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Trematodes (Flukes). Department of Parasitology, Xiangya Medical School, Central South University. General Introduction. Classification and Species. Phylum Platyhelminthes (flatworms) Class Trematoda Order Monogenea Order Aspidogastrea Order Digenea.

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Trematodes (Flukes)

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Trematodes flukes



Department of Parasitology,

Xiangya Medical School,

Central South University

Trematodes flukes

General Introduction

  • Classification and Species

  • Phylum Platyhelminthes (flatworms)

  • Class Trematoda

  • Order Monogenea

  • Order Aspidogastrea

  • Order Digenea

All trematodes parasitizing human belong to the

Order Digenea.

Trematodes flukes

General Introduction

  • Classification and Species

Common human trematodes:

Clonorchis sinensis (liver flukes)

Heterophyes heterophyes

Fasciolopsis buski

Fasciola heptica

Paragonimus westermani

Pagumogonimus skrjabini

Schistosoma japonicum

Echinochasmus japonicus

(lung fukes)

Trematodes flukes

General Introduction

  • Important species in China

Clonorchis Fasciolopsis Paragonimus Schistosoma

sinensis buski westermani japonicum

Trematodes flukes

General Introduction

  • Morphological characteristics

1、Adult worms

  • flattened, bilaterally symmetric, leaf-

    shaped or tongue-like

  • about 0.3-80.0mm in length

  • two suckers, an oral and a ventral sucker

  • Most of trematodes are hermaphroditic,

    except schistosomes

  • incomplete digestive tract, the caeca end

    blindly, without anus

  • Without body cavity (acoelomate)

Trematodes flukes

General Introduction

  • Morphological characteristics


  • oval or elliptical

  • different in size,depending

    on species

  • most species have an

    operculum or cap at one end,

    apart from schistosomes

  • In many species the egg contains

    a fully developed miracidium

Trematodes flukes

Introduction to trematode

  • Characteristics of life cycle

  • Typical developmental stages:








Trematodes flukes

General Introduction

  • Characteristics of life cycle

  • Requiring one or two intermediate hosts:

    1st intermediate host is usually snail in fresh water,

    the secondary intermidate host belongs to

    species of animals in water,such as fishes and


Trematodes flukes

General Introduction

  • Characteristics of life cycle

  • Alternation of generations:

  • Asexual generations in the intermediate host

  • Sexual generations in definitive host

  • They have their reservoir hosts. The fluke

    diseases are zoonoses.

Trematodes flukes

Clonorchis sinensis

(liver fluke)

The worms blocking the bile passages cause clonorchiasis, which finally may become the biliary cirrhosis.

Trematodes flukes


  • Clonorchis sinensis was named after it was first discovered in the bile passages of a Chinese carpenter in Calcutta, India in 1874 .

  • Heanley pulished the first record of an endemic area in Guangdong, south China in 1908.

  • The discovery of Clonorchis eggs in the fecal material from a corpse in the Warring States Period(475-221 B.C.) in 1975, reveal that C.sinensishas been prevalent in China for about 2300 years

Trematodes flukes


1、Adult worm

  • slender, lanceolated or

    sunflower seed-like(10-25mmX 3-5mm)

  • the oral sucker is slightly larger

    than the ventral sucker(located at

    1/5 of the body)

  • two deeply branched testes in

    tandem are located in the posterior

    third part of the body

  • hermaphroditic

Trematodes flukes



  • the smallest helminth egg (27~35μm X 12~20μm)

  • yellow-brown

  • an operculum

  • small shoulder-like protrusions

  • a small knob on the abopercular end

  • a miracidium inside

Trematodes flukes


3、Other stages





Trematodes flukes

Life Cycle

Trematodes flukes

Life Cycle

Adults Eggs Miracidum Sporocyst Redia Cercaria Metacercaria Adults

Definitive host


1st intermidate host

(snails in fresh water)

2nd intermidate host

(fish and shrimp)

Definitive host

  • 7 stages in life cycle: Adult worm, egg,miracidium, sporocyst, redia, cercaria, metacercaria

Trematodes flukes

Life Cycle

  • two intermediate hosts

The first intermediatehost:


Parafossarulus striatulus

Alocinma longicornis

The second intermediate hosts:

  • freshwater fish

    fish of Family Cyprinidae such as pseudorasbora parva (麦穗鱼), Cyprinus carpio(鲤鱼), Aristichthys nobilis(大头鱼), Mylopharyngodon piceus (青 鱼).

  • shrimps

Trematodes flukes

Life Cycle

Development in human




eating raw fish and shrimp

with metacercaria


Trematodes flukes

Life Cycle

Development in human





Bile ducts


Rich mucosal secretions

Life span

20-30 years

Trematodes flukes

Life Cycle

Development in human





In the feces

Trematodes flukes


  • Worms mechanical and chemical trauma stimulating proliferation of inflammatory reaction in the biliary epithelium

  • The wall of the bile ducts thickened ,fibrous tissue around the bile duct, and worm obstruction cause cholestasis

  • When bacteria infection occur, cause cholecystitis, cholangeitis, sometimes cholelithiasis happens

Trematodes flukes


  • Bile stream blockage also cause necrosis of local hepatic cells and regeneration of damaged tissue. As a result, biliary liver cirrhosis occur

  • Associate with cholangiocarcinoma and hepatic carcinoma

Trematodes flukes


Infected liver

Trematodes flukes


Histopathological findings of clonorchiasis (hematoxylin and eosin stain). Note the flukes (arrows) within the dilated bile ducts, biliary epithelial hyperplasia (arrowheads), and periductal fibrosis.

Trematodes flukes

Clinical Manifestation

  • Acute symptoms appear when the primary infection

    is heavy: sudden onset, chill, high fever, slight

    jaundice, hepatomegaly, eosinophilia, a few patients

    have splenomegaly, and weeks later, enter chronic


  • Continuous reinfection: cirrhosis and portal

    hypertension. In children it may cause malnutrition ,

    growth development disturbance, even dwarf

Trematodes flukes


  • Epidemiologic data:

  • in or coming from the endemic area

  • 2.The history of eating raw or inadequately cooked

  • freshwater fish and shrimp

  • Clinical data:

  • gastrointestinal symptoms, hepatomegaly,

  • cholangeitis, cholecystitis, etc.

Trematodes flukes


  • Etiological diagnosis

  • 1. discovery of eggs in feces

  • A. Direct smear

  • B. Concentration methods

  • 2. Biliary drainage from duodenum

  • Immunological tests (for reference only)

  • IHA (Indirect Hemagglutination)

  • ELISA (Enzyme Linked Immunosorbent Assay)

Trematodes flukes


  • Distributed in Asia (Far East region: China, Japan,

    Korea, Thailand, Kampuchea, Vietnam, and etc.)

  • In China, there are about 10 million infected individuals

    and it is found in 25 provinces, cities and autonomic

    regions except Xinjiang, Gansu, Inner Mongolia, Qinghai,

    Ningxia and Tibet. It is widely prevalent in the Southern

    China , such as Guangdong ,Guangxi Province and Hong


Trematodes flukes


  • The infection is related with the dietary habits andacquired by eating raw, frozen, inadequately cooked, dried, salted, smoked, or pickled freshwater fish,drunken shrimp, that harbor the metacercaria


Drunken shrimps

Porridge with raw fish slices

Trematodes flukes

Prevention and control

  • Control of the source of infection:

    Treat the patients and domestic animal(cats and dogs,

    etc.) at the same time.

    A. Praziquantel is the best choice of drug for the therapy

  • Dose: 15-25mg/kg, three times a day, for 2 days,

  • the total dose is 90-150mg/kg

  • B. Another choice of drug is Albendazole

Trematodes flukes

Prevention and control

  • Cut off the route of transmission:

  • A. Health education

  • B. Sanitary disposal of the excreta

  • C. Avoid eating raw or inadequately cooked

  • freshwater fish and shrimp.

Trematodes flukes


How many stages in the life cycle?

Adult worm, egg, miracidium, sporocyst, redia,

cercariae, metacercaria

Which stage is infective stage? And how?

Metacercaria; eating (Ingestion )

Which stage inhabit humans? And where?

Adults; Bile duck

Which stage is primary cause of the disease?


Which stage was detected for diagnosis?


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