Medical Microbiology

RNAviruses 437

Wherehygienicstandardsarehigh,dropletinfectionsalsoplayasignificant

role.Specialprophylacticmeasurestopreventinfectionswithcoxsackie-

virusesorechovirusesareneitherpracticablenorgenerallynecessary.

Salkintroducedadeadvaccinein 1954 forpoliomyelitisprophylaxis(IPV,

inactivatedpoliovaccine)consistingofthreepoliovirustypesinactivatedby

formalin.Fiveyearslater,thelivevaccine(OPV,oralpoliovaccineaccordingto

Sabin)wasintroduced,whichcontainsthreelivebutnolongerneurovirulent

poliovirusstrains,eithersinglyorincombination.TheWHOplantoeradicate

poliomyelitisworldwidewouldseemfeasiblewiththisvaccineasdemon-

stratedbyitseradicationinseveralcountriesincludingallofSouthAmerica.

PolioVaccines:ProsandCons

Thedeadorinactivatedvaccinehastheadvantageofalongstabilityperiodand

practicallyfoolproofapplicationsafety.Thedisadvantagesofthisvaccineformare

itshighcost,therequirementforthreeinjectionsandweakeroratleastshorter-

livedprotectionthanisprovidedbytheattenuatedform.Workisongoingonde-

velopmentofenhanced(eIPV)vaccinesofthistype.

Theadvantagesofthelivevaccineareitsoralapplicationroute,lowpriceandhigh

levelofefficiency.Onedisadvantageisitsthermolability,resultinginreducednum-

bersofseroconversions(morenonresponders)intropicalcountries.Anotherdiffi-

cultyispresentedbythe(1in 1! 106 )casesofparalysis(vaccination-associated

paralyticpoliomyelitis,VAPP)resultingfromavaccination.VAPPshowsahigher

levelofincidencethaninfectionsbythewildtypepoliovirusinindustrializedcoun-

tries,whichhasledpracticallyallthesecountriestoreturntousingIPV.

Hepatoviruses(HepatitisAVirus)

Pathogen.ThehepatitisAvirusdiffersinsomecharacteristicsfromentero-

viruses,towhichgroupitwaslongconsideredtobelong.Growthincellcul-

turesrequireslongadaptation.Onlyoneserotypeisknowntodate.

Pathogenesisandclinicalpicture.TheclinicalpictureofhepatitisA,so-

calledepidemicorinfectioushepatitis,differsinnomajorparticularsfrom

thatofhepatitisB(p.429).Thediseasenearlyalwaystakesabenigncourse.

Onlyasmallnumberoffulminant(andsometimeslethal)orchroniccourses

havebeendescribed.Thepathogenicprocessatfirstcorrespondstothatof

theenteroviruses,wherebyhepatitisAreplicatesintheintestineandthen,

afterabriefviremicepisode,attacksitstargetorgan,theliver.Diseaseman-

ifestationwiththispathogen,unlikemostoftheenterovirusesbutsimilarto

hepatitisB,involvesimmunologicalprocesses.

DiagnosisisbasedonIgMdetectionduetotheearlypresenceoftheseanti-

bodiesinpatientserum,infactsoearlythatalackofhepatitisAantibodiesat

theonsetofclinicalmanifestationsexcludeshepatitisA.

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Kayser, Medical Microbiology © 2005 Thieme