Amebiasis
Amebiasis: Excerpt from Professional Guide to Diseases (Eighth Edition)
Amebiasis, also known as amebic dysentery, is an acute or chronic protozoal infection caused by Entamoeba histolytica. This infection produces varying degrees of illness, from no symptoms at all or mild diarrhea to fulminant dysentery. Extraintestinal amebiasis can induce hepatic abscess and infections of the lungs, pleural cavity, pericardium, peritoneum and, rarely, the brain.
The prognosis is generally good, although complications — such as ameboma, intestinal stricture, hemorrhage or perforation, intussusception, or abscess — increase mortality. Brain abscess, a rare complication, is usually fatal.
Causes and incidence
E. histolytica exists in two forms: a cyst (which can survive outside the body) and a trophozoite (which can't survive outside the body). Transmission occurs through ingesting feces-contaminated food or water. The ingested cysts pass through the intestine, where digestive secretions break down the cysts and liberate the motile trophozoites within. The trophozoites multiply and either invade and ulcerate the mucosa of the large intestine or simply feed on intestinal bacteria. As the trophozoites are carried slowly toward the rectum, they are encysted and then excreted in feces. Humans are the principal reservoir of infection.
Amebiasis occurs worldwide but is most common in the tropics, subtropics, and other areas with poor sanitation and health practices. Incidence in the United States averages between 1% and 3% but may be higher among homosexuals and institutionalized people, in whom fecal-oral contamination is common.
Signs and symptoms
The clinical effects of amebiasis vary with the severity of the infestation. Acute amebic dysentery causes a sudden high temperature of 104° to 105° F (40° to 40.6° C) accompanied by chills and abdominal cramping; profuse, bloody, mucoid diarrhea with tenesmus; and diffuse abdominal tenderness due to extensive rectosigmoid ulcers.
Chronic amebic dysentery produces intermittent diarrhea that lasts for 1 to 4 weeks and recurs several times a year. Such diarrhea produces 4 to 8 (or, in severe diarrhea, up to 18) foul-smelling mucus- and blood-tinged stools daily in a patient with a mild fever, vague abdominal cramps, possible weight loss, tenderness over the cecum and ascending colon and, occasionally, hepatomegaly. Amebic granuloma (ameboma), commonly mistaken for cancer, can be a complication of the chronic infection. Amebic granuloma produces blood and mucus in the stool and, when granulomatous tissue covers the entire circumference of the bowel, causes partial or complete obstruction.
Parasitic and bacterial invasion of the appendix may produce typical signs of subacute appendicitis (abdominal pain and tenderness). Occasionally, E. histolytica perforates the intestinal wall and spreads to the liver. When it perforates the liver and diaphragm, it spreads to the lungs, pleural cavity, peritoneum and, rarely, the brain.
Diagnosis
CONFIRMING DIAGNOSIS Isolating E. histolytica (cysts and trophozoites) in fresh feces or aspirates from abscesses, ulcers, or tissue confirms acute amebic dysentery.
Diagnosis must distinguish between cancer and ameboma with X-rays, sigmoidoscopy, stool examination for amebae, and cecum palpation. In patients with amebiasis, exploratory surgery is hazardous; it can lead to peritonitis, perforation, and pericecal abscess.
Other laboratory tests that support the diagnosis of amebiasis include:
❑indirect hemagglutination test — positive with current or previous infection
❑complement fixation — usually positive only during active disease
❑barium studies — rule out nonamebic causes of diarrhea, such as polyps and cancer
❑sigmoidoscopy — detects rectosigmoid ulceration; a biopsy may be helpful.
Patients with amebiasis shouldn’t have preparatory enemas because these may remove exudates and destroy the trophozoites, thus interfering with test results.
Treatment
Drugs used to treat amebic dysentery include metronidazole, an amebicide at intestinal and extraintestinal sites; emetine hydrochloride, also an amebicide at intestinal and extraintestinal sites, including the liver and lungs; iodoquinol (diiodohydroxyquin), an effective amebicide for asymptomatic carriers; chloroquine, for liver abscesses, not intestinal infections; and tetracycline (in combination with emetine hydrochloride, metronidazole, or paromomycin), which supports the antiamebic effect by destroying intestinal bacteria on which the amebae normally feed.
When nausea and vomiting are present, I.V. therapy may be necessary until medications are tolerated by mouth.
Special considerations
❑Tell patients with amebiasis to avoid drinking alcohol when taking metronidazole. The combination may cause nausea, vomiting, and headache.
❑Antidiarrheals aren’t prescribed and can make the condition worse.
❑After treatment, stools should be re-checked to make sure the infection has been cleared.
Book Source Details
- Book Title: Professional Guide to Diseases (Eighth Edition)
- Author(s): Springhouse
- Year of Publication: 2005
- Copyright Details: Professional Guide to Diseases (Eighth Edition), Copyright © 2005 Lippincott Williams & Wilkins.
More About Amebiasis
More Medical Textbooks Online about Amebiasis
Review other book chapters online related to Amebiasis:
Medical Books Excerpts
- DIARRHEA
- "Differential Diagnosis in Primary Care" (2007)
- [ read ]
- Diarrhea
- "Handbook of Signs & Symptoms (Third Edition)" (2006)
- [ read ]
- Diarrhea
- "A Pocket Manual of Differential Diagnosis" (1999)
- [ read ]
- Amebiasis
- "Professional Guide to Diseases (Eighth Edition)" (2005)
- [ read ]
- Diarrhea
- "Professional Guide to Signs & Symptoms (Fifth Edition)" (2006)
- [ read ]
- Diarrhea
- "The 10-Minute Diagnosis Manual: Symptoms and Signs in the Time-Limited Encounter" (2000)
- [ read ]
- Diarrhea
- "Alarming Signs and Symptoms: Lippincott Manual of Nursing Practice Series" (2007)
- [ read ]
- Diarrhea
- "Signs & Symptoms: A 2-in-1 Reference for Nurses" (2007)
- [ read ]
- Diarrhea
- "The Diagnostic Approach to Symptoms and Signs in Pediatrics" (2006)
- [ read ]
- Diarrhea
- "Nursing: Interpreting Signs and Symptoms" (2007)
- [ read ]
Copyright notice for book excerpts: Copyright © 2008 Lippincott Williams & Wilkins. All rights reserved.
» Next page:
Diarrhea (Professional Guide to Signs & Symptoms (Fifth Edition))
Rate This Website
What do you think about the features of this website?
Take our user survey and have your say:
Website User Survey
Medical Tools & Articles:
Next articles:
Tools & Services:
Medical Articles:
Forums & Message Boards
- Ask or answer a question at the Boards:
