Medical Microbiology

Occurrence.Variousformsofleishmaniosesoccurinthewarmerregionsof

88 countriesinAsia,Africa,Europe(Mediterraneancountries!),andLatin

America(Fig.9. 7 ).Theannualnumberofnewcasesisestimatedat 1 .5– 2 mil-

lion(0.5millionVL, 1 – 1 .5millionCLandMCL).Bothgeographicdistribution

andcasenumbersarereportedtobeontheincrease(WHO, 200 0).

Parasitesandlifecycle.Themany(about 1 5)speciesofthegenusLeishmania

pathogenictohumansdonotshowmorphologicaldifferences.Theycanbe

differentiatedonthebasisofbiologicalcriteria,laboratoryanalyzes(mainly

isoenzymepatternsandDNAanalysis),thedifferentclinicalpictures,andepi-

demiologicalfacts(Table9. 4 ,p. 4 95).

Inhumansandothervertebrates,leishmaniasparasitizeinmononuclear

phagocyticcells(macrophages,monocytes,Langerhanscells)intheamasti-

goteform.TheGiemsa-stainedorganismsarerecognizableunderalight

microscopeasround-to-ovalcells2–5lmindiameterwithanucleusand

asmall,rod-shapedkinetoplast(Fig.9. 8 ).Arudimentaryflagellum,asingle

mitochondrionandothercellorganellesarealsorenderedvisibleontheelec-

tronmicroscopiclevel(seealsoTrypanosoma).

Theleishmaniaspeciesaretransmittedbyfemalemosquitoesofthe

generaPhlebotomus(OldWorld)andLutzomyia(NewWorld)knownas

“sandflies”(Fig.9. 9 and 11. 1 ).Theamastigotestagesoftheparasiteingested

bytheinsectwithabloodmealaretransformedinitsintestineintoslender,

flagellatepromastigoteforms 10 – 15 lmlong,whichmultiplyandmigrate

backintotheproboscis.Attropicaltemperaturesthisprocesstakesfiveto

eightdays.Wheninfectedsandfliestakeanotherbloodmealthepromastigote

formsareinoculatedintoanewhost(humansorothervertebrates).Inthe

494 9 Protozoa

Leishmanias

Fig.9. 8 a Leishmaniasinamacrophage.bLeishmaniainfantuminabursting

macrophage;Giemsastainingofabonemarrowsmear.

a b b^10 μm

9

Kayser, Medical Microbiology © 2005 Thieme