Amebiasis (Amoebic Dysentery) | Entamoeba histolytica, Pathogenesis, Signs & Symptoms, Treatment

Summary

Intestinal amebiasis, caused by *Entamoeba histolytica*, is a parasitic infection often leading to bloody diarrhea, abdominal pain, and potentially severe complications like liver abscesses. Transmission occurs via ingestion of cysts from contaminated food or water, which transform into trophozoites in the small intestine and invade the large intestine. Symptoms can range from asymptomatic to amoebic dysentery and abscess formation. Diagnosis includes serology, stool sampling, and biopsy. Treatment typically involves metronidazole for mild cases, and Iodoquinol or Paramycin for invasive infections. Early detection and treatment are crucial for managing this potentially serious condition.

Takeaways

• 😀 Intestinal Amebiasis, caused by *Entamoeba histolytica*, is a global infection affecting about 50 million people annually.
• 😀 *Entamoeba histolytica* is the most common cause of amoebic dysentery, but other species like *Entamoeba dispar* and *Entamoeba moshkovskii* can also cause infection.
• 😀 The infection begins when cysts of the amoeba are ingested from contaminated food, water, or via the fecal-oral route.
• 😀 Cysts are the infective stage and can survive in the environment for weeks to months, making them highly resilient.
• 😀 After ingestion, the cysts transform into trophozoites in the small intestine, which then invade the large intestine's mucosa and cause tissue damage.
• 😀 Trophozoites secrete proteinases that destroy intestinal proteins and cells, leading to tissue damage, inflammation, and bloody diarrhea.
• 😀 Another pathogenic mechanism involves trophozoites forming pores in infected cells, leading to cell lysis and increased intestinal permeability.
• 😀 Clinical symptoms of intestinal amebiasis include asymptomatic cases, amoebic dysentery (abdominal pain and bloody diarrhea), and amoebic abscesses, commonly in the liver.
• 😀 Amoebic abscesses can also occur in the lungs and brain, leading to serious systemic complications like hepatomegaly, right upper quadrant pain, and fever.
• 😀 Diagnosis of amebiasis involves serology, stool sampling for trophozoites, antigen testing, and possibly biopsy of colon tissue for invasive cases.
• 😀 Treatment for intestinal amebiasis includes metronidazole for mild cases, and iodoquinol or paramycin for more severe or invasive disease, including liver abscesses.

Q & A

What is intestinal amebiasis and which organism is responsible for it?

Intestinal amebiasis, also known as amoebic dysentery, is an invasive intestinal infection caused by the protozoan *Entamoeba histolytica*. This organism is the most common cause of amebiasis, although other species like *Entamoeba dispar*, *Entamoeba moshkovskii*, and *Entamoeba bangladeshi* can also cause similar infections.

How do people get infected with *Entamoeba histolytica*?

Infection occurs through the ingestion of cysts of *Entamoeba histolytica*, which are the infective stage. These cysts can contaminate food, water, or surfaces through the fecal-oral route. Once ingested, the cysts transform into trophozoites in the small intestine, which then travel to the large intestine and cause disease.

What are the two stages of *Entamoeba histolytica* and which one is infective?

The two stages of *Entamoeba histolytica* are the cyst stage and the trophozoite stage. The cyst stage is the infective form, capable of surviving in the environment and being ingested by a host. The trophozoite stage is the active, invasive form that causes disease in the intestines.

What is the primary mechanism by which *Entamoeba histolytica* causes tissue damage in the intestines?

*Entamoeba histolytica* causes tissue damage primarily through the secretion of proteinases that destroy host proteins. Additionally, the trophozoites directly attack intestinal cells, form pores in cell membranes, and disrupt tight junctions, leading to increased intestinal permeability and bloody diarrhea.

What are some of the common clinical features of intestinal amebiasis?

Common clinical features include asymptomatic infection, amoebic dysentery (characterized by abdominal pain, colitis, and bloody diarrhea), and amoebic abscesses. Amoebic abscesses most often occur in the liver but can also form in the lungs or brain, causing symptoms such as hepatomegaly, right upper quadrant pain, fever, and weight loss.

What is the mnemonic to remember the clinical features of intestinal amebiasis?

The mnemonic is 'Ame' ordered BLOOD LABS. 'Ame' refers to amoeba, and 'ordered' hints at diagnostic tests. 'Blood' refers to bloody diarrhea, 'L' stands for liver (where abscesses commonly occur), and 'Abs' refers to abscesses in other organs like the liver, lungs, and brain.

How can *Entamoeba histolytica* spread from the intestines to other organs?

*Entamoeba histolytica* can spread hematogenously (via the bloodstream) from the intestines to other organs such as the liver, lungs, and brain. This spread results in the formation of amoebic abscesses, most commonly in the liver.

What methods are used to diagnose intestinal amebiasis?

Diagnosis of intestinal amebiasis can be made through several methods, including serology (detecting antibodies), antigen testing, stool sampling for trophozoites, and sometimes biopsy of the colon to examine intestinal tissue for the presence of amoebas.

What are the primary treatments for intestinal amebiasis?

The primary treatment for intestinal amebiasis is **metronidazole**, which is effective for symptomatic cases. For more invasive disease or cyst involvement, **iodoquinol** or **paromomycin** may be used to target cysts and treat systemic infections.

Why is the cyst form of *Entamoeba histolytica* so resilient in the environment?

The cyst form of *Entamoeba histolytica* is highly resilient because it can survive in the environment for weeks to months. This survival ability allows the cyst to remain infectious until it is ingested by a new host, contributing to the spread of the disease.