Treatment for Infections Caused by Cestodes

TREATMENT FOR INFECTIONS CAUSED BY CESTODES

Cestodes, or tapeworms, are flattened dorsoventrally and are segmented. The tapeworm has a head with round suckers or sucking grooves. Some tapeworms have a projection (rostellum) that bears hooks. This head, or scolex (also referred to as the hold-fast organ), is used by the worm to attach to tissues. Drugs that affect the scolex permit expulsion of the organisms from the intestine. Attached to the head is the neck region, which is the region of growth. The rest of the worm consists of a number of segments, called proglottids, each of which contains both male and female reproductive units. These segments, after filling with fertilized eggs, are released from the worm and discharged into the environment.

Cestodes that parasitize humans have complex life cycles, usually requiring development in a second or in-termediate host. Following their ingestion, the infected larvae develop into adults in the small intestine. Although most patients remain symptom free, some have vague abdominal discomfort, hunger pangs, indi-gestion, and anorexia, and vitamin B deficiency may de-velop. In some cestode infections, eggs containing lar-vae are ingested; the larvae invade the intestinal wall, enter a blood vessel, and lodge in such tissues as muscle, liver, and eye. Symptoms are associated with the partic-ular organ affected.

Niclosamide

Mechanism of Action

For many years, niclosamide (Niclocide) was widely used to treat infestations of cestodes. Niclosamide is a chlorinated salicylamide that inhibits the production of energy derived from anaerobic metabolism. It may also have adenosine triphosphatase (ATPase) stimulating properties. Inhibition of anaerobic incorporation of in-organic phosphate into ATP is detrimental to the para-site. Niclosamide can uncouple oxidative phosphoryla-tion in mammalian mitochondria, but this action requires dosages that are higher than those commonly used in treating worm infections.

The drug affects the scolex and proximal segments of the cestodes, resulting in detachment of the scolex from the intestinal wall and eventual evacuation of the ces-todes from the intestine by the normal peristaltic action of the host’s bowel. Because niclosamide is not absorbed from the intestinal tract, high concentrations can be achieved in the intestinal lumen.The drug is not ovicidal.

Clinical Use

Niclosamide has been used extensively in the treatment of tapeworm infections caused by Taenia saginata, Taenia solium, Diphyllobothrium latum, Fasciolopsis buski, and Hymenolepis nana. It is an effective alternative to prazi-quantel for treating infections caused by T. saginata (beef tapeworm), T. solium (pork tapeworm), and D. latum (fish tapeworm) and is active against most other tape-worm infections. It is absorbed by intestinal cestodes but not nematodes. A single dose is usually adequate to pro-duce a cure rate of 95%.With H. nana (dwarf tapeworm), a longer treatment course (up to 7 days) is necessary. Niclosamide is administered orally after the patient has fasted overnight and may be followed in 2 hours by purg-ing (magnesium sulfate 15–30 g) to encourage complete expulsion of the cestode, especially T. solium, although this is not always considered necessary. Cure is assessed by follow-up stool examination in 3 to 5 months.With the availability of other agents, niclosamide is no longer widely used. The most widely employed agents are praz-iquantel and the benzimidazoles.

Adverse Effects

No serious side effects are associated with niclosamide use, although some patients report abdominal discom-fort and loose stools.