Description of the Sporulated Oocysts and Sporozoites of Four Species of Bovine Coccidia

Abstract

Detailed descriptions are given of the sporulated oocysts and sporozoites of the following species of coccidia from cattle: Eimeria bovis (Ziiblin, 1908) Fiebiger, 1912; E. auburnensis Christensen and Porter, 1939; E. ellipsoidalis Becker and Frye, 1929; and E. zurnii (Rivolta, 1878) Martin, 1909. Eleven or more species of coccidia of the genus Eimeria are currently recognized as occurring in bovine animals. Difficulty is often encountered in the identification of many of these species, partly because complete descriptions of their sporulated oocysts are lacking. Detailed descriptions of sporulated oocysts and sporozoites of four commonly encountered species of bovine coccidia are presented to augment the descriptions and illustrations reported by others (Becker and Frye, 1929; Becker, 1934; Christensen and Porter, 1939; Christensen, 1941; Hammond et al., 1946; and Davis and Bowman, 1952). The four species are Eimeria bovis (Ziiblin, 1908) Fiebiger, 1912; E. auburnensis Christensen and Porter, 1939; E. ellipsoidalis Becker and Frye, 1929; and E. zurnii (Rivolta, 1878) Martin, 1909. MATERIALS AND METHODS Oocysts of Eimeria bovis, E. auburnensis, E. ellipsoidalis, and E. zurnii were obtained from fecal samples collected from experimentally infected calves. Each sample was strained through a series of sieves, concentrated by repeated sedimentation, and the final sediment suspended in 2.5% potassium dichromate. Sporulation was induced by constant stirring of the mixture with a rotary mixer for several days. Before they were used, the oocysts were freed from potassium dichromate by repeated washing and centrifugation. The oocysts were then concentrated and freed from debris, using a modification of the differential sugar gradient described by Sharma et al. (1963). Our modified gradient was prepared by putting successively decreasing concentrations of sugar solutions into 50-ml centrifuge tubes as follows: 10.0 ml of saturated sugar solution; 8 ml of two parts water, five parts saturated sugar solution; 10 ml of one part water, Received for publication 5 February 1965. * Supported in part by research grant GB-785 from the National Science Foundation. Published as Journal Paper No. 444 Utah Agricultural Experiment Station. one part saturated sugar solution; 6 ml of two parts water, one part saturated sugar solution; 8 ml of water; and 6 to 8 ml of oocyst suspension added at the top. The tubes were centrifuged at 800 g for 5 min, after which time a layering of the oocyst suspension had occurred. The layering pattern, from the top of the tube to the bottom was: (1) clean layer, (2) cloudy layer, and (3) two dark opaque layers (containing most of the debris). Layers 1 and 2, containing most of the oocysts, were pipetted ff, and washed free of sugar by centrifugation. Measurements of 50 oocysts and sporocysts of each species were made from wet-mount preparations of the concentrated, sporulated oocysts. For drawings, preparations were used in which the oocysts were flattened under the pressure of a cover slip, sealed along its edges with vaseline. Free sporozoites were obtained by using the method of in vitro excystation described by Nyberg and Hammond (1964); oocysts pretreated with CO2 were incubated in bile-enzyme mixtures. The length, and the width at a point 3 ,u from the anterior end, of at least 10 free sporozoites of each species were measured. Measurements were also made at the widest point near the posterior end. A Zeiss microscope equipped with apochromatic objectiv s was used in determining the color of the oocysts. Illustrations were drawn to scale using both bright-field and phase-contrast microscopy.