Comparative ultrastructure of tachyzoites, bradyzoites, and tissue cysts of Neospora caninum and Toxoplasma gondii

The ultrastructure of tachyzoites, bradyzoites and tissue cysts of the NC-1 , NC-5 and NC-Liverpool strains of Neospora caninum are reviewed and compar ed with those of the VEG and ME-49 strains of Toxoplasma gondii. While each stage of N. caninum and T. gondii shared many ultrastructural characterist ics. each parasite stage also had certain features or organelles that could be used to distinguish the two parasites. Some of the most prominent ultra structural differences occurred in the number, appearance and location of r hoptries, looped-back rhoptries, micronemes, dense granules, small dense gr anules and micropores. The tissue cysts of both parasites were also basical ly similar, being surrounded by a cyst wall and not compartmentalised by se pta. The cyst wall of N. caninum was irregular and substantially thicker, 0 .5-4 mu m, than those of T, gondii which were smooth and 0.5 mu m thick. (C ) 1999 Australian Society for Parasitology Inc. Published by Elsevier Scien ce Ltd. All rights reserved.