Amoebiasis - Overview, Symptoms, causes

Edited By Irshad Anwar | Updated on Jul 02, 2025 05:18 PM IST

Entamoeba histolytica is a common protozoan parasite found in the large intestine of humans. It is acquired by faecal-oral transmission and can be sexually transmitted by oral-anal contact. Infection is commonly asymptomatic, but symptoms ranging from mild diarrhoea to severe dysentery may occur. The parasite is responsible for amoebiasis and liver abscesses. It is the third leading parasitic disease causing deaths in developing countries.

This Story also Contains

Life Cycle of Entamoeba Histolytica ( Amoebiasis)
Pathway of Amoebiasis in the Human Body
High-Risk Groups for Amoebiasis
Symptoms of Amoebiasis
Diagnosis of Amoebiasis
Prevention of Amoebiasis
Medications for Amoebiasis

Amoebiasis - Overview, Symptoms, causes

It is transmitted in areas where there is poor sanitation, which allows the contamination of drinking water and food with the stool of the people. It is most common in some of the Indian continents and also in parts of Central and South America. Amoebiasis is one of the important biology topics from the chapter Health and Diseases, CBSE class 12th.

Life Cycle of Entamoeba Histolytica ( Amoebiasis)

Entamoeba histolytica has a simple life cycle involving two main stages: the infectious cyst and the active trophozoite. Infection begins when cysts are ingested through contaminated food or water and excyst in the intestine, releasing trophozoites that invade tissues.

The life cycle of Entamoeba histolytica is quite simple and consists of the infective cyst and invasive trophozoite stages.
The life cycle is completed in a single host, i.e., human
Humans get infected with cysts of E. histolytica from contaminated food and water. Infection can also be acquired directly by anogenital or oro-genital sexual contact.
The mature cyst is resistant to the low pH of the stomach, so it remains unaffected by the gastric juices.
The cyst wall is then lysed by intestinal trypsin, and when the cyst reaches the caecum or lower part of the ileum, excystation occurs. The neutral or alkaline environment, along with the bile component, causes excystation.
Excystation of a cyst produces 8 trophozoites. Trophozoites are active and carried to the large intestine by the peristalsis of the small intestine. Trophozoites mature and divide by binary fission.
The trophozoites attach to the mucus lining of the intestine by lectin and secrete proteolytic enzymes, which cause tissue destruction and necrosis. When the parasite gets access to blood, it migrates and causes extra-intestinal diseases.
When the load of trophozoites increases, some of the trophozoites stop multiplying and revert to cyst form by the process of encystation.
These cysts are released in faeces, completing the life cycle.

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Pathway of Amoebiasis in the Human Body

After ingestion, cysts pass through the stomach and release trophozoites in the intestine, where they multiply and may invade the intestinal wall. In severe cases, they can enter the bloodstream and spread to the liver or other organs. This disease is generally caused by a protozoan named Entamoeba histolytica.

Pathways	Explanation
Mode of entry	Ingestion of Cysts happens through contaminated water and food. Majorly, it is due to direct contact with faecal matter.
The inactive form of the cysts	The cysts are capable of surviving in the soil or any harsh environment for months. This is because this parasite is in an inactive form.
Parasite activation	Cysts once enter the digestive system and release Trophozoites, the parasites are activated. Now, this active parasite usually reproduces inside the digestive tract and then migrates to the large intestine. Now these organisms burrow in the large intestine and cause the disease.
Transmission via food handlers	This is one of the most common ways of spreading the cysts of Entamoeba histolytica. The cysts spread while preparing food in unhygienic places.
Contaminated sources	The major sources of contamination are soil fertilisers and contaminated food with infected faeces.
Sexual transmission	A major possibility of transmission also happens when one is involved in activities like oral anal or anal sex with the infected person.

High-Risk Groups for Amoebiasis

People living in poor sanitary conditions, travellers to endemic areas, immunocompromised individuals, and institutionalised persons are at higher risk of developing amoebiasis. Amoebiasis is caused by several reasons, some of the major ones discussed below. There are certain conditions which allow the parasite to grow and spread the Amoebiasis disease.

People who come from areas that have poor sanitary conditions.
People who are living in developing areas lack clean water and proper sanitation infrastructure.
Healthcare workers who are exposed to infected patients or contaminated environments.
Food handlers who are in contact with contaminated food, especially in underdeveloped areas.
People engaged in oral-anal sexual practices with the infected person.
People who have weak immune systems and are prone to other diseases also have a high risk of Amoebiasis.

Symptoms of Amoebiasis

Common symptoms include abdominal pain, diarrhoea (which may be bloody), fever, fatigue, and weight loss. In severe cases, it may lead to liver abscesses and intestinal perforation. Symptoms of Amoebiasis are often confused with different diseases. Some of the major symptoms and their explanations are given below:

Symptoms	Explanation Of The Symptoms
Asymptotic Infection	This is the most common symptom among the patients. No visible symptoms in the infected person.
Acute Amoebiasis	Diarrhoea or dysentery with blood in the stools. The stools are more frequent than normal.
Chronic Amoebiasis	The symptoms include signs like pus in the stools, weight loss, fever and fatigue.
Intestinal Symptoms	Symptoms are generally visible after 1 to 4 weeks of ingestion of Cysts. Loose stools, Stomach Cramps, Abdominal pain, and bloating are some of the common signs.
Fulminant Colitis	Inflammation in the colon leads to abdominal pain, bloody diarrhoea and in the worst cases, perforation of the intestines.
Peritonitis	Major inflammation is seen in the abdominal lining due to intestinal perforation. This also causes severe abdominal pain, fever and in some cases, there is a possibility of life-threatening infection.
Liver Abscess	Continuous fever and pain in the upper right quadrant of the abdomen. There is also a sensation of tenderness in the region. Occurs only if the parasite has infected the liver, which leads to abscess formation.
Cardiac and Cerebral Symptoms	In rare cases, the parasite affects the heart or brain, which leads to serious complications. Often treated by surgery.
Respiratory symptoms	The parasite enters the main bloodstream and damages the lungs and heart. This also leads to difficulty in breathing.
Other complications	Amoebic ulcers are common when we talk about infection in the intestine. When the parasite affects the main bloodstream, it also leads to anaemia due to the blood loss. Continuous diarrhoea will push the body to a dehydrated state.

Diagnosis of Amoebiasis

Infection of Amoebiasis can occur in several parts of the body. This is the only reason why several tests and diagnosis methods are used to get accurate treatment. Some of the major ones are described below:

Diagnosis Methods	Diagnosis Explanation
Stool test	A stool sample is tested for the presence of E. histolytica The presence of the parasite confirms Amoebiasis.
Enzyme-linked Immunosorbent Assay ( ELISA)	There is a detection of the antigen for antibodies present in the stool. This confirms the Amoebiasis.
Enzyme Immunoassay (EIA)	There is testing for extra-intestinal Amoebiasis. This is not a stool-based test.
Indirect Hemagglutination (IHA)	Antibodies are detected in patients' blood. If the antibodies are absent, the test is repeated after 7 to 10 days for confirmation.
Radiography and ultrasonography	X-rays and ultrasound are used to identify liver abscesses or other organ involvement in the Amoebiasis infection.
Computer tomography ( CT)	There is detailed imaging of scans provided in the test, which helps to detect intestinal perforation, liver abscess and extra-intestinal infection involved. This also includes the scan of the brain and lungs.
Magnetic Resonance Imaging ( MRI)	This test is useful for detecting cerebral Amoebiasis and also the severity of damage caused due to liver abscess.
Liver function test	This is conducted when the liver abscess is confirmed. Abnormal activities of the liver confirm the presence of the parasite.
Colonoscopy and Biopsy	There is direct visualisation of perforation in the colon and tissue. This is detected through biopsy, which is performed to identify the ulcers caused by Amoebiasis.
Chest X-Ray	A process is used in pulmonary complications which is suspected during other tests. This is a rare case of Amoebiasis and is spread throughout the lungs.

Prevention of Amoebiasis

There is no certain way through which you can completely avoid Amoebiasis. But there are certain measures which you can take to prevent Amoebiasis. Some of these are mentioned below:

Access to safe and clean drinking water.
Hands must be washed regularly with soap and water.
Avoid consuming food from unhygienic places.
Avoid eating foods which are unwashed and produced raw.
Use proper sanitation facilities.
Dispose of the sewage properly to prevent contamination.

Medications for Amoebiasis

Amoebiasis is normally treated with a combination of different medicines at the same time. It is generally advised to visit a doctor to eradicate the parasite from your intestine and also other infected tissues and organs. Some of the commonly used medications are mentioned below:

Metronidazole or Tinidazole: Generally used to kill the E. histolytica present in the intestine and other tissues.
Paromomycin: One of the luminal agents which is used to eradicate parasites from the intestine.
Diloxanide Furoate: Another luminal agent which is used for eliminating cyst carriers.
Dehydroemetine: Used in severe cases of extraintestinal Amoebiasis and especially in the case of liver Abscess.
Chloroquine: Used in combination with other drugs to treat Liver Abscess

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Frequently Asked Questions (FAQs)

1. What is another name for Amoebiasis?

Amoebic dysentery is the other name for amoebiasis.

2. What is the prevention for Amoebiasis?

The water should be cleaned not by chlorine treatment but by boiling. The food should be cooked with proper safety. Safe disposal of excreta should be done.

3. What are the three major symptoms of Amoebiasis?

The three major symptoms of Amoebiasis are diarrhoea ( bloody), abdominal pain and fatigue.

4. What is Luminal amoebiasis?

Luminal amoebiasis is defined as a disease in which no clinical symptoms and signs of a disease are apparent.

5. What is the main cause of the spread of amoebiasis?

Contaminated water is main cause of amoebic dysentery.

6. What is the treatment for Amoebiasis?

The most common treatment for Amoebiasis is medications which involve medicines like Metronidazole or Tinidazole, this is followed by luminal agents like Paromomycin that help in eliminating the cyst.

7. How is amoebiasis diagnosed?

Amoebiasis is typically diagnosed through microscopic examination of stool samples to detect cysts or trophozoites. More advanced methods include antigen detection tests, PCR to identify parasite DNA, and serological tests to detect antibodies against Entamoeba histolytica.

8. Why is it important to distinguish Entamoeba histolytica from other Entamoeba species?

It's crucial to distinguish Entamoeba histolytica from non-pathogenic species like Entamoeba dispar because they look identical under a microscope but have very different clinical implications. Only E. histolytica causes disease, so accurate identification is essential for proper treatment and to avoid unnecessary medication.

9. Can a person have amoebiasis without showing symptoms?

Yes, many people infected with Entamoeba histolytica are asymptomatic carriers. They harbor the parasite without experiencing any symptoms but can still spread the infection to others through their feces, which contain infectious cysts.

10. What is the relationship between amoebiasis and inflammatory bowel disease (IBD)?

The relationship between amoebiasis and IBD is complex. Chronic amoebiasis can mimic the symptoms of IBD, leading to misdiagnosis. Additionally, some research suggests that past E. histolytica infection may increase the risk of developing IBD by altering gut immune responses and microbiome composition. Conversely, IBD patients may be more susceptible to severe amoebiasis due to their compromised intestinal barrier.

11. What are the potential applications of CRISPR technology in studying and treating amoebiasis?

CRISPR technology offers exciting possibilities for amoebiasis research and treatment. It can be used to create genetically modified E. histolytica strains to study gene function and virulence factors. In the future, CRISPR might be applied to develop new diagnostic tools or even therapeutic approaches targeting specific parasite genes.

12. What is the difference between a trophozoite and a cyst in the life cycle of Entamoeba histolytica?

Trophozoites are the active, feeding stage of Entamoeba histolytica that can cause tissue damage in the intestine. Cysts are the dormant, infectious stage that can survive outside the body and are responsible for transmission. Trophozoites transform into cysts when conditions become unfavorable, allowing the parasite to spread to new hosts.

13. What is the significance of the cyst stage in the transmission of amoebiasis?

The cyst stage is crucial for the transmission of amoebiasis because cysts can survive harsh environmental conditions, including chlorination of water. They remain viable outside the human body for weeks to months, allowing for widespread dissemination through contaminated food, water, or fomites.

14. What factors contribute to the virulence of Entamoeba histolytica?

The virulence of E. histolytica is influenced by several factors, including its ability to adhere to intestinal cells, secrete enzymes that break down tissue, resist the host's immune response, and form cysts that can survive harsh environmental conditions. Genetic variations in the parasite can also affect its virulence.

15. How does Entamoeba histolytica adapt to different environments in the human body?

E. histolytica adapts to different environments by altering its gene expression and metabolism. In the oxygen-poor environment of the large intestine, it relies on anaerobic metabolism. When invading tissues, it can tolerate higher oxygen levels and express genes for tissue destruction and immune evasion.

16. How does Entamoeba histolytica evade the complement system?

E. histolytica evades the complement system through multiple mechanisms. It can degrade complement proteins, express surface molecules that inhibit complement activation, and rapidly internalize and degrade surface-bound complement components. This evasion is crucial for the parasite's survival in the host.

17. What are the main treatment options for amoebiasis?

The main treatment for amoebiasis involves antiparasitic drugs like metronidazole or tinidazole to kill the trophozoites, followed by a luminal agent like paromomycin to eliminate cysts from the intestine. In severe cases, supportive care such as fluid replacement and pain management may be necessary.

18. Why is it important to complete the full course of treatment for amoebiasis?

Completing the full course of treatment is crucial to ensure all parasites are eliminated, including cysts in the intestine. Incomplete treatment can lead to recurrence of the infection and potentially contribute to drug resistance in the parasite population.

19. What is the role of zinc in the pathogenesis and treatment of amoebiasis?

Zinc plays a complex role in amoebiasis. It is essential for the immune system's function and can help reduce the severity and duration of diarrheal diseases. However, E. histolytica also requires zinc for its own survival and virulence. Understanding this balance is important for developing effective nutritional interventions for amoebiasis.

20. How does the genetic diversity of Entamoeba histolytica impact its virulence and drug resistance?

Genetic diversity in E. histolytica populations can lead to variations in virulence factors, host cell adherence, and tissue invasion capabilities. This diversity also influences the parasite's susceptibility to drugs, potentially contributing to treatment failures and the emergence of drug-resistant strains.

21. What is the role of nitric oxide in the host defense against amoebiasis?

Nitric oxide is an important component of the host's innate immune response against E. histolytica. It has direct amoebicidal effects and modulates inflammation. However, E. histolytica has developed mechanisms to detoxify nitric oxide, highlighting the ongoing evolutionary arms race between host and parasite.

22. How does Entamoeba histolytica enter the human body?

Entamoeba histolytica enters the human body through ingestion of contaminated food or water containing cysts of the parasite. These cysts are resistant to stomach acid and can survive passage through the digestive system to reach the large intestine, where they develop into active trophozoites.

23. How does Entamoeba histolytica cause tissue damage in the intestine?

Entamoeba histolytica trophozoites secrete enzymes that break down the intestinal lining, allowing them to invade the tissue. They also release toxins that cause inflammation and cell death. This process leads to the formation of characteristic flask-shaped ulcers in the intestinal wall.

24. What is amoebic liver abscess, and how is it related to intestinal amoebiasis?

Amoebic liver abscess is a serious complication of amoebiasis where Entamoeba histolytica trophozoites migrate from the intestine to the liver through the bloodstream. They form pockets of infection in the liver tissue, leading to abscesses that can cause severe pain and potentially life-threatening complications if left untreated.

25. How does amoebiasis impact the intestinal barrier function?

Amoebiasis significantly impacts intestinal barrier function. E. histolytica degrades mucus layers, disrupts tight junctions between epithelial cells, and induces apoptosis in host cells. This breakdown of the intestinal barrier can lead to increased permeability, allowing for bacterial translocation and potentially systemic infection.

26. How does amoebiasis affect the gut microbiome, and vice versa?

Amoebiasis can disrupt the normal gut microbiome by altering the intestinal environment and competing with commensal organisms. Conversely, the composition of the gut microbiome can influence susceptibility to E. histolytica infection and the severity of symptoms. This complex interaction is an active area of research in understanding and treating amoebiasis.

27. Why is amoebiasis more common in developing countries?

Amoebiasis is more prevalent in developing countries due to factors such as poor sanitation, lack of clean water, overcrowding, and inadequate healthcare systems. These conditions facilitate the spread of Entamoeba histolytica cysts through contaminated food and water sources.

28. What is the role of diet in preventing amoebiasis?

Diet plays a crucial role in preventing amoebiasis by avoiding contaminated food and water. Proper food handling, washing fruits and vegetables thoroughly, and drinking clean, boiled, or treated water can significantly reduce the risk of ingesting E. histolytica cysts.

29. How does personal hygiene contribute to preventing the spread of amoebiasis?

Personal hygiene, particularly handwashing with soap and water after using the toilet and before handling food, is essential in preventing the spread of amoebiasis. It helps break the fecal-oral transmission cycle by removing potential cysts from hands that could contaminate food or water.

30. How does urbanization affect the prevalence of amoebiasis?

Urbanization can both increase and decrease the prevalence of amoebiasis. In rapidly growing urban areas with poor infrastructure, overcrowding and inadequate sanitation can increase transmission. However, improved access to clean water and healthcare in developed urban areas can reduce prevalence.

31. What is the global economic impact of amoebiasis?

The global economic impact of amoebiasis is significant, particularly in developing countries. It includes direct healthcare costs, lost productivity due to illness, and the broader economic effects of reduced educational attainment and workforce participation in endemic areas.

32. What are the main symptoms of amoebiasis?

The main symptoms of amoebiasis include abdominal pain, cramping, watery or bloody diarrhea, fever, and weight loss. In severe cases, it can lead to dysentery with frequent, bloody stools and intense abdominal pain.

33. How does amoebiasis differ in its presentation between children and adults?

Amoebiasis often presents differently in children and adults. Children are more likely to experience severe symptoms like dysentery and are at higher risk for malnutrition and growth stunting. Adults may have more chronic or asymptomatic infections, but are at greater risk for extraintestinal complications like liver abscesses.

34. How does chronic amoebiasis contribute to intestinal dysbiosis?

Chronic amoebiasis can lead to intestinal dysbiosis by disrupting the normal balance of gut microbiota. The persistent inflammation, altered intestinal motility, and changes in the intestinal environment caused by E. histolytica can favor the growth of certain bacterial species while suppressing others, potentially leading to long-term changes in gut health.

35. How does amoebiasis affect children's cognitive development and school performance?

Chronic amoebiasis in children can impact cognitive development and school performance through multiple mechanisms. Malnutrition resulting from impaired nutrient absorption can affect brain development. Chronic inflammation may influence cognitive processes, and frequent illness can lead to school absenteeism, collectively impacting educational outcomes.

36. What is the role of iron in Entamoeba histolytica virulence?

Iron plays a critical role in E. histolytica virulence. The parasite requires iron for growth and expression of virulence factors. It has evolved sophisticated mechanisms to acquire iron from the host, including the ability to lyse red blood cells and utilize host iron-binding proteins. Understanding iron metabolism in E. histolytica could lead to new therapeutic strategies.

37. What is the role of autophagy in Entamoeba histolytica survival and virulence?

Autophagy plays a crucial role in E. histolytica survival and virulence. It helps the parasite adapt to stress conditions, recycle cellular components for energy, and eliminate damaged organelles. Autophagy also contributes to the parasite's ability to evade host immune responses and may be involved in the regulation of virulence factor expression.

38. How does climate change potentially affect the geographical distribution of amoebiasis?

Climate change could alter the geographical distribution of amoebiasis by changing temperature and precipitation patterns. Warmer temperatures might extend the range of E. histolytica into previously unsuitable areas. Changes in rainfall could affect water availability and quality, potentially increasing transmission in some regions while decreasing it in others.

39. How does Entamoeba histolytica interact with the gut-associated lymphoid tissue (GALT)?

E. histolytica inter

40. What are the challenges in diagnosing amoebiasis in resource-limited settings?

Diagnosing amoebiasis in resource-limited settings is challenging due to the lack of advanced laboratory facilities. Microscopy, while widely available, cannot distinguish between pathogenic E. histolytica and non-pathogenic species. Limited access to serological or molecular tests can lead to misdiagnosis or underdiagnosis, complicating treatment and control efforts.

41. How does amoebiasis interact with other intestinal parasites or pathogens?

Amoebiasis can interact with other intestinal parasites or pathogens in various ways. Co-infections may exacerbate symptoms, complicate diagnosis, or alter the effectiveness of treatments. Some interactions may be synergistic, increasing overall pathogenicity, while others might be competitive, potentially reducing the severity of individual infections.

42. What are the environmental factors that influence the survival of Entamoeba histolytica cysts?

Environmental factors affecting E. histolytica cyst survival include temperature, humidity, pH, and exposure to sunlight. Cysts can survive for weeks in moist, cool environments but are quickly destroyed by desiccation or high temperatures. They are also resistant to many common water treatment methods, complicating control efforts.

43. What role do commensal bacteria in the gut play in amoebiasis?

Commensal bacteria in the gut can influence amoebiasis in several ways. Some bacteria may compete with E. histolytica for resources or produce substances that inhibit its growth. Conversely, certain bacteria might provide nutrients or create conditions that favor the parasite's survival and virulence.

44. How does amoebiasis affect pregnancy and fetal development?

Amoebiasis during pregnancy can lead to complications such as severe anemia, preterm labor, and low birth weight. The infection may also increase the risk of vertical transmission to the fetus. Treating amoebiasis in pregnant women requires careful consideration of drug safety and potential impacts on fetal development.

45. What are the challenges in developing a vaccine against amoebiasis?

Developing a vaccine against amoebiasis is challenging due to the complex life cycle of E. histolytica, its ability to evade the immune system, and the lack of a suitable animal model for testing. Additionally, the parasite's antigenic variation and the incomplete understanding of protective immune responses complicate vaccine development.

46. How does the immune system respond to Entamoeba histolytica infection?

The immune system responds to E. histolytica infection by producing antibodies and activating immune cells like neutrophils and macrophages. However, the parasite has evolved mechanisms to evade or suppress the immune response, such as degrading antibodies and inducing apoptosis in immune cells.

47. How does climate change potentially impact the spread of amoebiasis?

Climate change can potentially increase the spread of amoebiasis by altering rainfall patterns, causing floods or droughts that affect water quality and sanitation. Warmer temperatures may also extend the geographical range of the parasite and increase its survival in the environment.

48. How does amoebiasis affect nutrient absorption in the intestine?

Amoebiasis can impair nutrient absorption by damaging the intestinal lining, reducing the surface area available for absorption. Inflammation and increased intestinal motility associated with the infection can also interfere with normal digestive processes, leading to malnutrition and weight loss.

49. What are the potential long-term consequences of untreated amoebiasis?

Untreated amoebiasis can lead to chronic intestinal inflammation, malnutrition, and anemia. In severe cases, it can cause peritonitis, toxic megacolon, or extraintestinal infections like liver abscesses. Long-term infection may also increase the risk of developing inflammatory bowel disease or colon cancer.

50. What is amoebiasis and how does it differ from other intestinal infections?

Amoebiasis is an intestinal infection caused by the protozoan parasite Entamoeba histolytica. Unlike bacterial or viral infections, amoebiasis is caused by a single-celled organism that can exist in both trophozoite and cyst forms. It primarily affects the large intestine and can cause symptoms ranging from mild diarrhea to severe dysentery.

51. What is the potential for using probiotics in the prevention or treatment of amoebiasis?

Probiotics show promise in both preventing and treating amoebiasis. Certain probiotic strains may help maintain a healthy gut microbiome, enhance the intestinal barrier function, and modulate the immune response against E. histolytica. Some studies suggest that specific probiotics could even have direct anti-amoebic effects, though more research is needed to establish their efficacy.