trematode. introduction taxonomic position phylum platyhelminthes class trematoda order digenea
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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