Medical Microbiology

Naegleria,Acanthamoeba,andBalamuthia

Causativeagentsofnaegleriosis,acanthamebosis,andbalamuthiosis

Free-livingamebaofthegeneraNaegleria,Acanthamoeba,andBalamuthiahavethe

potentialtoinfectvertebratesandtocausediseasesinhumans.Themorphological

characteristicsoftheseamebasinclude:nucleuswithlargekaryosome,lackofchro-

matingranulesatthenuclearmembrane(seeEntamoeba).Trophozoites:Naegleria

fowleri( 1 5–3 0 lm)withwidepseudopods,producesflagellatedstagesinwater;

Acanthamoebaspp.(2 4 – 56 lm)withfingerlikeprotrusions(“filopods”);Balamuthia

mandrillaris(1 2 – 60 lm)hasirregularlybranchedpseudopods.Allofthesegenera

producecysts.

Naegleria.Thecausativeagentofprimaryamebicmeningoencephalitis(PAM)is

Naegleriafowleri.Thisspeciesoccursworldwideinbodiesoffreshwater,especially

warmwaterinswimmingpools,storagecontainersorthermallypollutedlakesand

rivers,etc.

Infectionofhumansoccursbythenasalroutewithwatercontainingtrophozoites,

i.e.,duringaswimorshower.Theamebasmigratefromtheolfactoryepithelium

alongthenervetractsintotheCNSandcause,afteranincubationperiodoftwoto

seven(rarelyaslongas 1 5)daysahyperacutetoacutemeningoencephalitisthat

usuallyhasalethaloutcome.Theinfectionoccursmainlyinchildrenandyouths.

Sporadicoccurrenceisreportedfromallcontinents.TreatmentwithamphotericinB

hasbeensuccessfulinasmallnumberofcases.

Acanthamoeba.PotentialhumanpathogensinthisgenusincludeAcanthamoeba

culbertsoniandseveralotherspecies.Theseamebasoccurworldwideinsoil,

sand,dust(alsohousedust),air,andwater(alsointapwater).Thecystscansurvive

forseveralyearsinadrystateanddisseminatewithdust.Inhalationofcystswith

dustisconsideredtobeoneofthemaintransmissionroutes.Acanthamebasare

frequentcolonizersofhumannasalmucosaandhavebeenisolatedfromtheoral

mucosa,skinlesions,andthecornea.Fromtheportalofentry,theycanspread

hematogenouslytotheCNSandotherorgans.

Acanthamoebainfectionsinhumansfrequentlytakeanasymptomaticcourse.Ker-

atitisisobservedoccasionally,especiallyincontactlenswearers.Diagnosis:cultur-

ingofamebasfromconjunctivalandcontactlensrinsingliquids.Prevention:use

onlysterilelensrinsingliquid.Inrarecasesofgeneralizedinfection,Acanthamoeba

cancausegranulomatousamebicencephalitis(GAE)aswellasgranulomatousle-

sionsinthelungsandotherorgans,especiallyinimmunodeficientpatients.Bala-

muthiamandrillariscanalsocauseGAE.

Naegleria,Acanthamoeba,andBalamuthia 507

9

Kayser, Medical Microbiology © 2005 Thieme