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1、28CHAPTERJaneK.A.CookCoronaviridaeThefamilyCoronaviridaeisamemberoftheorderNidovirales,theonlyotherfamilyintheorderbeingtheArteriviridae.Thesearelinear,single-strandedRNAvirusesofpositivesense.TheCoronaviridaefamilyisdividedintotwogenera,CoronavirusandTorovirus,buto
2、nlyvirusesoftheCoronavirusgenushavebeenreportedtoinfectbirds.Coronavirusesareenveloped,pleomorphicbutusuallysphericalvirusparticlesof120–140nmindiameter.Theimportantantigenicandfunctionalproteinsarepresentasdistinct,club-shapedprojections(knownasspikes),spacedwidely
3、apartanddispersedevenlyoverthesurfaceofthevirion.Inadditiontoavianspecies,coronaviruseshavebeenreportedtoinfectcattle,dogs,cats,pigs,rodentsandhumans.Coronavirusesaredividedintothreegroups,basedonantigenicrelationshipsandgenesequencingdata.Allknownaviancoronaviruses
4、areplacedingroup3,althoughthereissomeexperimentalevidencetosuggestthatagroup2coronavirus,Bovinecoronavirus,caninfectturkeysandcauseentericdiseaseinthem.Thepossibilityexists,therefore,thatbirdsmaybeinfectedwithcoronavirusesbelongingtoothergroups.Thebest-knownaviancor
5、onavirusandthemostimportanteconomicallyandfromawel-farepointofview,isavianInfectiousbronchitisvirus(IBV;Fig.28.1),thetypespeciesoftheCoronavirusgenusandamajorpathogeninchickens.However,coronavirusesofturkeys,phea-santsandotheravianspeciesarenowrecognized.INFECTIOUSB
6、RONCHITISInfectiousbronchitiswasfirstreportedinNorthDakota,USA,in1931asanacute,highlyinfectiousrespiratorydiseaseofchickens.Itnowhasworldwidedistribution.Theprimarytar-getorganistherespiratorytract,whereinitialinfectionanddiseaseoccurs.IBValsoaffectsegg-layingperforma
7、nce,andrenaldamageassociatedwithinfectiousbronchitishasbecomeincreasinglyimportant,particularlyinbroilers.Economically,themostimportantaspectsaretheeffectsoneggproductionandqualityinlayinghensandproductionperformanceinbroil-ers,wheretheinitialrespiratoryinfectionisfr
8、equentlyexacerbatedbysecondaryinfections.340Ch28-S2862.indd3409/14/0710:35:03AMCoronaviridaeFig.28.1Infectiousbronchitisvirusnegativelysta
