Dark-field microscopy for detection of malaria in unstained blood films.

Pigment present in different forms of Plasmodium species infecting humans exhibits light scattering when blood films are viewed by dark-field microscopy. This facilitates the detection of parasite-infected cells owing to their brightly illuminated appearance. The technique was described long ago for the detection of certain highly pigmented forms of malarial parasites such as schizonts and gametocytes but has not found an application in routine diagnosis. Here, modifications are described which allow the detection of all forms of human malarial parasites, including ring forms, in unstained blood films. The technique offers the distinct advantages of rapid diagnosis, increased sensitivity, and adaptability to field work.