Content provided in partnership with

Health Care Industry

Common intestinal parasites - Practical Therapeutics

American Family Physician, March 1, 2004 by Corry Jeb Kucik, Gary L. Martin, Brett V. Sortor

Intestinal parasites cause significant morbidity and mortality throughout the world, particularly in undeveloped countries and in persons with comorbidities. Intestinal parasites that remain prevalent in the United States include Enterobius vermicularis, Giardia lamblia, Ancylostoma duodenale, Necator americanus, and Entamoeba histolytica.

E. vermicularis

E. vermicularis, commonly referred to as the pinworm or seatworm, is a nematode, or roundworm, with the largest geographic range of any helminth. (1) It is the most prevalent nematode in the United States. Humans are the only known host, and about 209 million persons worldwide are infected. More than 30 percent of children worldwide are infected. (2)

Most Popular Articles in Health: Fuel your workout: exercisers who eat before they work out have more energy ...; Soothe a dry, itchy scalp: 5 easy expert solutions; Cocktails and calories: Beer, wine and liquor calories can really add up. ...; The sour truth about apple cider vinegar - evaluation of therapeutic use; The, six best supplements you've never heard of: these secret weapons can ...; More »

Adult worms are quite small; the males measure 2 to 5 mm, and the females measure 8 to 13 mm. The worms live primarily in the cecum of the large intestine, from which the gravid female migrates at night to lay up to 15,000 eggs on the perineum. The eggs can be spread by the fecal-oral route to the original host and new hosts. Eggs on the host's perineum can spread to other persons in the house, possibly resulting in an entire family becoming infected.

Ingested eggs hatch in the duodenum, and larvae mature during their migration to the large intestine. Fortunately, most eggs desiccate within 72 hours. In the absence of host autoinfection, infestation usually lasts only four to six weeks.

Disease secondary to E. vermicularis is relatively innocuous, with egg deposition causing perineal, perianal, and vaginal irritation. (3) The patient's constant itching in an attempt to relieve irritation can lead to potentially debilitating sleep disturbance. Rarely, more serious disease can result, including weight loss, urinary tract infection, and appendicitis. (4,5)

Pinworm infection should be suspected in children who exhibit perianal pruritus and nocturnal restlessness. Direct visualization of the adult worm or microscopic detection of eggs confirms the diagnosis, but only 5 percent of infected persons have eggs in their stool. The "cellophane tape test" (Figure 1) can serve as a quick way to clinch the diagnosis. (6,7) This test consists of touching tape to the perianal area several times, removing it, and examining the tape under direct microscopy for eggs. The test should be conducted right after awakening on at least three consecutive days. This technique can increase the test's sensitivity to roughly 90 percent.

G. lamblia

G. lamblia is a pear-shaped, flagellated protozoan (Figure 2) that causes a wide variety of gastrointestinal complaints. Giardia is arguably the most common parasite infection of humans worldwide, and the second most common in the United States after pinworm. (8,9) Between 1992 and 1997, the Centers for Disease Control and Prevention (CDC) estimated that more than 2.5 million cases of giardiasis occur annually. (10)

[FIGURE 2 OMITTED]

Because giardiasis is spread by fecal-oral contamination, the prevalence is higher in populations with poor sanitation, close contact, and oral-anal sexual practices. The disease is commonly water-borne because Giardia is resistant to the chlorine levels in normal tap water and survives well in cold mountain streams. Because giardiasis frequently infects persons who spend a lot of time camping, backpacking, or hunting, it has gained the nicknames of "backpacker's diarrhea" and "beaver fever." (11)

Food-borne transmission is rare but can occur with ingestion of raw or undercooked foods. Giardiasis is a zoonosis, and crossinfectivity among beaver, cattle, dogs, rodents, and bighorn sheep ensures a constant reservoir. (12)

The life cycle of Giardia consists of two stages: the fecal-orally transmitted cyst and the disease-causing trophozoite. Cysts are passed in a host's feces, remaining viable in a moist environment for months. Ingestion of at least 10 to 25 cysts can cause infection in humans. (8,9) When a new host consumes a cyst, the host's acidic stomach environment stimulates excystation. Each cyst produces two trophozoites. These trophozoites migrate to the duodenum and proximal jejunum, where they attach to the mucosal wall by means of a ventral adhesive disk and replicate by binary fission.

Giardia growth in the small intestine is stimulated by bile, carbohydrates, and low oxygen tension. (7) It can cause dyspepsia, malabsorption, and diarrhea. A recent theory suggests that the symptoms are the result of a brush border enzyme deficiency rather than invasion of the intestinal wall. (9) Some trophozoites transform to cysts and pass in the feces.

Clinical presentations of giardiasis vary greatly. After an incubation period of one to two weeks, symptoms of gastrointestinal distress may develop, including nausea, vomiting, malaise, flatulence, cramping, diarrhea, steatorrhea, and weight loss. A history of gradual onset of a mild diarrhea helps differentiate giardiasis or other parasite infections from bacterial etiologies. Symptoms lasting two to four weeks and significant weight loss are key findings that indicate giardiasis.

Health Care Industry

Common intestinal parasites - Practical Therapeutics

American Family Physician, March 1, 2004 by Corry Jeb Kucik, Gary L. Martin, Brett V. Sortor

Find Research Guides for:

Find Featured Titles for: News

Most Popular Articles in Health

Most Popular Publications in Health