Medical Microbiology

Nematoda(Roundworms) 595

&Reactionstoadultparasites:enclosureofadultfilariaeinfibrousnodules

(onchocercomas),usually0.5– 2 cm(sometimesupto 6 cm)indiameterinthe

subcutisalongtheiliaccrest,ribs,scalp,etc.,morerarelyindeepertissues.

Nodulationoccursaboutonetotwoyearsafterinfectionandiseitherasymp-

tomaticorcausesonlymildsymptoms(Fig. 1 0. 16 c).

&Reactionstomicrofilariae:microfilariaeappearintheskinabout 12 – 15

(sevento 24 monthsp.i.).Initialsymptomsoccurafterabout 15 – 18 months:

forexample,pruritus,lossofskinelasticitywithdroopingskinfolds,papules,

depigmentation,andswellingoflymphnodes;bloodeosinophiliamayalso

bepresent.

&Eyechanges:“snowflake”cornealopacities,inlaterstagesclerosingker-

atitis,themaincauseofblindness,chorioretinitisandocularnerveatrophy;

tendencytowardbilateraldamage(Fig. 1 0. 16 d).

Diagnosis

&Adultparasites.Onchocercomascanbeidentifiedbypalpationandultra-

sonicimaging.Presenceoftheparasitescanbeconfirmedbysurgicalremoval

andexaminationofthecutaneousnodules.

&Microfilariaecanbefoundinskinsnipsaftertheprepatentperiod.APCR

isnowavailableforspecies-specificdetectionofOnchocercaDNA(Oncho-1 50

repeatsequence)inskinspecimens.Livingordeadmicrofilariaecanbeseen

intheanteriorchamberoftheeyewiththehelpofaslitlamporanophthal-

moscope.Varioustechniquesandantigens(e.g.,recombinantantigens)can

alsobeusedtodetectserumantibodies(Table 11. 5 ,p.625).

Therapy.Onchocercanodulescanberemovedsurgically.Suramin—aquite

toxicsubstanceeffectiveagainstmacrofilariae—isnownolongerused.It

wasrecentlydiscoveredthatO.volvulus,Wuchereriabancrofti,Brugiaspecies,

andseveralotherfilarialspeciescontainendosymbiontsofthegenusWol-

bachia(orderRickettsiales)thataretransovariallytransmittedfromfemales

tothefollowinggeneration.Studiesinanimalsandhumanshaveshownthat

prolongedtherapywithdoxycyclindamagesboththeendosymbiontsandthe

filariae.Theseresultscouldleadtoanewtherapeuticapproach.Ivermectinin

lowdosesishighlyeffectiveagainstmicrofilariae(seeprevention),andhas

someeffectonmacrofilariaeinrepeatedhigherdoses.

Preventionandcontrol.Protectiveclothingandapplicationofrepellentsto

theskincanprovidesomedegreeofprotectionfromblackflybites(seeMa-

laria).WHOprogramsinvolvingrepeatedapplicationsofinsecticidesto

streamsandriverswiththeaimofselectiveeradicationofthedevelopmental

stagesofSimuliidaeinwesternAfricahaveproducedimpressiveregionalre-

sults.Masstreatmentofthepopulationinendemicareaswithlow-doseiver-

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Kayser, Medical Microbiology © 2005 Thieme