Medical Microbiology

314 4 BacteriaasHumanPathogens

Pathogenesisandclinicalpicture.Humanbrucellosisinfectionsresultfrom

directcontactwithdiseasedanimalsorindirectlybywayofcontaminated

foods,inparticularunpasteurizedmilkanddairyproducts.Thebacteriain-

vadethebodyeitherthroughthemucosaoftheupperintestinalandrespira-

torytractsorthroughlesionsintheskin,thenenterthesubserosaorsubcutis.

Fromtheretheyaretransportedbymicrophagesormacrophages,inwhich

theycansurvive,tothelymphnodes,wherealymphadenitisdevelops.The

pathogensthendisseminatefromtheaffectedlymphnodes,atfirstlympho-

genouslyandthenhematogenously,finallyreachingtheliver,spleen,bone

marrow,andotherREStissues,inthecellsofwhichtheycansurviveand

evenmultiply.Thegranulomastypicalofintracellularbacteriadevelop.

Fromtheseinflammatoryfoci,thebrucellaecanenterthebloodstreaminter-

mittently,eachtimecausingoneofthetypicalfebrileepisodes,whichusually

occurintheeveningandareaccompaniedbychills.Theincubationperiodis

onetofourweeks.B.melitensisinfectionsarecharacterizedbymoresevere

clinicalsymptomsthantheotherbrucelloses.

Diagnosis.Thisisbestachievedbyisolatingthepathogenfrombloodorbiop-

siesincultures,whichmustbeincubatedforuptofourweeks.Thelaboratory

mustthereforebeinformedofthetentativediagnosis.Brucellaeareidenti-

fiedbasedonvariousmetabolicpropertiesandthepresenceofsurfaceanti-

gens,whicharedetectedusingapolyvalentBrucella-antiseruminaslideag-

glutinationreaction.Speciallaboratoriesarealsoequippedtodifferentiate

thethreeBrucellaspecies.

Antibodydetectionisdoneusingtheagglutinationreactionaccordingto

Gruber-Widalinastandardizedmethod.Indoubtfulcases,thecomplement-

bindingreactionanddirectCoombstestcanbeappliedtoobtainaserological

diagnosis.

Therapy.Doxycyclineisadministeredintheacutephase,oftenincombina-

tionwithgentamicin.Atherapeuticalternativeiscotrimoxazole.Theantibio-

ticregimenmustbecontinuedforthreetofourweeks.

Epidemiologyandprevention.Brucellosisisazoonosisthataffectsanimals

allovertheworld.InfectionswithB.melitensisoccurmostfrequentlyinMed-

iterraneancountries,inLatinAmerica,andinAsia.Themelitensisbrucelloses

seeninEuropeareeithercausedbymilkproductsimportedfromthesecoun-

triesoroccurintravelers.B.abortusinfectionsusedtobefrequentincentral

Europe,butthediseasehasnowpracticallydisappearedtherethankstothe

eliminationofBrucella-infestedcattleherds.Althoughcontrolofbrucellosis

infectionsfocusesonpreventionofexposuretothepathogen,itisnotneces-

sarytoisolateinfectedpersonssincetheinfectionisnotcommunicablebe-

tweenhumans.Thereisnovaccine.

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Kayser, Medical Microbiology © 2005 Thieme