Methods of malaria diagnosis which use reagents such as monoclonal antibodies or specific oligonucleotide sequences, thereby avoiding the use of the light microscope, have been developed and are being assessed. Other procedures which apply fluorochromes such as acridine orange in combination with fluorescence microscopy are also available. None of these alternative methods of diagnosis is reliable or cheap enough at present to replace the traditional use of blood films. Admittedly, the `old fashioned' way of diagnosing malaria requires skills only obtained after considerable experience. This atlas of malaria parasite images is intended to assist those working in haematology laboratories as they gain experience in the microscopical detection and identification of malaria parasites, the technique which will remain the `Gold Standard' for some time to come.

Although the forms of malaria parasites seen in a patient's blood represent points in a cycle of 48 (tertian) or 72 (quartan) hours of development, they are usually placed in categories based partly on morphology and partly on function. From a strictly zoological point of view all the asexual blood stages should be called schizonts since, from the time a merozoite enters an erythrocyte its destiny is to grow to maturity as a schizont and produce more merozoites. For convenience, however, the continuum of developing schizonts is usually broken into several stages. Recognition of these forms also has clinical significance because the presence of a particular stage (the mature trophozoites and schizonts of P. falciparum for example) may have prognostic implications. In the broadest terms, the stages usually recognised are the trophozoite (feeding animal), schizont (dividing parasite) and gametocyte (sexual parasite infective to the mosquito). Trophozoites are often separated into ring forms and late trophozoite stages. The rings are so called for the obvious fact that they look like signet rings; the red chromatin bead (nucleus) being the stone and the blue cytoplasm surrounding a clear vacuole, the band.

The variations in malaria parasite morphology usually follow typical patterns which may be sufficiently consistent to be used in identification. These characteristics are described below for the two most important species of human malaria, Plasmodium vivax and Plasmodium falciparum and in less detail for P. ovale and P. malariae. The features most commonly used are: