[Last Modified: ]

February 2009
Answer to Case 245

This was a case of malaria caused by Plasmodium falciparum.  Diagnostic features included:

• white blood cells with ingested pigment (Figure A).
• the presence of ring-form and developing trophozoites, including some with double chromatin dots.
• an absence of gametocytes and/or schizonts.

Although a thick smear is more sensitive than a thin smear, in most cases a thick smear is not adequate to determine the species of Plasmodium present.  In cases where the parasitemia is moderately high or greater, the lack of gametocytes and/or schizonts may be included in the algorithm for determining the species due to that ring-form and developing trophozoites are usually the only stages seen on stained blood films with P. falciparum.
Whenever determining the species of Plasmodium is not definitive by observation of morphological features, molecular techniques can be used to do so provided an appropriate blood specimen is available.

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