The document provides an overview of trematodes (flukes), particularly focusing on their general characteristics, morphology, life cycle, reproduction, and classification. Trematodes are flat, unsegmented worms with distinct life stages including eggs, miracidia, sporocysts, rediae, cercariae, and metacercariae, requiring at least two hosts for their development. They are classified based on their reproductive systems and habitat, highlighting medically significant species.

1. Trematodes (flukes)

2. Introduction to
Trematodes (flukes)
Subclass Digenea

3. Outline
• General characteristics of trematodes
– General morphology
– Attachment organ
– Digestive tract
• General life cycle and reproduction of trematodes
• General feature of the different stage of trematode
• Classification of trematodes

4. Learning objective
• At the end of this section the student will be
able to
– Explain the general feature of trematodes
– Describe the general morphology of the different
stage of trematodes
– Explain the general reproduction and life cycle of
trematode
– Explain the general feature of the different stage of
the trematode
– Classify and list medically important trematodes

5. General characterístis
Are generally flat, unsegmented, leaf shaped worms
(exception, schistosomes- cylindrical)

7. Vary in size from species just visible to the naked eye
to large fleshy species,

8.  Attachment organ
• Characteristics- 2
suckers
– Muscular oral sucker
surrounding mouth at
anterior end
– One or more suckers on
ventral surface (called
“ventral sucker,”
“posterior sucker,” or
acetabulum.”
Morphology

9. • Characteristics- 2
suckers
– Muscular oral sucker
– ventral sucker,
Attachment organ

10. Digestive tract
• Digestive tract consists of
mouth and esophagus
divides to “ “shaped.
• Vitellaria – yolk and
eggshell producing organs
connected to ovaries.
Y

11. Reproduction
• Sex organs - Most adult
digenetic trematodes
are monoecious (a
single organism
contains both male
(blue) and female
(orange) reproductive
organs)
• Schistosomes.;dieces
(separate sex)

12. General Life Cycle
• Are digenetic (Require at least two hosts)
• Have sexual and asexual generations
• Adults are endoparasites of vertebrates
• First intermediate host = a mollusc

13. General Life Cycle
Sexually mature Adult in DF host
Eggs in Feces
Miracidium
Released
in H2O
Miracidium
Infects Snail
Sporocyst-rediae-cercaria
Cercaria
Released
in H2O
Infect Definitive
Host Directly
Infect Secondary
Host, develop into
Metacercaria
which are later,
Consumed by
Definitive host
Intermediate host
Definitive host

14. • Miracidium: Free living, ciliated larva seeks the
intermediate host
• Sporocyst: Loses larval characteristics, grows in
the blood of molluscs and produces germ balls
• Redia: Sporocyct develops into active, feeding
larval stage with the germballs
• Cercaria: Free swimming larva that leaves the
mollusc and enters the definitive host where it
develops into an adult
• Metacercaria: Encycted (waiting) stage in second
intermediate host until it is eaten by the definitive
host, where it develops into an adult

15. Stages of Trematode Life Cycle
• Ova or egg
– Contains miracidium inside shell
– Usually have an operculum or
spine
– Eggs must be passed out of host
– May pass in feces either
• with miracidium developed
• with only a morula present
– Many of flukes have very
distinctive eggs.

16. Stages of Trematode Life Cycle
• Miracidium
– small ciliated, swimming form that
hatches from egg
– May be fully developed when passed
or develop outside of host
• May hatch in water and seek snail and
penetrate snail
• In this case, it contains penetration glands
that release histolytic or proteolytic
enzymes to help penetrate snail
• In some species do not hatch until eaten
by snail host. In these the miracidium is
not as prominent.

17. Stages of Trematode Life Cycle
• Sporocyst
– The miracidium develops into
sporocyst often in the digestive gland
of the snail.
– The sporocyst is an embryonic bag or
germinal sac that has asexual
reproduction occurring.
– The sporocyst will produce many
daughter stages called rediae or in
some cases daughter sporocysts. The
term daughter has nothing to do with

18. Stages of Trematode Life Cycle
• Rediae
– Larval stage in snail with precursor gut
and oral sucker
– Contains germ balls
– Some germ balls asexually reproduce to
yield more of the same (daughter
rediae) and others transform into next
larval stage ( cercariae)
– Some species they can live for many
years.

19. Stages of Trematode Life Cycle
• Cercariae
– Infective swimming stage that develops
in mollusk
– Leave the snail to find next host to
penetrate or to encyst in or on another
host or a substrate to be eaten by final
host
– These usually die within 24 hours of
release if not in proper place
– Variety of tail morphologies

20. • Furcocercus (forked tail as in
Schistosomes species),
• Microcercus (short stumpy
and rudimentary tail as in
Paragonimus westermani),
• Lophocercus ( large fluted
tail as in Clonorichis,
Heterophyes, Fasciola,
Fasciolobsis, Metagonimus)
and
• Pleurolophocercus (long tail
with fin folds as in
Opisthorchis)

21. Stages of Trematode Life Cycle
• Metacercaria
– This larval stage is the endstage
cercaria, tail is shed, and the
juvenile fluke is within a resistant
wall secreted by the fluke
– Cercaria that have this stage contain
cystogenic glands that helps the
organism encyst on vegetation.
– Cercaria that form metacercaria in
second intermediate hosts, often
have penetration glands that enable

22. Stages of Trematode Life Cycle
• Adult
– Always found in the definitive host
– Responsible for sexual reproduction
– Often restricted to specific region of host.
– Often very host specific.

23. Classifications
• Based on their reproductive systems.
– divided into two major categories
• The hermaphrodites flukes.
• The Schistosomes -separate sexes.

24. • Based on their habitat.
• Liver fluke.
– F. hepatica
– F. gigantica
– C vivereni
– O. sinensis
• Intestinal fluke
– F buski
– H. hetrophyes
– M. yokogawi
• Lung fluke
– P westermani
• Blood fluke
– S. mansoni
– S. hematobium
– S. japonicum
– S. intrecalatum
– S. mekongi