Host, Strain and Treatment Variation as Factors in the Pathogenesis of Toxoplasmosis

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  • Rocky Mountain Laboratory, National Microbiological Institute, National Institutes of Health, and the Department of Pathology and Oncology, University of Kansas School of Medicine, Hamilton, Montana
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The pathogenesis of toxoplasmosis is discussed under the headings of Host, Microorganism, Treatment and Time, in an attempt to integrate the many factors operating during infection. The obligate intracellular development of Toxoplasma, its ability to grow in many cells and the formation of a relatively inert cyst are the major microorganismal attributes determining pathogenesis. Whereas many natural hosts appear relatively resistant to many of the strains, the inability of some hosts to overcome infection or to develop an effective immunity and, furthermore, the presence of an infection-immunity (premunition), the development of hypersensitivity with chronic infection and the results of cyst rupture are the major host factors complicating pathogenesis.

Our knowledge of the shifting relative importance of each factor while infection progresses is inadequate. The analysis of the pathogenesis must take into account the effects of superimposition of different rates of a variety of processes. It has been shown that identical inocula can result in infections running a different course in different hosts, and how similar inocula of different strains or the institution of chemotherapy can alter the course of infection.