— Theinvasiveintestinalformresultsfromtheinvasionoftheintestinal
wallbythepathogenicE.histolyticaandreflectslargeintestinedisease.
Theintestinalpartsaffected(colon,cecum,rectum,sometimesterminal
ileum)showeithercircumscribedormoreexpandedlesionsofvaryingin-
tensity,rangingfromedematousswellingandreddeningtopinhead-sized
fociwithcentralnecrosisorlarger,bottle-shapedulcersextendingdeep
intotheintestinalwallwithswollenedgesandlargedecomposingfoci.
Theulcerssometimesperforateintotheperitonealcavity.Healingpro-
cesseswithscarformationmayreducetheintestinallumen;pronounced
inflammatoryprocessescanleadtoatumorlikethickeningoftheintestinal
wall(ameboma).Theacutediseaseusuallybeginswithabdominaldis-
comfortandepisodesofdiarrheaofvaryingduration,atfirstmushy
thenincreasingmucoid,includingblood-tinged,so-called“redcurrantjel-
lystools”inwhichamebascanbedetected,includingtrophozoitescon-
tainingerythrocytes.Insuchcases,antibodiesareusuallypresentinse-
rum.Thesymptomsmayabatespontaneously,butfairlyoftenarecidivat-
ingchroniccolitisdevelopsthatcanlastformonthsorevenyears.
&Extraintestinalforms
— Extraintestinalformsdevelopbecauseofhematogenousdisseminationof
E.histolyticaoriginatingintheintestine.Themostfrequentformistheso-
called“liverabscess,”whichmaydevelopinsomeinfectedpersons.Only
about 10 %ofpatientswithliverabscessesarealsosufferingfromamebic
colitis;coproscopicmethodsoftendonotrevealamebasinstool.Theliver
abscesscausesremittentfever(sometimeshigh),upperabdominalpain,
liverenlargement,elevationofthediaphragm,generalweakness,and
othersymptoms.Largeliverabscessesthatarenottreatedintimeareof-
tenlethal.Antibodiesaredetectableinmostcases(around 95 %)(seealso
Diagnosis).Otherformsofextraintestinalamebosisaremuchrarerand
includeinvolvementofthelungs,brain,andskin.
Immunity.Reinfectionsarepossiblesincesufficientimmunityisnotconferred
inthecourseofaninfection.Antibodiesareusuallydetectableinserumin
invasiveintestinalandextraintestinalamebosiscausedbyE.histolytica.
Diagnosis
&Intestinalamebosis
— Coproscopicdiagnosis.Fordiagnosisofintestinalamebosisabody-warm
stoolspecimenmustbefixedwithoutdelayinSAFsolutionandexamined
microscopicallyfollowinglaboratoryprocessing(p. 62 1).Asinglestool
analysishasastatisticalsensitivityofonly 50 – 60 %,butthiscanberaised
to 95 %byexaminingstoolspecimensfromthreeconsecutivedays.Since
E.histolyticaandE.dispararemorphologicallyindistinguishable,afinding
isclassifiedasE.histolytica/E.disparcomplex.EntamoebahistolyticaandOtherIntestinalAmebas 5039Kayser, Medical Microbiology © 2005 Thieme