Amebiasis is a disease prompted by the parasite Entamoeba histolytica. This article deals with its symptoms, diagnosis, and treatment.
Amebiasis is a disease produced by the parasite Entamoeba histolytica. An amebic infection usually involves the intestines causing GI symptoms. However, the parasite can migrate to other body places and cause complications. Amebiasis is more common in underdeveloped countries with poor sanitation in which the barriers between human feces and food and water supplies are insufficient.
Tropical regions such as some regions of Central America and South America, as well as African countries and India, have the most cases of amebiasis. The disease is relatively rare in developed countries. For example, in the United States, only around 0.4% of the population will suffer from amebiasis in a year. Of that 0.4%, only 1% will develop symptoms.
Unfortunately, asymptomatic individuals or people without symptoms can also transmit the disease through their feces. Worldwide, there are approximately 50 million cases of amebiasis each year; of those 50 million, around 500.000 will perish from complications of extraintestinal amebiasis. Amebiasis is the second biggest cause of death due to parasitic diseases after malaria. Keep reading to learn everything you need to know about this disease.
What causes amebiasis?
Entamoeba histolytica is the name of the parasite responsible for amebiasis. It is a small parasite that exits infected individuals through the feces as a cyst. The parasite can remain a cyst in the soil for months before someone ingests it in contaminated food or water.
The infective cyst then goes down into the small intestines, where it transforms into the active form of the parasite: a trophozoite. Furthermore, the trophozoite invades the intestinal walls causing damage and producing symptoms. Some of them can migrate beyond the intestines to the liver, the heart, the lungs, or even the brain. The parasite reproduces itself in the intestines producing cysts that are excreted in feces.
Also, there are other types of entamoeba capable of producing disease, although less severe than E. histolytica. These are Entamoeba dispar and Entamoeba moshkovskii.
What is the incubation period for amebiasis?
The incubation period is the time elapsed from infection (the moment someone ingests the cysts) and the appearance of symptoms. So, the incubation period for amebiasis is usually 2 to 4 weeks.
What are the symptoms of amebiasis?
According to public health authorities, only about 10% to 20% of infected individuals actually develop symptoms. The other 90% are asymptomatic carriers that can transmit the disease through their feces.
Intestinal amebiasis (also known as amebic colitis) is the most common clinical presentation. Diarrhea is the cardinal symptom, but not just any diarrhea. Amebic diarrhea is bloody and full of mucus; this combination of blood and mucus in the stool receives the name of dysentery and is common to several other infectious and not infectious diseases.
Besides, other common symptoms include abdominal pain, stomach cramping, and high fever with chills. Amebiasis symptoms persist for over two weeks, which is an essential difference from other causes of diarrhea and abdominal pain.
What are the complications of amebiasis?
Although uncomplicated intestinal amebiasis represents more than 90% of all cases, the extraintestinal disease does occur. It can lead to severe complications with a high mortality rate (people with these complications are in a life-threatening situation). Thanks to these complications, the number of people dying because of amebiasis is second only to malaria, if only considering parasitic infections.
The formation of an amebic liver abscess is the most common complication of amebiasis. Approximately 4% of patients with amebic colitis develop an amebic liver abscess. It is a collection of pus in the liver due to parasite migration. The cardinal signal is high-grade fever with chills combined with pain and tenderness in the upper right quadrant of the abdomen and weight loss.
In some cases, this abscess ruptures into the abdominal cavity causing amebic peritonitis. The infection can expand into the right lung, causing cough and chest pain while breathing or coughing. When the infection reaches the lungs, the cough typically comes with an odorless brown discharge.
Sometimes, the parasite enters the blood and reaches the brain producing abscesses there. These patients with cerebral amebiasis can have a sudden intense headache, nausea, vomiting, and mental status changes. The most serious complication is pericardic amebiasis. The parasite breaks through the membrane that protects the heart producing heart failure symptoms.
An ameboma is a rare complication in which the parasite triggers the production of large quantities of scar tissue that results in a mass in the right upper abdominal quadrant. This mas is usually mistaken for a tumor. In countries with a high prevalence of amebiasis, the infection can cause acute appendicitis that requires surgical intervention.
What diseases can imitate amebiasis?
Several diseases produce very similar symptoms to amoebic dysentery or resemble a hepatic abscess.
- Inflammatory Bowel Disease (ulcerative colitis)
- Viral hepatitis
- Typhoid fever
- Bacterial liver abscess
- Primary hepatic carcinoma
What are the risk factors for amebiasis?
In the developed world, infection is rare.
The most important risk factors include the following:
- Traveling to an endemic country with a deficient sanitary policy
- Living in institutions with poor sanitary conditions (prisons and nursing houses)
- Sexual practices that involve fecal-oral contact
- Having a compromised immune system due to corticosteroid treatment, HIV, cancer, or any other condition
Populations with an increased chance of getting the complications of the disease include:
- Small children
- Oncologic patients
- Malnourished persons
- Pregnant women
How do you know if you have amebiasis?
The most common way of diagnosing amebiasis is detecting the parasite in a stool sample. Laboratory personal searches for cysts of trophozoites under the microscope.
Sometimes, there aren’t any parasites in a single sample, although the patient indeed has the infection. Therefore, to decrease the risk of false negatives (when a test comes out negative although the person has the disease), the lab will examine three stool samples. When the parasite migrates to other organs, it may not appear in the stool. Cases of the extraintestinal disease require additional tests.
Antibody detection tests are very helpful blood tests in diagnosing cases of the extraintestinal disease. These tests detect amebiasis in over 70% of patients with colitis and 99% of patients with an amebic abscess. However, false negatives are common in the first 7 to 10 days of infection.
Furthermore, imaging studies are very useful in diagnosing liver abscess. Both upper abdominal ultrasonography and CT scans can easily detect the abscess. In cases of cerebral amebiasis, a cranial CT scan is an important part of the diagnosis.
In cases where the attending physician is not sure if the liver abscess is due to amebiasis or another infection, it might perform a percutaneous liver aspiration. A fine needle is inserted into the area guided by ultrasonography to take a sample of the abscess during the procedure. However, most prefer to avoid it if possible because of the risk of complications.
Routine blood tests may also reveal some characteristic findings such as:
- An elevated white blood cell count
- Elevated liver enzymes
- Elevated bilirubin levels
- Mild anemia
- Elevated erythrocyte sedimentation rates
What is the treatment for this infection?
In developed countries, every infected person should receive treatment, even those that are asymptomatic. Metronidazole is the treatment of choice for invasive amebiasis, and diloxanide furoate is the treatment of choice for asymptomatic carriers. The latter term is used for people who carry the parasite, although they do not manifest the disease.
Amebic abscess smaller than 10 cm are also cure with metronidazole, but bigger abscesses require surgical drainage.
Patients with the following conditions may require surgical intervention:
- Perforated liver abscess and amebic peritonitis
- Massive GI bleeding due to E. histolytica
- Toxic megacolon (a common complication in patients taking corticosteroids)
- Failure to respond to metronidazole after four days of effective treatment.
- A large left-sided liver abscess (due to its proximity to the heart, these abscesses have a higher risk of turning into amebic pericarditis).
- Severely ill patients
How is amebiasis prevented?
The key to preventing amebiasis has good hygiene. Some useful measures include:
- Washing your hands before eating
- When traveling abroad, stick to bottled water or boil the local water 20 minutes before drinking it
- Avoid drinking water from fountains
- Elude milk, cheese, and other unpasteurized products
- Avoid eating food from informal food vendors
- Wash all fruits and vegetables with water before eating them
- Avoid sexual practices that involve fecal-oral contact
Is reinfection possible?
Yes, unfortunately, an infection with an entamoeba does not provide lifelong immunity. Individuals that have had the disease are just as likely to get reinfected as anyone in the general population. Some laboratories are currently working on developing a vaccine, but these trials are just in their infancy. Many years may pass by before the first vaccine is released to the public.
What is the prognosis of amebiasis?
Most cases resolve within a week of beginning treatment with metronidazole, even those with liver abscess. However, although symptoms resolve, radiological evidence of an abscess can remain for months or even years.
Moreover, the mortality of an amebic liver abscess is below 1% thanks to antibiotic therapy. However, in the context of perforation, that number rises to 7%.
Other extraintestinal manifestations have a higher mortality rate. Pulmonary infections have a 20% mortality, pericarditis a 40% mortality rate, and cerebral amebiasis 90% mortality rate. Some intestinal disease cases evolve into fulminating colitis with a mortality rate between 1% and 9%.
Do you have symptoms of this infection?
This tool is an Amebiasis Symptoms Checker. It gathers the most important signs, symptoms, and risk factors for this disease. Therefore, it would tell anybody who uses it the likelihood of their symptoms because of amebiasis. Using this tool is free and would only take a few minutes.