Development of the sheep–canid cycle of Sarcocystis tenella

Abstract

Sheep (37) were inoculated orally with 104 to 66 .times. 106 S. tenella sporocysts from dogs or coyotes and necropsied between 1 to 276 days postinoculation (DPI). Two single zoites were found in submucosal arteries of small intestines of lambs 3 and 6 DPI. At 9-21 DPI, numerous 1st-generation meronts were found in mesenteric arteries, intestinal blood vessels and occasionally in other organs. The 1st-generation meronts were 37.0 .times. 27.3 .mu.m in sections and 54.4 .times. 46.6 .mu.m smears. At 16-40 DPI, 2nd-generation meronts were found in capillaries of several organs; renal meronts were 20.6 .times. 12.0 .mu.m in sections. Merozoites were found in peripheral blood at 14-16 DPI and at 25-32 DPI. Earliest sarcocysts were found at 35 DPI and contained 1-3 metrocytes. At 40 DPI, sarcocysts were up to 97 .times. 10 .mu.m and contained 1-13 metrocytes. Bradyzoites formed between 52 and 66 DPI. At 75 DPI, sarcocysts had cross-striated walls and were infective for coyotes. Dogs and coyotes fed infected meat shed sporocysts in feces 9-10 days later. Gamonts were found in the small intestine between 8 and 21 h postinoculation and sporulation was completed within 8 days.