histolytica

Entamoeba histolytica is a human pathogenic protozoan parasite responsible for amoebiasis, a disease spectrum ranging from asymptomatic carriage to invasive intestinal disease and extraintestinal infections. It belongs to the genus Entamoeba; humans are the primary hosts.

Transmission occurs via ingestion of resilient cysts in contaminated water or food. In the small intestine, cysts excyst to release trophozoites that migrate to the colon, where they colonize the mucosa. Trophozoites can cause tissue destruction by invading the mucosa and, less commonly, disseminate via the portal system to the liver, causing abscesses. Cysts excreted in stool complete the life cycle.

Clinical presentation varies. Many infections are asymptomatic. Symptomatic intestinal disease presents with abdominal pain, cramps, and bloody, sometimes mucus-containing diarrhea (dysentery) and may include weight loss. Extraintestinal infection most often affects the liver, producing fever and right upper quadrant pain; hepatomegaly and liver abscess are possible.

Diagnosis: Microscopy of stool can reveal cysts with multiple nuclei or trophozoites with ingested red blood cells. However, microscopy cannot reliably distinguish E. histolytica from nonpathogenic species such as E. dispar. Therefore antigen detection assays or PCR are increasingly used, along with imaging for liver abscess.

Treatment: Invasive disease is treated with a tissue amebicide (metronidazole or tinidazole) followed by a luminal amebicide (paromomycin, diloxanide furoate, or iodoquinol) to eradicate intestinal carriage. Liver abscesses may require drainage. Prevention focuses on safe water, proper sanitation, and hand hygiene to minimize fecal-oral transmission.