Life-cycle of Isospora mehlhornii sp. nov. (Apicomplexa: Eimeriidae), parasite of the Egyptian swallow Hirundo rubicola savignii

Abstract

Fifty-seven Hirundo rubicola savignii swallows were collected from Damietta, Tanta, Dakahlyia and Sharkia Provinces, Egypt. They were examined for coccidian parasites. The percentage of infection with Isospora stages was 12.3%. After diagnosis it was noted that the parasites belong to a new species. The unsporulated oocysts were spherical, measuring 25.7–31.9 μm in diameter with a mean of 28.3 μm. A micropyle, polar granule and oocyst residuum were absent. Sporocysts appeared lemon-shaped and measured 19.6–24.5 μm × 12.5–17.5 μm with a mean of 22.9 × 14.4 μm. Stieda body and the sporocyst's residual body were clearly visible. Sporozoites measured 11–14.2 × 4.4–5.1 μm with a mean of 11.4 × 4.7 μm. Sporulation time was 72 h at room temperature (25 °C). Endogenous stages including schizogony and gamogony were detected in epithelial cells of the duodenum, jejunum and ileum of the host. Schizogony consisted of two generations. Mature first generation schizonts reached up to 11 μm in diameter and produced merozoites measuring 3.5 × 1.7 μm. Mature second generation schizonts measured 17.2 × 12.3 μm and produced merozoites measuring 11.8 × 2.2 μm. Gamogonic stages were differentiated into microgamonts and macrogamonts. Mature microgamonts were spherical and measured 23.2 μm in diameter, producing curved microgametes measuring 4.5 × 0.7 μm. The ovoid macrogametes measured 19.6 × 14.7 μm and were characterized by a large nucleus and nucleolus. Early, more or less spherical, oocysts were detected inside the intestinal epithelial cells and in the intestinal lumen. They measured 19.6 μm in diameter. The sporont measured 17.2 μm in diameter. Cytochemical studies on schizogony, gamogony and oocysts were accomplished and showed distribution of polysaccharides and composition of the oocyst wall.