Click here to view next page of this article

 

New Treatments for Intestinal Helminths

Intestinal helminth infestations most commonly affect travelers, migrant laborers, refugees, children of foreign adoptions, and the homeless. Parasitic infections may be associated with day care centers and overseas travel.

Clinical Evaluation

Intestinal helminth infections are usually asymptomatic, but serious infections may cause symptoms ranging from abdominal discomfort to severe pain. Anorexia nausea, diarrhea, pruritus, rectal prolapse, bowel obstruction, and death may occur.

Hives and eosinophilia may develop, and the worms may sometimes spontaneously exit the body through the anus.

Stool Examination

Examination of the stool for ova and parasites is the most important test for helminthic infection.

Stools are collected using plastic wrap under the toilet seat. A spatula is then used to collect samples, preferably portions with visible mucus or blood. Fresh stool may also be obtained by rectal examination.

Enterobiasis intestinal helminths, parasites, worms

Pinworms (Enterobius vermicularis) are the most common helminth. Pinworms present as anal pruritus in irritable children, and they are most common in temperate regions. Many patients are asymptomatic. Heavier infections may cause insomnia, restlessness, vulvovaginitis, loss of appetite, and intractable anal itching.

Pinworms are about 10 mm in length. The female worm has a pin-shaped tail. At night, worms migrate through the anus, then deposit their eggs and die on the perianal skin. Microscopic eggs infest clothing, bedding, and other surfaces, often spreading to the entire family.

Pinworms are best diagnosed by examining the perianal skin. The stool is usually negative for ova and worms. To obtain the eggs, a tongue blade covered with clear tape is placed sticky-side down over the unwashed perianal skin in the morning. Specimens are collected on three separate mornings, then taped to glass slides and taken to a laboratory for examination.

The elongate, colorless eggs measure 50 to 60 Ám and are flattened on one side. Glistening adult worms may also be visualized if the anus is examined with a flashlight late at night or early in the morning.

Treatment

Mebendazole (Vermox), one 100-mg tablet orally, is safe and effective, except in pregnant women. A second dose is given 10 days later. The entire family is treated.

Infested clothing and bedding are washed, fingernails are kept trimmed, and the perianal area should be kept clean. Dogs and cats do not spread this infection. Relapses are common.

Ascariasis

Roundworms (Ascaris lumbricoides) measure up to 18 inches in length. The infection is fairly common in the rural southeastern United States and is frequent among immigrants. A. lumbricoides only infests humans.

In the gut, adult worms may aggregate, causing intestinal obstruction at the ileocecal valve. However, most patients experience only vague abdominal discomfort or nausea.

Treatment

Mebendazole (Vermox), 100 mg bid for three days.

A follow-up examination of stool for ova and parasites should be performed in two months because treatment may fail. Family screening is necessary.

Trichuriasis

Whipworm (Trichuris trichiura) infestation is less common than Ascaris infestation, occurring in the southeastern states and in foreign immigrants.

Whipworm eggs incubate in the soil. When swallowed, they travel to the colon.

Less Common Parasites

Hookworms

Hookworms develop in the soil from eggs in feces. The larvae are capable of penetrating the bare feet and causing a pruritic rash. The larvae eventually reach the small intestine.

Adult hookworms are about 10 Ám in length, with a hooked anterior end that they use to consume 0.03-0.15 mL of blood per day and may live for 10 to 15 years.

Strongyloidiasis

Filariform larvae are capable of penetrating intact skin. It may persist for 40 years or more in the small intestine, and it can also be spread as a sexually transmitted disease. Persistent unexplained eosinophilia in a patient from a region where Strongyloides infection is endemic should prompt serologic testing because stool specimens are often negative.

Symptoms of strongyloidiasis are usually absent but may include pruritus, pneumonia, abdominal cramping, and colitis. Treatment consists of thiabendazole (Mintezol).

Tapeworms

Taenia saginata, the beef tapeworm, is transmitted through consumption of inadequately cooked beef. Tapeworms may reach 10 to 15 feet in length in the gut. Diagnosis is made by passage of ribbon-like tapeworm segments from the rectum or by the discovery of the eggs in a stool.

Taenia solium, or pork tapeworm, is far more dangerous than T. saginata since its eggs can cause cysticercosis, the invasion of human tissue by developing larval forms. In severe cases, the larvae may invade the central nervous system, causing neurocysticercosis.

T. solium is found in immigrants from Central and South America. Patients with neurocysticercosis frequently present with seizures.

The fish tapeworm, Diphyllobothrium latum, is occasionally transmitted through the consumption of undercooked fish, especially fish from the Great Lakes region. It can occasionally causes megaloblastic anemia.

The dwarf tapeworm, Hymenolepis nana, is the most common tapeworm in the U.S. This tapeworm is 1 inch in length, and it may continually autoinfect the patient through fecal-oral contact. Ingestion of food contaminated with mouse droppings may spread the infection. H. nana infection may cycle in immigrant children for years.