Comparison of immunological and molecular methods for the diagnosis of infections with pathogenic Sarcocystis species in sheep

Sheep may be infected by four species of Sarcocystis: Sarcocystis tenella and Sarcocystis arieticanis are pathogenic, Sarcocystis gigantea and Sarcocystis medusiformis are non-pathogenic. The two pathogenic species may cause abortion or acute disease during the early phase of infection and chronic disease during the late phase of infection. Thus far, diagnosis of sarcocystiosis has been limited, because traditional diagnostic tests based on the detection of Sarcocystis-specific antibodies are only genus-specific and, thus, cannot differentiate between pathogenic and non-pathogenic Sarcocystis species. In addition, most of these tests can only detect chronic sarcocystiosis. Therefore, diagnosis of acute sarcocystiosis or Sarcocystis-induced abortion has been based mainly on post-mortem examination, i. e. after the animal had succumbed to the disease. Recently, we have established species-specific PCR assays based on unique ribosomal RNA gene sequences of S. tenella and S. arieticanis. These assays enable the diagnosis and differentiation of infections with S. tenella and S. arieticanis in sheep intra vitam during the acute phase of the disease and, therefore, facilitate for the first time comprehensive studies on the epidemiology and importance of infections with pathogenic Sarcocystis species in sheep.