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

IV. Pre-Erythrocytic Schizonts and/or Hypnozoites of Chesson and North Korean Strains of Plasmodium Vivax in the Chimpanzee

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  • * Laboratory Research Branch, National Hansen's Disease Center, Carville, Louisiana 70721
  • Department of Tropical Medicine and Medical Parasitology, Louisiana State University Medical Center, New Orleans, Louisiana 70112
  • Delta Regional Primate Research Center (Tulane University), Covington, Louisiana 70433
  • § Department of Pure and Applied Biology, Imperial College, London SW7, England
  • Malaria Branch, Center for Infectious Diseases, Centers for Disease Control, Atlanta, Georgia 30333
  • Laboratory of Parasitic Diseases, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Bethesda, Maryland 20852
  • ** Biomedical Research Institute, Rockville, Maryland 20852

In a continuing reexamination of plasmodial tissue stages within the context of the hypnozoite theory of malarial relapse, 2 strains of Plasmodium vivax with distinct and disparate relapse characteristics in humans were studied in chimpanzees. Following intravenous inoculation of massive numbers of salivary gland sporozoites, both the frequently relapsing Chesson strain and a North Korean strain characterized by predominantly delayed relapses exhibited relapse patterns and antimalarial sensitivity in the splenectomized chimpanzee essentially indistinguishable from those seen in humans. Examination of hepatic biopsies obtained at 7 and 10 days after infection revealed both pre-erythrocytic (pre-e) schizonts and hypnozoites in tissue obtained from the animal infected with the Chesson strain, but only rare hypnozoites (no pre-e schizonts) at 7 days in the animal infected with the North Korean strain. These findings, combined with the comparability of relapse behavior—which indicates the suitability of the chimpanzee as a model for the natural (human) host-parasite relationship—are essentially as predicted by the hypnozoite theory, despite the small numbers of tissue forms seen. Pre-erythrocytic schizogony of the Chesson strain in the liver was essentially indistinguishable from that of other strains studied, also underlining the suitability of this model system for tissue stage studies of P. vivax.

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