Question

Identify the organism related to the blood smear image.

• A. P. falciparum
• B. S. Typhi
• C. Treponema pallidum
• D. Toxoplasma gondii

Hint:

Multiple ring-form trophozoites inside red cells with high parasitaemia means P. falciparum.

Answer 1

The Correct Option is A

Step 1: The thin blood smear shows red blood cells containing ring-shaped trophozoites, including a single red cell holding multiple rings. This appearance identifies the malaria parasite Plasmodium falciparum.
Step 2: Two features are typical of P. falciparum - the early ring-form trophozoites and a very high parasitaemia, with many red cells parasitised and sometimes multiple rings within one cell. Such heavy infection is far more common with falciparum than with the other plasmodia.
Step 3: On smear technique, thick smears are used to detect the parasite at low density, while thin smears, as shown here, allow species identification, which is how falciparum is pinned down.
Step 4: The distractors do not fit a smear of ring forms inside red cells - Salmonella Typhi is a bacterium diagnosed by culture, Treponema pallidum is a spirochaete seen by dark-field microscopy or serology, and Toxoplasma gondii forms tachyzoites and tissue cysts, not intra-erythrocytic rings. Hence the organism is P. falciparum.