Crescent shaped or banana shaped gametocytes are seen in infection with?

Appeared in: NIA - 29 January 2023

Explanation

Plasmodium falciparum is uniquely identified by its distinctive crescent-shaped or banana-shaped gametocytes.
These are the mature sexual stages of the parasite that circulate in the blood and are responsible for transmission from humans to mosquitoes.
The presence of these forms on a peripheral blood smear is a pathognomonic sign of falciparum malaria.

Option A: The gametocytes of Plasmodium vivax are not crescent-shaped. They are typically large and round or oval.
Option C: The gametocytes of Plasmodium malariae are round or oval and tend to be compact and smaller than those of P. vivax. They are not crescent-shaped.
Option D: The gametocytes of Plasmodium ovale are also round to oval, similar to P. vivax. They are not crescent-shaped.

Clinical Relevance

Nursing practice connection: Knowing Microscopic identification of Plasmodium species based on gametocyte morphology helps nurses interpret findings accurately and avoid errors in routine assessment, medication administration, and patient teaching.
Identifying crescent-shaped gametocytes on a blood smear is a definitive diagnosis for P. falciparum malaria, which is a medical emergency requiring immediate intervention.
Unlike other species, P. falciparum can cause severe complications like cerebral malaria, acute respiratory distress syndrome (ARDS), and multi-organ failure. Early diagnosis is key to preventing mortality.
What if? If a blood smear shows only ring-stage parasites and no gametocytes, a diagnosis of P. falciparum should still be highly suspected if there are multiple rings per red blood cell, appliqué forms (rings at the cell periphery), or high parasite density. Treatment for falciparum should be initiated presumptively in such cases due to the risk of rapid progression to severe disease.

How to Approach the Question

This is a factual recall question that tests knowledge of parasite morphology.
Identify the keywords in the stem: "crescent shaped" or "banana shaped gametocytes".
This is a classic, high-yield feature in parasitology.
Systematically recall the key microscopic features of each Plasmodium species listed in the options.
Associate the unique crescentic gametocyte shape with Plasmodium falciparum.
Eliminate the other options, as they all have round or oval gametocytes.

Concept Tested & Keywords

Concept Tested: Microscopic identification of Plasmodium species based on gametocyte morphology.
Stem keywords: Crescent shaped, banana shaped, gametocytes, infection
Lead-in keywords: seen in
Negative lead-in flag: false

QNOFm0FOUp-46I0tzJKvN0

E6 Medicine Harrison 22e Part 1 p. 1801-1803

Practise the full NIA - 29 January 2023

Attempt every question from this paper in a timed mock, then review the full solution for each one.