Download Background: Human intestinal infection with the fish tapeworm, or

Diphyllobothrium latum
A. Classification
Phylum: Platyhelminthes
Class: Cestoda; also called Tapeworm
Order: Pseudophyllidea
Genus/Species : Diphyllobothrium latum
Common Name: Broad Tapeworm
B. Morphology
Adult: Diphyllobothrium latum is the largest parasite of humans, reaching lengths up to 15 m and
consisting of a chain of 3,000 to 4,000 segments called proglottids, each up to 2 cm wide. Proglottids
are continuously produced by the scolex, or holdfast, and mature as they move down the body of the
worm. Since proglottid is the term for complete set of sex organs each segment serves as a separate
reproductive unit with a tiny uterine pore on the surface. Mature segments produce eggs until they
die and are shed. Like all tapeworms, it lacks a digestive system and thus obtains food by absorbing
it through their outside surface called a tegument.
Diphyllobothrium latum have been found as long as 32 ft. and can produce millions of eggs per day.
---Proglottid:
The Diphyllobothrium latum is characterized by the fact that the proglottid is broader
than it is long. It averages 2 to 4 mm long by 10 to 12 mm wide. It also is characterized by its uterus coiled into a rosettelike appearance and the location of the genital pore at the center of each proglottid.
Figure 1. Prglottid of the Diphyllobothrium
latum.
Figure 2: Mature Proglottids of Diphyllobothrium latum. These proglottids tend to be passed in strands of variable
length in the stool. There are numerous testes throughout and a bilobed ovary. Red arrow =ovary. Black arrow=
genital/uterine pore
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---Scolex:
The Scolex of the tapeworm is used for the attachment of the worm to the mucosa of the host. It is
normally 2-3mm long with an almond shape. The order Pseudophyllidea and thus Diphyllobothrium
latum is characterized by a scolex with a pair of linear sucking grooves instead of suckers and hooks.
Bothria means “sucking groove” and is thus found in the name of this species.
Figure 3: Scolex (holdfast) of Diphyllobothrium latum.
EGG:
Diphyllobothrium latum Eggs are oval or elliposoidal with an operculum. They measure 58-75
by 40-50 µm. They are characterized by their rather large size and a small knob visible at the
opposite site of the operculum. They are about half the size of Fasciola hepatica eggs.
However, sometimes this knob is hard to distinguish. The eggs are passed in the stool
unembryonated.
Figure 4: Egg of Diphyllobothrium latum.
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C. Lifecycle and Epidemiology
Figure 5: Lifecycle of the Diphyllobothrium
latum.
These worms have an amazing lack of specificity and the definitive host can be a human, bear, dog ,
cat, sea lion, walrus, weasel, otter, badger, etc.
1. The unembryonated eggs leave the definitive host through the feces.
2. Once they have reached appropriate conditions the eggs mature in about 20 days.
3. The developed eggs produce oncospheres (the earliest stage of differentiation), that hatch
into coracidia, a ciliated embryo
4. Next the first intermediate host, a freshwater crustacean, ingests the coracidia and they
develop into procercoid larvae. If you recall in Paragonimus the crustacean acts as the second
intermediate host.
5. A second intermediate host, usually a minnow or small freshwater fist, then ingests the
crustacean and procercoid larvae are released from the crustacean and migrate into the fish flesh
where they develop into a plerocercoid larvae (sparganum). This is the infective stage for
humans.
6. Humans generally don’t eat minnows or small freshwater fish, however, most of the second
intermediate hosts are eaten by larger predator fish and the plerocercoid larvae migrate to the
musculature of the predator fish.
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7. After a human as eaten raw or uncooked fish, plerocercoids develop into immature adults and
then into mature adult tapeworms, which reside in the small intestine.
8. The adults attach to the intestinal walls using to bilateral groves known as the bothria.
9. Eggs appear in feces in about 5-6 weeks.
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The small intestine is about 6 m long, and this tapeworm can reach up to 15 m long!
It can also produce 1 million eggs per day!, that’s 20 times as many as F. hepatica.
Average life span is up to 13 years
Figure 6: Plerocercoid larvae in muscles and viscera of a freshwater fish.
D. Geographic Distribution
Diphyllobothrium latum is found throughout the world mainly in places in places where humans
depend on fish from lakes and rivers. Highest prevalence is found in areas where fish are eaten raw
or undercooked such as: Alaska, Canada, Russian Federation, Baltic countries, and the Scandinavian
region.
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Figure 8. Areas represented in dark green indicate reported cases of Diphyllobothriasis in the world.
E. Pathology and Symptoms.
Infection with Diphyllobothrium latum is often asymptomatic and can last as long as decades.
Persons with light I may experience abdominal pain, vomiting, diarrhea, and weight loss with onset
about 10 days after consumption of raw or insufficiently cooked fish. In some infections there may
be a severe Vitamin B12 deficiency and anemia caused by the obstruction of Vitamin B12 absorption
coupled with high absorption rates of the vitamine by the tapeworm.
F. Diagnosis
The disease is diagnosed by finding operculate eggs, eggs with lids, in the patient's feces upon
microscopic examination. These eggs may be concentrated by sedimentation but not by flotation.
They are difficult to distinguish from the eggs of the trematode Nanophyetus spp. from salmon.
G. Treatment
Praziquantel or Biltricide is used in the treatment of several different infestations and the drug of
choice for diphyllobothriasis. The dose used depends on the infection to be treated. Doses below are
specifically for diphyllobothriasis.
 The adult dosage is usually 5-10 mg/kg PO as a single dose.
 The pediatric dosage, greater than 4 years old is 5-10 mg/kg PO as a single dose.
Niclosamide or Niclocide is an alternative therapy for diphyllobothriasis. The doses below are for
diphyllobothriasis. The drug inhibits mitochondrial oxidative phosphorylation and glucose uptake in
parasite.
 The adult dosage is 2 g PO as a single dose.
 The pediatric dosage is 40 mg/kg PO as a single dose.
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The outcomes with single-dose therapy are excellent; however there is a need for an occasional retreatment.
H. Public Health Strategies/Eradication
Eradication cannot occur because of the large and diverse populations of reservoir hosts.
Deterrence/Prevention:
Cooking fish to a temperature of 133° F or higher for longer than 5 minutes or by freezing fish to 0°
F for 24 hours will kill the plerocercoid larvae, making the food safe to eat. This can also be
achieved by pickling in brine under very rigid conditions.
Education:
Educating people about the effective ways of making freshwater fish safe for consumption is
imperative to reducing the risk of infection. Educating people about the greater risk of contracting
these organisms through the use of human excrement and dead fish matter as fertilizers.
Work Cited:
Abu-Zeid, Y.A. “Parasitolgy” United Arab Emirates University. Department of Biology. February 2,
2005. <http://faculty.uaeu.ac.ae/~youssefa/homepage/diphylob.htm>
Baron, Samuel MD. Medical Microbiology. University of Texas Medical Branch at Galveston,
Texas. 1996. February 2, 2005.
<http://www.ncbi.nlm.nih.gov/books/bv.fcgi?rid=mmed.section.4713>
“Foodborne Pathogenic Microorganisms and Natural Toxins Handbook.” U.S. Food and Drug
Administration. January 2005. February 2, 2005. <http://vm.cfsan.fda.gov/~mow/chap26.html>
Graphic Maps. World Atlas.com. 2004. February 2, 2005.
<http://worldatlas.com/aatlas/imagee.htm>
Keas, Brian E. “Intestinal Parasites: Diphyllobothrium latum” Michigan State University. 1999.
February 2, 2005. <http://www.msu.edu/course/zol/316/dlatgut.htm>
Nolan, Tom Dr. “Diphyllobothrium latum homepage. 2004. University of Pennsylvania. February 2,
2005. <http://cal.vet.upenn.edu/dxendopar/parasitepages/cestodes/d_latum.html>
“Parasites and Health: Diphyllobothrium” Division of Parasitic Diseases. December 2003. February
2, 2005.
<http://www.dpd.cdc.gov/dpdx/HTML/Diphyllobothriasis.htm>
Rai, Alia MD. “Diphyllobothrium latum infection” E Medicine World Medical Library. November
2002. February 2, 2005. <http://www.emedicine.com/ped/topic597.htm#target1>
“Spaganosis.” Ohio State University. 2004. February 2, 2005.
<http://www.biosci.ohio-state.edu/~parasite/sparganosis.html>
Presented by:
Amir Abyaneh
Adam Wimer
Hillary Shields
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February 2005
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