Electron microscopy of the Plasmodium falciparum trophozoites and the tissues these have infected in severe tropical malaria

The paper provides the results of the comprehensive electron microscopic examination of the venous blood and internal organ tissue samples obtained when studying the imported case of tropical malaria. The study was aimed to assess the fine structure of the erythrocytic stages of Plasmodium falciparum and alterations of the affected tissues in severe tropical malaria. The venous blood, cerebral cortical tissue and myocardial samples were examined by light microscopy and electron (scanning and transmission) microscopy. Numerous Plasmodium falciparum trophozoites were found in blood. Multiple Maurer's clefts were found in the cytoplasm of the infected erythrocytes. Abnormal intercellular contacts between the infected and unaffected erythrocytes were revealed, which resulted in their adhesion and rosette formation (erythrocyte rosetting/e-rosetting). When studying cortical tissue and myocardial samples, fixation of the affected erythrocytes on the endothelium (erythrocyte adhesion) was noted in the capillary lumen. Rosetting and erythrocyte adhesion lead to capillary thrombosis, disruption of microcirculation and sequestration of tissues in vital organs (parasite sequestration). The identified morphological features of the pathogens causing tropical malaria and the affected tissues determine the parasites’ capability of changing properties of the infected erythrocytes’ cell membranes, which leads to formation of abnormal intercellular contacts and constitutes one of the main mechanisms underlying the Plasmodium falciparum virulence.