Copyright 0 1996by The American Societyof ‘l@opica1Medicine and Hygiene SHORT REPORT: ROSETTE FORMATION IN PLASMODIUM 0 VALE INFECTION

Abstract. Red blood cells infected by mature stages of Plasmodium ovale obtained from a 56-year-old Thai patient formed rosettes readily with uninfected erythrocytes. Ex vivo, the ring stage-infected erythrocytes matured well under the in vitro conditions used for P. falciparum culture, and the infected erythrocytes formed rosettes when the parasites became mature trophozoites. These rosettes were stable and remained intact until completion of schizogony. Plas modium ovale rosettes were similar to those formed by P. falciparuin- and P. vivax-infected erythrocytes. Rosette formation appears to be a common property of three species of human plasmodia. Four species of plasmodia cause malaria in humans. Of these, only Plasmodiumfalciparum infections are potentially lethal. ' The pathology of severe falciparum malaria is related to sequestration in which infected erythrocytes stick in the deep vasculature and the resultant slowing of blood flow and focusing of toxic damage causes vital organ dysfunction.2 ‘I\woin vitro phenomena observed are thought to be related to this mechanism: cytoadherence or the adhesion of infected erythrocytes to vascular endothelial cells,3 and rosette fo