Medical Microbiology

558 10 Helminths

ThenumberofpersonsinfectedwithOpisthorchisandClonorchisisestimated

at 17 million,withabout 350 millionpersonsatriskforinfection(WHO,

1 995).

Lifecycleandepidemiology.ThedefinitivehostsofOpisthorchisandClon-

orchisspeciesarefish-eatingmammals(cats,dogs,pigs,etc.)andhumans,

inwhichthesetrematodescolonizethebileducts.Thelifecycleofthese

organismsinvolvesvariousspeciesofaquaticsnails(Bithynia,etc.)asthe

firstintermediatehostsandfreshwaterfishspeciesasthesecondintermedi-

atehosts.Theinfectivemetacercariaearelocalizedinthemusculatureof

thefishand,whenrawfishisingested,entertheintestinaltractofthede-

finitivehost,fromwheretheymigratethroughthecommonbileduct(ductus

choledochus)intotheintrahepaticbileducts.Theprepatentperiodisfour

weeks.

Pathogenesisandclinicalmanifestations.OpisthorchisandClonorchisinfec-

tionscauseproliferationsofthebileductepithelium,cystlikedilatation,in-

flammation,andfibrosisofthebileductwallsaswellasconnectivetissue

proliferationinthehepaticparenchyma.Ahighincidenceofbileductcarci-

nomashasbeenreportedfromareasinwhichC.sinensisandO.viverriniare

endemic.Clinicalsymptomsofmoresevereinfectionsincludevariablefever,

hepatocholangiticsymptomswithhepatomegaly,leukocytosis,upperab-

dominalpains,anddiarrhea.

Diagnosis,therapy,andprevention.Diagnosisismadebydetectionof

eggs(26– 32 lmlong)instoolorduodenalfluid(Fig. 1 0. 1 ,p.543).Differential

diagnosismustalsoconsidertheeggsofHeterophyesheterophyes,Metagoni-

musyokogawai,andothertrematodespecies.Serumantibodiesarefoundin

someinfectedpersons.Thedrugofchoiceispraziquantel;albendazolecan

alsobeused.Reliablepreventivemeasuresincludeboilingorfryingfishtokill

themetacercariae,whichdieattemperaturesaslowas 708 C,andfreezingto

–1 08 Cforfivedays(WHO, 1 995).

Paragonimus(LungFlukes)

Causativeagentsofparagonimosis

&LungflukesofthegenusParagonimus,endemicinpartsofAsia,Africa,and

America,parasitizeinpulmonarycystsandcauseatuberculosis-likeclinical

picture.Followingdevelopmentintwointermediatehosts(freshwatersnails

andcrabsorcrayfish),infectivestages(metacercariae)canbetransmittedto

humansbyeatingthecrabsorcrayfishuncooked.Parasiteeggsaredetectable

insputumorstool. &

10

Kayser, Medical Microbiology © 2005 Thieme