Parasitology

1. Diphyllobothrium Latum
2019
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2. Introduction
• Diphyllobothrium latum, the fish tapeworm, is
the longest tapeworm in humans, averaging
ten meters long (Also referred to as broad
tapeworm).
• Infection with Diphyllothrium latum causes
diphyllothriasis and is acquired by eating
infected raw fish.
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3. Distribution
• D. Latum is worldly distributed in river and
lake areas of Europe, Uganda, North America
and far East
• It is also found in parts of Asia, south America,
central Africa
• In countries like India, where fish is eaten only
after cooking, the infection does not occur.
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4. Habitat
• The adult worm is found in the small intestine
(ileum) of humans, cats, dogs, foxes where it
lies folded in several loops with the scolex
embedded in the mucosa.
• The first host of the larva is the Crustacean of
genus Cyclops or Diaptomus
• The second host of the larva is a fresh water
fish and there are a number of various species
that can serve as intermediate host
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5. Transmission
• Transmission is by ingesting the infective larva
known as plerocercoid in raw or insufficiently
cooked fresh water fish such as trout, perch or
pike
• Unlike the other tapeworms described, the life
cycle of D. latum requires two intermediate hosts
i.e. Crustacean and fish
• Definitive hosts include humans and fish eating
animals such as dogs, cats, foxes, bear and
leopards
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6. The life cycle of D. latum
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7. Life cycle cont…
After ingestion of plerocercoid larva
Plerocercoid becomes attached to wall of the
small intestine and within 2-4 weeks develops
into a mature tapeworm
Many eggs are produced and discharged
directly by the worm into the lumen of the
intestines and passed in feces
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8. Life cycle cont…
• For the life cycle to be continued, the eggs
must reach fresh water
• Within 1-2 weeks, the eggs mature and hatch
releasing spherical ciliated embryos called
coracidia
• The coracidia are ingested by a crustacean like
crabs, lobsters, crayfish, shrimp, krill, woodlice
and barnacles
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9. Life cycle cont…
• Within few weeks, elongated larvae called
Procercoids develop inside the crustacean
• The infected crustacean is ingested by a fresh
water fish
• In the second intermediate host, the Procercoid
are released and develop into infective
plerocercoid which migrate to the muscles and
connective tissue of the fish
• The life cycle is completed by human or animal
definitive host eating fish containing
plerocercoids
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11. Clinical features and pathology
• D. latum can live for many years in human host
• Approximately four out of five cases are
asymptomatic and may go many years without
being detected
• Symptoms of Diphyllobothiriasis are generally
mild, and can include diarrhea, abdominal pain,
vomiting, weight loss, fatigue, constipation and
discomfort etc. due to toxins released by
tapeworm
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12. Clinical features and pathology cont…
• Occasionally megaloblastic anaemia may
develop due to uptake of vit B12 by the
tapeworm in competition with the host
• It is more likely to occur when the tapeworm
is situated in the upper part of the jejunum
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13. Morphology of adult D. latum
• The adult worm is composed of three fairly
distinct morphological segments: the scolex
(head), the neck, and the lower body.
• Each side of the scolex has a slit-like groove,
which is a bothrium for attachment to the
intestine.
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14. Morphology of adult D. latum cont…
• The scolex attaches to the neck, or
proliferative region.
• From the neck grow many proglottid
segments which contain the reproductive
organs of the worm.
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15. Adult worm
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16. Morphology of adult D. latum cont…
• Adults can shed up to a million eggs a day.
• In adults, proglottids are wider than they are
long (hence the name broad tapeworm).
• As in all pseudophyllid cestodes, the genital
pores open mid-ventrally
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17. Laboratory diagnosis
• Confirmation of D.latum infection is by;
Finding eggs in feces
Occasionally detecting mature segments in
feces
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18. Examination of faeces for D. latum eggs
• Many eggs are usually present in the faeces
because they are constantly discharged
through the uterine pore.
• They can therefore be easily detected by
direct examination of a fecal specimen
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19. Identification features of D. latum
eggs
• It is yellow-brown and oval
in shape, measuring about
70 x 45µm.
• Has an operculum (lid)
which is usually difficult to
see.
• Contains a mass of
granulated yolk cells
surrounding an
undeveloped ovum.
• Sometimes a small
projection is visible at the
non- operculated end of the
egg.
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20. Identification features of a D. latum
segment
• Often not found in the faeces
because they tend to disintegrate
in the intestines.
• When found, they often appear
shrunken and empty.
• Undamaged mature segments of
D. latum are wider than they are
long, measuring 10–20mm across
by 3–7mm long.
• The genital pore is found in the
centre of the segment and not on
the lateral margin as is the case
with Taenia species.
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21. Measures to prevent and control D. latum
infection
• Avoid eating raw or undercooked fish which may
contain plerocercoids.
• Health education about proper preparation of
fish. Fish that is thoroughly cooked, brined, or
frozen at -10 °C for 24–48 hours can be consumed
without risk of D. latum infection.
• Screening and successful treatment of people
infected with the parasite
• Preventing the eggs reaching water by providing
adequate latrines combined with health
education.
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22. Thank you
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