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