Trematode

Introduction

Taxonomic position Phylum platyhelminthes Class Trematoda Order Digenea

Species Reside in

Clonorchis sinensis hepatic bile duct

Fasciolopsis buski Small intestine

Paragonimus westermani

Lung, subcutaneous, etc.

Schistosoma japonicum

S.mansoni, etc portal system

Trematodes that have medical importance

General features

Leaf-like flattened bodies with no body cavity; with oral and ventral suckers to aid attachment to their hosts

The tegument is a syncytial layer equipped with spines and muscles

Digestive system degenerated，with a mouth, enclosed by the oral sucker but no anus. mouth→pharynx →esophagus → two digestive tracts

Hermaphrodite or monoecious except blood flukes (dimorphism) , possessing both male and female reproductive organs, the appearance and position of which are very important taxonomically

General featuresGeneral features

Reproductive system of trematode

Female: ovary, oviduct, ootype, Mehlis’ gland, seminal receptacle, Laurer’s canal, vitellaria, vitelline duct, & uterus

Male: testis, vas efferens, seminal vesicale, cirrus,&cirrus pouch

Life cycle is complicated – indirect life cycle Usually need one or two intermediate host –

bio-helmiths The first intermediate hosts are usually fresh w

ater snails

General featuresGeneral features

Eggs can only develop (hatch) in the fres

h water Asexual phase:

Eggsmiracidium in watersporocyst in snail redia cercaria release in water encysted metacercaria in second intermediate host – infective stage

Sexual phase Preadult (Juvenile)migrated to favo

rable residing site adult worm lay eggs

General featuresGeneral features

cercaria metacercaria

rediasporocyst

miracidiumegg

Encysted metacercaria is usually the infective stage (Schistosoma-- cercaria)

Egg has operculum except blood fluke Features reflecting adaptation to parasitism

Organs of attachment developed Retardation of digestive system Highly developed reproductive system

General featuresGeneral features

Clonorchis sinensis (liver fluke,肝吸虫 )

Introduction

found from the biliary passage of a Chinese in Calcutta, India in 1874 firstly.

Clonorchis sinensis is known as the oriental or Chinese liver fluke because it is distributed throughout Japan, Korea, China and Vietnam

It is estimated that there are more than 30,000,000 humans getting infection in these areas

It is a food-borne pathogen, causes clonorchiasis

The parasite also infects a number of other animals, including dogs, cats, pigs, and rodents, and these animals serve as reservoirs of infection --- zoonosis

Morphology

Adult: 1- 2.5 cm, flat, size and shape like the seed of sunflower

With oral sucker and

ventral sucker

The two testes of the male

productive organ are

branched

Younger worm Sucker & spine

oral sucker pharynx

ceca

ventral sucker

vitellaria

Seminal receptacle

uterus

ovary

Testis Excretory bladder

digestive tract

Eggs

Average 29×17µm, yellow brown

The smallest helminth egg Light bulb shape which also l

ooks like sesame or water melon seeds

Operculum with distinctive shoulders

Spine or knob on posterior end

Contains miracidium when discharged

operculum shoulders spine/knob well-developed

miracidium

cercaria

metacercaria

Life cycle

Need two intermediate hosts 1st intermediate host: fresh water snails, miracid

ium developed to cercaria in intestine 2nd intermediate host: fresh water fishes or shri

mps, cercaria to metacercaria in muscles Infective stage: metacercaria

Infective route: oral consumption of infective stage

Definitive host: human being Reservoir host: dogs, cats -- zoonosis

Lodging site: hepatic bile duct

Life cycleLife cycle

1st intermediate host: fresh water snails

Parafossarulus striat

ulus

Alocinma longicornis

Bithynia fuchsianus

2nd intermediate host: fresh water fishes and shrimps

Minnows or

carps

Pathogenesis Stage responsible for the pathogenesis:

adult worm Mechanical irritation – suckers

Toxic effects – excretions, secretions, metabolites

Biological interference – nutrition deprivation

Invasion of biliary epithelium inflammation cell infiltration and proliferation thickening of the duct wall occlusion extensive involvement fibrosis of the liver hepatocirrhosis

PathogenesisPathogenesis

Adult worm in hepatic bile duct

rabbit infected with Clonorchis sinensis shows fibrosis of the bile duct

rabbit infected with Clonorchis sinensis shows hepatocirrhosis

hepatocirrhosis

Clinical features

Asymptomatic to heavy bile duct diseases Hepatomegaly, jaundice, pancreatitis, bile du

ct stones, biliary cancer

Maximum worm burden report >70,000 worms

In child, symptoms are usually more serious, could also show malnutrition, nanoid, anemia and sometime causes death

Enlargement of liver and spleen

Clonorchiasis patients Clinical featuresClinical features

Clonorchiasis patients

Hepatocirrhosis with ascites nanoid kid

Clinical featuresClinical features

Diagnosis

History of eating raw fish or shrimps

Etiological exams Kato-Katz method Sedimentation method is the choice for

fecal or duodenal aspiration examination if egg burden is low

Immunological diagnosis ELISA for specific antibodies or circulating

antigens

Epidemiology and control Distributed in the Far East including China, Korea, Japan,

Vietnam and far east part of Russia

In china, it covers 25 provinces with the highest prevalence in Guangdong (5,000,000 cases), totally 10,000,000 reported cases over the country in year 2003 survey

Dietary habit is the hard part for the disease control

Factors associated with endemic: Existence patients and reservoir hosts (cats &

dogs)

Presence of first & second intermediate hosts in the same water body

Mode of fish breeding

Dining habit and custom

Epidemiology and controlEpidemiology and control

Control measurements: Hygiene education – avoid eating raw or under

cooked freshwater fishes; separate the raw and cooked food preparation area

Protect fish pond from being contaminated by the feces

Control of reservoir hosts – pets at home, no raw fresh-water fish for cats

Cure patients and carriers – Praziquantel (drug of first choice), 25mg/kg， tid×3d

Epidemiology and controlEpidemiology and control