Question

What is the investigation of choice for invasive amebiasis?

• A. ELISA
• B. Biopsy
• C. IHA (Indirect Haemagglutination Assay)
• D. PCR

Hint:

Stool exam is often negative once the amoeba invades tissue, so serology becomes the test of choice.

Answer 1

The Correct Option is A

Step 1: Understanding the Question:
Invasive amebiasis means Entamoeba histolytica has moved out of the gut lumen into the bowel wall or a distant organ, most often the liver, to form an abscess. The question asks which test best confirms this invasive stage.

Step 2: Key Concept:
Once the parasite invades tissue, trophozoites are no longer shed freely in stool, so stool microscopy is often negative in invasive disease, even when the infection is active and severe. The body does mount a strong antibody response against the invading parasite, and this response is what the best test should pick up.

Step 3: Detailed Explanation:
ELISA for antiamebic antibodies is over 90 percent sensitive in invasive amebiasis, including amebic liver abscess, and becomes positive within a week of invasion, which makes it the current test of choice.
IHA also detects antibodies but is less sensitive than ELISA and stays positive for years after a past infection has already cleared, so it cannot tell a doctor whether the disease is currently active.
Biopsy, taken at colonoscopy, can show trophozoites invading the colon wall, but it is invasive, carries a risk of perforation in inflamed tissue, and is not practical for an abscess sitting deep in the liver.
PCR on stool is good for confirming E. histolytica in the gut and telling it apart from the harmless look alike E. dispar, but it is not the standard test once the disease has already become invasive and systemic.

Step 4: Final Answer:
Serology by ELISA is the most sensitive and practical test for invasive amebiasis, so the answer is ELISA.