A structural study of the Neospora caninum oocyst

Oocysts of Neospora caninum were collected from the faeces of a dog fed mou se brains containing tissue cysts of the NC-beef strain of N. caninum. Spor ulated oocysts were spherical tb subspherical, and were 11.7x11.3 mu m. The length/width ratio was 1.04. No micropyle or oocyst residuum was present. Polar granules were not present, although occasionally tiny refractile gran ules were seen among sporocysts. Sporocysts were ellipsoidal, did not conta in a Stieda body, and were 8.4x6.1 mu m. The length/width ratio for sporocy sts was 1.37; A spherical or subspherical sporocyst residuum was present, a nd was composed of a cluster of small, compact granules of 4.3x3.9 mu m, or was represented by many dispersed granules of similar size. Sporozoites we re elongate and 7.0-8.0x2.0-3.0 mu m in situ. No refractile bodies were pre sent and the nucleus was centrally or slightly posteriorly located. The fea tures of the oocyst of N. caninum are similar to those of Hammondia heydorn i oocysts from dog faeces and Toxoplasma gondii and Hammondia hammondi oocy sts from cat faeces. (C) 1999 Australian Society for Parasitology Inc. Publ ished by Elsevier Science Ltd. All rights reserved.