Medical Microbiology

588 10 Helminths

LifeCycleofFilariae

Insect:!Ingestionofmicrofilariawithabloodmeal!developmentinthoracic

musculaturewithtwomoltingstobecomeinfectivelarva!migrationtomouth

partsandtranmissionintoskinofanewhostthroughpuncturewoundduringthe

nextbloodmeal.

Human:!Migrationtodefinitivelocalizationsandfurtherdevelopmentwithtwo

moremoltingstoreachsexualmaturity.

WuchereriabancroftiandBrugiaspecies

Causativeagentsoflymphaticfilariosis

Parasitesandoccurrence.About 120 millionpeoplein 80 countriessuffer

fromlymphaticfilariosiscausedbyWuchereriabancroftiorBrugiaspecies

(one-thirdeachinIndiaandAfrica,therestinsouthernAsia,thePacificre-

gion,andSouthAmerica),and 1. 1 billionpeopleareatinfectionrisk(WHO,

200 0).(Table 1 0. 4 ).HumansaretheonlynaturalfinalhostsofW.bancrofti

andthemostwidelydisseminatedBrugiastrains.Thereare,however,other

Brugiastrainsusingalsoanimalsasfinalhosts(cats,dogs,andmonkeys).

Lifecycleandepidemiology.TheintermediatehostsofW.bancroftiandB.

malayiarevariousdiurnalornocturnalmosquitogenera(Table 1 0. 4 ).The

developmentofinfectivelarvaeintheinsectsisonlypossibleathighenvi-

ronmentaltemperaturesandhumiditylevels;inWuchereriabancroftithe

processtakesabout 12 daysat 288 C.Followingaprimaryhumaninfection,

thefilariaemigrateintolymphaticvesselswheretheydeveloptosexual

maturity.Microfilariae(Mf)donotappearintheblooduntilafterthree

monthsattheearliest(B.malayi,B.timori)orafterseventoeightmonths

(W.bancrofti).Tables 1 0. 4 andFig. 1 0. 17 showtheirspecificcharacteristics.

Theadultparasitessurviveforseveralyears.

Pathogenesisandclinicalmanifestations.ThepathologiescausedbyW.

bancroftiandBrugiaspeciesareverysimilar.Theinitialsymptomscanappear

asearlyasonemonthp.i.althoughinmostcasestheincubationperiodisfive

to 12 monthsormuchlonger.Thedifferentcoursestakenbysuchinfections

canbesummarizedasfollows:

&Asymptomaticinfection,butwithmicrofilaremiathatcanpersistfor

years.

&Acutesymptomaticinfection:inflammatoryandallergicreactionsinthe

lymphaticsystemcausedbyfilariae!swellingoflymphnodes,lymphan-

gitis,intermittentrecurrentfebrileepisodes,generalmalaise,swellingson

legs,arms,scrotumandmammae,funiculitis,orchitis.

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Kayser, Medical Microbiology © 2005 Thieme