Medical Microbiology

392 7 GeneralVirology

tion,travel,andhumanincursionintoisolatedbiotopes(examplesinclude

theEbola,RiftValleyfever,WestNile,pulmonaryHanta,andbatrabies

viruses).

Host-CellReactions

&Possibleconsequencesofviralinfectionforthehostcell:

— Cytocidalinfection(necrosis):viralreplicationresultsdirectlyincell

destruction(cytopathology,so-called“cytopathiceffect”incellcultures).

— Apoptosis:thevirusinitiatesacascadeofcellulareventsleadingtocell

death(“suicide”),inmostcasesinterruptingtheviralreplicationcycle.

— Noncytocidalinfection:viralreplicationpersedoesnotdestroythehost

cell,althoughitmaybedestroyedbysecondaryimmunologicalreactions.

— Latentinfection:theviralgenomeisinsidethecell,resultinginneither

viralreplicationnorcelldestruction.

— Tumortransformation:theviralinfectiontransformsthehostcellintoa

cancercell,wherebyviralreplicationmayormaynottakeplacedepend-

ingonthevirusand/orcelltypeinvolved. &

CellDestruction(CytocidalInfection,Necrosis)

Celldeathoccurseventuallyafterinitialinfectionwithmanyviralspecies.

Thiscytopathologicalcelldestructionusuallyinvolvesproductionofviral

progeny.Virusproductioncoupledwithcelldestructionistermedthe“lytic

virallifecycle.”Celldestruction,whethernecroticorapoptotic(seebelow)is

thereason(alongwithimmunologicalphenomena)forthediseasemani-

festedinthemacroorganism(seePathogenesis,p.396ff.).

Structuralchangesleadingtonecrosis:morphologicalchangescharacteris-

ticofagiveninfectingviruscanoftenbeobservedintheinfectedcell.The

effectsseeninvirallyinfectedcellculturesarewell-knownandaredesig-

natedby theterm“cytopathiceffect”(CPE).Theseeffectscanalso be

exploitedfordiagnosticpurposes(p.405).Theyincluderoundingoffandde-

tachmentofcellsfromadjacentcellsorthesubstrate,formationofmulti-

nucleargiantcells,cytoplasmicvacuoles,andinclusionbodies.Thelatter

arestructuresmadeupofviraland/orcellularmaterialthatformduring

theviralreplicationcycle,e.g.,viralcrystalsinthenucleus(adenoviruses)

orcollectionsofvirionsandviralmaterialinthecytoplasm (smallpox

viruses).Althoughthesestructuralchangesinthehostcelldocontribute

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Kayser, Medical Microbiology © 2005 Thieme