INTRODUCTION TO TREMATODES
Dr.Jagadeesh (P.G)27-7-15
• Helminths are elongated, flat or round worm,
parasites. Few mm to meters in size.
• Eukaryotic, multicellular and bilaterally
symmetrical.
• Belong to two phyla
Platyhelminths----class-cestoidea,tramatodea
and monogenea
Nemathelminthis
• Class-Cestoidea---Order---Pseudophyllidea---Family---Diphyllobothriidae—
Genus---Diphyllobothrium and Spirometra
Order– Cyclophyllidiae--Family—Taeniidae—
Genus---Taenia and Echinococcus
Family--- Hymenolepidiidae--Genus---Hymenolepsis
Family---- Dipylidiidae—
Genus---Diphylidium
properties
Cestodes
Trematodes
Shape
Tape like, segmented Leaf like,
unsegmented
Elongated,cylindrical and
unsegmented
Head end
Suckers present,
some have hooklets
Suckers present no
hooklets
No sucker, no hooklets
some have buccal cavity
Alimentary canal
Absent
Present incomplete
Complete mouth-anus
Body cavity
Absent
Absent
present
Life cycle
2 host
except H .nana and
D.latum
3 host
Except schistosomes
1 host except filarial
worms and
Dracunculosis
sex
Monoecious
Mono
Diecious
Larval forms
Cysticircus
Hydatid cyst
Coenurus
Cystcercoid
Corcidium,
Plerocercoid
Procercoid
Cercaria
Metacercaria
Redia
Miracidium
Sporocyst
Nematodes
Rhabditiform larva
Filariform larva
Microfilaria
• Trematodes or flukes belong to—
Phylum-------Platyhelminths
Class----------Digenea
• Trematodes or flukes are unsegmented ,flat
and leaf like .
• They have suckers but no hooklets .
• They have incomplete alimentary canal .
• No body cavity and are monoecious .
• Require three hosts .
• Larval form includes-Cercaria,Metacercaria
,Redia , Meracidium and Sporocyst .
Classification of Trematodes
ORDER
SUPER FAMILY
FAMILY
GENUS
Strigeida
Schistosomatoide Schistosomatidae Schistosoma
a
SPECIES
S.haematobium
S.mansaoni
S.Japonicum
S.mekongi
S.intercolatum
Echinostomatida
Paramphistomat
oidea
Echinostomatoid
ae
Plagiorchida
Opisthorchiodea
Zygocotylidase
Fasciolidae
Ophisthorchide
Heterophydae
Gastrodiscoides
G.hominis
watsonius
W.watsoni
Fasciola
F.hepatica
Fasciolepsis
F.buski
Opisthorchis
Felineus,viverrini
Clonorchis
C.sinensis
Heterophyses
H.heterophyes
Metagonium
M.yokogawai
• Classification based on habitat
Blood Trematodes—
Schistosoma hematobium-vesical
venous plexus
Schistosoma mansoni ,S.japonicumrectal and portal venous plexus
contd
• Hepatic Trematodes
Fasciola hepatica and
Fasciola gigantica-both resides in liver
Clonorchis species—in bile duct
Opisthorchis species—in bile duct
contd
• Intestinal Trematodes
Small intestine—
Fasciolopsisbuski,Heterophyses species
Metagonimus species ,Watsonius species
• Large intestine –Gastrodiscoides species
• Lung Trematode-- Paragonium
Westermani
General characteristics
• Trematodes exist in three morphological
forms—adult form, egg and larva .
• Adult worm unsgmented and flattened
dorsoventrally ,some may have thick fleshy
bodies( Schistosomes ).
• Size 1 mm to 60mm
• They have two suckers to attach to
host .
• Oral sucker is anterior and surrounds
mouth.
• Ventral sucker or acetabulum on
ventral surface .
• Digestive system—It is incomplete , consist
of anterior mouth , muscular pumping
pharynx continue as esophagus.
• Esophagus bifurcates infront of ventral
sucker into a pair of blind intestinal pouchs
called caeca or crura
• It may be simple as in C .sinensis or
branched as in F.hepatica or may reunite to
form a single caecum.
• The anus is absent.
• Most trematodes are hermoprodite
except Schistosomes which are diecious .
• Male sexual organ consists of number of
testes present near cecal end , vas
efference arise from each testes and join
to form a common vas diference .
• It runs via seminal vesicle and opens at
genital pore situated near ventral sucker .
• Female reproductive organs consists
of—an ovary present near the ventral
sucker.
• Vitelline glands surrounding ovary,ovi
duct ,ootype and a uterus contaning
eggs that opens behind the ventral
sucker
• The excretory system is bilaterally
symmetrical.
• Contains flamme cells and collecting
tubules which lead to a median
bladder opening at the posterior end
of body,usually on the dorsal aspect .
• The nervous system consists of paired
ganglia at the anterior end . From this
nerves extend anteriorly and
posteriorly
• They are oviparous .
• Eggs are operculated except that of
schistosomes .
• Larva of trematodes have many
forms—miracidium ,sporocyst ,
redia,cercaria and metacercaria .
Trematode eggs
Life cycle
• They complete their life cycle in three different
hosts—one definitive and two intermediate .
• First intermediate host is fresh water snail or
mollusc and second is either an aquatic plant or
fish or crab .
• Schistisomes dont need a second host .
• Mode of transmission—man get infected by
eating aquatic plants ,fishes harboring infective
forms (metacercaria ) or by penetration of free
living cercariae
Development in definitive host
• Young trematodes migrate to their habitat ,grow into
adult worm , sexually mature and begins laying eggs.
• Eggs in urine, feces or sputum gain access to water .
• Depending on embryonation ,eggs show three
different types of development
 Eggs if embryonated hatch to release miracidia and
infect intermediate host i.e snail (Schistosomes ) .
 Non embryonated eggs first mature in water then
hatch to release miracidia (Paragonium ,Fasciola) .
Eggs embryonated but hatch only on ingestion by
suitable snail host (Clonarchis .Ophisthorchis )
Development in first intermediate host
• Miracidium is the free swimming ciliated larva ,
penetrate suitable intermediate host.
• Miracidium contains apical gland which release
proteolytic enzyme help in penetration.
• In liver or lymph space of intermediate host ,
miracidium tranforms into sporocyst .
• Asexual multiplication doesnt occur at this stage
except in schistosomes .
Contd
• Sporocysts develop to become radiae ,which
multiply to produce second generation rediae or
transform into cercariae .
• A single miracidium can give rise to a large
number of cercariae .
• No radiae stage in Schistosomes
• Based on morphology of tail cercariae can be
divided into four types .
• In schistosomes , cercariae are infective to man ,
Where as in other trematodes metacercariae are
infective
Types of cercarial larvae of Trematodes
• Furcocercus cercaria –elongated body with
forked tail (Schistosomes )
• Microcercus cercaria—oval body with short
stumpy tail (Paragonimus )
• Lophocercus cercaria—Crecaria armed with
spines, large fluted tail ,conspiuious eye spot
(Clonarchis )
• Pleurolophocercus cercaria-spines ,pigmented
eye spot and long keeled tail (Opisthorchis )
Types of cercaria
• Furocercus cercaria—elongated body with forked
tail—Schistosomes.
• Microcercus cercaria---oval body with short stumpy
tail—Paragonimus
• Lophocercus cercaria---Cercaria armed with spines
and has large fluted tail and conspicious eye—
Clonarchis.Metagonium
• Pleurolophocercus Cercaria—armed with spines
,pigmented eye spots with long keeled tail
Development in second intermediate host
• After ingestion by fish or crab ,the
cercarial larvae develop into
metacercariae which are the
infective form to definitive host
Answer the questions
• Classify trematodes based on their habitat ?
• Write short note on morphology of flukes ?
• Write differences between Cestodes , Trematodes
and Nematodes ?
• Name the larval forms of trematodes ?
• Name the types of cercarial larvae of Trematodes