Medical Microbiology

Trypanosoma

CausativeagentsofAfricantrypanosomosis(sleepingsickness)

andAmericantrypanosomosis(Chagasdisease)

&TrypanosomabruceigambienseandTrypanosomabruceirhodesiensecause

Africantrypanosomosis(sleepingsickness)inhumans,whichpresentsinter

aliaasfeverandmeningoencephalitis.Inachronicform(T.gambiense)the

diseaseoccursmainlyinwesternandcentralAfrica,whereastheacuteform

(T.rhodesiense)ispredominatelydistributedineasternandsoutheastern

Africa.Thetrypanosomesaretransmittedbythebitesoftsetseflies(Glossi-

na).Antelopesandotherwildordomesticanimalsserveasreservoirhosts

ofvaryingsignificance.Trypanosomacruzi,thecausativeagentofAmerican

trypanosomosis(Chagasdisease)occursinhumansandmanyvertebrate

animalsinCentralandSouthAmerica.Itistransmittedinthefecesof

bloodsuckingreduviidbugs.Inrecentyears,considerableprogresshas

beenmadeinthecontrolofChagasdisease. &

General.ThegenusTrypanosoma(fromtrypanon:borerandsoma:body)

belongstothefamilyTrypanosomatidae(subphylumKinetoplasta)(Table

9. 1 ).Onefeatureofthisfamilyisthatvariousformsdevelopduringthe
   lifecycleinvertebratesandvectors(insect)involved.Themorphologically
   differentiatedformsincludespindly,uniflagellatestages(trypomastigote,
   epimastigote,promastigote)andarounded,amastigoteform(Fig.9.3b).
   ThetrypomastigoteformofthegenusTrypanosomahasthefollowingchar-
   acteristicfeatures:acentralnucleus,anelongatedmitochondrioncontaining
   thekinetoplastinitsposteriorsection,anareafreeofcristaewithespecially
   denselypackedDNA(Fig.9.3a).Closeto,butoutsideofthemitochondrion
   isthebaseoftheflagellum,whichoriginatesintheplasmaticbasalbody.
   Theflagellumisatfirstenclosedbytheflagellarpocket,andthenemerges
   ontothesurfaceoftheorganismandrunstotheanteriorendoftheorganism
   asapullingflagellum.Theflagellaradhereslocallytothecellsurfaceso
   thatan“undulatingmembrane”isfoldedoutduringmovement—visible
   underalightmicroscope.Specialorganellesofthekinetoplastidsarethe
   membrane-enclosedglycosomes,whichcontainglycolyticenzymes.The
   cellisenclosedbyanelementarymembrane,whichinthebloodstream
   stagesiscoveredbyasurfacecoatorglycocalyx(seebelow).Spiralmicro-
   tubulesformingacytoskeletonarearrangedalongtheinnercellmembrane
   (seeFig.9.3aformorecellorganelles).Intheepimastigoteandpromastigote
   forms,thekinetoplastandbaseoftheflagellumarenearthenucleusormore
   towardtheanteriorend.Intheamastigoteform,areducedflagellumis
   visiblebyelectronmicroscopy,butitdoesnotemergeontothecellsurface
   (Fig.9.3b).

Trypanosoma 483

9

Kayser, Medical Microbiology © 2005 Thieme