Microbiology Cheat Sheet
Malaria: Smear Patterns
Malaria smear patterns for NEET-PG and FMGE: falciparum banana gametocytes, malariae band forms, vivax Schuffner dots, Duffy antigen, hypnozoites, and RDTs.
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Malaria: Smear Patterns
Malaria smear patterns for NEET-PG and FMGE: falciparum banana gametocytes, malariae band forms, vivax Schuffner dots, Duffy antigen, hypnozoites, and RDTs.
This topic covers the etiopathogenesis, clinical evolution, and laboratory diagnosis of malaria, focusing on species identification from Giemsa-stained blood smears.
High-yield lines
- Malaria is caused by Plasmodium transmitted by female Anopheles mosquitoes, with five species infecting humans.
- Plasmodium falciparum is the most lethal species, invading red cells of all ages and causing cerebral malaria via sequestration.
- Giemsa-stained thick and thin blood smears are the gold standard: thick smears screen by concentrating parasites, and thin smears identify species.
- Banana or crescent-shaped gametocytes are pathognomonic of P. falciparum, while band-form trophozoites are pathognomonic of P. malariae.
- P. falciparum shows only ring forms and gametocytes in peripheral blood, as trophozoites and schizonts are sequestered.
- Schuffner dots in an enlarged red cell indicate P. vivax or P. ovale, while Maurer clefts indicate P. falciparum.
- P. vivax requires the Duffy blood group antigen for red cell invasion, so Duffy-negative individuals are resistant to P. vivax but not P. falciparum.
- Hypnozoites in P. vivax and P. ovale cause relapses, and primaquine eliminates them after G6PD testing to prevent haemolysis.
- Cerebral malaria is caused by sequestration of parasitised red cells in cerebral microvasculature via PfEMP1 binding to endothelium, not direct brain invasion.
- The HRP-2 rapid diagnostic test is specific for P. falciparum but persists after treatment, while pLDH detects all species and declines with cure.
- P. malariae causes quartan fever with a 72-hour cycle and can recrudesce decades later without forming hypnozoites.
- Sickle cell trait (HbAS) protects against severe falciparum malaria, whereas sickle cell disease (HbSS) is not protective.
- Artemisinin-based combination therapy treats uncomplicated falciparum malaria, and IV artesunate is the drug of choice for severe disease.
- Chloroquine must not be used for P. falciparum due to widespread resistance.
Mapped competency codes
- MI2.5
- MI2.6
Continue into the full chapter
This summary maps to MI2-cvs-and-blood.
Frequently Asked Questions
What smear finding is pathognomonic of Plasmodium falciparum?
Banana or crescent-shaped gametocytes, along with delicate multiple ring forms per red cell.
Why are Duffy-negative individuals resistant to P. vivax?
P. vivax uses the Duffy blood group antigen as its red cell entry receptor, so Duffy-negative red cells resist invasion, though not P. falciparum.
What is the difference between thick and thin blood smears?
Thick smears screen by concentrating parasites 20 to 40-fold, while thin smears preserve red cell morphology for species identification.
Which parasite stages cause relapse and how are they eliminated?
Hypnozoites of P. vivax and P. ovale cause relapse; primaquine eliminates them after G6PD testing to avoid haemolysis.
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