Entamoeba histolytica is a microscopic parasite that causes amoebiasis, a disease primarily affecting the intestines. The parasite can also spread beyond the intestines to other organs, leading to more serious health complications. It is found worldwide, with higher prevalence in tropical and subtropical regions.
How E. histolytica Spreads
The primary way E. histolytica spreads is through the fecal-oral route, occurring when a person ingests the parasite’s hardy cyst form. These cysts are often found in food or water contaminated with human feces and can survive for weeks to months in the external environment. Transmission is also facilitated by direct person-to-person contact, including through oral-anal sexual practices or contact with contaminated hands of food handlers. Once ingested, cysts transform into trophozoites in the small intestine, which then migrate to the large intestine.
Signs and Symptoms of Infection
Infection with E. histolytica can manifest in a range of ways, from showing no symptoms at all to causing severe dysentery. Approximately 90% of those infected may remain asymptomatic, carrying the parasite without experiencing illness. Even asymptomatic individuals can continue to excrete cysts, potentially spreading the infection to others.
When symptoms do appear, they often develop gradually over one to three weeks. Common intestinal symptoms include abdominal pain, diarrhea, and stools that may contain blood or mucus. In more severe cases, known as amebic dysentery, individuals may experience frequent semi-liquid stools, intense abdominal pain, and fever.
Beyond the intestines, the parasite can cause extra-intestinal manifestations if trophozoites spread through the bloodstream. The most common extra-intestinal complication is an amebic liver abscess, a collection of pus in the liver. Symptoms of a liver abscess include fever, right upper quadrant abdominal pain, and tenderness.
Identifying and Treating the Infection
Diagnosing E. histolytica infection involves analyzing stool samples. Microscopic examination can identify trophozoites or cysts in stool, though this method may not always differentiate E. histolytica from other morphologically similar Entamoeba species. To improve accuracy, molecular tests like Polymerase Chain Reaction (PCR) are increasingly used to detect the parasite’s DNA in stool, offering higher sensitivity and specificity.
For cases where the infection has spread beyond the intestines, such as liver abscesses, imaging techniques like ultrasonography, CT scans, or MRI may be used for diagnosis. Treatment for active E. histolytica infections, especially those causing symptoms or extra-intestinal disease, involves oral medications such as metronidazole or tinidazole. Following this initial treatment, a luminal amoebicide like paromomycin is prescribed to eliminate any remaining cysts in the intestines.
Preventing E. histolytica Infection
Preventing E. histolytica infection involves maintaining good hygiene and ensuring safe food and water practices. Avoid consuming untreated water or ice. Boiling water is an effective method for killing E. histolytica cysts.
Careful food hygiene is also important, including thoroughly washing fruits and vegetables with clean water, especially if they are to be eaten raw. Eat only well-cooked food and avoid raw or undercooked meats and seafood. Handwashing with soap and water, especially after using the toilet and before preparing or eating food, reduces the risk of transmission.