Amoebic liver abscess

Amoebic liver abscess (ALA) is a type of liver abscess caused by the protozoan Entamoeba histolytica. It is the most common extraintestinal manifestation of amoebiasis, which is a parasitic infection that primarily affects the intestines. ALA is a significant health problem in tropical and subtropical regions, where sanitation and hygiene are often poor. However, it can occur in any part of the world due to global travel and immigration.

Etiology

The causative agent of ALA, Entamoeba histolytica, is transmitted via the fecal-oral route. Infection occurs by ingesting food or water contaminated with fecal matter containing the cyst form of the parasite. Once in the digestive tract, the cysts transform into trophozoites, which can invade the intestinal mucosa, causing dysentery or spreading to other organs, most commonly the liver, via the bloodstream, leading to the formation of an abscess.

Pathophysiology

After Entamoeba histolytica trophozoites invade the intestinal lining, they can enter the portal venous system, reaching the liver. In the liver, the immune response to these trophozoites leads to the formation of an abscess. The abscess is typically filled with a thick, brownish pus, often described as "anchovy paste" due to its appearance. The abscess can compromise liver function and, if not treated, may rupture, leading to peritonitis or spread to other organs.

Clinical Presentation

Patients with ALA may present with a range of symptoms, including right upper quadrant abdominal pain, fever, weight loss, and jaundice. Physical examination may reveal hepatomegaly or tenderness over the liver. Symptoms can develop weeks to months after the initial intestinal infection, making the diagnosis challenging.

Diagnosis

Diagnosis of ALA involves a combination of clinical presentation, laboratory tests, and imaging studies. Serological tests can detect antibodies against Entamoeba histolytica. Ultrasound or computed tomography (CT) scans of the abdomen are used to identify the presence of liver abscesses. In some cases, aspiration of abscess contents may be necessary to distinguish ALA from a bacterial liver abscess.

Treatment

Treatment of ALA includes the use of anti-amoebic drugs, such as metronidazole or tinidazole, followed by a luminal agent to eliminate any remaining parasites in the intestine and prevent recurrence. Large abscesses may require drainage, either percutaneously under imaging guidance or surgically.

Prevention

Prevention of ALA focuses on improving sanitation and hygiene practices to reduce the risk of Entamoeba histolytica infection. This includes ensuring access to clean water, proper sewage disposal, and practicing good hand hygiene.

Epidemiology

ALA is most prevalent in tropical and subtropical areas, particularly in regions with poor sanitation. It affects males more frequently than females, especially those between the ages of 20 and 40. Travelers to endemic areas are also at risk.

Complications

If left untreated, ALA can lead to severe complications, including rupture of the abscess into the peritoneal cavity, pleural space, or pericardium, leading to peritonitis, pleuritis, or pericarditis, respectively. Secondary bacterial infection of the abscess can also occur.