Definition

Amoebic liver abscess refers to an accumulation of pus in the liver caused by infection from the parasite Entamoeba histolytica. While uncommon in children, it tends to affect more men than women among adults. Globally, an estimated 40-50 million people contract the infection annually, with higher prevalence in developing countries.

Causes

The condition is triggered by an infection with Entamoeba histolytica, a parasite excreted through feces. The parasite can spread via contaminated food, water, or hands that have come into contact with fecal matter in the form of cysts. Additionally, transmission may occur through sexual contact involving feces. Once ingested, cysts release smaller cells, called trophozoites, into the small intestine. These trophozoites travel to the large intestine, where they may either remain without causing symptoms, penetrate the intestinal lining, or enter the bloodstream to infect other organs, such as the liver, lungs, and brain. Trophozoites multiply by division or produce cysts, both of which can be found in feces. While trophozoites quickly die outside the body and are vulnerable to stomach acid if ingested, cysts have a protective wall, allowing them to survive for days to weeks.

Upon reaching the liver, the parasites cause inflammation and subsequent cell death, leading to the formation of a pus-filled cavity. The pus typically consists of dead liver cells, cell debris, and liquified tissue.

Risk Factors

This parasite is prevalent worldwide, particularly in warmer, tropical climates, and thrives in densely populated areas with poor sanitation. It poses significant health risks in regions such as Africa, Latin America, Southeast Asia, and India. Additional risk factors for developing amoebic liver abscess include residing in or traveling to tropical areas, alcoholism, cancer, compromised immunity (e.g., due to HIV/AIDS), malnutrition, advanced age, pregnancy, and the use of steroid medications.

Symptoms

The most common symptoms of amoebic liver abscess include fever and abdominal pain, typically lasting fewer than 14 days. Abdominal pain is often continuous, dull, and burning, located primarily in the upper right abdomen, sometimes radiating to the right shoulder or upper back. The pain may intensify with coughing, walking, deep breathing, or lying on the right side. Additional symptoms can include nausea, vomiting, weight loss, diarrhea, and respiratory issues. Bloody diarrhea occurs in about 7% of cases, although many patients report a history of severe bloody diarrhea several months prior. Respiratory symptoms, such as coughing and chest pain, may also be present, with the cough either dry or producing a brown, odorless fluid.

Diagnoses

The diagnostic process typically begins by assessing vital signs such as temperature, blood pressure, pulse, and respiratory rate. In cases of amoebic liver abscess, fever is commonly detected. A physical examination of the abdomen may reveal an enlarged, tender liver. Pain is often localized above the liver, beneath the ribs, or between two ribs, and is usually felt in the upper right or upper middle abdomen, depending on the abscess's position. A lung examination may also be performed to check for any lung involvement, often indicated by abnormal lung sounds. Additionally, an eye exam may be conducted to assess whether the patient is jaundiced due to the infection.

Laboratory tests may include a complete blood count, which often reveals an elevated white blood cell count. Blood chemistry tests, such as bilirubin levels (particularly in jaundiced patients) and liver enzyme tests, may also be performed. Stool samples can be analyzed microscopically, tested for parasitic antigens, or cultured. Antibody and serum antigen tests are frequently used when amoebic infection is suspected.

Imaging tests, though unable to directly identify the cause of an abscess, can be useful in detecting its presence. Ultrasonography (USG) is often used as an initial test. A computed tomography (CT) scan can help differentiate abscesses from tumors and is also a viable first-line imaging option. Nuclear imaging, although capable of distinguishing between bacterial and parasitic abscesses, is seldom used due to its high cost and limited availability.

Managements

The primary treatment for amoebic liver abscess is antibiotic therapy, typically administered for 7-10 days, although some antibiotics can be given for as few as 3 days. The initial aim is to eliminate the amoeba. Following treatment of the abscess, antibiotic therapy continues to eradicate amoebic cells in the intestines, preventing recurrence. In many cases, the abscess resolves with antibiotic use, though further intervention may be necessary in some instances.

If the abscess is at risk of rupture (e.g., if it exceeds 5 cm in size), is located in the left lobe of the liver (where rupture could lead to infection of the abdominal cavity or the heart's outer layer), or if antibiotic treatment fails after 5-7 days, aspiration of the abscess may be required. Aspiration may also be considered when distinguishing between amoebic and bacterial liver abscess is difficult.

No specific dietary changes are required for patients, though maintaining good food and hand hygiene is essential to avoid reinfection. Patients are advised to rest for several days during the course of therapy.

Complications

Amoebic liver abscess may rupture into the chest, abdomen, or the outer layer of the heart, significantly increasing the risk of infection in areas exposed to the pus. Such infections can be fatal, with amoebiasis ranking as the second leading cause of parasitic death worldwide, following malaria. The greatest risk of death arises when the abscess ruptures into the heart. Other complications may include fluid accumulation near the lungs or the formation of abnormal channels between the respiratory system and the pleural lining (lungs' outer layer).

Prevention

Preventing amoebic liver abscess centers on avoiding exposure to the parasite. This can be achieved by practicing good personal hygiene, regularly washing hands with clean water and soap, particularly before meals, and ensuring food is properly prepared. Travelers to high-risk areas should consume food or fruits they have cooked or peeled themselves and avoid drinking local water, including beverages with ice cubes. In cases where multiple people in a community suddenly develop bloody diarrhea, an investigation into the source of infection is critical. In such areas, vegetables should be cleaned with strong detergent and soaked in vinegar for 15 minutes to destroy cysts. If these methods are not feasible, boiling the vegetables is an alternative, as simple soaking is insufficient due to the protective wall of the cysts.

When to See a Doctor?

Immediate medical attention is advised if symptoms such as fever and upper right abdominal pain arise, especially for individuals with a history of severe bloody diarrhea a few months earlier or those who have traveled to or resided in areas with poor sanitation. Although most cases are treatable with antibiotics, complications, including death, can occur if left untreated.

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