Amoebiasis

Introduction

About 10 percent of the world's population is infected with E.Histolytica. It is the third most common cause of death (after Schistosomiasis and Malaria) from parasitic infections. It has a very high incidence in tropical countries like India, Mexico, Central and South America. About 90 percent of infections are asymptomatic (do not produce any symptoms) and the remaining 1O percent produces a spectrum varying from dysentery to amoebic liver abscess.





Cause and Pathogenesis

It is caused by a protozoa, Entamoeba Histolytica. It is commonly spread by water contaminated by faeces or from food served by contaminated hands. Even vegetables grown in soil contaminated by faeces can transmit the disease. When the cyst of Entamoeba Histolytica enters the small intestine, active amoebic parasites (trophozoites) are released, which can invade the epithelial cells of the large intestines, causing flask-shaped ulcers. It can also spread to other organs like the liver, lungs, and brain by invading the venous system of the intestines. If it invades the liver, it causes formation of the typical anchovy paste like pus. Asymptomatic carriers pass cysts in the faeces.

Symptoms and Signs


It can either occur as intestinal or extra-intestinal amoebiasis.

Intestinal amoebiasis


The most common type of amoebic infection is asymptomatic cyst passage. Symptomatic patients initially have lower abdominal pain and diarrhoea and later develop dysentery (with blood and mucus in stool). Fulminant infection with high grade fever, severe abdominal pain and profuse diarrhoea occurs in children and in patients receiving steroids. Severe gastric distention of the bowel can occur. Amoebomas (inflammatory mass lesion developing in chronic amoebiasis) can present like a malignancy.

Extra-intestinal amoebiasis


Patients show symptoms of fever and right upper abdominal pain. Jaundice is rare. Amoebic liver abscesses can also present as pyrexia of unknown origin. The abscess can sometimes rupture into the pleural, peritoneal or pericardial cavities.

Investigations and Diagnosis


Stool examination is the commonest examination done for diagnosis. Though neutrophils and Charcot-Leyden crystals can be found, haematophagous trophozoites are diagnostic. Since trophozoites are killed rapidly by water or drying, at least three fresh stool specimens have to be examined for a positive diagnosis. Fresh stool or concentrated stool examination is positive in 75 to 95 percent of patients. Serology is positive in more than 90 percent patients with invasive amoebiasis.

Barium studies are contraindicated in acute amoebic colitis for fear of perforation. Ultrasound, CT and MRI scans of the abdomen can be useful in diagnosing hepatic amoebiasis. Since abscesses resolve slowly or may even increase in size during treatment, clinical response is more important in the follow-up rather than repeated scans.

Acute intestinal amoebiasis should be differentiated from organisms causing traveller's diarrhoea (which is due to a bacteria called Escherischia Coli) and also inflammatory bowel disease. Amoebic liver abscess has to be differentiated from pyogenic abscess which are seen in older patients with underlying bowel disease or after surgery.





Treatment and Prognosis

Asymptomatic patients can be treated with luminal agents like Liodoquinol or Diloxanide Furoate. Patients with acute colitis require supportive therapy (rehydration) and Metronidazole, followed by luminal agents. Metronidazole is also the drug of choice for amoebic liver abscess. Second line agents like Chloroquine and Emetine are no longer used. Prognosis is generally good with treatment unless complications of abscess rupture occurs when surgical intervention may be required.

Prevention


Treatment of asymptomatic cyst carriers and good sanitation and water facilities are fundamental in the prevention of amoebiasis. Vaccines are not available.


Source

Dr. V.Ramasubramaniam MBBS, MD, MRCP.



Dr.V.Ramasubramaniam is an Assistant Professor of Medicine and heads the Division of Infectious Diseases at the Sri Ramachandra Medical College and Research Institute

More about Dr Ramasubramaniam.