Medical Microbiology

442 8 VirusesasHumanPathogen

puberty.Thevaccineistoleratedsowellthatpriorimmunestatuschecksare

notrequired.

Arboviruses

Theterm“arbovirus”(arthropodbornevirus)wasoriginallyusedasasynonymfor

togavirus.Itisnownolongeranofficialtaxonsinceitrefersonlytothearthropod

vectors,whereasthevarietyofvirustypestransmittedbythisrouteismuchgreater,

includingforinstancetogavirusaswellasflavivirustypes.

Flaviviruses

&Virusesintheflavivirusfamily(Flaviviridae)includethegeneraFlavivirus,

Hepacivirus,andPestivirus.Flaviviruses(theprototypebeingtheyellowfever

virus[Latin:flavus,yellow])aretransmittedbyarthropods.Theycauseabi-

phasicinfectionthatcanhaveseriousconsequences(hemorrhagicfeverwith

ahighlethalityrate).Insouthernandeasterncountries,thesevirusesaresig-

nificanthumanpathogens.Onlyonerepresentativeofthisfamily,thetick-

borneencephalitispathogen,isencounteredinEurope.

Thehepaciviruses(hepatitisC[HCV]andhepatitisGviruses)arenot

arthropodborne.HCVistransmittedmainlyinblood(transfusions,blood

products,intravenousdruguse)andisafrequentcauseofchronicdisease

(7 0 %ofcases),includingcirrhosisoftheliverandhepatocellularcarcinoma.

ThehepatitisGvirus(HGV)isrelatedtoHCVandhasnotbeencharacterized

indetailasyet.

Pestivirusesareonlyimportantinveterinarymedicine. &

Flavivirusesshowmorphologicaluniformitywithanicosahedralcapsidand

closefitting,spikedenvelope.Thesizeofthecapsidisabout 30 nmandthe

wholevirionmeasures 45 nm.Thegenomeoftheflavivirusesisasingle-

strandedsenseRNAabout 10 kbinsize.Itcodesforthreestructuralandseven

nonstructuralproteins.Bothcotranslationalandposttranslationalprotein

processing(cleavage,p.388),similartowhatisseeninthepicornaviruses,

hasbeendescribed.Themorphogenesisofthevirusoccursattheendoplas-

micreticulum,intothelumenofwhichthefinishedvirusesbud.Thesechar-

acteristicshavenotbeendirectlydemonstratedforthehepatitisCvirus,

whichcannotbeculturedinvitro.

Thepestivirusescausesevereanimalepidemics(e.g.,swinefever).They

arenottransmittedbyarthropods.

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Kayser, Medical Microbiology © 2005 Thieme