Page 125 - Medical Parasitology_ A Textbook ( PDFDrive )

118 11 Cestodes: Tapeworms

Table 11.1 Classification of cestodes of medical importance based on order and habitat
Habitat of adult Habitat of larval stage in
Order Genus/Species worm in human human
Pseudophyllidea Diphyllobothrium latum Small intestine —
Spirometra — Plerocercoid larva in
subcutaneous tissues and
other organs
Cyclophyllidea Taenia saginata Small intestine —
Taenia solium Small intestine Larva in subcutaneous
tissues and other organs
Echinococcus granulosus — Hydatid cyst is most
commonly found in the liver
followed by lungs and other
organs
Hymenolepis nana Ileum Cysticercoid larva in the
intestinal villus

Clinical disease can be caused by the adult worm or the larval form. In general,
adult worm causes mild disease or are asymptomatic, while the larvae can pro-
duce serious illness and complications, particularly when they lodge in the CNS
or eyes. Classification of cestodes of medical importance based on order and
habitat is shown in Table 11.1.

Pseudophyllidean Tapeworms

Diphyllobothrium latum

Common name Fish tapeworm/Broad tapeworm

Distribution
Its infection occurs in central and northern Europe, particularly in the Scandinavian
countries. It is also found in Siberia, Japan, North America and Central Africa.
Dogs, cats and many wild animals may be naturally infected.
Habitat
The adult worm is found in the small intestine of human, usually in the ileum.

Morphology
Adult measures up to 10 m or more. It is the largest tapeworm inhabiting the small
intestine of human. Scolex is spatulate or spoon shaped, about 2–3 mm long and 1 mm
broad (Fig. 11.1a). It has 2 slit like longitudinal dorsoventral sucking grooves (bothria).
Neck is thin and unsegmented. Strobila consists of 3000–4000 proglottids (Fig. 11.1b).
Proglottids are wider than they are long. The genital pores open midventrally.
Egg is broadly ovoid, about 65 μm by 45 μm, with a thick, light brown shell. It
has an operculum at one end (Fig. 11.1c). It is passed in faeces and completes devel-
opment in freshwater. The egg is not infective to humans.