Cestode Infections: Essentials of Diagnosis

General Considerations

A number of species of adult tapeworms have been recorded as human parasites, but only 6 infect man frequently. Taenia saginata, the beef tapeworm, and T solium, the pork tapeworm, are cosmopolitan and common. The fish tapeworm, Diphyllobothrium latum, is most often found in northern Europe, Japan, and the Great Lakes region of the USA. The dwarf tapeworms, Hymenolepis nana and H diminuta, are cosmopolitan throughout the tropics and subtropics. The dog tapeworm, Dipylidium caninum, is occasionally reported in children in Europe and the Americas.

The adult tapeworm consists of a head (scokx), which is a simple attachment organ, a neck. and a chain of individual segments (proglottids). H nana adults are rarely more than 2.5-5 cm (1-2 inches) long. Beef, mutton, and fish tapeworms often exceed 10 feet in length; gravid segments detach themselves from the chain and escape from the host intact, or rupture. releasing eggs in the feces. In the case of T saginata, the most common tapeworm found in man in the USA. eggs are expelled from the segments after they pass from the host. The eggs hatch when ingested by cattle. releasing embryos which encyst in muscles as cysticerci. Man is infected by eating undercooked beef containing viable cysticerci. In the human intestine the cysticercus develops into an adult worm.

The life cycle of T solium is similar except that the pig is the normal host of the larval stage. Man may be infected by the larval pork tapeworm, however, if he accidentally ingests T solium eggs. As in the pig, the larvae find their way to many parts of the body and encyst as cysticerci. Only those lodging in the brain ordinarily produce symptoms (cerebral cysticercosis).

The intermediate hosts of the fish tapeworm are various species of fresh water crustaceans and fish. Eggs passed in human feces are taken up by crusta ceans which are in turn eaten by fish. Human infection results from eating raw or poorly cooked fish.

The H nana life cycle is unusual in that both larval and adult stages of the worms are found in the human intestine. Adult worms expel infective eggs in the intestinal lumen. Newly hatched larvae invade the mucosa, where they develop for a time before returning to the lumen to mature. H nana, requiring no inter-mediate host, can be transmitted directly from man to man. A similar dwarf tapeworm, H diminuta, is a common parasite of rodents. Many arthropods, such as rat fleas, beetles, and cockroaches, serve as intermediate hosts. Man is infected by accidentally swallowing the infected arthropods, usually in cereals or stored products. Multiple dwarf tapeworm infections are the rule, whereas man rarely harbors more than one or 2 of the larger adult tapeworms.

Dipylidium caninum infections generally occur in young children living in close association with infected dogs or cats. Transmission results from swallowing the infected intermediate hosts, fleas or lice.

Spargana, or larval stages of certain tapeworms in frogs, reptiles, birds, and some mammals, may produce a variety of clinical conditions (sparganosis) ranging from local tender swellings (eg, eye) to a form of cutaneous larva migrans. One form is proliferating, invading all soft tissues. Infections are acquired from frog or other meat poultices, eating the raw flesh of small animals, or ingesting infected copepods in water. The diagnosis is usually made after surgical removal, but local physicians will make early diagnoses. Infections in animals are widespread; in humans more local, depending upon individual habits.

Clinical Findings

A. Symptoms and Signs: Adult tapeworms in the human intestine ordinarily cause no symptoms. Occasionally weight loss or vague abdominal complaints may be associated with heavy infections or large worms. Heavy infections with H nana may, however, cause diarrhea, abdominal pain, anorexia, weight loss, and nervous disturbances, particularly in children. In 1-2% of those harboring the fish tapeworm, a macro-cytic anemia of considerable severity may be found. The anemia may be accompanied by glossitis, lethargy, and signs of nerve damage. In cysticercosis most larval tapeworms lodge in muscles or connective tissues where they remain silent and eventually calcify; in the brain, however, they may cause a wide variety of manifestations. Epileptic seizures, mental deterioration, personality disturbances, and internal hydrocephalus with headache, giddiness, papilledema, and nerve palsies are among the more common consequences of brain involvement.

B. Laboratory Findings: Infection by a beef tape-worm is often discovered by the patient when he finds one or more segments in his clothing or bedding. To determine the species of worm such segments must be flattened between glass slides and examined microscopically. Most tapeworm infections are detected by laboratory examination of stool specimens for eggs and segments. In cysticercosis x-rays often reveal calcified cysticerci in muscles, but those in the CNS rarely calcify and cannot be seen radiologically. When cysticerci lodge in the 4th ventricle the CSF pressure may be abnormal, and the fluid may show increased numbers of mononuclear cells and tapeworm scolices. Skin and complement fixation tests are also available as aids in diagnosis of cysticercosis.

When fish tapeworm macrocytic anemia is discovered, the marrow will be found to be megaloblastic, and hydrochloric acid is usually present in the stomach. This anemia is attributed to the affinity of the worm for dietary vitamin B12.

Differential Diagnosis

Since most tapeworm infections are asymptomatic, a differential diagnosis need rarely be considered. When vague abdominal complaints and weight loss are present stool examinations are essential to rule out other forms of intestinal parasitism and primary gastrointestinal disorders. Fish tapeworm anemia may mimic pernicious anemia, but the presence of gastric hydrochloric acid and positive stool examinations will establish the diagnosis.

Complications

Pork tapeworm infection may be complicated by cysticercosis if the patient unwittingly contaminates his hands with eggs and transfers them to his mouth. For such a patient vomiting is also a hazard in that eggs may be propelled up the small intestine into the stomach, where they may hatch. The macrocytic anemia occasionally associated with D latum infection also constitutes a potentially serious complication.

Treatment

A. Specific Measures:

1. Niclosamide (Yomesan®) is the drug of choice for a11 tapeworms. Some authorities recommend quinacrine for T solium on the grounds that cysticercosis is theoretically possible after treatment with niclosamide. This hazard may be overemphasized since no cases of cysticercosis have been reported after use of niclosamide. However, when the drug is used for T solium infection, an effective purge should be given within I-2 hours after treatment in an attempt to eliminate mature segments before they disintegrate and release ova.

Give 4 tablets (2 gm) thoroughly chewed as a single dose for T saginata, T solium, and D latum, and daily for 5-7 days for H nana. The drug should be administered in the morning on an empty stomach. Niclosamide rarely has side-effects and can be given to outpatients without prior or posttreatment purges. Niclosamide is available in the USA only from the Parasitic Disease Drug Service, Center for Disease Control, Atlanta.

2. Quinacrine hydrochloride (Atabrine®) is an alternative drug for tapeworms, but in T solium infection care should be taken to avoid vomiting (some possibility of subsequent cysticercosis). On the day preceding treatment the patient should have only a liquid diet, with nothing but water or milkless tea or coffee for supper. On the evening before treatment, give a saline purge or a soapsuds enema. Ion the morning of treatment, withhold breakfast and confine the patient to bed. Give chlorpromazine (Thorazine®), phenobarbital, or a similar sedative to prevent vomiting. One hour later, give quinacrine in the range of 0.5 gm for children weighing 40-75 lb; to 1 gm for adults or children weighing over 100 lb. The dose may be divided to reduce the risk of vomiting, but all of it must be given within about 30 minutes. Administer quinacrine by duodenal tube if the patient persistently regurgitates the drug.

Two hours later (2 hours after the last dose, if divided doses are given), repeat the saline purge. No food should be permitted until the bowels move copiously.

3. Paromomycin (Humatin ®), an antibiotic not appreciably absorbed from the gastrointestinal tract, is effective for the treatment of T solium and T saginata in a single dosage of 75 mg/kg (maximum, 4 gm). Gas-trointestinal side-effects are common but not severe.

4. Dichlorophen, 6 gm as a single dose, is also an effective drug for T saginata, T solium, D latum, and H nana. Dichlorophen is not available in the USA.

5. Aspidium oleoresin- Use of this drug, which is toxic and frequently contraindicated, is no longer justified for helminths that cause relatively little trouble and are amenable to the newer drugs.

B. Follow-Up Care: If parasitologic cure is to be established immediately, the head (scolex) must be found in posttreatment stools. For quinacrine, stools are examined for several days; for niclosamide, a laxative is given 2 hours after treatment and stools are collected in a preservative for 24 hours. To facilitate examination, toilet paper must be disposed of separately. If no head is found, continue to examine the stools for eggs or proglottids once a month for 6 months.

Prognosis

Because the prognosis is often poor in cerebral cysticercosis, the eradication of a T solium infection is a matter of much greater urgency than that of the other tapeworm infections, which are usually benign. With careful treatment adult tapeworms can be eliminated safely.

Source : Family Physician

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