mononuclearphagocyticsysteminvariousorgans(spleen, liver,lymph
nodes,bonemarrow,bloodmonocytes,etc.),causinginfectionsthatarenor-
mallylethalwithouttreatment.
Basicresearchusinganimalmodelshasprovidedandexplanationfor
thesedifferences:thecourseofaninfectionisapparentlydependenton
theactivationofvariousTlymphocytesubpopulationsbyLeishmaniaanti-
gens.ActivationofTH1cellsinvolvesproductionofIFNc,whichactivates
macrophagesthatexertaprotectiveeffectbykillingLeishmaniaorganisms
by means ofa nitricoxide-mediatedmechanism.Ontheotherhand,
whenTH2cellsareactivatedlargeamountsofIL-4andIL-1 0 areproduced,
whichinhibitNOactivity,thusreducingorevenpreventingeliminationofthe
parasites.Productionofantibodiesisalsogreatlyincreased,buttheydonot
playasignificantroleinimmuneprotection.Findingsinpatientsareinac-
cordancewiththeseinterpretations:inCL,highconcentrationsofIFNcwere
found,butinseverecasesofVLthelevelsofIL-4andIL-1 0 wereraisedand
IFNcconcentrationswerelow.ThesituationissimilarinsevereformsofMCL.
Itwouldappearthatthecell-mediatedimmuneresponseinCLprotectseffi-
ciently,buttheimmuneresponseinadvancedVLandsomeformsofMCLis
moreorlesssuppressed.Incaseswheretheimmunedefensesareaddition-
allyweakenedbyAIDS,alatentLeishmaniainfectionmaybeactivatedand
takeafulminantsymptomaticcourse.Inendemicregions,therisktoacquire
aLeishmaniainfectionisincreasedforAIDSpatientsby 100 – 1000 times.Most
ofthecasesofAIDS-associatedleishmaniosis(about 50 %)registeredtodate
(1 990 – 199 8)werereportedfromareasinwhichL.infantumisendemicin
southwesternEurope(Italy,France,Spain,Portugal)(othersfromIndia,Afri-
ca,LatinAmerica,etc.)(WHO, 1 999).BesidesL.infantum,coinfectionswith
otherLeishmaniaspecieshavealsobeenfoundinAIDSpatients(e.g.,L.do-
novani,L.braziliensis,L.tropica).
Epidemiology.Table9. 4 refersbrieflytotheepidemiologyofthisdisease.In
centralEurope,leishmaniosisdeservesattentionasatravelers’disease,espe-
ciallytheVLimportedfromMediterraneancountries.MajorVLepidemics
haveoccurredrecentlyinvariouspartsoftheworld,e.g.,insouthernSudan
with 100000 deathsinapopulationof< 1 million(WHO, 200 0).
Diagnosis.AnetiologicaldiagnosisofVLismadebymeansofdirectparasite
detectioninaspiratematerialfromlymphnodesorbonemarrow(inHIVpa-
tientsalsointheenrichedbloodleukocytefraction)inGiemsa-stained
smears(uncertain!),incultures(inwhichpromastigotesdevelop)orusing
PCR.CultivationandPCRhaveaboutthesamehighlevelofsensitivity.Anti-
bodiesaredetectableinnearlyallimmunocompetentpatients(around 99 %),
but 40 – 50 %ofHIV-coinfectedpatientsareseronegative(Table 11. 5 ,p.625).
Diagnosisofacutaneousleishmaniosisisusuallybasedonclinicalevi-
dence.Etiologicalverificationrequiresdirectparasitedetection(seeabove)498 9 Protozoa9
Kayser, Medical Microbiology © 2005 Thieme