Development of the Ox - Cat Cycle of Sarcocystis hirsuta

The ox-cat cycle of Sarcocystis hirsuta was studied by killing 18 calves between 7 and 110 days after inoculation (DAI) with sporocysts from cats. At 7 DAI, sporozoites were found free and within leukocytes in the lumen of arteries associated with mesenteric lymph nodes and in endothelial cells of mesenteric arteries. First-generation meronts were found 7-23 DAI in arteries associated with mesenteric lymph nodes and intestines. Meronts matured between 7 and 10 DAI. Firstgeneration meronts were 37.2 x 22.3 /z,m and contained more than 100 merozoites, which measured 5.1 x 1.2 /jim. Merozoites measuring 5.4 x 1.5 jam were found free in the peripheral blood of a calf 11 DAI. Second-generation meronts were found in capillaries of striated muscles and heart 15-23 DAI; meronts matured between 15 and 16 DAI. Second-generation meronts were 13.9 x 6.5 jam and contained three to 35 merozoites that measured 4 x 1.5 /x.m. Second-generation individual merozoites were seen within myofibers and in tissue macrophages in muscles 16-23 DAI. Sarcocysts formed between 25 and 75 DAI in striated muscles, but not in heart; esophagus was the most heavily infected organ. At 30 DAI, a sarcocyst contained two metrocytes. At 62 DAI, sarcocysts were up to 550 /LAITI long and 35 ju,m wide and contained only metrocytes; the wall was up to 3 /Am thick and cross-striated. Bradyzoites developed between 62 and 75 DAI. Mature sarcocysts were up to 800 /tm long and the wall was up to 6 /^m thick. Sarcocysts became infective for cats at 75 DAI. Cats shed sporocysts and oocysts 8-10 days after ingesting infected muscles. Of the three species of Sarcocystis that occur in the ox (S. cruzi [S. bovicanis], S. hirsuta [S. bovifelis], and S. hominis [S. bovihominis]), developmental stages of only S. cruzi are known (for review see Levine and Ivens, 1981). In this report the development of S. hirsuta is described. Clinical signs and lesions will be reported separately. Materials and Methods Inoculation of calves Sporocysts of S. hirsuta were obtained originally by feeding tongue and esophagus of a naturally infected cow from the Montana State University Agricultural Experiment Station to a specific-pathogen-free (SPF) cat. Sporocysts were collected from intestinal scrapings and stored in a balanced salt-antibiotic mixture (Dubey, 1980, 1981). Two experiments were performed. In experiment 1, seven 8-12-week-old calves were killed 75, 88, 89, 104, 110, 170, and 220 days after oral inoculation (DAI) with 1 million, 1 million, 250,000, 1.4 million, 5,000, 5,000, and 5,000 sporocysts, respectively, and their muscles were fed to 22 SPF cats. In experiment 2, 11 1-2-week-old calves were necropsied 7, 10, 15, 16, 20, 23, 30, 35, 42, 62, and 82 DAI with 15, 25, 1, 15, 25, 15, 15, 1, 1 ,3 , and 1 million sporocysts, respectively. Two 7-day-old calves served as uninoculated controls, and were killed 30 and 82 days after the initiation of the experiment. Inoculated calves were housed separately from uninoculated calves for 7 DAI, and their excreta were incinerated to kill sporocysts that might have passed unexcysted in their feces. They were fed milk until 6-8 weeks of age and then were fed grain and hay. Calves in experiment 1 were housed outdoors and had access