Introduction To Tapeworms

1. Class Cestoidea – Tapeworms – Chap. 20 & 21
Tapeworms are entirely endoparasitic.
Adults inhabit the ________________________________of
vertebrate definitive hosts.
Life cycles involve larval development in 1 or 2 intermediate
hosts.
Of the two subclasses, cestodes of medical and veterinary
importance occur in the SUBCLASS EUCESTODA

2. General Tapeworm Morphology
Tapeworms are polyzoic and
consist of 3 regions:
a.
b.
c.

3. General Tapeworm Morphology
•Scolex - anterior attachment structure
Is is NOT a __________________________
Structures for attachment differ in the 2
important orders:
●
Order Pseudophyllidea - scolex contains
slit-like suckers called
____________________________
●
Order Cyclophyllidea - scolex contains
______________________________
and a central domed area called the
_____________________________
with or without hooks
Scolex is an important taxonomic structure.
2. Neck - undifferentiated region posterior to
scolex

4. General Tapeworm Morphology
3. Strobila - linear series of segments or
proglottids
Proglottids are continuously formed posterior to
the neck region in a process called
strobilization.
As new proglottids are formed, the older
proglottids move posteriorly and become
sexually mature.
●
immature proglottids –
●
mature proglottids –

●
gravid proglottids -

5. General Tapeworm Morphology
• Gravid proglottids cont:
Male and female organs in gravid proglottids
degenerate as the uterus fills with eggs.
Gravid proglottids often detach from the strobila:
- disintegrate during passage through the
digestive tract releasing eggs in the feces
- or are released intact in the feces.

6. Tapeworm Tegument
Structure of the tapeworm tegument
is similar to that of trematodes.
1. Syntegument - outer anucleate
syncytial cytoplasmic layer containing
mitochondria and secretory bodies.

Major difference involves the presence
of _____________________________
on the surface
●
microvilli-like projections but
with a dense core
●
increase absorptive area.
●
Glycocalyx covers the
microtriches.

7. Tapeworm Tegument
2. Cytotegument - nucleated cell
bodies lying beneath the
tegumental muscles and connected
to syntegument.

8. Tapeworm Tegument
Microtriches showing the dense core

Tapeworm tegument

9. Functions of the Tapeworm Tegument
1. Because tapeworms lack a digestive tract,
_________________________________ are absorbed
through tegument.

2. Tegument protects the tapeworm from host
______________________________________
This is especially important as adults live in the small
intestine where digestive enzymes occur.
3. Tegument protects the tapeworm from
_____________________________________________.
This is important in larval forms that live in many habitats in
host body.

10. Parenchyma
System of loose cells filling space in the proglottid.
Many parenchymal cells contain _____________________________________
- a characteristic structure in tapeworms.
These are circular structures consisting of concentric rings.
Possible functions are (1)
___________________________________________
(2) ______________________________________________
Calcareous corpuscles are
best seen in living specimens.

11. Reproductive Organs
Tapeworms are _________________________________- each
proglottid is a reproductive individual with both male and female organs.
Male system develops first
Structures begin to form in the immature proglottids and are fully
developed in mature proglottids.
Structures are:
many testes (# varies from 3 to 100's)
vasa efferentia
vas deferens (often highly coiled)
cirrus sac with cirrus
common genital pore

12. Reproductive Organs
Female system - structures form and become functional in mature
proglottids.
Structures are:
1 ovary
vitellaria - scattered or compact
Mehlis' gland
uterus (contains eggs in branches)
vagina (carries sperm to ootype)
common genital pore
Most of the female organs disappear
in gravid proglottids except for the
egg-filled uterus.

13. Taxonomy of the Class Cestoidea
Contains 13 orders but only 2 orders contain
tapeworms of medical and veterinary importance.

Order Pseudophyllidea

Order Cyclophyllidea

14. Order Pseudophyllidea - Chapter 21
Contains some of the largest tapeworms known - lengths
of 10-30 feet are common
Characteristics of the order:
1. scolex contains
_______________________________ -
slit-like adhesive organs

15. Order Pseudophyllidea - Chapter 21
Characteristics of the order cont:
2. male and female genital
openings are separate and
located midventrally in the
proglottid

3. __________________________
are scattered throughout the proglottid
4. gravid proglottid is not shed;
eggs are released through
________________________________

♂
♀
Uterine
pore

16. Order Pseudophyllidea
Characteristics of the order cont:
5. life cycles are complex involving 3 hosts:
first intermediate host - ____________________
second intermediate host - _______________________
definitive host - _________________________

Two species of medical importance

17. Diphyllobothrium latum
Common name - the BROAD FISH TAPEWORM
broad - indicates that the proglottids are wider than long
fish - indicates that the definitive host is infected by eating raw or
poorly cooked fish
DISTRIBUTION - _________________distribution (not tropical)
Occurs in northern Europe, Asia, and North America
In North America, it is common in the Arctic and the Great Lakes
Region
In Wisconsin?

18. Adult of Diphyllobothrium latum
Scolex with bothria
Little difference between mature and gravid
proglottids
●
proglottids are ________________________
●
uterus is
_____________________________
Strobila reaches length of 30 feet

19. Adult of Diphyllobothrium latum
Eggs are shed from gravid proglottids through uterine pore (difficult to see)
- up to 1,000,000 eggs released/day
- egg in feces is diagnostic - has ________________________________ and
_______________________________________

20. Adult of Diphyllobothrium latum
DEFINITIVE HOSTS -
_________________________________________________
Common hosts include bears, dogs, cats, foxes, mink,
raccoons, walruses, seals, and humans.
Adults show low host specificity.

21. Life Cycle of Diphyllobothrium latum
1. Adult tapeworm occurs in the
___________________________of
carnivore or human definitive host.
2. Eggs are shed in the feces into
water.
3. Eggs embryonate in water and a
___________________________
hatches from each egg after several
weeks.

22. Life Cycle of Diphyllobothrium latum
Coracidium consists of outer
ciliated embryophore and
inner oncosphere containing
six hooks
embryophore
oncosphere

23. Life Cycle of Diphyllobothrium latum
4. Free-swimming coracidium
is eaten by ________________
1
st
intermediate host.
5. In copepod's midgut,
embryophore ruptures and
_________________________
uses its 6 hooks to penetrate
midgut.
Oncosphere migrates to the
copepod hemocoel.
6. In the hemocoel, the
oncosphere elongates to
become the
_________________________

24. Life Cycle of Diphyllobothrium latum
7. Infected copepod is eaten
by a ___________________
2
nd
intermediate host
(Almost any fish including
minnows will work)

8. Procercoid burrows
through the fish gut and
migrates to the muscles
where it transforms into a
________________________
(scolex and neck)

25. Life Cycle of Diphyllobothrium latum
9. Larger fish - northern
pike, walleye, perch, salmon,
trout - eat smaller infected
fish.
Plerocercoid will live in these
fish but undergoes no further
development
These fish are
________________________
and increase chances of
reaching the definitive host.

26. Life Cycle of Diphyllobothrium latum
10. Carnivore or human
definitive host is infected by
eating raw or poorly cooked
fish containing plerocercoids.
Worms attach to the wall of
the small intestine and
become sexually mature in
1 to 2 weeks

28. Life Cycle Stages of Diphyllobothrium latum
Copepod first intermediate host
containing the procercoid
Fish second intermediate host
containing the plerocercoid

29. Diphyllobothrium latum infections
Fish in the Great Lakes are common second intermediate hosts
and are heavily parasitized with plerocercoids - up to 50-75%
prevalence
Bears are common definitive hosts due to their fish-eating habits.
Dogs and cats become definite hosts when fed scraps of fish.

30. Diphyllobothrium latum infections
Humans become infected by
____________________________________________________
- gefilte fish (Scandanavian)
- sushi and sashimi (Japanese)
- cerviche (Latin American)

31. Pathology of Diphyllobothrium latum
Human infections cause:
1. ___________________________________________
(diarrhea, nausea, intestinal cramps).
2. some cases result in ____________________________________
- adult D. latum absorbs high levels of __________________
- lack of this causes decreased rbc production and anemia
Parasite is never life threatening.

32. Diagnosis & Treatment of Diphyllobothrium latum
DIAGNOSIS - ID egg in feces -
egg has distinct operculum
and abopercular knob


TREATMENT – drugs ___________________________________
are effective in eliminating adult tapeworms

33. Diphyllobothrium mansonoides
Causative agent of a human disease called
______________________________________
- disease results when humans become ___________________
________________________________________________
- old name for plerocercoid was sparganum - hence the name
sparganosis
- humans are NEVER definitive hosts

34. Diphyllobothrium mansonoides
Adult tapeworm is morphologically similar to D. latum.

35. Life Cycle of Diphyllobothrium mansonoides

1. Adult tapeworm occurs in the small intestine of a ___________________
definitive host.
2. Eggs are shed in water and a __________________________ hatches.
3. Coracidium is eaten by _______________________ and procercoid develops.

36. Life Cycle of Diphyllobothrium mansonoides

4. Copepod is eaten by second intermediate host - can be almost
___________ ________________________. Common hosts are fish, frogs,
snakes, and mice.
5. Plerocercoid (= sparganum) occurs primarily in the
___________________________________________
6. Cat becomes infected by eating infected second intermediate.

37. Life Cycle Stages of Diphyllobothrium mansonoides


Plerocercoid beneath the skin
(subcutaneous location) in a mouse
second intermediate host
Procercoid in copepod first
intermediate host

38. Human Infections of Diphyllobothrium mansonoides


Humans can serve as
accidental hosts of the
_______________________
Humans are infected by 3
methods:
1. _____________________
_______________________
_______________________
_______________________
Procercoid penetrates
intestinal wall and migrates
into the subcutaneous
regions as the plerocercoid.

39. Human Infections of Diphyllobothrium mansonoides


2. __________________
____________________
____________________
____________________
Plerocercoid migrates to
subcutaneous tissues and
undergoes no further
development.

40. Human Infections of Diphyllobothrium mansonoides


3. __________________
_____________________
_____________________
_____________________
Plerocercoid crawls out of
this host into
human.

41. Human Infections of Diphyllobothrium mansonoides

A few cases have
involved finding
plerocercoids in the

__________________
from this method of
infection.

42. Human Infections of Diphyllobothrium mansonoides
Parasite is rare - only about 40 cases of human sparganosis have
been reported in the U.S.
Parasite is diagnosed and treated by
_____________________________________________________

43. Diphyllobothrium mansonoides
Unusual occurrence is the production of
a chemical called __________________
________________________________
This chemical acts much like
_______________________________
and causes a great increase in size of a
mammalian second intermediate host
(mice).
This hormone, however, does not effect
humans.