Case #245 - February, 2009
A 64-year-old man returned from a trip to Africa with fever and chills. He went to a local hospital for medical assistance. A blood specimen was collected and sent to Hematology for work-up, including Parasitology. Only a thick blood smear stained with Giemsa was available to be reviewed by the pathologist. Figures A–C represents what was observed in 300 fields at 1000x magnification. What is your diagnosis? Based on what criteria? What, if any, follow-up would you recommend?
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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Images presented in the monthly case studies are from specimens submitted for diagnosis or archiving. On rare occasions, clinical histories given may be partly fictitious.
DPDx is an educational resource designed for health professionals and laboratory scientists. For an overview including prevention, control, and treatment visit www.cdc.gov/parasites/.