Tapeworms

1. Tapeworms

2. General
• Complete absence of an alimentary canal: no mouth, no gut, no anus; all
nutrients are acquired through a specialized tegument
• Endoparasitic with sexually mature worms living in the alimentary tract
and associated ducts of all classes of vertebrates
• Larval stages infect both vertebrates and invertebrates
• The life cycle require one or two intermediate hosts, in each of which the
tapeworm undergoes a specific phase of development

3. Morphology of the Cestodes
The Adult Parasite
The body of the adult tapeworm may be divided into three region
I. The Scolex -
The "head" and attachment organ of the parasite
There are four main types of scolex, by which the tapeworm may be taxonomicaly classified.
a) A Bothria
This is composed of a pair of shallow, elongated, weakly muscular grooves. Tapeworms of the
order Pseudophyllidea are equipped with bothria on their scolices.

4. b) A Bothridia
These are broad, leaflike muscular structure, exhibiting a large degree of variation. Some
bothridia are sessile, some are stalked, whilst others are hooked with accessory suckers.
Tapeworms of the order Tetraphyllidea and others are equipped with bothridia
(Rhinebothrium sp,)
c) Acetabulate Suckers
order Cyclophyllidea (four acetabulate suckers)
additional features at the apex of the scolex such as;
- Glandular areas
- Protrusible suckers
- Suckers armed with hooks
- Hooks (e.g. Taenia)
- A Rostellum, an muscular proboscide, often covered with hooks
(e.g.Hymenolepis, Echinococcus, Dipylidium)

7. • the bi-lobed ovary lies in the posterior portion
of the proglottid
• the oviduct, arising from the ovary, continues
anteriad as a coiled uterus, opening to the
exterior through the midventral uterine pore
• eggs are expelled via the uterine pore
• vitellaria are scattered throughout the
proglottid;
•numerous testes are medullary in their
distribution
Family Diphyllobothriidae
Diphyllobothrium latum (broadfish tapeworm)
• Parasitizes fish eating mammals (including humans)
• Large worms and extraordinary size is partially due to anapolysis
• Adult reproductive system possesses a common genital atrium into which male and female
genital pores open on the midventral surface of each proglottid

11. Epidemiology
• In the small intestine of the definitive host, it attaches to the mucosa and grows at a rate of
about 30 proglottids a day (maturity in 3-5 weeks)
•D. latum infection is limited to areas where fresh fishes are commonly eaten
• Coldwater, FW fishes (including pike, salmon, trout) serve as s. intermediate hosts
• In Finland and some of the Baltic communities, humans display a relatively high incidence
•about 50-70% of the northern and walleye pike found in some lakes in the northern US and
Canada harbor plerocercoids of D. latum
• Humans maintain the endemicity of this parasite through inadequate sanitation, practice of
eating raw or improperly cooked fish,
coupled with the presence of suitable intermediate hosts

12. Symptoms and Diagnosis
• Rarely is more than a single worm found in an infected human, and many victims
display few if any symptoms
•Most common: abdominal pain, weight loss, weakness, and nervous disorders
•Symptoms are attributed to the patient’s reaction to the parasite’s metabolic wastes,
degenerating proglottids, or to irritation of the intestinal mucosa
• Occasionally, the worm is found in the upper portions of the jejunum, in which case it
can compete with the host for ingested vitamin B12; this vitamin is important in the
synthesis of hemoglobin and deprivation causes megaloblastic anemia in the human host

13. Sparganosis
When procercoids of some species belonging to the genus Spirometra are
accidentally ingested (e.g. swallowing copepods while drinking water) they can
migrate from the gut and develop into plerocercoids in subcutaneous tissue,
brain and the eye ball.

15. Order: Cyclophyllidea
• Possess scolices with 4 suckers
• Most species possess a rostellum with hooks
• Usually a single compact, postovarian vitelline gland
• Number of testes varies from one to several hundred
• Most tapeworms of birds and mammals belong to this group

16. Family Taeniidae
Taenia solium (“human pork tapeworm”)
• Humans are definitive hosts as well as rats, monkeys
• It is common in humans in areas where raw or improperly cooked pork is a regular element
of the diet
• The scolex is armed with 2 circles of 22 to 32 rostellar hooks
• The hooks are of 2 sizes
and alternate in the 2 circular rows

17. Taeniasis

18. Life cycle cont.
•

19. Epidemiology
• The prevalence of pork tapeworm infection in humans varies by region
• The very low incidence in the US can be attributed to the isolation of pigs from human
feces
• Religious dietary proscriptions forbidding pork consumption by adherents of Islam and
Judaism render human infection very rare in Moslem countries and in Israel
• However, it is common in other parts of Africa, India, China, and several countries in
South and Central America

20. Global distribution of cysticercosis

21. Symptamology and Diagnosis
• The armed scolex may cause irritation of the mucosal lining, and there have been
cases in which the scolex perforated the intestine, leading to peritonitis
• However, the greatest hazard to human health associated with this parasite is infection
with the cysticercus, causing the sometimes dangerous disease known as human
cysticercosis
•Human infection is due to ingestion of eggs
• This may result from:
-hand to mouth self infection
- from eating food contaminated with eggs by unsanitary food handling practices

22. Symptamology and Diagnosis cont.
While common sites for infection by cysticerci are the skeletal muscles and the brain,
they can develop in practically any organ of the body, including the eyes and lungs, and
heart.
Neurocysticercosis - section of a human brain containing numerous Taenia
cysticerci.

23. Cysticercosis

24. Symptamology and Diagnosis cont.
• Cysts are tolerated in muscles and subcutaneous tissues (heavy infections can cause muscle
spasms weakness and general malaise)
• Developing cysts elicit a host inflammatory response often resulting in fibrous
encapsulation
• Calcification of the cyst may occur after 1 year (the disease may become asymptomatic)
• The most serious symptoms arise about 5-10 years after the infection as a result of dead and
dying cysticerci
• The degenerating parasite tissues and associated fluid also elicit a host inflammatory
reaction that can be very severe, even fatal (anaphylaxis)
• Cysts developing in the CNS, sense organs, or heart can exert mechanical pressure and
cause severe neurological symptoms
• Violent headaches, convulsions, local paralysis, vomiting and optic disturbances are
common

25. Treatment
• Surgery is the recommended treatment for cysticerci in the fluid spaces of the
body
• NC: Antiparasitic treatment should be given in combination with
corticosteroids and anticonvulsants to reduce inflammation surrounding the
cysts and lower the risk of seizures. Surgical intervention more likely to be
needed in intraventricular, or spinal neurocysticercosis.
• Praziquantel and some steroids (e.g. dexamethasone) are effective in
reducing edema and alleviating some of the symptoms of cerebral cysticercosis
•Treatment recommendations for subcutaneous cysticercosis includes surgery,
praziquantel and albendazole.

26. Taenia saginata (beef
tapeworm)
•Common among humans
• Large tapeworms (35-60 cm long; about
1000 proglottids)
• Scolex is unarmed; no rostellum or hooks
• The morphology of the mature proglottids in
this species is similar to that of T. solium
except that T. saginata has a bi-lobed ovary
and about twice as many testes as T. solium

28. Epidemiology
• Humans acquire infection by eating raw or improperly cooked beef
infected with cysticerci
• Cattle develop cysticerci by grazing in fields upon which human
excrement has been deposited either through fertilization with “night
soil” or from poor sanitation
• Pastures flooded by rivers and creeks contaminated with human
excrement are another source of infection among cattle

29. Symptamology and Diagnosis
• T. saginata taeniasis in humans is often characterized by such
symptoms as abdominal pain, greatly diminished appetite, and
weight loss
• These symptoms are especially common in patients already
debilitated by malnutrition or some other illness
• Unlike victims of T. solium infection, T. saginata victims do not
develop cysticercosis, and the prognosis is generally good

30. Taenia saginata
15 – 35 primary lateral uterine branches
Taenia solium
7 – 13 primary lateral uterine branches

31. • The eggs of Taenia solium and T. saginata are indistinguishable from
each other, as well as from other members of the Taeniidae. The eggs
measure 30-35 micrometers in diameter and are radially-
striated. The internal oncosphere contains six refractile hooks.

32. Echinococcus
• As adults, these are the smallest tapeworms of the
family Taeniidae, e.g. 2-8 mm long; 3-4 proglottids
(one immature, one mature, and one gravid
proglottid)
• Adult worms inhabit the small intestine of a wide
variety of canines and occasionally cats
• The juvenile forms of these worms are huge and
are capable of infecting humans, resulting in a
series disease called hydatidosis

33. The world distribution of Echinococcus species: E granulosus is
endemic in the red areas, and E vogeli is endemic in the dark green
areas.

34. E. granulosus Life cycle

35. Hydatid Cyst: Unilocular Type
• At maturity, the cyst wall contains 2 layers:
-a thick, laminated, noncellular outer tegument called the ectocyst,
-an inner, germinal epithelium that produces the protoscolices called the endocyst
• Brood capsules attached to the germinal epithelium by the stalk, the pedicel, extend into
the fluid filled cavity of the cyst
•In large cysts, these capsules may rupture, and the freed protoscolices (arrows), which
sink to the bottom of the bladder, are commonly known as hydatid sand

36. Hydatid Cyst: Unilocular Type cont.
•Each brood capsule contains 10-30 protoscolices
• The average fertile primary cyst is estimated to contain more than 2 million
protoscolices
• If a cyst ruptures within a host, each liberated protoscolex can produce a daughter cyst

37. Symptamology and Diagnosis
• The presence of unilocular cysts elicits a host inflammatory reaction that results in
encapsulation of the cyst
• The primary pathology of the cyst is impairment of the organs from mechanical pressure
• Increased pressure resulting from cyst growth may cause the surrounding tissues to atrophy
• The brain, kidneys, spleen and vertebral column may also be invaded, producing symptoms
ranging from seizures to kidney dysfunction
• Protoscolices, freed by the rupture of cysts, enter the circulatory system and are transported
to tissues throughout the body where they produce secondary echinococcosis
• The rupture of cysts also releases hydatid fluid which sometimes causes severe allergic
reactions
• If a significant amount of fluid enters the bloodstream it can cause anaphylactic shock

38. Treatment
• Surgery remains the preferred treatment for unilocular hydatidosis
• Following drainage of the cyst fluid, replacement with 2% formalin for 5 min kills the
protscolices and the germinal epithelium
• In any surgical procedure for cyst removal, care should be taken to avoid rupturing the
cyst
• Symptoms of allergic reaction, respond best with antihistamines
• Benzimidazoles has been used to successfully reduce the size of unilocular cysts

39. A figure showing a surgery procedure to remove
hydatid cyst from a human patient
A hydatid cyst (*) in the
cranium of a child (the ruler at
the top measures 6 inches long,
and the child's brain is below
the hydatid cyst). This
infection resulted in the child's
death.

40. Photograph shows the excised cyst, which contained yellowish fluid and
multiple smaller cysts within a thick capsule. The patient recovered well after
surgical treatment.

41. Echinococcosis

42. Family Dilepididae
Dipylidium caninum
• A common tapeworm of dogs, cats and
humans (especially children)
• It is easily recognizable because each
proglottid has 2 sets of reproductive
organs with a genital atrium on each
lateral edge
• The eggs are encapsulated in egg
capsules; each capsule contains 8-25
eggs

44. Epidemiology
• Most human infections are in children younger than 8 years
old, with a large percentage under 6 months
• Transmission to humans usually results from accidental
ingestion of infected fleas or lice or from allowing dogs and
cats to lick the mouths of children soon after the pet has bitten
an infected arthropod

45. Family Hymenolepididae
• A large family that occurs in both birds and mammals
• Only 2 species Hymenolepis (Vampirolepis) nana and
Hymenolepis diminuta infect humans

47. Hymenolepis (Vampirolepis) nana
• Known as the dwarf tapeworm of mice and humans
• Mature proglottids are much broader than they are long
• Male system has 3 spherical testes, bi-lobed ovary

48. Autoinfection
• Autoinfection can exacerbate the condition by increasing the
number of worms
• Eggs released from gravid proglottids, instead of passing to the
exterior to infect new hosts, hatch in the small intestine and re-
infect the same host
• The freed oncosphere penetrates a villus and repeats the cycle

49. Hymenolepis diminuta
• Hymenolepis diminuta is a common parasite of rats throughout the world; it
occasionally parasitizes humans
• Hymenolepis diminuta exhibits a typical 2 host life cycle, utilizing a grain-ingesting
insect such as a flour beetle as an intermediate host
• Insects are infected when they consume rodent feces containing either gravid
proglottids or eggs
• The oncosphere penetrates the intestinal wall of the insect and enters the hemocoel
where it develops into the cysticercoid stage
• The most common intermediate hosts are grain beetles belonging to the genus
Tribolium or Tenebrio
• Humans acquire infections by eating cereals, dried fruits, etc. that contain infected
insects