Entamoeba histolytica

Entamoeba histolytica

Etiology:  Infection is established by ingestion of Entamoeba histolytica cysts which release trophozoites.

Epidemiology

 Food or drink contaminated with E.histolytica cysts and direct fecal-oral contact are the most common means of infection.

Untreated water and human feces used as fertilizer are important sources of infection.

Food handlers carrying amebic cysts may play a role in spreading the infection.

The pathogenecity of E. histolytica is believed to be dependent on two mechanisms:

       1- Cell contact.

       2- Toxin exposure.

· Once the trophozoites invade the intestinal mucosa, they produce tissue destruction (ulcers) with little local inflammatory response.

· The organisms multiply and spread through the wall underneath the intestinal epithelium to produce flask shaped ulcers.

· These lesions are commonly seen in the caecum, transverse colon, and sigmoid colon.

· Amebae may produce similar lytic lesions if they reach the liver.

· Rarely the infection may extend extraintestinally to lungs and brain.

Clinical manifestations

1- Intestinal amebiasis

  · The onset is usually gradual with colicky abdominal pain and frequent bowel movements.

  · Diarrhea is frequently associated with tenesmus.

  · Stools are blood-stained and contain fair amount of mucus with few leukocytes.

  · The attacks of dysentery are recurrent in untreated cases.

Complications

    a- Ameboma.

    b- Toxic megacolon.

    c- Extraintestinal extension.

    d- Local perforation and peritonitis may occur.

2- Hepatic amebiasis

· There is diffuse liver enlargement and tenderness.

· In few cases liver abscesses develop and are accompanied by fever and abdominal pain. 

· Changes in the base of the right lung, pleural effusion and elevation of the diaphragm.

· Rupture into the peritoneum, thorax or through the skin occurs when diagnosis and therapy are delayed.

Laboratory examination of hepatic amebiasis

  · Slight leukocytosis and moderate anemia.

  · Non-specific elevation of liver enzymes.

  · Stool examination for amebae is negative in more than 50% of patients with liver abscess.

  · Ultarsonography, computed tomography (CT), MRI or isotope scans can localize and delineate the size of the abscess cavity.

Diagnosis

· Patients with invasive colitis show occult blood in stools.

· Detection of the parasite or cysts in the stools.

· When stool samples are negative for 3 days, segmoidoscopy is done and biopsy is taken.

· Indirect hemagglutination test may be helpful in the diagnosis of invasive intestinal amebiasis and amebic liver abscess.

Treatment

All individuals with E. histolytica trophozoites or cysts in their stools whether     symptomatizing or not should be treated.

Asymptomatic cyst carriers:  is treated with one of the following drugs:

· Iodoquinol: 30-40mg/kg/day orally in 3 divided doses for 20 days.

· Diloxanide furoate 10mg/kg/24h divided into 2 doses for 10 days. The drug should not be used in children < 2 years of age.

Invasive amebiasis is treated by:

· Metronidazole 50 mg/kg/24hr for 10 days orally followed by iodoquinol 30-40mg/kg/24hr for 20 days.

· In fulminant cases, dehydroemetine (IM or SC and never IV) is added for the first few days in a dose of 1mg/kg/day.

· Amebic liver abscess is treated with metronidazole. Chloroquine, which concentrates in the liver, may be used. Aspiration of large lesions or left lobe abscesses may be necessary if  rupture is imminent or if the response to treatment is poor. Aspiration of the abscess revealed chocolate brown pus.