HYMENOLEPIS NANA (The dwarf tapeworm)

GEOGRAPHICAL DISTRIBUTION

The infection is commoner in both temperate and tropical regions of the world such as Egypt, Sudan, Thailand, India, Japan, South America and Southern Europe.

LOCATION IN HOST

The worm is found attached to the mucosa of the small intestine.

MORPHOLOGY

The worm is small and measures 25-45mm*0.5-0.9mm. It consists of 100-200 segments. The small scolex measures 140-480µm and has a rostellum with single row of hooks

There are four suckers on the scolex. The neck is usually long. The segments close to the neck are short while the mature segments are broader than long. The eggs are globular and have thin outer vitelline membranes; 40-60µm separated from the inner which measures about 20-30µm.The latter is the embryophore and encloses the embryo which is ‘lemon’ shaped. On either end is polar thickening from which a few filaments extend.

LIFE CYCLE

Man is the definitive host. This is the only tapeworm known to have no intermediate host. The gravid segments are generally disrupted and eggs are passed in the faeces of the infected person. When ingested by man the onchosphere penetrates the small intestinal villi to form the cysticercoid stage. Within a short time (4 days) the cysticercoid re-enter the lumen and mature into adults. Autoinfection is possible.

PATHOGENESIS AND CLINICAL FEATURES

Mild infections are generally asymptomatic. But when large numbers of worms are found (>1000) enteritis with abdominal pain, diarrhea, nausea and vomiting may occur. These symptoms are probably due to the toxemia or allergic reactions to metabolic products of the worms.

EPIDEMIOLOGY

The infection is common in children than adults. The transmission is usually hand to mouth and via food and water. Infection is common in institutionalized children.

DIAGNOSIS

This is done by demonstrating characteristics eggs in the faeces.

PREVENTION AND CONTROL

Treatment of diagnosed cases and improvement of personal hygiene help to reduce the infection prevalence.

TREATMENT

Niclosamide is the drug of choice. The dose should be repeated after 10 days. Large number of persisting cysticercoids makes it difficult to obtain a radical cure. Other option is praziquantel, as it acts against both the adult worms and the cysticercoids in the intestinal villi.