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Intestinal Cestodes 167

tapeworm lives in the small intestine and, because the
organism is hermaphroditic, it can mate with itself. After MICROSCOPIC DIAGNOSTIC
self-fertilization occurs, eggs are produced and these un- FEATURE
embryonated eggs leave the human host while contained
within the feces. Because no development has occurred
General Classification—Cestode (fish
until the eggs are released, the egg disintegrates in fresh
tapeworm)
water and a ciliated embryo called the coracidium is
freed into the water where it infects the first intermedi- Organism Diphyllobothrium
ate host, a copepod crustacean of the genus Cyclops. latum “worm”
A procercoid larval form develops in the copepod and Specimen Required Stool specimen
the infected crustacean is eaten by a second intermedi- Stage Scolex and proglot-
ate host, which is a freshwater fish. If the undercooked tids are detected;
or uncooked freshwater fish is eaten by a human or other although the egg
mammal, infection occurs. A scolex emerges for attach- is most commonly
ment to the intestinal wall and the tapeworm matures in detected
the small intestine. Size Worm may reach a
length of up to
10 meters
Disease Transmission
Shape Scolex has two sucking
Infections with the D. latum organism due to diet are en- grooves (bothria); pro-
glottid has prominent
demic in some parts of the world including Alaska, the
rosette-shaped uterus
Great Lakes region, and countries of the Scandanavian
Motility Not demonstrated in
peninsula, Latin America, Africa, and Asia where fish is a
D. latum larvae
large part of the diet. If the first intermediate host, which
Other Features Proglottid wider
is the copepod, is ingested by humans through contami-
than it is long, with a
nated water, the procercoid larvae may develop into a
rosette-shaped uterus
sparganum, a process called sparganosis, where the lar-
Scolex is 2–3 mm long
vae migrate into the human’s subcutaneous tissues.
and is elongated with
two sucking grooves
Laboratory Diagnosis opposite each other
dorsally and ventrally
D. latum
Proglottids and the scolex of D. latum are seldom found
in the examination of human feces. Definitive diagnosis
is usually accomplished by detection of the characteristic
eggs of D. latum from human feces.
Finding the characteristic eggs of D. latum is the
most often used diagnostic feature and also enables dif-
ferentiation from the eggs of the fluke Paragonimus west-
ermanni. This tapeworm egg lacks the “shoulders” near
the operculum that are found in fluke eggs.

Treatment and Prevention

Praziquantel and niclosamide are the drugs of choice for
D. latum infections. If a sparganum (larval stage of certain
tapeworms, especially of the genera Diphyllobothrium) Delmar/Cengage Learning
occurs, surgical removal may be required. Prevention of
infection includes avoiding raw or undercooked fish and