Fig. 1. Life cycle of
Sarcocystis suihominis.
1 Motile sporozoites hatch from the ingested sporocysts inside the intestine of the
intermediate host, i.e. swine.
2 Two generations of schizonts are formed (5–6 and 12–17 days after infection) inside endothelial cells of blood vessels, giving rise to 60–100 merozoites by
endopolygeny.
3 Free motile merozoites; first-generation merozoites enter other endothelial cells and form schizonts, whereas merozoites of the second generation induce formation of
tissue cysts.
4 Cyst formation inside typical cells (muscle fibers, brain cells); within these cysts the parasites are reproduced by repeated
endodyogeny leading to thousands of cyst merozoites which are situated inside chamber-like hollows.
5 When the final host man has eaten cyst-containing raw or insufficiently cooked meat, the cyst merozoites are set free and enter cells of the lamina propria.
6 Formation of female (macrogametes;
6.3) via gamonts (
6.1; 6.2) within 14 h after infection.
7 Fusion of
gametes. 8 Formation of the
oocyst wall around the
zygote. 9–11 Formation of two sporocysts (containing four sporozoites each) inside the host cells. The smooth
oocyst wall often becomes disrupted. Thus, fully sporulated oocysts are found in the feces (
11).
DM, developing merozoites;
DR, disrupted oocyst wall;
HC, host cell; N, nucleus;
NH, nucleus of the host cell;
OW, oocyst wall;
PC,
primary cyst wall;
PV,
parasitophorous vacuole; RB, residual body;
S,
sporocyst; SP,
sporozoite;
WB, oocyst
wall-forming bodies (for further details see
Table 1).
