Human isosporiasis. Considerations on the 28 cases

Abstract

The authors report the finding of twenty-eight cases of human infection with coccidia belonging to the genus Isospora. These cases were found in 22.836 stools examination from December, 1942, through June 1950. The material was divided in two groups: the first (table 1) composed by 15 cases in which the parasite was identified as Isospora hominis (Raillet and Lucet 1891). In the second group (table 2) were included the others 13 cases in which the coccidium was identified as Isospora belli Wenyon 1923. In the first group of this series the coccidium was discharged in the faeces usually as a single sporocyst containing four vermiform sporozoites (illus. 1, 2 and drawing 1). The average size of these sporocysts corresponds to 14.8 microns in the length by 9.8 microns in breadth. Only in three cases ripe oocysts with 2 sporocysts each containing four sporozoites (illus. 3, 4) were found together with the isolated tetrazoic sporocysts.

It is important to emphasize that in all these 15 cases the coccidia were discharged in the faeces in the mature stage. On the other hand, in 13 cases of the second group only the unsegmented oocysts were found in the faeces. Rarely oocysts containing two sporoblasts were found in freshly passed faeces. In this group of cases the oocysts are usually unsegmented when discharged in the faeces but in about forty eight hours at room temperatura the sporocysts containing four sporozoites have developed (illus. from 5 to 12 and drawings 2, 3). Therefore, differently of which occurs in the cases included in the first group, it is in the external medium that oocyst complete its development. The average size found for the oocysts was 28.3 microns in the length by 13.5microns in the breadth. The average size of the sporocysts correspond to 12.9 microns in length by 10 microns in breadth. After a brief discussion on the nomenclature of the coccidia of man and others comments suggested by their findings, the authors conclude that: 1) Man is infected by two species of coccidia of the genus Isospora; 2) These species are respectivelly: Isospora hominis (Raillet and Lucet 1891) and Isospora belli Wenyon 1923; 3) In spite of the morphological resemblance between Isospora hominis found in man and Isospora bigemina Stiles 1878 which parasites dogs, was not proved yet that they are identical; 4) In the material studied it was not possible to demonstrate the pathogenic action of Isospora hominis in the man, as either the clinical symptoms were absent or occurred together with other intestinal parasitosis;

5) Referring to the infection by Isospora belli, in their material, the authors observed the three following possibilities: a) the presence of Isospora belli without any clinical symptoms; b) the presence of gastrointestinal symptoms which might have been credited to other coexisting parasites; c) the presence of enteric symptoms caused by Isospora belli infection.