ThepathogenicgermsYersiniapestis,Y.pseudotuberculosis,Y.enterocoliticaandY.ruckeribelongtothegenusYersiniaasamemberoftheenterobacteriaceafamily.Allthespeciesofmedicalimportanceoccurfacultativelyinsidethecells,whichleadstothecharacteristicalinflammationofthelymphatictissueinthecourseofanillness.Yersiniaenterocoliticaistakenuporally,andthesymptomsinapatientareterminalileitisaswellasdiarrhoea.Itisdifficulttomakeaseparationfromappendicitisbydifferentaldiagnosis.Inthecourseofaretardedimmunologicalreaction,extraintestinalmanifestationslikeerythemanodosum,uveitis,andarthritiscanappear.IthasbeenclaimedthatthebackgroundforareactivearthritiscausedbyYersiniaconsistsinthelocalsynthesisofantibodiesinthejoints(synovialfluid).
Yersiniacanbecharacterizedwithoutproblemsbystandardizedbacterialtests,afterisolationinapureculture.Followingahumandisease,abovealltheSEROtypesO3,O8andO9arefound.Cross-reactivitiestoBrucellaaredescribedandhavetobetakenintoaccountbythedifferentialdiagnosis.TheclassicalserologicaldetectionmethodhasalwaysbeentheWidaltest.FurtherincreasinglypopularmethodsaretheHAT,theKBRtestaswellastheELISA.Theenzymeimmunoassayischaracterizedontheonehandsidebyahighsensitivity,butalsobythepossibilitytodifferentiatebetweenIgGandIgA/IgMantibodies.TheimmunoglobulinclassesIgAandIgMshouldbereferredtoasacriteriumofinterpretationforanactiveprocess,whenanarthriticdiseaseissUSPected.Becausethereexistsalsoanimmunologicalsimilaritywiththethyrotropinreceptor,thetestcanalsobeemployedfortheconfirmationoftheautoimmuneGraves’disease.Asaconfirmatorytestwiththepossibilityofanidentificationofseparatebacterialproteinsaswellasfortheexclusionofcross-reactivities,theWesternBlotmethodhasprovedsuccessful.