nef):inhibitsoractivatesviraltranscriptionasre-
quired,influencesT-cellactivation,reducesCD4expression.
— vpr:controlsrateofreplication.
— vpx:onlyinHIV2,controlsrateofreplication.
— vpu:onlyinHIV 1 ,contributestoviralrelease,increasesCD4turnover.8Kayser, Medical Microbiology © 2005 Thieme