An Unusual Feature of Malaria: Exflagellated Microgametes of Malarial Parasites in Human Peripheral Blood

Exflagellation of the malaria parasite microgametocyte usually occurs in the gut cavity of Anopheles mosquitoes following an infective blood meal. Exflagellation is a very rare event in human blood. Due to its rarity, the appearance of this structure in a peripheral blood smear will easily create a diagnostic dilemma. We report a case of malaria with exflagellated microgametes in human blood that was initially mistaken for a double infection of Plasmodium and another blood flagellate. The patient was a 29-year-old Parkistani man presenting with fluctuating fever accompanied by chills and fatigue for 4 days. Initial peripheral blood smear examination showed a number of Plasmodium ring forms, trophozoites, and gametocytes. Additionally, several filamentous structures resembling blood flagellates were seen. With these features, an initial diagnostic impression of combined infection of malaria and blood flagellate was made. Later, we determined that these structures resembling blood flagellates were exflagellated microgametes of malarial parasite. Therefore, the knowledge that exflagellation may appear in human blood with Plasmodium species infection and being more familiar with differentiation of the morphologic features of other species infection can prevent further possible misinterpretation. (Korean J Clin Microbiol 2012;15:151-153)