Parasitology lecture about cestodes

1. Cestodes
• Adult worms live in the human intestine,
where they attach to the epithelium using
suckers on the anterior portion ( scolex).
• From the scolex arises a series of
progressively developing segments called
proglottids.
• The mature distal segments contain eggs,
which may either be released directly into
the faeces,or are carried out with an intact
detached proglottid.

2. Continuation:
• The eggs are taken by the intermediate host and
hatch in the gut into larvae (oncospheres). The
larvae penetrate the intestinal wall of the host
(pig or cattle) and encyst in the tissues.
• Man ingests the cyst in undercooked meat and
the cycle is completed when the parasite excyst
in the stomach and develop into adult worm in
the small intestine.
• The infections are usually solitary, but several
adult tapeworms may coexist.

3. Continuation:
• The exception to this life cycle are the
dwarf worm, Hymenolepis nana, which
has no intermediate host and is
transmitted from person to person by
faeco-oral route and Taenia solium which
produces cysticercosis.

4. Taenia saginata:
• T. saginat, the beef tapeworm, may reach a
length of several metres.
• It is common in all countries where
undercooked beef is eaten.
• The adult worm cause few if any symptoms.
• Infection is usually discovered when
segments are found in faeces or on
underclothing.
• Infection can cleared with a single dose of
praziqantel 10 mg/kg.

5. Taenia solium and cysticercosis:
• T. solium, the pork tapeworm, is not so
large as T. saginata.
• The scolex has, in addition to suckers, two
circular rows of hooklets anterior to the
suckers.
• The adult worm is found only in man
following the eating of undercooked pork
containing cystcerci.

6. Human cysticercosis:
• This results from ova being swallowed or
gaining access to the human stomach by
regurgitation from the person’s own adult
worm.
• The larvae are liberated from eggs in the
stomach, penetrate the intestinal mucosa
and are carried to many parts of the body
where they develop and form cysticerci.
• Common locations are the subcutaneous
tissue and skeletal muscles.

7. Clinical features:
• When superficially placed, cysts can be
palpated under the skin. Here they cause
few or no symptoms and will eventually die
and become calcified.
• Equally common is infection in the central
nervous system.
• Heavy brain infection, especially in
children may cause features of
encephalitis.

8. Clinical features:
• More commonly cerebral signs do not
occur until the larvae die, 5-20 years later.
• Epilepsy, personality changes, staggering
gait or signs of internal hydrocephalus are
the most common features.

9. Diagnosis:
• Calcified cysts in muscles can be
recognized radiologically.
• In the brain less calcification takes place
and larvae are only occasionally
demonstrated radiologically but usually by
CT.
• Subcutaneous nodules should be excized
for histopathology.

10. Management:
• Adult T. solium can be destroyed by praziuantel
or niclosamide.
• Praziquantel improves the prognosis of cerebral
cysticercosis; the dose is 50mg/kg in 3 divided
doses daily for 10 days.
• Prednisolone 10 mg 8 hourly is also given for 14
days, starting one day before the praziquanel.
• Antiepileptic should be given until reactions in
the brain subsided.