2. DIPHYLLOBOTHRIASIS
Diphyllobothriasis is defined as human intestinal
infection with the cestode D latum, D
nihonkaiense, or other broad tapeworm species. It
is acquired by ingestion of inadequately cooked or
frozen freshwater, anadromous, or marine fish
containing larvae called plerocercoids, either in fish
muscle or on serosal surfaces.
3.
4. Adult D latum is the largest human parasite and can
grow to a length of greater than 20 meters and live
for decades. It is capable of causing vitamin B-12
deficiency through dissociation of the vitamin from
intrinsic factor and consumption of the vitamin. This
is rare today, but low vitamin B-12 levels have been
reported in up to 40% of patients with D
latum infestation and 5% of patients with A
pacificus infestation. Clinical anemia and
neurological disease is much rarer (< 2%).
6. PATHOPHYSIOLOGY:
Fish tapeworms have a complex life cycle, with humans,
other fish-eating mammals, and birds as their definitive
hosts
Adults are long ribbonlike creatures originally identified
based on scolex and egg morphology; increasingly,
cytochrome oxidase (cox1) molecular testing has
clarified nosology and epidemiology. Except for D
latum, which appears specifically adaptive to humans as
the preferential host and is by far the most common
species involved in human infection, most other species
rely on nonhuman definitive hosts, and humans are
incidentally infected.
7. A full-grown Diphyllobothrium worm can range from 1-15
m in length and is the longest human tapeworm. It
consists of up to 3000-4000 proglottids. The scolex, as
noted, has 2 sucking grooves, also called bothria, which
attach to small-intestinal mucosa. Proglottids are
typically wider than they are long and contain
hermaphroditic sexual parts. Humans and other animals
may be infested with multiple worms simultaneously.
In the gravid state, the worms have a distinctive
rosettelike uterus in the center. Each adult worm sheds
many thousands of operculated eggs every day. To
complete their maturation, the eggs must reach water to
be eaten by one of 40 species of crustacean copepods
and cyclops, within which the procercoid matures.
10. ETIOLOGY
Diphyllobothriasis is caused by ingestion of raw, undercooked,
or unfrozen infected fish and subsequent intestinal infection.
The main causative organisms are D latum and D
nihonkaiense, but other Diphyllobothrium and similar species
have also been reported as infecting agents, albeit much less
frequently. Examples include the following:
D dendriticum
A pacificus
D balanopterae
Diphyllobothrium alascense
Diphyllobothrium cameroni
12. PHYSICAL EXAMINATION
D latum has an unusual affinity for vitamin B-12,
and the presentation of diphyllobothriasis may
resemble that of megaloblastic anemia. No typical
examination findings are noted, except for those
seen in severe cases of anemia. Because
significant anemia affects less than 2% of persons
infected with D latum, most patients with
diphyllobothriasis have no signs of illness.
13.
Passage of proglottids
Indigestion or dyspepsia
Abdominal discomfort
Other, less common, symptoms include the following:
Fatigue
Diarrhea
Dizziness
Weakness (rare)
Numbness of extremities
Sensation of hunger
Pruritus ani
14. COMPLICATIONS
Rarely, patients with diphyllobothriasis may need surgical relief for obstruction or
replacement of vitamin B-12 or iron.
In addition to the conditions listed in the differential diagnosis, other problems to
be considered include the following:
Other infections associated with uncooked fish or aquatic food, such as
anisakiasis, capillariasis, paragonimiasis, liver flukes,
angiostrongyliasis, and sparganosis generally tend to be more acute and painfully
symptomatic diseases.)
Vitamin B-12 deficiency due to pernicious anemia, malnutrition, or malabsorption
Beef or pork tapeworm, which presents as passage of proglottids
15. PROGNOSIS
Diphyllobothriasis carries an excellent prognosis. D
latum is not invasive, and mortality due to
diphyllobothriasis is rare. Patients are often frightened
and emotionally upset at the passage of worm parts for
a long period of time unless treated. Single-dose
therapy is usually effective, although some treatment
failures have been reported, and repeat treatment is
occasionally needed.
Occasionally, infestation can lead to severe
megaloblastic anemia or intestinal obstruction. Although
it is well described, macrocystic anemia and
neurological disease is extremely rare. Gastrointestinal
(GI) obstruction is also rare but may occur, especially
when numerous worms are present
17. LABORATORY STUDIES
Laboratory studies that may be used in the diagnosis of diphyllobothriasis include
the following:
Microscopic stool examination for ova and parasites
Complete blood count (CBC) - Eosinophilia may be present
Hemoglobin level and hematocrit - These may be below or at the lower end of the
reference range
Mean cell volume - This may be above or at the higher end of the reference range
Peripheral smear
Vitamin B-12 level
Folate level
18. Diagnosis of D latum infection is based on identification
of the operculated eggs in the stool (see the images
below). Usually, this is not difficult, because of the large
quantity of eggs (≥1 million) produced each day.
The anemia produced by diphyllobothriasis is typically
associated with increased free hydrochloric acid in
gastric juice, in contrast to the relative achlorhydria
invariably observed in true pernicious anemia.
A multiplex polymerase chain reaction (PCR) has been
described.
19. Treatment of diphyllobothriasis is pharmacologic. Because the parasite’s biochemical pathways
are different from those of the human host, drug toxicity is directed toward the parasite, the egg,
or the larvae. Mechanisms of action vary within a drug class. Antiparasitic actions may include
the following:
Inhibition of microtubules, causing irreversible block of glucose uptake
Tubulin polymerization inhibition
Depolarizing neuromuscular blockade
Cholinesterase inhibition
Increased cell membrane permeability, resulting in intracellular calcium
Loss
Vacuolization of the schistosome tegument
Increased cell membrane permeability to chloride ions via chloride channels alteration
20. TREATMENT
Antimicrobial agents are used to eradicate the
infecting organism (most often, D latum).
Praziquantel is the drug of choice; niclosamide is
an alternative.
Niclosamide (Niclocide)
DOC; inhibits mitochondrial oxidative
phosphorylation and glucose uptake in the parasite.
Praziquantel (Biltricide)
21. LABORATORY STUDIES
Laboratory studies that may be used in the diagnosis of
diphyllobothriasis include the following:
Microscopic stool examination for ova and parasites
Complete blood count (CBC) - Eosinophilia may be
present
Hemoglobin level and hematocrit - These may be below
or at the lower end of the reference range
Mean cell volume - This may be above or at the higher
end of the reference range
