Hymenolepis: Introduction, Morphology, Life Cycle, Clinical Features

Hymenolepis: Introduction, Morphology, Life Cycle, Clinical Features, Pathogenesis, Lab Diagnosis And Treatment

Introduction of Hymenolepis

Hymenolepis is one of the most common cestodes of humans in the world ( also known as Dwarf tapeworm or Rodentolepis nana or Vampirolepis nana or Hymenolepis fraterna or Taenia nana), especially among children. Usually most common in temperate zones. Lives in the small intestine of man. Also found in rodents especially in rats and mice.

Scientific classification

The scientific classification of Hymenolepis is as follows-

Kingdom: Animalia
Phylum: Platyhelminthes
Class: Cestoda
Order: Cyclophyllidea
Family: Hymenolepididae
Genus: Hymenolepis
Species: H. nana

Binomial name

Hymenolepis nana

Geographical Distribution

Cosmopolitan

Habitat

Small intestine (distal part of the ileum)

Morphology of Hymenolepis

Adult worm

Greek: Nanos – dwarf, it is a small species, seldom exceeding 40 mm long and 1 mm wide. scolex bears a retractable rostellum armed with a single circle of 20 to 30 hooks. Scolex also has four suckers or a tetrad. The neck is long and slender, segments are wider than long.

Eggs of Hymenolepis

Liberated in feces by the gradual disintegration of terminal segments.
Spherical or oval in shape, 30-45 µm
Two distinct membranes
Outer membranes are thin and colorless.
Inner embryophore encloses an oncosphere with 3 pairs of hooklets
Space between two membranes –filled with yolk granules and polar filaments emanating from little knobs at either end of embryophores.

Life Cycle of Hymenolepis

No intermediate host

Ingestion of eggs with contaminated edibles

Ingested egg

Oncosphere penetrating the intestinal wall

Cysticercoid in intestinal villi( 4 days after infection)

Adult worm ( 12 days after ingestion of eggs)

Eggs in stools ( 30 days after infection)

Again cycle repeats

Indirect cycle (Intermediate hosts)

Murine insect to man

Rat fleas, beetles, ingest eggs from human stools ( intermediate hosts)

Cysticercoid in the hemal cavity of the rat flea

And again cycle repeats.

Mode of transmission

Feco-oral route

Pathogenesis

Hymenolepis nana lodges itself in the intestines and absorbs nutrients from the intestinal lumen. In human adults, the tapeworm is more of a nuisance than a health problem, but in small children, many H. nana can be dangerous. Larva causes the most problem in children. The larva will burrow into the walls of the intestine, if there are enough tapeworms in the child, severe damage can be inflicted. Done by absorbing all the nutrition from the food the child eats. Individuals that are heavily infected are a result of internal autoinfection.
Symptoms are due to allergic responses or systematic toxemia caused by waste products of the tapeworm. Light infections are usually symptom-less. Infection with more than 2000 worms can cause
enteritis,
abdominal pain,
Diarrhea,
loss of appetite, restlessness, irritability, restless sleep, anal and nasal pruritis.

Clinical Features

Abdominal pain
Diarrhea
Pruritis

Laboratory Diagnosis of Hymenolepis

Examination of feces for the finding of characteristic eggs.

Microscopic examination of stool
Concentration technique (salt flotation)

Treatment of Hymenolepis

Praziquantel and
Niclosamide

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