EnzymeimmunoassayforthequalitativedeterminationofIgA-classantibodiesagainstParainfluenzavirus(Type1,2and3)inhumanserumorplasma(citrate).Parainfluenzavirusesareimportantviralpathogenscausingupperandlowerrespiratoryinfectionsinadultsandchildren.ThevirusesbelongtothefamilyofParamyxoviridae.TheyareenvelopedsinglestrandedRNAviruseswithsphericalorpleomorphicshape.Parainfluenzavirusesarerelativelylargevirusesofabout150-300nmindiameter.Onthebasisofantigenicdifferencestheyaredividedintofoursubtypes,ofwhichtype4isdividedintotwosubtypes.Parainfluenzavirus1and3belongtotheparamyxovirusgenus.Parainfluenzavirus2,4aand4bbelongtotherubellavirusgenusalongwithmumps.Thevirusisubiquitous;infectionsoccurasepidemicsaswellassporADIcally.Parainfluenzavirusesaresensitivetodetergentsandheatbutcanremainviableonsurfacesforupto10hours.Transmissionoccursviadroplets,aerosolsandfomites(virusessurviveonsurfaces).Parainfluenzavirusinfectionsareprimarilychildhooddiseases,thehighestage-specificattackratesforcroupoccurinchildrenbelowtheageof3years.Type3infectionsoccurearliestandmostfrequently,sothat~50%ofchildrenareinfectedduringthefirstyearoflifeandalmostallby6years,asdeterminedbySEROepidemiologicalstudies.Antibodiesagainsttypes1and2areacquiredlessrapidlybut80%ofchildrenhaveantibodiesby10yearsofage.Type4virusesinducefewclinicalillnessesbutinfectionsarecommon,70-80%ofchildrenhaveantibodiesby10yearsofage.Inallagegroups,theincubationperiodappearstobefivetosixdays.Crouporlaryngotracheobronchitisisthecommonestclinicalmanifestationofinfection.Parainfluenzavirusesarefounduncommonlyassociatedwithotherrespiratorytractinfectionsinchildrensuchastracheobronchitis,bronchiolitis,andbronchopneumonia.Occasionally,amildnon-specificillnessisseenafterparainfluenzavirusinfection.Inadults,thevirusisusuallylimitedtocausinginflammationintheupperpartsoftherespiratorytract.