Continuing Education Activity

Amebiasis or amoebic dysentery is a parasitic intestinal infection caused by any of the amoebas of the Entamoeba group. It may be asymptomatic or present with abdominal pain, diarrhea, or dysentery. This activity reviews the evaluation and management of amebiasis and explains the interprofessional team's role in improving care for patients with this condition.

Objectives:

• Identify the role of the protozoa Entamoeba histolytica in the etiology of amebiasis.
• Outline the pathophysiology of amebiasis.
• Describe the use of stool microscopy in the evaluation of amebiasis.
• Review the importance of collaboration and communication among the interprofessional team to improve patients' outcomes affected by amebiasis.

Introduction

Amebiasis or amoebic dysentery is a common parasitic enteral infection. It is caused by any of the amoebas of the Entamoeba group. Amoebiasis may present with no symptoms or mild to severe symptoms, including abdominal pain, diarrhea, or bloody diarrhea. Severe complications may include inflammation and perforation, resulting in peritonitis. People affected may develop anemia.[1][2][3]

If the parasite reaches the bloodstream, it can spread through the body and end up in the liver, causing amoebic liver abscesses. Liver abscesses can occur without previous diarrhea. Diagnosis is typically by stool examination using a microscope. An increased WBC count may be present. The most accurate test is specific antibodies in the blood.

Prevention of amoebiasis is by improved sanitation. Two treatment options are possible, depending on the location. Amoebiasis in tissue is treated with metronidazole, tinidazole, nitazoxanide, dehydroemetine, or chloroquine. A luminal infection is treated with diloxanide furoate or iodoquinoline. Effective treatment may require a combination of medications. Infections without symptoms require treatment, but infected individuals can spread the parasite to others.

Amoebiasis is present all over the world. Each year, about 40000 to 110000 people die from amoebiasis infection.

E. histolytica is classified as a category B biodefense organism because of its environmental stability, ease of dissemination, resistance to chlorine, and its ability to easily spread through contaminated food products. Besides the GI tract, E. histolytica can affect many organ systems.

Etiology

The protozoan Entamoeba histolytica causes amebiasis. There are three species of intestinal amoebas. Entamoeba histolytica causes most symptomatic diseases. Entamoeba dispar is nonpathogenic, and Entamoeba moshkovskii is reported increasingly, but its pathogenicity is unclear. These organisms are spread via the oral-fecal route. The infected cysts are often found in contaminated food and water. Rare cases of sexual spread have also been reported.

Epidemiology

Amebiasis occurs worldwide but is predominantly seen in developing countries due to decreased sanitation and increased fecal contamination of water supplies. Globally, approximately 50 million people contract the infection, with over 100000 deaths due to amebiasis reported annually. The principal source of infection is ingestion of water or food contaminated by feces containing E. histolytica cysts. Hence, travelers to developing countries can acquire amebiasis when visiting the endemic region. Those who are institutionalized or immunocompromised are also at risk. The organism E. histolytica is viable for prolonged periods in the cystic form in the environment. It can also be acquired after direct inoculation of the rectum, from anal or oral sex, or from equipment used for colonic irrigation. Despite the global public health burden, there are no vaccines or prophylactic medications to prevent amebiasis.[4]

Pathophysiology

E. histolytica is a pseudopod-forming, protozoal parasite that causes proteolysis and tissue lysis. Humans are the natural hosts. Amoebic infection occurs by the ingestion of mature cysts in fecally-contaminated food or water or from the hands. Excystation of the mature cysts occurs in the small intestine, and trophozoites are released; the trophozoites then move to the large intestine. The trophozoites increase by binary fission and produce cysts. Both stages pass in the feces. The cysts can survive days to weeks in the external environment because of the protection provided by the cyst wall. The cyst is responsible for further transmission of the parasite. Ingestion of only a small number of organisms can cause disease.

Histopathology

Histology of the intestinal infection is nonspecific. It usually reveals discrete ulcers, mucosal thickening, and edematous mucosa. Sometimes flask-shaped ulcers may be seen in the submucosal layers. In some patients, flask-shaped ulcers are seen.

History and Physical

Although most cases of amebiasis are asymptomatic, many patients with E. histolytica present with a spectrum of illness. The incubation period from amebiasis is between 2 to 4 weeks.

Symptoms range from mild abdominal cramps and watery diarrhea to severe colitis producing bloody diarrhea with mucus. Young people tend to have a more severe disease compared to older individuals. Fulminant colitis can present with bloody diarrhea in some patients. Risk factors include the use of corticosteroids, poor nutrition, young age, and pregnancy. Toxic megacolon can be a complication and is associated with very high mortality.

A few patients may develop invasive extraintestinal disease. The most common extraintestinal manifestations are an amoebic liver abscess. A liver abscess develops in less than 4% of patients and may occur within 2 to 4 weeks after the initial infection. Liver abscess usually presents with right upper quadrant pain, fever, and tenderness to palpation.

An amoebic liver abscess may rupture into the pleural cavity or pericardium, presenting as pleural or pericardial effusion; however, this is a rare occurrence. Rarely, amebiasis may affect the heart, brain, kidneys, spleen, and skin. One can also develop proctocolitis, toxic megacolon, peritonitis, brain abscess, and pericarditis. Hence, amebiasis is a leading parasitic cause of death in humans.

Evaluation

Amebiasis can be diagnosed by a demonstration of the organism using direct microscopy of stools or rectal swabs. However, the organisms are seen in only 30% of patients.

Antigen detection using an enzyme-linked immunosorbent assay and polymerase chain reaction techniques is often done. However, the most promising detection method is the loop-mediated isothermal amplification assay because of its rapidity, operational simplicity, high specificity, and sensitivity. An ultrasound or CT scan evaluates for extraintestinal amebiasis.[5][1]

Cultures can be done from fecal or rectal biopsy specimens or liver aspirates. Cultures are not always positive, with a success rate of about 60%.

Liver aspiration using CT-guided imaging is often performed when there is a collection in the liver. The liver aspiration usually reveals a chocolate-like or thick, dark viscous fluid. Liver aspiration is indicated when the abscess is large, or there is a threat of imminent rupture.

A colonoscopy is done to obtain scrapings of the mucosal surface. It is appropriate when the stool studies are negative for amebiasis.

Blood tests may reveal the following:

• Elevated WBC
• Eosinophilia
• Elevated bilirubin and transaminase enzymes
• Mild anemia
• Elevated ESR

Imaging studies may be required depending on the presentation. Ultrasound can identify a liver abscess.

Treatment / Management

The primary therapy for symptomatic amebiasis requires hydration and the use of metronidazole and/or tinidazole. These two agents are dosed as follows:

• Metronidazole dosing for adults is 500 mg orally every 6 to 8 hours for 7 to 14 days. 
• Tinidazole adult dosing is 2 g orally each day for 3 days.

Luminal agents such as paromomycin and diloxanide furoate are also used. An amoebic liver abscess can be managed by aspiration using CT guidance in combination with metronidazole. Surgery is sometimes required to treat massive gastrointestinal bleeding, toxic megacolon, perforated colon, or liver abscesses not amenable to percutaneous drainage.[6][7][8]

Differential Diagnosis

• Colitis caused by E. coli, Yersinia, or Campylobacter
• Pericarditis
• Perforated bowel
• Diverticulitis
• Hepatitis A
• Cholecystitis
• Shigellosis/salmonellosis

Prognosis

If left untreated, amoebic infections have very high morbidity and mortality. In fact, mortality is second only to malaria. Amoebic infections tend to be most severe in the following populations:

• Pregnant women
• Postpartum women
• Neonates
• Malnourished individuals
• Individuals who are on corticosteroids
• Individuals with malignancies

When the condition is treated, the prognosis is good, but recurrent infections are common in some parts of the world. The mortality rates after treatment are less than 1%. However, amoebic liver abscesses may be complicated by an intraperitoneal rupture in 5% to 10% of cases, potentially increasing the mortality rate. Amoebic pericarditis and pulmonary amebiasis have a high mortality rate exceeding 20%.

Today with effective treatment, mortality rates are less than 1% in patients with uncomplicated disease. However, rupture of an infected amebic liver abscess carries a high mortality.

Complications

• Toxic megacolon
• Fulminant necrotizing colitis
• Rectovaginal fistula
• Ameboma
• Intraperitoneal rupture of liver abscess
• Secondary bacterial infection
• Extension of infection from the liver into the pericardium or pleura
• Dissemination in the brain
• Bowel perforation
• Stricture of the colon
• Gastrointestinal bleeding
• Empyema

Consultations

Once the diagnosis of amebiasis is made, consult with the general surgeon, gastroenterologist, and infectious disease specialist may be appropriate.

Deterrence and Patient Education

• Avoid drinking contaminated water.
• Use bottled water when traveling.
• Purify water with tetraglycine hydroperiodide.
• Avoid consumption of raw salads and fruits. Peel off the skin of the fruit if possible.
• Thoroughly wash all vegetables before cooking.

Enhancing Healthcare Team Outcomes

Amebiasis is a relatively common parasitic infection. An important component of treatment is patient education via an interprofessional team. The primary caregiver, nurse practitioner, specialty care nurse, and pharmacist should educate all travelers on maintaining good personal hygiene, sanitation, and avoiding high-risk sexual practices. The E. histolytica cysts are relatively resistant to disinfection of water with chlorine. Drinking boiled or bottled water is advised. All food should be washed, and the skin of fruits should be peeled. If abdominal pain symptoms, cramps, and diarrhea persist, a visit to the healthcare provider is recommended. Physicians and nurse practitioners diagnose amebiasis and recommend treatment. Specialty trained nurses in infection control and gastroenterology should assist in coordinating care and assisting with patient and family education. The pharmacist should educate the patient on the importance of hydration and medication compliance and coordinate with the clinician on antimicrobial agent selection. Communication between these professionals as part of the interprofessional healthcare team will improve care coordination, leading to better outcomes.[9] [Level 5]

When treated promptly, the outcomes are good.