Entamoeba Histolytica: A Comprehensive Guide to Amebiasis

25.12.202209.06.2023 by alexxlab

What is Entamoeba histolytica. How is it transmitted. What are the symptoms of amebiasis. How is amebiasis diagnosed. What are the treatment options for Entamoeba histolytica infection. Can amebiasis be prevented. What are the complications of untreated amebiasis.

Содержание

Understanding Entamoeba Histolytica: The Causative Agent of Amebiasis

Entamoeba histolytica is a protozoan parasite responsible for causing amebiasis, a potentially serious intestinal infection. This microscopic organism exists in two forms: the hardy cyst form, which can survive in the environment for extended periods, and the active trophozoite form, which invades and damages the intestinal lining.

The impact of E. histolytica on global health is significant. While 90% of infections remain asymptomatic, approximately 50 million people worldwide develop symptomatic amebiasis annually, resulting in an estimated 100,000 deaths. This makes E. histolytica the third leading cause of death from parasitic infections globally.

How is Entamoeba histolytica transmitted?

E. histolytica is primarily transmitted through the fecal-oral route. This occurs when individuals ingest food or water contaminated with E. histolytica cysts. Poor sanitation, inadequate hygiene practices, and contaminated water sources contribute to the spread of this parasite, particularly in areas with limited access to clean water and proper sanitation facilities.

The Global Epidemiology of Amebiasis

Amebiasis is a worldwide health concern, with a disproportionate impact on regions with lower socioeconomic conditions and inadequate public health infrastructure. Countries such as India, various African nations, Mexico, and parts of Central and South America report higher prevalence rates of E. histolytica infection.

For instance, a three-year study conducted in Bangladesh revealed that 2.2% of dysentery cases in preschool children were attributed to E. histolytica. In rural areas of Mexico, the seroprevalence of E. histolytica has been reported to be as high as 42%.

Who is at risk for Entamoeba histolytica infection?

Residents of endemic areas with poor sanitation
Travelers to regions with high prevalence rates
Immigrants from endemic areas
Individuals with compromised immune systems
Men who have sex with men (due to potential fecal-oral transmission during sexual activities)

In developed countries like the United States, amebiasis is relatively rare, accounting for approximately 5 deaths per year. Cases in these regions are typically associated with individuals who have traveled to or immigrated from endemic areas.

The Pathophysiology of Entamoeba Histolytica Infection

The pathogenesis of E. histolytica infection is a complex process involving the interaction between the parasite and the host’s immune system. When an individual ingests E. histolytica cysts, they transform into trophozoites in the intestinal lumen. These trophozoites can then invade and penetrate the intestinal mucosa, leading to tissue destruction and inflammation.

How does Entamoeba histolytica cause damage to the intestinal lining?

The trophozoites adhere to colonic epithelial cells using a specific galactose-N-acetylgalactosamine lectin. This adherence initiates a cascade of events:

Direct cell damage: Trophozoites cause cytolysis and apoptosis of epithelial cells.
Inflammatory response: Damaged cells release interleukin-1α and precursor interleukin-1β.
Cytokine production: IL-1β activates NF-κB, leading to the production of additional inflammatory mediators.
Neutrophil and macrophage attraction: These immune cells are drawn to the site of infection.
Amplification of damage: Neutrophils damaged by trophozoites cause further harm to colonic epithelial cells.
Ongoing inflammation: Macrophages release TNFα and other mediators, perpetuating the inflammatory process.

Clinical Manifestations of Amebiasis

Amebiasis can present with a wide spectrum of clinical manifestations, ranging from asymptomatic colonization to severe, life-threatening disease. The most common form of symptomatic amebiasis is amoebic colitis, which typically develops 2-4 weeks after ingestion of E. histolytica cysts.

What are the symptoms of amoebic colitis?

Patients with amoebic colitis may experience:

Abdominal pain and cramping
Bloody diarrhea
Tenesmus (a feeling of incomplete evacuation)
Weight loss
Fever (in severe cases)

In some cases, E. histolytica can spread beyond the intestinal tract, leading to extraintestinal amebiasis. The most common form of extraintestinal disease is amoebic liver abscess, which typically presents with right upper quadrant pain, fever, and hepatomegaly.

Diagnostic Approaches for Entamoeba Histolytica Infection

Accurate diagnosis of E. histolytica infection is crucial for appropriate management and to differentiate it from other causes of diarrhea or liver abscesses. Several diagnostic methods are available, each with its own advantages and limitations.

How is amebiasis diagnosed?

The following diagnostic approaches may be used:

Microscopic examination of stool samples: This can detect cysts or trophozoites but requires expertise and may not differentiate between pathogenic E. histolytica and non-pathogenic species.
Antigen detection tests: Enzyme immunoassays (EIA) can detect E. histolytica-specific antigens in stool samples with high sensitivity and specificity.
Serology: Antibody detection tests are useful for diagnosing extraintestinal amebiasis but may remain positive for years after infection.
PCR: Molecular methods can detect E. histolytica DNA in stool samples or tissue specimens with high sensitivity and specificity.
Imaging studies: Ultrasonography, CT, or MRI can be helpful in diagnosing amoebic liver abscesses.

Treatment Strategies for Amebiasis

The treatment of amebiasis depends on the clinical presentation and the severity of the infection. A combination of drugs is often used to eradicate both intestinal and tissue infections.

What are the treatment options for Entamoeba histolytica infection?

The standard treatment regimen typically includes:

Metronidazole or tinidazole: These are the drugs of choice for treating invasive amebiasis, including amoebic colitis and liver abscess.
Paromomycin or diloxanide furoate: These luminal agents are used to eradicate intestinal cyst carriage after treatment with metronidazole or tinidazole.
Supportive care: This may include fluid and electrolyte replacement, particularly in cases of severe diarrhea.

In cases of amoebic liver abscess, percutaneous drainage may be necessary if there is no response to medical therapy or if there is a risk of rupture.

Prevention and Control of Entamoeba Histolytica Transmission

Preventing the spread of E. histolytica is crucial for reducing the global burden of amebiasis. Public health measures and individual actions can significantly impact transmission rates.

Can amebiasis be prevented?

Yes, several preventive measures can reduce the risk of E. histolytica infection:

Improved sanitation: Proper disposal of human waste and access to clean toilets.
Safe water supply: Treatment and protection of water sources to prevent contamination.
Personal hygiene: Regular handwashing, especially before handling food and after using the toilet.
Food safety: Washing fruits and vegetables thoroughly, avoiding raw or undercooked foods in endemic areas.
Education: Raising awareness about transmission routes and prevention strategies.
Travel precautions: Taking care with food and water consumption when visiting endemic areas.

Complications and Long-term Consequences of Amebiasis

While many cases of amebiasis resolve without significant complications, severe or untreated infections can lead to serious health consequences.

What are the potential complications of untreated amebiasis?

Untreated E. histolytica infection may result in:

Fulminant colitis: A severe form of amoebic colitis that can lead to colon perforation and peritonitis.
Toxic megacolon: Extreme dilatation of the colon, which can be life-threatening.
Liver abscess rupture: This can lead to peritonitis or, if the abscess ruptures into the pleural cavity, empyema.
Brain abscess: A rare but severe complication of disseminated amebiasis.
Chronic post-infectious irritable bowel syndrome: Some patients may develop long-term gastrointestinal symptoms after acute amebiasis.

Early diagnosis and appropriate treatment are essential to prevent these potentially life-threatening complications.

Future Directions in Amebiasis Research and Management

As E. histolytica continues to pose a significant global health challenge, ongoing research is crucial for improving our understanding of the parasite and developing more effective strategies for prevention and treatment.

What are the current areas of focus in amebiasis research?

Current research efforts are concentrating on:

Vaccine development: Creating an effective vaccine against E. histolytica could significantly reduce disease burden in endemic areas.
New drug targets: Identifying novel therapeutic targets to overcome potential drug resistance and improve treatment efficacy.
Rapid diagnostic tools: Developing point-of-care tests for quick and accurate diagnosis, especially in resource-limited settings.
Host-parasite interactions: Understanding the molecular mechanisms of pathogenesis to identify new intervention strategies.
Epidemiological studies: Conducting large-scale studies to better understand transmission patterns and risk factors in different populations.

These research directions hold promise for improving the prevention, diagnosis, and treatment of amebiasis, ultimately reducing its global impact on human health.

Entamoeba histolytica Infection – StatPearls

Continuing Education Activity

Entamoeba histolytica is a protozoan that causes intestinal amebiasis as well as extra-intestinal manifestations. Although 90 percent of E. histolytica infections are asymptomatic, nearly 50 million people become symptomatic, with about 100,000 deaths yearly. This activity reviews the evaluation and treatment of amebiasis caused by Entamoeba histolytica and highlights the role of the interprofessional team in evaluating and treating patients with this condition.

Objectives:

Identify the etiology of Entamoeba histolytica medical conditions and emergencies.
Describe components of evaluation in the work-up for Entamoeba histolytica.
Summarize the management options available for Entamoeba histolytica.
Outline interprofessional team strategies for improving care coordination and communication to advance Entamoeba histolytica and improve outcomes.

Access free multiple choice questions on this topic.

Introduction

Entamoeba histolytica is a protozoan that causes intestinal amebiasis as well as extraintestinal manifestations. Although 90 percent of E. histolytica infections are asymptomatic, nearly 50 million people become symptomatic, with about 100,000 deaths yearly.[1] Amebic infections are more prevalent in countries with lower socioeconomic conditions.[2]

Etiology

Entamoeba histolytica is transmitted by the ingestion of amebic cysts through fecal-oral contact, usually through contaminated food or water sources.[3][4]

Epidemiology

Entamoeba histolytica continues to be an important global health issue being the third leading cause of death from parasitic infections.[5] Although 90 percent of E. histolytica infections are asymptomatic, nearly 50 million people become symptomatic, with up to 100,000 deaths yearly.[6] Those infected by Entamoeba are mostly colonized by either E. histolytica or E. dispar. E. histolytica is the pathogenic form and can cause amoebic colitis and extraintestinal amoebiasis. E. dispar is considered to be nonpathogenic and causes no signs of disease.[2]

Infection occurs worldwide, with a higher prevalence in countries of low socioeconomic status and poor public health. Countries with a high rate of infections include India, Africa, Mexico, and Central and South America. For example, a three-year study conducted in Bangladesh showed that 2.2% of dysentery cases were caused by E. histolytica in preschool children.[7] In rural areas of Mexico, the seroprevalence of E. histolytica has been reported as high as 42%.[8] Risk factors for infection are mostly related to fecal-oral transmission and have been due to poor hand hygiene, defecation into water sources such as rivers, and being in close proximity with animals. In developed countries such as the United States, amebiasis infections are rare, accounting for at least 5 deaths per year, and are commonly seen in individuals that have had exposure to endemic areas such as immigrants or recent travelers. [8]

Amoebic colitis generally affects males and females of all ages equally. There are reports of increased risk of infection from gay or bisexual males due to the risk of fecal-oral contamination through oral and anal sex.[2] Factors that are associated with increased risk for complicated infection and mortality are associated with the following: pregnancy, corticosteroid treatment, malignancy, malnutrition, and alcoholism. Amoebic liver abscess infections are at least 3 times more likely to affect middle-aged men between the ages of 18 and 50.[2]

Pathophysiology

There are two forms E. histolytica can take: the cyst form, which can survive in the environment for a prolonged period, and the trophozoite stage, which is the active and invasive form. After the ingestion of the cyst form, trophozoites can be formed, which can invade and penetrate intestinal mucosa destroying epithelial cells and inflammatory cells.

The pathogenesis of infection by trophozoites is due to the adherence of colonic epithelial cells through a specific galactose-N-acetylgalactosamine lectin. [2] Through the direct adherence of trophozoites to the colonic epithelial cells, the colonic epithelial cells die off through cytolysis and apoptosis, which results in the release of interleukin-1α and precursor interleukin-1β. IL-1β activates NF-κB in distal cells to produce cytokines and other inflammatory mediators such as COX-2, interleukin-1, and interleukin-8. Amoebic cysteine proteinases can also convert precursor IL-1β to active IL-1β, which can further facilitate the process. These cytokines and inflammatory mediators subsequently attract neutrophils and macrophages. Neutrophils can be damaged by direct contact with trophozoites which can cause more damage to colonic epithelial cells resulting in the release of more mediators. Macrophages release other mediators as well, such as TNFα, which further contributes to inflammation.

The pathological range includes mucosal inflammation, thickening, ulcers, and necrosis, leading to perforation. Amoebic cysteine proteinases can also contribute to trophozoites’ ability to suppress a host’s immune response by being able to cleave and inactivate anaphylatoxins C3a, C5a, IgA, and IgG. [2] Trophozoites can reach other areas of the body, most commonly the liver, which can cause tissue necrosis and abscess formation.[7]

History and Physical

The majority of E. histolytica infections are asymptomatic; however, up to 10% of asymptomatic individuals infected can develop the disease over time.[8] E. histolytica most commonly causes intestinal amoebiasis but can also affect the liver, respiratory tract, heart, and brain.

Gastrointestinal: Symptoms typically have a gradual onset, usually over one to three weeks. Common symptoms include diarrhea, bloody stools, weight loss, and abdominal pain.[2]

Liver: Amoebic liver abscess formation is the most common extraintestinal complication. It can be seen in months to years after an individual has had exposure to an endemic area. Symptoms include fever and right upper quadrant pain. Exam findings may include hepatomegaly with hepatic tenderness. Less than 10 percent of patients have jaundice. Common laboratory findings include leukocytosis without eosinophilia, elevated alkaline phosphatase, transaminitis, and elevated erythrocyte sedimentation rate.

Respiratory tract: Pleuropulmonary involvement is a rare complication that causes atelectasis and transudative pleural effusions. In rare cases, an amoebic liver abscess can rupture into the pleural space causing empyema or hepato-bronchial fistula causing fevers, coughing, and respiratory distress.[2]

Cardiac infection: Cardiac infection is an even less common complication than pleuropulmonary disease and occurs with a liver abscess ruptures into the pericardium and presents with symptoms of pericarditis or cardiac tamponade.

Brain infection: Amoebic brain abscesses are very rare with sudden onset symptoms such as headache, vomiting, and mental status changes with rapid progression to death.[2]

Evaluation

Historically amoebic infections were diagnosed by microscopy with the identification of trophozoites; however, this method was unable to distinguish between E. histolytica and E. dispar infections. Now, there are many tools used for diagnosis with stool polymerase chain reaction (PCR) having the highest sensitivity in distinguishing E. histolytica from E. dispar. Other diagnostic modalities available include stool microscopy, stool antigen detection, serology, stool molecular studies, and colonoscopy with a histologic examination.[2]

Stool microscopy: This diagnostic method is advantageous, being widely available with minimal equipment needed and can be used to screen for other parasites. Disadvantages include poor sensitivity, reported at <60%, with the inability to differentiate from other Entamoeba species and relies on the experience or skills of the observer.[8][9]

Stool antigen detection: This method is simple with a quick turnaround time and has the advantage of being able to differentiate between E. histolytica and E. dispar. There are a wide number of commercially available antigen detection kits using enzyme-linked immunosorbent assay (ELISA), radioimmunoassay, or immunofluorescence that have varying sensitivities of up to 88%. [10][8][9]

Serology: Has high sensitivity and specificity with quick turnaround time but is not helpful in distinguishing between an acute or previous infection. Antibodies are not detectable in an active infection until at least a week into the infection and will remain detectable in individuals for years.

Stool molecular studies: Considered to be the gold standard with high sensitivity of 92% to 100% and specificity of 89% to 100%. Testing is becoming more widely available but is considered to be more expensive, requiring appropriate equipment and kits and requiring a skilled technician.

Colonoscopy with histologic examination: Not used for routine diagnosis but can be used to look for other causes of symptoms. Used to look for characteristic findings of amebic ulcers or erosions with the identification of trophozoites or cysts with biopsy specimens.[8]

Treatment / Management

Due to the risk of spread and the risk of developing extraintestinal manifestations, all E. histolytica infections need to be treated.

Metronidazole is the first-line treatment for intestinal amebiasis and amebic liver abscess followed by a luminal agent. Typical dosing for metronidazole is 500 to 750 mg orally 3 times a day for 7 to 10 days in adults.[2] Metronidazole can be safely used in children at a dosing of 35 mg/kg to 50 mg/kg per day divided into three doses.[2] Luminal agents include the following: paromomycin, diiodohydroxyquin, or diloxanide furoate. Dosing for paromomycin is 25 mg/kg to 30 mg/kg per day divided into three doses for 7 days, diiodohydroxyquin is 650 mg orally for 20 days, diloxanide furoate is 500 mg orally three times a day for 10 days.[2]

Alternatives to metronidazole include tinidazole, ornidazole, and nitazoaxanide.

In patients with fulminant amoebic colitis or signs of peritonitis, broad-spectrum antibiotics should be started. Surgical intervention may be required with bowel perforation or toxic megacolon.

In uncomplicated cases of amebic liver abscess, it has been shown that there is no benefit to drainage in addition to medical therapy. [11] In situations where there is a lack of clinical response to antibiotic therapy, aspiration or catheter drainage may be necessary.[2]

Pleuropulmonary infections should be treated by aspiration of amebic pleural effusion followed by antimicrobial therapy such as metronidazole with a luminal agent.[12]

Differential Diagnosis

The differential diagnosis for E. histolytica intestinal amebiasis includes:

Bacterial pathogens: Shigella, Escherichia coli, Salmonella, Campylobacter, and Clostridioides difficile
Inflammatory bowel disease
Ischemic bowel disease

The differential diagnosis for E. histolytica extraintestinal amebiasis includes:

Pyogenic liver abscess
Echinococcal disease
Malignancy

Prognosis

Uncomplicated infections and early treatment have a mortality rate of less than 1 percent. Risk factors for complicated infections and increased mortality include the following:[13]

Fulminant amoebic colitis is associated with 40% mortality. [13] Amebic liver abscess with prompt medical treatment has been highly effective, with mortality rates between 1 and 3 percent.[2] Pleuropulmonary amebiasis is associated with mortality up to 16%, while cardiac involvement has a mortality of up to 30%.[14]

Complications

Complications of E. histolytica infection can involve any of the following:[2]

Asymptomatic infection
Symptomatic noninvasive infection
Acute proctocolitis
Fulminant amoebic colitis with perforation
Toxic megacolon
Chronic non-dysenteric colitis

Extraintestinal conditions resulting from E. histolytica infection include the following:[2][15][16]

Liver abscess
Pleuropulmonary disease
Brain abscess
Peritonitis
Pericarditis
Genitourinary disease
Perianal cutaneous amebiasis
Hepatic vein thrombosis
Inferior vena cava thrombosis
Ameboma
Appendicitis

Deterrence and Patient Education

You can reduce your chances of getting bacterial and parasitic infections such as E. histolytica by watching what you eat and proper hand hygiene. If a person is traveling outside of the United States, they need to be sure to do the following:

Avoid drinking tap water. Drink bottled beverages and brush your teeth with bottled water. Avoid ice in drinks as they are commonly made from tap water.
Avoid eating raw fruits and vegetables cleaned with tap water.
Eat well-cooked food when traveling, avoiding undercooked fish or meats.
Avoid eating street vendors in carts or stands.
Frequently wash hands after using the restroom, touching animals, before eating, or handling trash.

A patient should see a clinician if you have any of the following symptoms with any recent travel out of the country if:

They have a fever of 102 degrees F (40 degrees C) or higher.
They have severe abdominal pain.
They have bloody diarrhea.
They have been sick for longer than two weeks.

Enhancing Healthcare Team Outcomes

Amebiasis is a relatively common parasitic infection worldwide. Occurring much more commonly in endemic areas of poor socioeconomic status. An important component of prevention is patient education through interprofessional communication. Physicians, nurse practitioners, nurses, and pharmacists should educate patients if they are traveling to endemic areas in the world on common steps they can take to reduce their chance of contracting amebiasis. Specifically, they should educate patients to avoid consumption of tap water and avoid raw fruits and vegetables that have been cleaned with tap water. Patients should be encouraged to contact their healthcare provider if they have symptoms of diarrhea and blood stools after traveling to an endemic area. Open communication, especially in obtaining a good history, will be critical in early diagnosis and treatment. Following treatment, the prognosis has been proven to be favorable.[17]

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References

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: Disclosure: Arthur Chou declares no relevant financial relationships with ineligible companies.
: Disclosure: Richard Austin declares no relevant financial relationships with ineligible companies.