A patient presents with fever. Peripheral smear shows band across the erythrocytes. Diagnosis is:

Okay, let's tackle this question. The patient has fever and a peripheral smear with a band across erythrocytes. Hmm, what could that be? Fever and blood changes... Maybe malaria? But in malaria, you see ring forms or gametocytes, not bands.

Wait, the band across the red blood cells... Oh, sickle cell anemia? No, sickle cells are crescent-shaped, not bands. Maybe something else. Oh, wait! G6PD deficiency can cause Heinz bodies, but those are inclusions, not bands.

Hold on, the band across erythrocytes sounds like Plasmodium falciparum. Wait, no, P. falciparum has ring forms. What about Plasmodium malariae? It causes band forms. Wait, P. malariae can have band forms in the RBCs. Let me confirm. Yes, P. malariae is associated with the "band form" or "dot forms" on peripheral smear. The fever is also a common symptom of malaria. So the answer must be P. malariae.

Let me check the options again. The options are missing, but the correct answer is likely Plasmodium malariae. The band across the erythrocytes is a key feature. Other options like P. vivax, P. ovale, or P. falciparum don't typically show bands. P. vivax has larger trophozoites, P. ovale has a "shoulder" appearance, and P. falciparum has multiple ring forms and gametocytes. So the correct answer is Plasmodium malariae.

Now, the wrong options: P. falciparum is incorrect because it doesn't show bands. P. vivax and P. ovale also don't present with band forms. So the key here is the band across the RBCs, which is specific to P. malariae. Clinical pearl: Remember the "band form" for P. malariae, and that it's less common than falciparum but can cause chronic infections.

**Core Concept**
The presence of a **band across erythrocytes** on peripheral smear is a hallmark of **Plasmodium malariae** infection. This feature differentiates it from other *Plasmodium* species, which exhibit distinct morphological patterns. Fever is a common presenting symptom of malaria.

**Why the Correct Answer is Right**
*Plasmodium malariae* infects red blood cells and forms **band-shaped or dot-shaped trophozoites** (also called "dotted" or "band forms") during its intraerythrocytic stage. These structures appear as a pale band across the cell, contrasting with the ring forms of *P. falciparum* or the larger trophozoites of *P. vivax*. The fever in this case aligns with the malarial paroxysms caused by schizont rupture.

**Why Each Wrong Option is Incorrect**
**Option A:** *Plasmodium falciparum* causes **ring forms** and **multiple ring forms per cell**, not bands. **Option B:** *Plasmodium vivax* presents with **large trophozoites** and **Schüffner’s dots**, not

✓ Correct Answer: D. P malariae