Medical Microbiology

Platyhelmintha(syn.Platyhelminthes) 559

Occurrence.AtleastnineParagonimusspeciesareknowntobeparasitesof

humans.TheyarefoundinEastandSoutheastAsia(Paragonimuswestermani,

Paragonimusheterotremus,andParagonimusuterobilateralis),inNorthAmer-

ica(Paragonimuskellicotti),andinCentralandSouthAmerica(Paragonimus

mexicanus,etc.).Thenumberofinfectedpersonsisestimatedatabout 21 mil-

lion(WHO, 1 995).

Parasites,lifecycle,andepidemiology.Theplump,approx. 7 – 15 mmlong,

coffeebean-likeParagonimusspeciesdifferinappearancefromothertrema-

todes.Thesexuallymatureparasitesliveincystlikedilatationsinthelungs,

usuallyinconnectionwiththebronchialtree.Theyellow-brown,operculated

eggs(about 80! 50 lm)laidbytheadultwormsareshedeitherinsputumor

stool(Fig. 1 0. 1 ,p. 54 4).Thelifecyclethencontinuesinwater,wherea

miracidiumdevelopsineachegg,hatchesandinvadesanintermediate

host.Egg-shapedcercariaewithshorttailsdevelopinthefirstintermediate

host,afreshwatersnail(Semisulcospiraandnumerousothergenera).Thecer-

cariaeencystinthesecondintermediatehost(Crustaceae:crayfishorcrabs)

toformtheinfectivemetacercariae.Whenasuitabledefinitivehostingests

thecrustaceansuncooked,theyoungtrematodeshatchinthesmallintestine,

migratethroughtheperitonealcavitytothediaphragmandfinallyintothe

lungs.Theprepatentperiodistwotothreemonths.Parasitesthatdeviate

fromthenormalmigrationroutemayenterotherorgans(e.g.,thebrain

ortheskin).Eggsdistributedinthebloodstreaminduceinflammatorygran-

ulomasinvariousorgans.

Besideshumans,crustaceaneatingmammals(Felidae,Canidae,pigs,etc.)

playasignificantepidemiologicalroleasreservoirhosts.

Younglungflukescanbelocalizedinthemusculatureofpigsandother

“transporthosts”andbetransmittedtohumanswhoingesttherawmeatof

theseanimals.

Clinicalmanifestations.Typicalcasesareclinicallycharacterizedbypulmon-

arysymptoms(chroniccough,bloodyexpectoration,thoracicpain).Parasites

followingthenormalordeviantmigrationroutescanalsocauseabdominal,

hepatic,pancreaticorCNSsymptoms,orskinlesions(swelling,nodules).

Diagnosis,therapy,andprevention.Anetiologicaldiagnosisisbasedon

detectionofeggsinsputumorstool(Fig. 1 0. 1 ,p. 54 4)andofserumantibodies

(Table 11. 5 ,p.625).Regardingthedifferentialdiagnosisespeciallytubercu-

losismustbekeptinmind.Thedrugofchoiceispraziquantel,buttriclaben-

dazolecanalsobeused(seeFasciola,p.556).Cookingcrustaceansbefore

eatingthemisareliablepreventivemeasure.

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Kayser, Medical Microbiology © 2005 Thieme