Amoebiasis

Overview:

The second most common parasitic disease-related cause of death globally is amoebiasis. Entamoeba histolytica, the pathogen that causes the illness, is a powerful protozoan parasite. The intestinal mucosa is invaded by E histolytica trophozoites, which release proteinases that break down host tissues, engulf red blood cells, and kill host cells upon contact. This results in amoebic colitis. Sometimes, amoebas manage to get past the mucosal barrier and enter the liver through the portal circulation. There, they cause abscesses that are filled with liquefied cellular debris and a few E histolytica trophozoites that encircle dead and dying hepatocytes. Amoebic liver abscesses grow uncontrollably and were once nearly always fatal, but they can now be cured with a single antibiotic dose, even in cases of large abscesses.

Types of Amoebiasis:

Amoebiasis can be classified into two main types based on the location and impact of the infection:

Intestinal Amoebiasis: This is the most common form, where the parasite Entamoeba histolytica infects the large intestine. It can range from asymptomatic to causing severe symptoms like bloody diarrhoea and colitis.
Extraintestinal Amoebiasis: This occurs when the parasite invades beyond the intestines, most commonly leading to liver abscesses. However, it can also affect other organs such as the lungs, brain, and heart.
Additionally, various species of Entamoeba can cause amoebiasis, with Entamoeba histolytica being the most common and pathogenic. Other species include:

Entamoeba dispar
Entamoeba moshkovskii
Entamoeba hartmanni
Entamoeba coli

While E. histolytica is known to cause disease, E. dispar and E. moshkovskii are generally considered non-pathogenic and are often found in asymptomatic individuals. E. hartmanni and E. coli are also non-pathogenic and do not cause symptoms.

It’s important to correctly identify the species involved, as treatment may vary depending on whether a pathogenic or non-pathogenic species causes amoebiasis.

Symptoms:

The symptoms of amoebiasis can vary from mild to severe, and not everyone infected with the parasite will experience symptoms. When symptoms do occur, they may include:

• Abdominal cramps
• Bloody diarrhoea or diarrhoea with mucus
• Nausea and vomiting
• Loss of weight
• Intermittent fever
• Rectal bleeding without diarrhoea, which can occur in children
• Chronic diarrhoea

In more severe cases, if left untreated, amoebiasis can lead to complications such as fulminant or necrotizing colitis, toxic megacolon, rectovaginal fistula, bowel perforation, gastrointestinal bleeding, stricture formation, peritonitis, and empyema.

Causes:

Amoebiasis is caused by the protozoan parasite Entamoeba histolytica. The primary mode of transmission is the fecal-oral route, which can occur through:

Contaminated food and water: Consuming food or water contaminated with faeces containing the parasite cysts.
Poor sanitation: Living in or visiting areas with inadequate sanitation facilities increases the risk of exposure to the parasite.
Oral-anal sexual practices: Engaging in oral-anal sex with an infected person can lead to transmission.
Direct and indirect contact: Either directly or indirectly, coming into contact with the stool of infected individuals can cause infection.

The infection begins when the cysts are ingested and reach the digestive tract, where they transform into the active trophozoite form and multiply, leading to symptoms. To prevent amoebiasis, practising good hygiene, treating water before consumption, washing vegetables thoroughly, and avoiding practices that can lead to faecal-oral transmission are important.

Risk factors:

The risk factors for acquiring amoebiasis include:

Travel to tropical regions with poor sanitary conditions, a common setting for transmitting Entamoeba histolytica.
Poor sanitation, including inadequate disposal of human waste and a lack of clean water supplies, can lead to contamination and the spread of the parasite.
Consumption of contaminated food or water, especially in areas where the infection is endemic.
Oral-anal sexual practices can directly transmit the parasite.
Close contact with an infected individual, particularly in institutions like prisons, where sanitation may be poor.
Immunosuppression, which can be due to conditions like HIV/AIDS, cancer, or the use of corticosteroids, makes individuals more susceptible to infection.
Alcohol use may affect the body’s ability to fight off infections.
Malnutrition can weaken the immune system.
Age extremes, such as very young children or the elderly, who may have weaker immune systems.
Pregnancy can alter immune responses and increase susceptibility.

It’s important to note that while these factors can increase the risk, not everyone exposed to them will develop amoebiasis. Preventive measures like practising good hygiene, treating water before consumption, and ensuring safe food handling can help reduce the risk of infection.

Possible Complications:

If left untreated, amoebiasis can lead to several serious complications:

Fulminant or necrotizing colitis: A severe form of colitis that can cause the colon to become necrotic.
Toxic megacolon: A condition where the colon rapidly expands and may become perforated.
Rectovaginal fistula: An abnormal connection between the rectum and vagina, which can result from severe intestinal infection.
Bowel perforation: A hole in the wall of the intestine, which can lead to peritonitis (inflammation of the abdominal lining).
Gastrointestinal bleeding: Severe bleeding within the gastrointestinal tract.
Stricture formation: Narrowing of the intestine due to chronic inflammation and scarring.
Peritonitis: Inflammation of the peritoneum, often due to infection from a perforated bowel.
Empyema: Accumulation of pus in the pleural cavity, usually due to infection.

Other complications can include:

Liver abscess: The most common extraintestinal complication, where pus accumulates in the liver.
Lung amebiasis (pleuropulmonary amebiasis): When the parasite spreads to the lungs, leading to lung abscesses.
Anaemia: Due to chronic blood loss from intestinal bleeding.

These complications underscore the importance of early diagnosis and treatment to prevent the progression of the disease.

Prevention:

Preventing amoebiasis involves several measures to reduce the risk of infection by the Entamoeba histolytica parasite. Here are some key prevention strategies:

Maintain proper hygiene: Regular handwashing with soap and water, especially after using the bathroom and before handling food, is crucial.
Water treatment: Boil water for at least one minute to kill any parasites before drinking, especially in uncertain water safety.
Safe food handling: Wash vegetables thoroughly with clean water, and consider soaking them in acetic acid or vinegar for 10-15 minutes before consumption to reduce the risk of contamination.
Avoid fecal-oral transmission: This includes avoiding oral-anal sexual practices and ensuring that any sexual activity is conducted with proper hygiene practices.
Improved sanitation: This includes separating food and water from faeces and improving sanitation systems in areas where infection is common.

By following these preventive measures, the risk of contracting amoebiasis can be significantly reduced. It’s also important to be aware of the risk factors and practice these preventive measures, especially when travelling to or living in areas with poor sanitation.

When to see a doctor:

Consult the doctor immediately if anyone in your family has symptoms of amoebiasis, such as Diarrhea with blood or mucus, Diarrhea that lasts longer than two weeks, or Abdominal pain.

Diagnosis:

The diagnosis of amoebiasis involves several tests to confirm the presence of the Entamoeba histolytica parasite. Here are the common diagnostic methods:

Stool test: Microscopy of fresh stool can reveal trophozoites or cysts of E. histolytica. Stool antigen detection tests can also confirm the presence of the parasite.
Blood test: A blood test can check for leukocytosis, an indicator of infection, and antibodies against E. histolytica.
Polymerase chain reaction (PCR): This test is used to detect and differentiate E. histolytica from non-pathogenic amoebas.
Imaging tests: In cases of extraintestinal infections, imaging tests such as ultrasound or CT scans may be used to identify liver abscesses or other complications.
Culture test: This is done with faecal or rectal biopsy specimens or aspirates of a liver abscess to identify the parasite.
ELISA test: An enzyme-linked immunosorbent assay can detect E. histolytica in the stool sample.
Loop-mediated isothermal amplification assay: This test detects E. histolytica in cases of hepatic amoebiasis.

Treatment:

The treatment of amoebiasis typically involves a combination of medications to address both the active infection and any remaining parasites in the intestines. Here’s a general outline of the treatment approach:

Anti-parasitic medications: For invasive amoebiasis or cases involving intestinal or extraintestinal infection, antiprotozoal drugs such as metronidazole or tinidazole are used to kill the active parasites.
Luminal agents: After the invasive disease is treated, luminal amoebicides like paromomycin or iodoquinol are prescribed to eliminate any remaining parasites in the intestines, which helps prevent relapse.
Amebicides: In cases of hepatic amoebiasis, drugs like chloroquine may be used alongside antiprotozoal drugs to target liver abscesses.
Antibiotics: If there is a risk of or an existing secondary bacterial infection, especially in cases of bowel perforation, broad-spectrum antibiotics such as penicillin may be administered.
Intravenous therapy: Intravenous administration of fluids and electrolytes may be necessary to replace those lost due to severe diarrhoea.
Dietary management: During recovery, it’s recommended to eat plain soft foods like rice, cooked cereal, plain noodles, applesauce, and bananas. Foods that may irritate the stomach, such as acidic, spicy, fatty foods, meat, and raw vegetables, should be avoided.

It’s important to follow the healthcare provider’s instructions and complete the full course of medication to ensure the infection is fully treated. Additionally, practising good hygiene and food safety measures can help prevent reinfection.