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Observations on Early and Late Post-Sporozoite Tissue Stages in Primate Malaria

I. Discovery of a New Latent Form of Plasmodium cynomolgi (the Hypnozoite), and Failure to Detect Hepatic Forms Within the First 24 Hours After Infection^*

W. A. Krotoski^,**,, P. C. C. Garnham, R. S. Bray^,,, D. M. Krotoski, R. Killick-Kendrick^,,, C. C. Draper^||, G. A. T. Targett^|| AND M. W. Guy^||

Previous work in this laboratory has demonstrated the ability of the immunofluorescence technique to detect pre-erythrocytic stages of the primate malaria parasite, Plasmodium cynomolgi bastianellii, in hepatic tissue obtained as early as 48 hours after sporozoite inoculation. In an attempt to visualize still earlier post-sporozoite stages, hepatic tissue obtained from a rhesus monkey infected with 12,000,000 sporozoites was examined at 2, 12, 24, and 48 hours after inoculation, employing antisera reactive with both invertebrate and vertebrate stages of the parasite. Tissue was also obtained at 7, 50, 102, and 105 days after sporozoite inoculation, and was examined for adequacy of the hepatic infection and for the presence of late exoerythrocytic schizonts. Although a new, previously unrecognized, uninucleate latent stage of 5 µm diameter (the "hypnozoite") was detected among large maturing schizonts in the 7-day and later biopsies, no intrahepatic parasites were found in tissue taken at 24 hours or earlier, despite the presence of up to 61 7-day schizonts and eight hypnozoites per 5 x 8 mm section. Pre-erythrocytic forms again were detected at 48 hours, though in far smaller numbers than expected on the basis of the density of parasites at 7 days after infection. The significance of these observations is discussed in the context of previous negative findings.

Accepted for publication June 4, 1981.

^* Portions of this work were presented at the 29th Annual Meeting of The American Society of Tropical Medicine and Hygiene, Atlanta, Georgia, 4–7 November 1980, and at the 10th International Congress of Tropical Medicine and Malaria, Manila, The Philippines, 9–15 November 1980.

Supported, in part, by Bureau of Medical Services Grant ORL 79-27-76, Health Services Administration, U.S. Public Health Service, Department of Health and Human Services.

Tropical Infectious Disease Research Program, Clinical Research Department, U.S. Public Health Service Hospital, New Orleans.

^** Address reprint requests to Dr. W. A. Krotoski, Laboratory Research Branch, National Hansen's Disease Center, Carville, LA 70723.

Department of Pure and Applied Biology, Imperial College of Science and Technology, Ascot, Berks., U.K.

Member, External Staff, Medical Research Council, England.

^|| Departments of Tropical Hygiene and Medical Protozoology, London School of Hygiene and Tropical Medicine, London, U.K.