What is Entamoeba histolytica Infection?
Entamoeba histolytica is a type of microscopic parasite that can lead to a condition called intestinal amebiasis, which affects the intestines, and other issues outside of the intestines. While around 90 percent of people infected with E. histolytica don’t show symptoms, nearly 50 million people start experiencing symptoms every year, and sadly, around 100,000 people die from this infection. This parasitic infection is found to be more common in countries with poorer living conditions.
What Causes Entamoeba histolytica Infection?
Entamoeba histolytica is a type of parasite that usually enters the body when someone consumes food or drinks water that’s been contaminated by the parasite’s cysts. This typically happens when the food or water has been in contact with infected feces. This is often referred to as the “fecal-oral” route of transmission.
Risk Factors and Frequency for Entamoeba histolytica Infection
Entamoeba histolytica is a major global health problem, ranking third in deaths caused by parasitic infections. While most people who are infected don’t show symptoms, about 50 million people do get sick, and up to 100,000 die from it each year. There are two types of this parasite: E. histolytica, which causes disease, and E. dispar, which doesn’t cause any symptoms.
People all over the world can get infected, but it’s more common in countries with low income levels and poor public health systems. These countries include India, Africa, Mexico, and parts of Central and South America. In Bangladesh, for example, a study found that 2.2% of dysentery (severe diarrhea) cases seen in preschool children were caused by E. histolytica. In rural Mexico, up to 42% of people have had the infection. The way people usually catch it is through exposure to feces, either from poor hand hygiene, using water sources contaminated with human waste, or from being near animals. In wealthy countries like the United States, these infections are rare and are mainly seen in people who have recently been to places where the infection is common, such as immigrants or travelers.
- Amoebic colitis, a disease caused by this parasite, can affect people of any age, regardless of their gender.
- Gay or bisexual men may have a higher risk of catching it because of potential exposure to feces during sex.
- People who are pregnant, those on corticosteroid treatment, people with cancer, those suffering from malnutrition, and alcoholics are at a greater risk of having a severe infection and dying from it.
- Amoebic liver abscess, another disease caused by this parasite, is three times more likely to affect men aged 18 to 50.
Signs and Symptoms of Entamoeba histolytica Infection
E. histolytica is a type of infection that doesn’t show symptoms in most people. However, about 10% of these silent infections can turn into a disease over time. This infection commonly affects the intestines but can also impact the liver, respiratory tract, heart, and brain.
- Gastrointestinal: If it’s affecting your digestive tract, you might start feeling symptoms slowly over one to three weeks. These symptoms can include upset stomach, bloody stools, weight loss, and abdominal pain.
- Liver: Sometimes, the infection can cause a liver abscess, which shows up as a complication after months or even years of exposure. Symptoms of a liver abscess can include fever and pain in the upper right side of your abdomen. Your doctor may find that your liver is enlarged and tender. Less than 10% of patients turn yellow (jaundice). Lab tests might show increased white blood cell count, increased levels of a certain type of liver enzyme, and a higher rate of red blood cell sedimentation.
- Respiratory tract: It’s very unusual for this infection to affect your lungs. If it happens, you might have lung collapse (atelectasis) and a buildup of clear fluid in your lung (transudative pleural effusions). Sometimes, a liver abscess could burst into the pleural space, causing infected fluid (an empyema) or a connection between the liver and bronchial tubes. This could lead to symptoms like fever, cough, and difficulty breathing.
- Cardiac infection: Even more rarely, the infection can extend to the heart, particularly if a liver abscess breaks into the space around your heart. If this happens, you could experience symptoms of inflammation of the outer coverings of the heart (pericarditis) or compression of the heart due to excess fluid (cardiac tamponade).
- Brain infection: In the rarest of cases, the infection can affect the brain. Symptoms like severe headaches, vomiting, changes in mental state, and rapid progression towards serious illness or death can occur suddenly.
Testing for Entamoeba histolytica Infection
In the past, doctors diagnosed amoebic infections by looking under a microscope for a type of amoeba called a trophozoite. However, this method wasn’t perfect because it didn’t clearly tell the difference between amoebas of the E. histolytica and E. dispar varieties.
Now, there are lots of newer ways to diagnose these infections; the most effective of these is stool polymerase chain reaction (PCR). PCR is a way of analyzing a sample to see if it contains certain types of genetic material (in this case, from amoebic parasites). This method is excellent at telling E. histolytica from E. dispar.
There are several other ways to diagnose these infections:
– Stool microscopy: This means looking at a stool sample under a microscope. This method is easy and cheap but not very accurate (less than 60%), and it won’t definitely identify the type of amoeba. The results also depend a lot on the skills of the person looking at the sample.
– Stool antigen detection: Another way to analyze a stool sample, this test identifies certain proteins (antigens) produced by amoebas. It’s a quick and easy way to tell E. histolytica from E. dispar. However, the success rates of these tests can vary.
– Serology: This blood test can detect if your body has produced antibodies against the parasites, indicating you’ve been infected. It’s fast and accurate but doesn’t tell if you were infected recently or in the past. It’s important to note that these antibodies won’t appear in an active infection until at least a week after the infection started, so the test might not catch fresh infections.
– Stool molecular studies: This is another way to analyze stool samples, and it’s considered to be the most reliable. It has a high success rate, but it requires special equipment and trained technicians, making it a bit more pricey than other methods.
– Colonoscopy with histologic examination: This procedure involves inserting a long, thin tube into the colon to look for amoebic ulcers or other issues. The doctor then takes small tissue samples (biopsies) to examine under a microscope looking for amoebas. It’s not usually used for routine amoebic infection diagnosis, but it can be helpful when other causes of symptoms need to be ruled out.
Treatment Options for Entamoeba histolytica Infection
Every E. histolytica infection needs to be treated due to its ability to spread widely and cause symptoms outside the intestine.
Metronidazole is the medication most often recommended for treating intestinal amebiasis (a parasitic infection of the intestine) and amebic liver abscess (a collection of pus in the liver due to amebiasis). After taking Metronidazole, another medication that works in the intestines (known as a luminal agent) is prescribed. Luminal agents may include medications such as paromomycin, diiodohydroxyquin, or diloxanide furoate.
If metronidazole cannot be used, other possible alternatives include medicines like tinidazole, ornidazole, and nitazoaxanide.
In severe cases of amoebic colitis (an infection of the colon), or if symptoms of peritonitis (an inflammation of the lining of the abdomen) are present, all-purpose antibiotics should be given. In these situations, a surgical procedure may be needed if there is a hole in the bowel or if toxic megacolon (a dangerous expansion of the large intestine) occurs.
For uncomplicated amebic liver abscess, there’s no added advantage in draining the abscess in addition to the usual medical treatment. However, if the patient doesn’t respond properly to the antibiotic therapy, then aspiration or catheter drainage (medical procedures to remove the collected pus) might be necessary.
If the infection spreads to the lungs (pleuropulmonary infections), they are managed by first draining the excess fluid from the lungs (amoebic pleural effusion) followed by appropriate medicines like metronidazole paired with a luminal agent.
What else can Entamoeba histolytica Infection be?
The conditions that your doctor might consider when diagnosing E. histolytica intestinal amebiasis, an intestinal infection, include:
- Bacterial infections caused by Shigella, Escherichia coli, Salmonella, Campylobacter, and Clostridioides difficile
- Inflammatory bowel disease
- Ischemic bowel disease (a condition where the blood supply to the intestines is reduced)
If the E. histolytica has spread beyond the intestines (this is known as extraintestinal amebiasis), the doctor might think about:
- Pyogenic liver abscess (a pocket of pus in your liver)
- Echinococcal disease (a parasitic infection)
- Cancer or malignancy
What to expect with Entamoeba histolytica Infection
Uncomplicated infections treated at an early stage often have a mortality rate of less than 1%. However, certain factors can lead to more serious infections and increase the risk of mortality. These factors include:
- Young age
- Pregnancy
- Being on corticosteroid treatment
- Having cancer
- Malnutrition
- Alcoholism
A severe form of amoebic colitis comes with a high mortality rate of 40%. On a more positive note, prompt medical treatment of an amoebic liver abscess has proven to be very effective, with mortality rates falling between 1 to 3%.
Regrettably, amoebas affecting the area around the lungs and heart can result in higher mortality levels. Pleuropulmonary amebiasis, when amoebas affect the lungs, has a mortality rate of up to 16%. Cardiac involvement, where amoebas affect the heart, can have a mortality rate of up to 30%.
Possible Complications When Diagnosed with Entamoeba histolytica Infection
Complications from an E. histolytica infection could include:
- No symptoms at all
- Having symptoms but no invasion into other tissues or organs
- An infection in your rectum and colon that comes on suddenly
- A severe infection in your colon with a hole or tear
- A condition where your colon swells dramatically
- A lasting infection in your colon without dysentery or severe diarrhea
This type of infection can also result in conditions beyond your intestines, including:
- Abscess or pocket of pus in your liver
- Lung disease
- Abscess in your brain
- Inflammation in the lining of your abdomen
- Inflammation in the sac surrounding your heart
- Urinary and genital conditions
- A skin condition near your anus
- A clot in your liver vein
- A clot in the large vein that carries blood back to your heart
- A growth in your intestines
- Appendicitis or inflammation of your appendix
Preventing Entamoeba histolytica Infection
To lower the risk of getting bacterial and parasitic infections like E. histolytica, it’s essential to be careful with diet and maintain good hand cleanliness. For those traveling outside the U.S., here are some useful tips:
- Avoid drinking tap water. Instead, choose bottled beverages and use bottled water for brushing your teeth. Also, steer clear of adding ice to your drinks as it’s usually made from tap water.
- Stay away from raw fruits and vegetables washed with tap water.
- Make sure to eat foods that are well-cooked, particularly while traveling. Avoid eating undercooked fish or meats.
- Avoid consuming food from street vendors, carts, or stands
- Make a habit of washing your hands regularly, especially after using the restroom, touching animals, before meals or after handling trash. This can prevent infections.
If you’ve recently traveled outside of the country and encounter any of the symptoms listed below, you should consider visiting a doctor:
- You have a fever reaching or exceeding 102 degrees F (40 degrees C).
- You’re experiencing severe abdominal pain.
- You’re passing bloody diarrhea.
- Your sickness has lasted more than two weeks.
