TheRickettsiaCoxiellaburnetii,aworldwidedistributedpathogen,isresponsIBLeforthediseaseknownasQfever.Thesmallgram-negative,obligateintracellularbacteriumreproducesinthedigestivesystemofticks(Dermacentormarginatus)andplacentaltrophoblasts.Asaresulttickfaecesandafterbirthsofinfectedmammals(particularlysheep)arehighlyinfectious.Occupationalgroupswithdirectcontacttofarmanimalsareatparticularriskofinfection.Inthisgroup,antibodiesagainstCoxiellaburnetiicanbedetectedin30to70%.Infectionusuallyresultsfrominhalationofcontaminatedaerosols,especiallyduringdrysummermonths.
Theincubationtimeisaroundtwotofourweeks.Clinicalsymptomsaredevelopedin30to50%;theremainingindividuals(50to70%)revealsubclinicalornon-specificsymptoms.Influenza-likesymptomsareoftenevident.Inabout50%ofcasesanatypical,interstitialpneumoniadevelops.Lessfrequently,theinfectionresultsinahepatitis.Inafewcases,theacutephasemaybecomplicatedbymeningoencephalitis,myocarditisorpericarditis.Ifnottreatedthepathogenpersistsin1to11%ofallcasesinavarietyoforgans,whichendsaftermonthsoryears,inachronicinfection.Chroniccoursesoftenleadtoanendocarditis(especiallypatientswithheartvalvedisease)and/orgranulomatoushepatitis.About65%ofchronicQ-fevercasesarelethal.
Followingaprimaryinfectionantibodiesdirectedagainstthephase2antigenareproducedduringtheacutephaseofQfeverdisease.IgMantibodiesappearapproximatelyaftertwoweeksfollowedbyIgGwithintwomonthspostinfection.WhileIgMantibodiescanbedetecteduptothreemonthspostinfection,IgGisfrequentlydetectableforuptofiveyears.OnlywhenaninfectionentersthechronicstageIgAandIgGdirectedagainsttheC.burnetiiphase1antigenappear.TheseantibodiesareparticularlysignificantwhendiagnosingQfeverendocarditis.Duetothefact,thatIgMantibodiesdirectedagainstphase1antigenarenotpresentafteralongertimeperiod,thereisnosenseofIgMdetectionduringachroniccourse.Rheumatoidfactorsaresignificantlyincreasedinthechronicphase.
DuetothelackofcharacteristicclinicalsymptomsofacuteandchronicQfeverinfection,diagnosisisbasedprimarilyonSEROlogictechniques.TheuseofELISAtestsystemsisrecommendedbytheWHOduetoitshighsensitivityandspecificityandthepossibilitytoperformadifferentialanalysisoftheantibodyresponse.
Followingdiseasesshouldbeconsideredfordifferentialdiagnosis:Chlamydiainfections,Mycoplasmapneumoniae-infections,Legionellapneumophila-andLegionellamicdadeiinfections,Virus-pneumoniasandLeptospirosis.