A Summary of the Newer Knowledge of Toxoplasmosis

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Abstract
Reported cases of human toxoplasmosis, although not numerous, have a widespread distribution and have been recognized in numerous places in the Western Hemisphere and in Europe. The disease has been less frequently recognized in other parts of the world. Infection in lower animals is more widespread. The occurrence of antibodies in various population groups indicates that man is frequently exposed to infection with Toxoplasma gondii. The percentage of positive reactors usually increases with age. Present evidence indicates that the infection is more prevalent in warm, moist areas, than in cold or hot, dry climates. It is not yet possible to analyze the significance of such data. Because of frequent infection in domesticated animals with which man is associated, it has been assumed that these animals serve as reservoir-hosts and that man acquires his infection from them. It has also been assumed that infection may be acquired through the oral route, or that it may be transmitted by insects. Exposure through the contaminative route would seem unlikely, owing to the low resistance of the organism to environmental factors. Equivocal results have been obtained in experiments in which animals have been fed meat that contained the proliferative forms of the parasite. On the other hand, more consistent findings have resulted from the feeding of material that contained the pseudocysts, which are more resistant than the proliferative forms. In spite of a large amount of experimental work, transmission by insects has not been proved, although certain of the results would seem to warrant further investigation. Toxoplasmosis may be classified as congenital and acquired. Acquired toxoplasmosis has been categorized in accordance with its varying clinical manifestations into exanthematic, cerebrospinal, ophthalmic, and lymphadenopathic forms. Clinical diagnosis of acquired toxoplasmosis is difficult, if not impossible, and must be augmented by laboratory procedures, such as serologic tests (especially the dye test) and the subinoculation of animals. Of the large number of drugs that have been tested by screening with animals, the combination of pyrimethamine and the sulfonamides has yielded the best results. On the other hand, pyrimethamine may produce disagreeable reactions and, in large or continued dosage, it may be responsible for various hematologic changes, including a megaloblastic type of anemia.

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