Amoebiasis

Amoebiasis, also known as amoebic dysentery, is an intestinal illness caused by a protozoan parasite called Entamoeba histolytica. It is primarily spread through contaminated food or water, especially in areas with poor sanitation. The parasite can live in the large intestine without causing symptoms. Still, it invades the intestinal wall in some cases, leading to symptoms like abdominal pain, diarrhoea (often with blood or mucus), and fever.

1.0Introduction

• Entamoeba histolytica is a protozoan parasite that causes a common gastrointestinal infection in humans. 
• While many individuals remain asymptomatic, around 10% of infected people develop symptoms, and in some cases, the disease can progress to become potentially life-threatening, contributing significantly to global morbidity and mortality.

2.0Classification of Amoebiasis

Amoebiasis is generally classified into two major forms:

• Intestinal Amoebiasis: This form is confined to the gastrointestinal tract. Invasive cases may develop, with symptoms ranging from mild abdominal discomfort and diarrhoea to severe, acute fulminant dysentery.
• Extraintestinal Amoebiasis: When the parasite spreads beyond the intestines, it most commonly affects the liver, resulting in liver abscesses. In more severe cases, it can also involve other organs such as the lungs, brain, spleen, and skin.

3.0Pathogenicity and Transmission of Entamoeba histolytica

• Certain strains of E. histolytica are potentially pathogenic. 
• These strains can be classified into at least 17 distinct zymodemes—groups of organisms that differ based on the electrophoretic mobility of one or more enzymes. 
• Among these, 7 zymodemes are identified as potentially pathogenic, while the remaining 11 are non-pathogenic. Pathogenic strains originate from specific zymodemes, and the variations in isoenzymes are believed to determine their ability to invade host tissues.
• E. histolytica exists in two forms:
• Trophozoite (vegetative form): Active, invasive form that causes tissue damage.
• Cyst (dormant form): Infective and environmentally resistant.
• The parasite multiplies in the host and encysts, excreting cysts in faeces. 
• Once ingested (usually through contaminated food or water), cysts release trophozoites, which invade the intestinal wall, especially the caecum, ascending colon, and rectum. 
• In severe cases, trophozoites may enter the bloodstream and reach organs such as the liver, causing abscesses.
• Cysts are the primary infective form and can remain viable for several days in moist conditions found in faeces, water, sewage, or soil, especially at lower temperatures. Notably, cysts resist chlorine but are readily destroyed by drying or heating. Conversely, trophozoites are short-lived outside the human body and are not significant in disease transmission.

4.0Source and Transmission of Infection

• Humans are the sole reservoir of Entamoeba histolytica infection. 
• The immediate source of transmission is faeces containing infective cysts. Many infected individuals remain asymptomatic and serve as healthy carriers, unknowingly spreading the parasite. 
• An infected carrier is estimated to shed up to 15 million cysts per day in their stool.
• These carriers pose a significant public health risk, especially when involved in food preparation and handling, as they can contaminate food and water sources, facilitating the spread of the disease.

Period of Communicability

• An infected individual can remain contagious for as long as they continue to excrete cysts, which may persist for several years if the infection goes unrecognized and untreated.

Susceptibility and Occurrence

• All age groups are susceptible to amoebiasis.
• The disease shows no preference for sex or race—it can affect anyone regardless of demographic background.
• Amoebiasis is often a household infection, spreading among close contacts through shared environments and poor hygiene practices.

5.0Environmental and Societal Factors Influencing Spread

• Amoebiasis is more strongly linked to poor sanitation and low socio-economic conditions than to climate alone.
• Practices such as using night soil (human faeces) as fertilizer significantly contribute to disease transmission.
• Regions with distinct wet and dry seasons are particularly affected.
• Increased incidence during rainy seasons is common, likely because cysts survive longer in moist conditions, raising the risk of transmission.
• Epidemic outbreaks can occur when sewage contaminates water, especially in areas with inadequate sanitation infrastructure.

6.0Modes of Transmission of Entamoeba histolytica

Faecal-Oral Route:

• Transmission commonly occurs through the consumption of contaminated food or water.
• Water-borne epidemics may arise due to heavy contamination of drinking water supplies.
• Raw vegetables, especially those irrigated with sewage-contaminated water, are a major source of infection.
• Viable cysts can also be present on unwashed hands and under fingernails, contributing to person-to-person transmission.

Direct Contact / Sexual Transmission:

• Transmission through oral-rectal contact is documented, particularly among men who have sex with men (MSM).

Mechanical Vectors:

• Flies, cockroaches, and rodents can carry infective cysts and contaminate food and beverages, aiding in the spread of infection.

7.0Prevention of Amoebiasis

(a) Sanitation

• Safe disposal of human excreta is crucial.
• Promoting handwashing after defecation and before eating is a key preventive measure.
• Addressing social and economic barriers to hygiene is essential.
• Community participation is vital in implementing effective sanitation practices.
• Sanitary systems must be appropriate to the local context and environment.

(b) Water Supply Protection

• Prevent faecal contamination of drinking water sources.
• E. histolytica cysts can survive for days or weeks in water.
• Chlorination alone (at normal levels) is not effective in killing cysts.
• Sand filtration can help remove cysts, but boiling and proper filtration are more reliable.

(c) Food Hygiene

• Protect food and drink from exposure to faeces and flies.
• Disinfect raw vegetables and fruits using: A 5–10% acetic acid solution, or Full-strength vinegar.
• Wash produce thoroughly under running water with detergents to remove cysts.
• Food handlers, being key transmitters, should be: Regularly screened, Treated if necessary and Educated in proper food hygiene and handwashing practices.

(d) Health Education

• Public education plays a long-term role in prevention.
• Informing communities about transmission routes, personal hygiene, and safe practices can significantly reduce the spread of amoebiasis.