Medical Microbiology

riorofcarsfortsetsefliesandspraywithinsecticides.Glossinafliesaretar-

getedbyinsecticidesprayingsinpreventiveprograms.Morerecently,the

fliesarealsobeingcaughtininsecticide-chargedtrapsusingattractantcolors

andodors.

Trypanosomacruzi

CausativeagentofAmericantrypanosomosis(Chagasdisease)

Occurrence.HumanChagasdiseaseisendemicinCentralandSouthAmerica

andiscausedbyTrypanosomacruzi(discoveredin 1908 byChagas).This

parasitecirculatesinendemicsylvaticfocibetweenvertebratesandinsects

(reduviidbugs),thelattertransmittingittohumans.Untilafewyearsago,the

endemicareaofChagasdiseaseextendedfromMexicotosouthernArgentina.

Inrecentyearsparasitetransmissiontohumanshasbeenreducedorpre-

ventedinsomecountries(Argentina,Brazil,Chile,Paraguay,Uruguay)by

controlmeasures.Thenumberofinfectedpersonsiscurrentlyestimated

tobe 16 – 18 million(WHO, 200 0).

Causativeagentandlifecycle.Inthenaturalcycle,thereduviidbugsingest

trypomastigoteformsofT.cruziinbloodmealsfrominfectedhosts(verte-

brateanimals,humans).Intheintestineofthevector,theparasitesconvert

intointensivelymultiplyingepimastigotestages,andlaterintotrypomasti-

goteformsthatareexcretedinfecesaftersixtosevendays.Atsubsequent

bloodmeals,infectedreduviidsexcretedroppingsfromwhichthetrypomas-

tigotesinfectthehostthroughskinlesions(e.g.,lesionsofbugbites)orthe

mucosa(e.g.,conjunctiva).

Onceinthehumanbody,theparasitesarephagocytosedbymacrophages

orinvadeothercells,mainlymusclecells(heart,skeletal,orsmoothmuscu-

lature)aswellasneuroglialcells.Withinthecells,theytransformintoamas-

tigoteforms(1.5–4.0lm)andmultiplybybinaryfission.Cellsfilledwithupto

500 parasitesarecalled“pseudocysts.”Afteraboutfivedaystheparasitesde-

velopintototheepimastigoteformandthenthetrypomastigoteformand

returntothebloodstream,whereuponthecellinfectioncycleisrepeated.

TheT.cruziorganisminthebloodofinfectedhosts(vertebrateanimals,

humans)is 16 – 22 lmlong.Ithasapointedposteriorendandalargekine-

toplast.Multiplicationdoesnottakeplaceintheblood.

Epidemiology.ThebloodsuckingbugsofthefamilyReduviidaefindahiding

placeforthedayandquestforfoodatnight.Thenaturalhabitatsofthese

insectsarenests,animaldens,andotherplacesfrequentedbyvertebratean-

imalswhosebloodprovidestheirsustenance.Somespeciesofreduviids(e.g.,

Triatomainfestans,Rhodniusprolixus,Panstrongylusmegistus)haveinvaded

domestichabitats(alsoinurbanareas!)andaretypicallyfoundinsimplehu-

mandomiciles.PotentialcarriersofT.cruziincludeover 150 speciesofwild

Trypanosoma 491

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Kayser, Medical Microbiology © 2005 Thieme