[One of the possible ways of propagation of the unicellular parasites Sarcocystis muris in the musculature of the intermediate host]. / Odin iz vozmozhnykh putei rasprostraneniia odnokletochnykh parazitov Sarcocystis muris v muskulature promezhutochnogo khozaina.

ABSTRACT

20 laboratory mice (Mus musculus) were fed each a single dose of 20,000 Sarcocystis muris sporocysts to be then sacrificed 1, 2.5, 4, 6 and 10 months following infection (p.i.). A visual infection of the murine corps demonstrated that the number of sarcocysts per animal increased regularly as the time of infection was progressing, being eventually higher after 6 and 10 months p.i. than within 1-4 months p.i. This phenomenon was poorly understood from the knowledge that the tissue cysts (sarcocysts) are able to increase in size, rather than in number, and that the original number of sarcocysts largely depends on the number of precystic merozoites available. In our experiments, each of 20 mice was fed an equal number of sporocysts, and thus the number of precystic merozoites ought to be expected also more or less equal. EM investigation of murine skeletal muscles 6 and 10 months p.i. revealed, along with numerous normal sarcocysts, the presence of some separate, individual zoites, both within and outside the muscle fibre, in the endomysium. Besides, a colony of zoites, living freely without any visible common wall, was detected within a muscle fibre adjacent to another one, containing a sarcocyst of normal structure. These zoites may have originated from one or more sarcocysts, whose cyst walls were spontaneously broken, time after another, and thus led the cyst cells go out. These discharged zoites could either perish, being enzymatically degraded, or penetrate the neighbouring muscle fibres to proceed their further development. The colony making zoites were confined to two cell types only the intermediate cells and the merozoites (gamonts). No metrocytes were recognized due, presumably, to inability of these little differentiated cells, devoid of penetrative organelles, to invade the host muscle cell. The colony of zoites turned out to be a developing population of live cells, able to destroy progressively the harbouring muscle fibre, except its basal membrane and sarcolemma. It does not seem unlikely that the outer coverings of the infected cell could be transformed eventually into a cyst wall to make, thus, a new sarcocyst. The above phenomena have never been found in murine muscles earlier than 6 months p.i. Although these facts are few and far between, they may prompt a possible mechanism of sarcocyst increase in number, in the intermediate host with age, even without any additional sporocyst contamination.