Tropical Infectious Disease Research Program, Clinical Research Department, U.S. Public Health Service Hospital, Vector Biology and Control Division, Bureau of Tropical Diseases and Scientific Services Division, Bureau of Laboratories, Center for Disease Control, Biology Department, Tulane University, New Orleans, Louisiana 70118
Detection and specific identification of the 48-hour exoerythrocytic stage of the primate malaria parasite, Plasmodium cynomolgi bastianellii, was accomplished by means of a highly specific indirect immunofluorescence technique (IFA) applied to hepatic tissue fixed in Carnoy's solution. The 48-hour forms appeared as round-to-slightly-oval bodies of average mean diameter 3.0 µm (9 parasites) and lying within the cytoplasm of individual hepatic parenchymal cells; each possessed one to three non-fluorescent nuclei or nuclear sections (mean 1.6) within the brightly fluorescent parasitic cytoplasm. In contrast, 72-hour parasites (6) had an average mean diameter of 4.0 µm and a mean of 2.2 nuclei. Restaining of IFA preparations with the Giemsa-colophonium method confirmed the plasmodial nature of fluorescent forms, despite some modification of staining characteristics produced by the prolonged exposure of sections to the aqueous phase of the IFA procedure. Exoerythrocytic forms could not be detected in biopsies obtained 24 hours following sporozoite inoculation.