The Behavior of Toxoplasma with Notes on Its Taxonomic Status

Because toxoplasmosis is now known to be a common human infection, and sometimes a very serious one, it is receiving an increasing amount of study. The organism itself, however, has had surprisingly little careful attention. This is evidenced by the striking differences in the way in which the subject is treated by authors of many of the standard texts in parasitology and protozoology. There is general agreement that Toxoplasma is probably a protozoan, but little as to what kind of a protozoan it may be. Kudo (1950), for example, put Toxoplasma with the BABESIIDAE, one of 3 families in the order HAEMOSPORIDIA. Since the other 3 genera of the family are all parasitic in the erythrocytes of vertebrates, and two of the three are known to be tick-transmitted, this disposition of Toxoplasma seems at least illogical. Belding (1952) remarked (p. 240) Flagella have been observed in a few specimens, thus, by implication at least, suggesting that the genus should be placed with the MASTIGOPHORA, since true flagella do not occur at any stage of the sporozoan lifecycle. He nevertheless included it with Unclassified Sporozoa. Toxoplasma receives similar treatment in most other currently used texts in protozoology and parasitology. In some, the authors are even more non-committal, placing the parasite under a heading such as Parasites Of Doubtful Nature. Chandler (1949) went a little farther than most in stating is uncertain whether it is a protozoan or a fungus, although it is more probably the There are still authors who omit it altogether. Very lately the suggestion has again been made that the real affinities of this parasite may be with the SARCOSPORIDIA. Biocca (1949) remarked on the fact that, although Toxoplasma and Sarcocystis have certain characteristics in common, they are easily distinguishable. Piekarski (1950) took essentially the same position, but Muhlpfordt (1951) has apparently shown that the Sabin-Feldman dye test gives positive results both with toxoplasmosis and sarcosporidiosis. It has long been recognized that many human cases diagnosed as the latter condition were really the former. The problem was considered in some detail by Kean and Grocott (1945), and Biocca (1949) went so far as to claim that probably half the reported human cases of sarcosporidiosis were in fact toxoplasmosis. The case is further complicated by the existence of other species of parasites