# Amoebiasis and Amoebic Liver Abscess > Amoebiasis and amoebic liver abscess for NEET-PG Medicine: Entamoeba histolytica, anchovy-sauce pus, serology, aspiration and metronidazole. - Canonical URL: https://prepelephant.com/topics/neet-pg/medicine/amoebiasis-and-amoebic-liver-abscess - Exam / course: NEET-PG · Subject: Medicine - Publisher: PrepElephant (https://prepelephant.com) — Prepared and reviewed by the PrepElephant Academic Review Team - First published: 2026-10-08 - Last updated: 2026-10-08 - Reference basis: Harrison's Principles of Internal Medicine; Sleisenger and Fordtran's Gastrointestinal and Liver Disease; Mandell, Douglas and Bennett's Principles and Practice of Infectious Diseases - How to cite: "Amoebiasis and Amoebic Liver Abscess", PrepElephant, https://prepelephant.com/topics/neet-pg/medicine/amoebiasis-and-amoebic-liver-abscess ## Direct answer Amoebiasis is infection with Entamoeba histolytica, acquired by the faecal-oral route, and its most important extraintestinal form is amoebic liver abscess. The abscess is usually solitary, lies in the right lobe and causes fever with right upper quadrant pain, and aspirated pus is classically brown, anchovy-sauce in colour and sterile on routine bacterial culture. Serology is highly sensitive, and metronidazole is the drug of choice for tissue disease. ## What you must remember - **Organism:** Entamoeba histolytica; cysts are ingested, excyst in the small bowel and invade the colonic mucosa. - **Classic colitis:** flask-shaped ulcers with undermined edges, bloody diarrhoea, and trophozoites containing ingested red cells on stool microscopy. - **Anchovy-sauce pus:** the brownish, odourless pus of amoebic liver abscess, which is characteristically sterile on bacterial culture. - **Site:** usually solitary and in the right lobe, most often in the dome, with left lobe involvement a minority finding. - **Serology:** indirect haemagglutination and ELISA are highly sensitive and stay positive long after infection, so a titre cannot separate past from current disease. - **Metronidazole:** the drug of choice for tissue disease, given for a course of about seven to ten days, followed by a luminal agent such as diloxanide furoate to clear cysts. - **Aspiration:** indicated for left-lobe abscesses, impending rupture, or failure to improve after several days of metronidazole. ## A pathway from fever to a sterile pus Consider a 40-year-old man who drinks heavily and presents with a week of fever, right upper quadrant pain and a tender, enlarged liver. Ultrasound shows a 6 cm hypoechoic cavity in the dome of the right lobe without a thick, septated wall, which fits an amoebic abscess. 1. **Confirm with serology:** Serology is the first confirmatory step. 2. **Read stool results cautiously:** Stool microscopy is often negative because the intestinal infection has settled, so a negative stool examination does not exclude the diagnosis. 3. **Start metronidazole:** With a classic right-lobe lesion and a positive serology, metronidazole is started intravenously and then orally, and fever usually settles within several days. 4. **Reserve aspiration:** Aspiration is reserved for a left-lobe abscess, a lesion at risk of rupture, or failure to improve after about five days. Drawn pus is sent for bacterial culture to exclude a pyogenic abscess. 5. **Complete with a luminal agent:** A luminal agent such as diloxanide furoate completes treatment, clearing cysts that could otherwise cause relapse. 6. **Follow up:** Follow-up ultrasound confirms resolution over the following weeks. ## Where the examiner tries to catch you Examiners like the contrast with pyogenic abscess. - **Trap:** Excluding amoebiasis because the bacterial culture is negative. — **Correct:** Amoebic pus is sterile on bacterial culture, so a negative culture never rules out amoebiasis, while thick, malodorous, culture-positive pus points to a bacterial cause. - **Trap:** Reading a positive antibody test as proof of an active abscess. — **Correct:** Serology shows exposure at some time and cannot tell an active abscess from an old infection, so the diagnosis rests on the clinical picture, imaging and response to metronidazole. - **Trap:** Giving a luminal agent alone for a liver abscess. — **Correct:** Metronidazole kills tissue trophozoites, while luminal agents act only in the bowel, so a luminal agent alone is a serious error. - **Trap:** Assuming microscopy separates E. histolytica from E. dispar. — **Correct:** The two cannot be separated on microscopy, and antigen-based tests resolve this, a favourite viva question. ## Frequently asked questions ### Which test best supports the diagnosis of amoebic liver abscess? Amoebic serology by indirect haemagglutination or ELISA is the most useful supporting test for amoebic liver abscess, as it is positive in the large majority of patients. Ultrasound or CT then localises a solitary right-lobe cavity, while stool microscopy is often negative because the intestinal infection has usually resolved. ### What is the drug of choice for amoebic liver abscess? Metronidazole is the drug of choice for amoebic liver abscess, given orally for about seven to ten days, and it acts on the trophozoites in the liver tissue. It must be followed by a luminal amoebicide such as diloxanide furoate, because metronidazole alone does not reliably eradicate cysts in the bowel. ### When is aspiration indicated in amoebic liver abscess? Aspiration is indicated in amoebic liver abscess for left-lobe lesions, abscesses at risk of rupture into the pericardium or peritoneum, and those that fail to improve after several days of metronidazole. ### Why is anchovy-sauce pus sterile on culture? Anchovy-sauce pus is the thick brownish fluid of an amoebic liver abscess, made of necrotic liver tissue and red cells rather than bacteria, so routine bacterial culture is sterile. A negative culture therefore does not exclude amoebiasis, and the diagnosis rests on serology, imaging and response to metronidazole. ### Why does metronidazole need a luminal agent in amoebiasis? Metronidazole treats the invasive tissue disease but does not reliably clear cysts from the bowel lumen, so these cysts can cause relapse or continued transmission. A luminal agent such as diloxanide furoate or paromomycin therefore completes treatment, and it is given even when stool microscopy is negative.