Amoebiasis

 

Amoebiasis: Understanding this Intestinal Parasitic Infection

Amoebiasis, also known as amoebic dysentery, is a common infection caused by the parasite Entamoeba histolytica. This parasitic infection affects the intestines and can cause severe diarrhea, abdominal pain, and other symptoms. Despite being preventable, amoebiasis continues to be a major public health concern, particularly in developing countries with poor sanitation and hygiene practices.

Causative Organism and its Form

The amoebic parasite responsible for causing amoebiasis is Entamoeba histolytica, a single-celled parasite that belongs to the phylum Excavata. This parasite exists in two different forms: the non-pathogenic cyst form, and the pathogenic trophozoite form.

The cyst form is the infective stage, and is passed in the stool of infected individuals. The cysts are resilient and can survive for several days outside of the body, making them a potent source of infection. When ingested, the cysts release trophozoites, which are the active, invasive stage of the parasite.

The cyst form 

The trophozoite form of Entamoeba histolytica is capable of burrowing into the intestinal wall and causing significant damage. In severe cases, the trophozoites can invade other parts of the body, including the liver, and cause complications such as abscesses. As the trophozoites multiply, they can also form new cysts, which can be passed in the stool and infect other individuals.

The trophozoite

Life Cycle of the Causative Organism

The life cycle of Entamoeba histolytica begins with the ingestion of the infective cyst form. Once in the body, the cysts release trophozoites, which multiply and invade the intestinal wall. Over time, the trophozoites can cause significant damage to the intestinal wall and may even spread to other parts of the body, causing complications such as liver abscesses. As the trophozoites multiply, they can also form new cysts, which can be passed in the stool and infect other individuals.

Life Cycle of the Causative Organism

source: CDC

1. Colitis (Amebic Dysentery)

Colitis, also known as amebic dysentery, is an intestinal infection caused by the parasite Entamoeba histolytica. This condition is characterized by inflammation of the colon, which can lead to symptoms such as diarrhea, abdominal pain, and cramping.

Predisposed groups to amebic colitis are:

• very young patients,
•  pregnant women,
•  recipients of corticosteroids, 
• malnourished individuals.
• HIV

2. Extraintestinal Manifestations

In some cases, the infection caused by Entamoeba histolytica can spread beyond the intestine, leading to extraintestinal manifestations. These manifestations can occur when the parasite invades other parts of the body, such as the liver, lungs, heart, or brain.

Liver Abscess (Most Common)

Liver abscess is the most common extraintestinal manifestation of amebic dysentery. This occurs when the parasite invades the liver, causing inflammation and the formation of a pus-filled mass, known as an abscess. Symptoms of liver abscess can include fever, chills, abdominal pain, and jaundice.

 Structure of Amebic liver Abscess

3 zones:

1. Inner zone: 

this area is liquifactive necrosis

filled with brown thick fluid( Anchovy cause)

No pus cells

A.L,A is Not real abscess because no pus cells 

No trophozoite . No pus cells

2. Intermediate zone : 

liver cells+RBCS+WBCS+ trophozoite( no cyst)

3. Outer zone: 

normal hepatocyres

Pleuropulmonary Manifestations

In rare cases, the parasite can invade the lungs, causing pleuropulmonary manifestations. These manifestations can include pneumonia-like symptoms, such as coughing, chest pain, and shortness of breath.

Cardiac and Cerebral Dissemination

In even rarer cases, the parasite can invade the heart or brain, causing cardiac or cerebral dissemination, respectively. These conditions can lead to serious and potentially life-threatening complications, and require prompt medical attention.

Clinical Picture

The symptoms of amoebiasis can range from mild to severe, and can develop anywhere from a few days to several weeks after infection. Common symptoms include:

Diarrhea (sometimes bloody)

Abdominal pain

Nausea

Vomiting

Loss of appetite

Weight loss

In severe cases, the parasite can spread to other parts of the body, causing liver abscesses and other complications.

Diagnosis

Diagnosis of amoebiasis is typically made through a combination of stool tests and imaging studies. Stool tests, such as the O&P (ova and parasite) exam, can detect the presence of Entamoeba histolytica cysts or trophozoites. Imaging studies, such as CT scans or ultrasound, can help detect the presence of liver abscesses or other complications.

Treatment

Treatment for amoebiasis typically involves antibiotics, such as metronidazole or tinidazole. These medications target the trophozoite form of the parasite, and can help clear the infection from the body. In severe cases, the parasite can be difficult to eradicate and may require a combination of medications and other interventions.

Prevention

Preventing amoebiasis is relatively straightforward, and involves practicing good hygiene and avoiding contaminated food and water. Some key steps to prevent amoebiasis include:

1. Washing hands regularly, especially before eating and after using the bathroom
2. Avoiding close contact with infected individuals
3. Avoiding contaminated food and water
4. Practicing safe food handling and preparation techniques
5. Using proper sanitation facilities, and avoiding open defecation

Conclusion,

Amoebiasis is a common and preventable parasitic infection that affects the intestines. By understanding the causative organism, its life cycle, clinical picture, diagnosis, treatment, and prevention, individuals can take steps to reduce their risk of infection and protect themselves and their communities from this serious public health concern.