Tissue cyst forming coccidia; Toxoplasma gondii and Neospora caninum as a cause of disease in farm animals

Introduction Toxoplasma gondii and the closely related Neospora caninum are important obligate intracellular apicomplexan parasites causing a wide range of diseases in different host species. Their life cycles are similar, consisting of a) asexual stage where multiplying tachyzoites trigger lesion development in different tissues and eventually develops to persistent tissue cysts in intermediate hosts (mainly CNS and muscular tissue) and b) sexual stages where oocysts are produced in intestinal tissues of the final hosts. The final hosts for T. gondii are all felids (the domestic cat is most important), and the dog is presently the only definitive host known for N. caninum. Although the two parasites are closely related they do exhibit important differences, for example, T. gondii is known to be a major cause of reproductive failure in sheep, but is not an important pathogen in abortion and congenital infection in cattle, whereas the opposite is true for N. caninum.