Tapeworms
Tapeworm infestation
DESCRIPTION: Tapeworms,
which can be parasitic in humans, are cestodes which in their adult
phase are segmented flatworms that may reside in the
gastrointestinal tract. Adult worms consist of a head (scolex),
which attaches to the host; the neck (germinal region); and a
segmented body (strobila), with individual segments (proglottid)
containing sets of male and female reproductive organs that produce
eggs. The life cycle of all but one tapeworm (Hymenolepis nana)
requires an intermediate host, where they grow as larval forms in
tissue that is then ingested by the final host such as humans, where
it subsequently develops as an adult. Hymenolepis nana can
complete all stages of development in humans, helping to make it the
most common tapeworm in humans. Most tapeworm infections are
confined to the gastrointestinal tract, however somatic disease can
occur with Taenia solium eggs being ingested (Cysticercosis),
or with Echinococcus infections, making infections with these more
serious. Neurocysticercosis is the most common inpatient disorder
due to parasite infection. Tapeworms/their usual intermediate
host/and type of infection in humans/description include:
 | Taenia saginata/beef/intestinal worm/
Takes 2-4 months after ingestion to become adult tapeworm. 3-10
meters long. Usually single tapeworm. Proglottids are motile and
can crawl out of anus. May live 30 years. |
| Taenia solium/pork/a.) intestinal worm,
b.) Cysticercosis, a somatic infection/2-4 months to become
adult worm. 3 meters long, occasionally multiple. Proglottids
not motile. May live up to 25 years. Ingestion of encysted
larvae (cysticerci) cause intestinal tapeworm. Ingestion of
T. solium eggs causes Cysticercosis. Eggs look identical to
T. saginata eggs. |
| Diphyllobothrium latum and other
species/fresh water fish/intestinal worm/longest adult tapeworm
- up to 25 meters. Matures to adult in 3-5 weeks.
|
| Hymenolepis nana/rodent, insects, or even
the human themselves/intestinal worm/ Mature to adult worms in
10-12 days. Seldom exceeds 40 mm long. Proglottids rarely seen
in stool. Eggs can autoinfect individual, or occasionally
insects (especially meal worms). Fecal oral transmission
possible. Lifespan 4-10 weeks, but autoinfection can perpetuate
infection. Usually self cleared by adolescence. |
| Echinococcus granulosis and
Echinococcus multilocularis/humans, sheep, cattle are
intermediate hosts with dogs the definitive hosts for granulosis.
Foxes or coyotes are definitive hosts for multilocularis with
rodents the intermediate hosts. Somatic infections: a.) hydatid
disease of liver, spleen, etc., b.) alveolar hydatid
disease/Adult worm lives in dogs (or rodents), human ingests
eggs, larvae hatch and are carried through circulation to
various organs such as liver and lungs where develop into
hydatid cysts which enlarge causing symptoms perhaps 5-20 years
later. |
| Hymenolepis diminuta/rodents and
insects/intestinal worm/90 cm long. Humans rare accidental host
by swallowing contaminated mealworms or grain beetles in grain.
|
| Dipylidium caninum/dogs and cats and
fleas/intestinal worm/10-70 cm long. Motile proglottids, shape
of cucumber seeds, can crawl out anus. Rare accidental infection
of humans from ingesting infected flea that came from dogs or
cats. |
System(s)
affected: Gastrointestinal, Nervous
Genetics: N/A
Incidence/Prevalence in USA:
Occurs infrequently in USA. More often associated
with immigrant population and ethnic groups with certain cultural
eating habits. Can be endemic in other parts of the world, where
fecal contamination can get into water or food source.
Predominant age:
All ages affected. Hymenolepis nana and diminuta
more common in children.
Predominant sex:
Male = Female
CAUSES: Eating the infective form of the parasite either by
eating contaminated food such as undercooked beef, pork, fish, or
infected insects that may be in cereals or grains, or through
fecal-oral contamination.
ICD-9-CM:
122.x Echinococcus (4th digit specifies location of disease)
123.x Other cestode infection (specific organisms coded separately
with 4th digit)
123.9 Cestode infection, unspecified (tapeworm (infection)
NOS)
REFERENCES:
Isselbacher KJ, et al (eds): Harrison's Principles of
Internal Medicine 13th Edition, New York, McGraw-Hill, 1994
Liu LX, Weller PF: Antiparasitic Drugs. New England
Journal of Medicine 1996 May 2; 334(18): 1178-1184
Miranda A: Neurocysticercosis. Amer Fam Phys
1993;47(5):1193-1197
Schantz PM: Tapeworms (cestodiasis).
Gastroenterology Clinics of North America 1996;25(3):637-653
Wyngaarden JB, Smith LH, Bennett JC (eds): Cecil
Textbook of Medicine. 19th Ed. Philadelphia, W.B. Saunders Co., 1992
Web references:
CDC -
National Center for Infectious Diseases
CDC -
Parasitology
The name for the parasitic flatworms forming the class Cestoda.
All tapeworms spend the adult phase of their lives as parasites in
the gut of a vertebrate animal (called the primary host). Most
tapeworms spend part of their life cycle in the tissues of one or
more other animals (called intermediate hosts), which may be
vertebrates or arthropods.
There are several species of Taenia that
humans are likely to encounter. These include two
species for which humans serve as the definitive
host: Taenia saginata (now often called
Taeniarhynchus saginatus), the beef tapeworm;
and T. solium, the pork tapeworm. Several
species of Taenia also infect dogs and cats (e.g.,T.
pisiformis), and humans are likely to
encounter these when they note the presence of these
tapeworms' proglottids in their pets' feces
The fish tapeworm is a broad, long worm, often growing to lengths of
3-7 feet at maturity and capable of attaining 30 feet. It is the
longest tapeworm invading humans with as many as 4,000 segments (proglottids).
The main body of the worm is virtually filled with male and female
reproductive organs allowing it to produce an incredible number of
eggs, often more than 1,000,000 a day. The adult attaches to the
wall of the intestine with the aid of two sucking grooves located in
its head (scolex).
This tapeworm is
sometimes called a broad fish tapeworm, because the reproductive
segments are usually broader than they are long. The adult is ivory
or grayish-yellow in color and can live in humans for 20 years.
Humans are the final host of this worm, but first it must pass
through a tiny freshwater crustacean, and then to a fish. The larva
that infects people, a 'plerocercoid', is frequently found in the
intestines of freshwater and marine fish. It is sometimes found in
the flesh of freshwater fish or in fish that are migrating from salt
waters to fresh water for breeding.
You can be infected
by eating raw, lightly cooked, under-processed freshwater or certain
migratory species of salmon, perch, pike, pickerel, and turbot. The
popularity of eating raw fish dishes, such as Japanese sushi and
sashimi, helps to spread this disease. Cooks who sample their fish
dishes before they are properly cooked put themselves at risk of
being infected. Fish tapeworms are found wherever humans, bears, and
other fish-eating mammals defecate in the same lakes and streams
from which this fish are obtained.
Most infected
people do not produce any symptoms. During the acute stage of
disease, which has its onset about 10 days after eating raw or
insufficiently cooked fish, the symptoms may be similar to other
tapeworm infections. This includes symptoms such as diarrhea,
abdominal discomfort and pain, flatulence, vomiting, nausea, and
weakness. Chronic infestations may produce some of the same symptoms
or only vague discomforts including fullness in the upper abdomen,
water retention, loss of weight, and malnutrition. Some people are
constantly hungry because the tapeworms are eating most of the food.
There are times when the worm gets so large that it will cause a
colon blockage. In some people a severe anemia may develop, because
of this tapeworm's ability to consume most of its host's vitamin
B12. Folate may be reduced as well. With the anemia that results,
neurological symptoms can manifest including numbness, loss of
vibration sense, and even some eye symptoms
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