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Intestinal Cestodes 173

in the small intestine where the scolex attaches itself to
the intestinal mucosa; there the adult tapeworm thrives MICROSCOPIC DIAGNOSTIC
and reproduces. Gravid proglottids are passed from the FEATURE
body following disintegration and the infective eggs may
contaminate foodstuffs and work areas. The infective
General Classification—Cestode (dwarf
eggs may then be ingested by animals, including humans,
tapeworm)
which develop into cysticercoid larvae and the infectious
cycle begins. It is possible for the eggs to hatch in the Organism Hymenolepis nana
intestine and in this case cysticercoid larvae develop into Specimen Required Stool specimen
adult forms without leaving the intestine of the host, re-
Stage Cyst or trophozoite
sulting in a process called autoinfection.
Size Adults are up to
40 mm in length
Disease Transmission
Shape Segmented
Infection usually begins by ingesting infectious eggs, ex- Motility Not demonstrated
cept in the cases of autoinfection where the eggs “hatch” Other Features Direct fecal-oral
in the intestine. As for most parasites, prevention is the best transmission
method for controlling the infection. A study in one north-
eastern state revealed that possibly one-third of the rats sold H. nana
in pet stores in that state were infected by H. nana. Proglottid

Laboratory Diagnosis

Adult worms and proglottids are seldom recovered from
stool specimens. The usual process of diagnosis involves
the recovery of eggs from fecal specimens.
H. nana is the most prevalent tapeworm found in the
United States. It is unusual in the fact that it is a tapeworm
that requires no intermediate host, as mice, other rodents,
and humans may all be infected by ingestion of the eggs.
The scolex is similar to that of Taenia saginata and must Gravid uterus
be differentiated between the two species of tapeworm.
Ovum
Treatment and Prevention
Polar filaments
Treatment for H. nana infections is usually the adminis-
tration of praziquantel. Prevention entails cleaning of the
areas of food storage, rodent control, and sanitary prac-
tices in food handling and personal practices. Control of
Hooklets
beetles and fleas where grains and cereals are stored will
also contribute greatly toward the prevention of infec-
tions with H. nana.
Delmar/Cengage Learning
HYMENOLEPSIS DIMINUTA

Hymenolepsis diminuta resembles that of H. nana.
Hymenolepis worms are often found in rat intestines.
Because the organism is common in warmer climates, in-
fections are common in the southeastern United States.