High density of 'spiky' excrescences covering the surface of an erythrocyte infected with Plasmodium malariae.

This Atomic Force Microscope image shows the surface of a Plasmodium malariae trophozoite-infected red blood cell isolated from a Burmese patient suffering from quartan malaria (top). Of note, the P. malariae-infected cell (bottom left) is covered with dense ‘spike-like’ excrescences (mean height: 7·59 nm; mean diameter: 52·95 nm), which are morphologically distinct from the larger, more rounded ‘knob’ structures found on a Plasmodium falciparum-infected red cell (mean height: 19·65 nm; mean diameter: 96·64 nm) (bottom right). The ‘knobs’ on red cells containing mature asexual forms of P. falciparum assist the infected cells to bind/sequester to the vascular endothelium under shear flow conditions and thus avoid splenic clearance. The function of P. malariae spikes (which we have observed on every sexual and asexual stage examined in isolates from Indonesia and Thailand) is not known. The sample from which the P. malariae pictured was isolated (Mae Sod, Tak, Thailand) had the diagnosis confirmed by polymerase chain reaction. This picture is artificially coloured. The horizontal black scale bars represent 1 μm. The two lower images are identical in scale and orientation.