Toxoplasma Cysts in the Human Heart, an Electron Microscopic Study

Abstract

Electron microscopic study of the cyst form of Toxoplasma gondii in the human heart, obtained from an elderly patient at postmortem, revealed relatively well-preserved organisms. The morphological details of the organisms are in essential agreement with observers who studied toxoplasma in other mammals. The hollow nature of peripheral fibrils is demonstrated in our study. The absence of the villus-like structure of the outer portion of the cyst wall suggests that the nature of the cyst wall varies with the host organs. It is suggested that an interaction between host cells and parasites produces the cyst wall. There is no evidence that the heart muscle cell, with the extruded nucleus, constitutes the cyst wall or that the cell membrane of the heart muscle participates in cyst wall formation. Binary fission as one method of reproduction of the cystic form of Toxoplasma gondii is added as a new finding, in addition to the previously described methods of reproduction. Electron microscopic investigations of Toxoplasma gondii have been reported in recent literature. Most of the studies have been done on laboratory animals inoculated with this organism (Gamham et al., 1962; Gavin et al., 1962; Gustafson et al., 1954; Ludvik, 1956, 1958; Wanko et al., 1962; Frenkel et al., 1951). We have studied the encysted form in the heart muscle of a patient with disseminated chronic toxoplasmosis. The patient was a 64year-old white female, who suffered from a long-standing hemolytic anemia and terminal febrile complication. Postmortem examination revealed unsuspected diffuse, acquired chronic toxoplasmosis, involving the heart, lung, liver, ileum (with several ulcers), kidney, thyroid, and bone marrow. No specific treatment such as pyrimethamine or sulfonamide had been given. The clinical features of this case are presented elsewhere (Kalderon et al., in press). There has been no previous report on the ultrastructure of Toxoplasma cysts in human organs. Although material obtained at postmortem may suffer inadequate fixation for study by electron microscopy, the opportunity to study Received for publication 27 November 1963. * Dr. Y. Kikkawa is a postdoctoral research fellow of the New York Heart Association. Part of this work is supported by Grant A-2967C5 of the National Institute of Arthritis and Metabolic Diseases, National Institutes of Health, Bethesda, Maryland. such human material is rare and the quality of the preservation encountered in our studies seems to warrant its description. MATERIALS AND METHODS Portions of formalin-fixed left ventricle heart muscle known to contain cysts of Toxoplasma were postfixed in 1% osmium tetroxide for 2 hr. The fixative was buffered at pH 7.3 with Veronal to which sucrose had been added. The tissue was dehydrated with alcohols and embedded in Epon 812. One-micron thick sections were made on a Porter Blum microtome and examined under the light microscope. When organisms were found, thin sections were made for electron microscopic study. Sections were stained with both 2% uranyl acetate and lead hydroxide and examined with an RCA EMU 3C electron microscope. Ilford photomechanical plates type N60 recorded the image.