How the Malaria Parasite Invades Its Host Cell, the Erythrocyte

Abstract

This chapter presents a discussion on how the malaria parasite invades its host cell, the erythrocyte. The author attempts to present a survey of what has been learned about the process of malarial invasion into erythrocytes by morphological and biochemical approaches, and to point out some of the problems involved in studying this complex phenomenon. Malaria, a disease of humans and of a number of animals, is caused by protozoa of the genus Plasmodium. All species of Plasmodium are by necessity parasites, requiring for their development both a vertebrate and an invertebrate (mosquito) host. One crucial aspect governing the propagation of all Plasmodia is their necessity for invading the erythrocytes of the vertebrate host, making invasion a prime target for investigation. The definitive vector for malaria is the female Anopheles mosquito. More than 50 of the approximately 200 known Anopheles species can transmit malaria. When a mosquito bites an infected individual, it ingests circulating intraerythrocytic gametocytes of Plasmodium. Propagation in the vertebrate host is initiated by the bite of the infected mosquito, which introduces sporozoites into the bloodstream, whence they rapidly disappear into the parenchymal cells of the live. The chapter presents a brief survey of some of the topographic landmarks encountered by a malarial merozoite as it invades a human erythrocyte. The process of merozoite invasion into RBCs has been studied both by light and electron microscopy. The combined approach has provided much insight into the events leading up to and following invasion in temporal, morphological and ultrastructural terms. The term invasion entails at least five levels of interaction between invading merozoites and erythrocytes, which are as follows: attachment, reorientation, RBC membrane invagination, merozoite internalization, and resealing of the RBC membrane. The chapter concludes by discussing that the invasion of malarial parasites into erythrocytes is a complex, multistep phenomenon, involving specific receptors and the participation of the cytoskeletal elements of both the parasite and the host cell.