Medical Microbiology

Nematoda(Roundworms) 587

NematodalInfectionsofTissuesandtheVascularSystem

Filarialnematodes,theMedinaworm,andTrichinellaarediscussedinthis

sectionalongwithinfectionscausedbythelarvaeofvariousnematode

species.

Filarioidea(Filariae)

Causativeagentsoffilarioses

&ThenematodegeneraofthesuperfamilyFilarioidea(orderSpirurida)will

besubsumedhereunderthecollectivetermfilariae,andthediseasesthey

causearedesignatedasfilarioses.Inthelifecycleoffilariaeinfectinghumans,

insects(mosquitoes,blackflies,fliesetc.)functionasintermediatehostsand

vectors.Filariosesareendemicinsubtropicalandtropicalregions;inother

regionstheyareobservedasoccasionalimportedcases.Themostimportant

filariosisisonchocercosis,thecausativeagentsofwhich,Onchocercavolvulus,

istransmittedbyblackflies.Microfilariaeofthisspeciescancausesevereskin

lesionsandeyedamage,evenblindness.Diagnosisofonchocercosisisbased

onclinicalsymptoms,detectionofmicrofilariaeintheskinandeyes,aswell

asonserumantibodydetection.Otherformsoffilariosesincludelymphatic

filariosis(causativeagent:Wuchereriabancrofti,Brugiaspecies)andloaosis

(causativeagent:Loaloa).Dirofilariaspeciesfromanimalscancauselungand

skinlesionsinhumans(seep.605). &

General.Filariaearethreadlike(filum:thread)nematodes.Thelengthof

theadultstages(=macrofilariae)ofthespeciesthatinfecthumansvaries

between 2 – 50 cm,wherebythefemalesarelargerthanthemales.Thefe-

malesreleaseembryonatedeggsorlarvaecalledmicrofilariae.Theseare

about0.2–0.3mmlong,snakelikestagesstillsurroundedbyanextendedegg-

shell(sheathedmicrofilariae)ortheyhatchoutofit(unsheathedmicrofilar-

iae)(Fig. 1 0. 17 p.592).Theycanbedetectedmainlyintheskinorinblood

(Table 1 0. 4 ).

Basedontheperiodicappearanceofmicrofilariaeinperipheralblood,

periodicfilariaspeciesaredifferentiatedfromthenonperiodiconesshowing

continuouspresence.Theperiodicspeciesproducemaximummicrofilaria

densitieseitheratnight(nocturnalperiodic)orduringtheday(diurnalperi-

odic).Differentinsectspecies,activeduringthedayornight,functionas

intermediatehostsaccordinglytomatchthesechanginglevelsofmicro-

filaremia.

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Kayser, Medical Microbiology © 2005 Thieme