Amoebiasis,causes, transmission, complications, prognosis, treatment and preventions

AMOEBIASIS

     Amebiasis is a parasitic infection of the intestines caused by the protozoan Entamoeba histolytica, or E. histolytica. 

    Amoebiasis is caused by the protozoan Entamoeba histolytica.             Amoebiasis is often asymptomatic but may cause dysentery and invasive extra-intestinal disease.
      Entamoeba dispar, another species, has been thought in the past to be non-pathological but in vitro and in vivo experiments suggest it is capable of causing liver damage.

    Humans are the only reservoir, and infection occurs by ingestion of mature cysts in food or water, or on hands contaminated by faeces.  The cysts of E. histolytica enter the small intestine and release active amoebic parasites (trophozoites), which invade the epithelial cells of the large intestines, causing flask-shaped ulcers. Infection can then spread from the intestines to other organs - eg, the liver, lungs and brain, via the venous system.Asymptomatic carriers pass cysts in the faeces and the asymptomatic carriage state can persist indefinitely. E. dispar is the parasite most commonly found in such carriers. Cysts remain viable for up to two months.Invasive amoebiasis most often causes an amoebic liver abscess but may affect the lung, heart, brain, urinary tract and skin. 

      Epidemiology

     E. histolytica infects approximately 50 million people worldwide, of which approximately 100,000 die annually.   It is the third most common cause of death (after schistosomiasis and malaria) from parasitic infections.   It is very common in South and Central America, West Africa and Southeast Asia. It is rare in temperate climates.  Increasing prevalence is seen in men who have sex with men who engage in oral-anal sex.  Travellers and immigrants and residents of institutions are also at risk. About 90% of infections are asymptomatic and the remaining 10% produce a spectrum of disease varying from dysentery to amoebic liver abscess.

       Presentation

The incubation period may be as short as seven days and tissue invasion mostly occurs during the first four months of infection.

     Persons at great risks of getting AMOEBIASIS

• People who have traveled to tropical locations with poor sanitation
• Immigrants from tropical countries with poor sanitary conditions
• People who live in institutions with poor sanitary conditions, such as prisons
• Men who have sex with other men
• People with compromised immune systems and other health conditions

       Intestinal amoebiasis

The most common type of amoebic infection is the asymptomatic passage of cysts, found to be mainly associated with E. dispar infection.

   Symptomatic patients initially have lower abdominal pain and diarrhoea and later develop dysentery (with blood and mucus in stool).Amoebic colitis with dysentery: loose stools with fresh blood. The patient is usually generally well with mild or moderate abdominal pain. Symptoms often fluctuate over weeks or even months with the patient becoming debilitated.Abdominal tenderness in one or both iliac fossae but may be generalised. There is palpably thickened gut, and low fever. There is abdominal distension in more severely ill patients passing relatively small amounts of stool sometimes.Amoebic colitis without dysentery: a change in bowel habit, bloodstained stools, flatulence and colicky pain, tenderness in the right iliac fossa or other places over the colon. This may disappear or progress to dysentery.Rectal bleeding: this may occasionally be the only sign, with or without tenesmus (common in children).Amoeboma:Abdominal mass, which is usually in the right iliac fossa.May be painful and tender.Fever, altered bowel habit and there may be intermittent dysentery.May be symptoms of partial or intermittent bowel obstruction.Fulminant colitis: this is more likely in children and in patients taking steroids; high-grade fever, severe abdominal pain, increasing distension of the abdomen with vomiting plus watery diarrhoea. Absent bowel sounds. X-ray may show free peritoneal gas with acute gaseous dilatation of the colon.Localised perforation and appendicitis: deep ulcer may cause sudden perforation with peritonitis or may leak causing pericolic abscess or retroperitoneal infection. May also resemble simple appendicitis, often with signs of dysentery.

       Hepatic amoebiasis

     There is usually no current, and often no history of, dysentery.It usually occurs within eight weeks to one year of infection.It presents with sweating and pyrexia, a painful liver or diaphragm, together with weight loss often appearing insidiously, but pain may appear abruptly.     Fever is typically remitting with a prominent evening rise with brief rigors and profuse sweating.Often there is anaemia and a dry painful cough.          There is liver enlargement with localised tenderness in the right hypochondrium, epigastrium and intercostal spaces overlying the liver.  An epigastric mass from a left-lobe lesion may be found.  Upward enlargement may cause bulging of the right chest wall with raised upper level of liver dullness on percussion. Reduced breath sounds or crepitations at the right lung base may be heard.

    Abscess may extend into adjacent structures, usually the right chest, peritoneum and pericardium. If it extends into the lung, it produces hepatobronchial fistula with expectoration of brownish, necrotic liver tissue. May also cause peritonitis, pericarditis, brain abscess or genitourinary disease.

    Differential diagnosis

Other causes of infective Colitis, ulcerative colitis, colorectal cancer.       In chronic infection, other possible diagnoses include Crohn's disease, ileocaecal tuberculosis, diverticulitis, anorectal lymphogranuloma venereum.  Amoebic liver abscess has to be differentiated from pyogenic abscess which may occur particularly in older patients with underlying bowel disease or after surgery.

    Investigations

    FBC (leukocytosis), raised ESR, abnormal LFTs (raised alkaline phosphatase and transaminases).

     Stool examination:Microscopic stool examination for trophozoites should be performed in patients with diarrhoea..  

     Examination of 3 to 6 stool samples and concentration techniques may be required due to low specificity.

     E. histolytica should be differentiated from other Entamoeba spp.  The World Health Organization now recommends that intestinal amoebiasis should be diagnosed with specific stool E. histolytica testing (eg, cultures, antigen testing or PCR) rather than examining stool for ova and parasites.Serology: antibody testing is positive in nearly 100% of cases of liver abscess, 89-100% of invasive bowel disease and nearly 100% of patients with amoeboma.

    PCR tests (faeces, abscess aspirate or other tissues).

    Barium studies are contra-indicated in acute amoebic colitis because of the risk of perforation. 

    Ultrasound, CT and MRI scans of the abdomen can be useful in diagnosing hepatic amoebiasis.Ultrasound- or CT-guided liver abscess aspiration.

    Proctoscopy, sigmoidoscopy or colonoscopy: mucosal scrapings for biopsy and E. histolytica  testing.    Abscesses resolve slowly and may increase in size during treatment and so clinical response, rather than repeated scans, is more important in monitoring progress.

    HOW CAN I PREVENT AMOEBIASIS?

       Proper sanitation is the key to avoiding amebiasis. Follow this regimen when preparing and eating food.

• Thoroughly wash fruits and vegetables before eating.
• Avoid eating fruits or vegetables unless you wash and peel them yourself.
• Stick to bottled water and soft drinks.
• If you must drink water, boil it or treat it with iodine.
• Avoid ice cubes or fountain drinks.
• Avoid milk, cheese, or other unpasteurized dairy products.
• Avoid food sold by street vendors.