Quantitative parasitemia in calves fed Sarcocystis cruzi sporocysts from coyotes.

For the quantitation of parasitemia, seven 7- to 10-day-old calves were orally inoculated with 2 virulent isolates of Sarcocystis cruzi from coyotes. Three calves were each given 2.5 million sporocysts of the 1st isolate; these calves died 31, 35, and 33 days later. The other 4 calves were given 2, 1, 0.76, and 0.38 million sporocysts of the 2nd isolate; these calves died or were euthanatized at 34, 44, 43, and 55 days after inoculation. Buffy coat smears from 7 ml of jugular blood of each calf were examined daily from day 14 after inoculation to time of necropsy. Merozoites were found in peripheral blood of all calves between days 25 and 46. The numbers of merozoites in 3 calves given identical inocula of the 1st isolate were 62, 48, and 17. The numbers of merozoites in the 4 calves given the 2nd isolate were 185, 11, 70, and 61, with decreasing dosages, respectively. The number of merozoites ranged from 0.14 to 9.8/ml of blood. More than 97% of merozoites were intracellular in mononuclear cells and 2.8% were extracellular in blood. Of 454 merozoites, 18 had 2 nuclei and 5 contained 2 dividing zoites; all dividing organisms were intracellular.