Bar-structure in bovine erythrocytes infected with Theileria sergenti

The purpose of this study is to elucidate some morphological characteristics of the bar-structure in bovine erythrocytes infected with Theileria sergenti. The bar-structure, the veil or the both were observed in infected erythrocytes. Infected bovine erythrocytes were classified into four types according to the included structures. Infected cells containing bar-structures increased with the progress of parasitemia. In Giemsa-stained blood preparations, bar-structures appeared purplish-red and measured a mean of 1.6 micron in length and up to 0.1 micron in width. Bar-structures were usually straight, sometimes S-shaped, and located in the periphery of infected erythrocytes. In the direct fluorescent antibody test with T. sergenti-positive bovine serum both piroplasms and bar-structures exhibited fluorescence. However, in the indirect fluorescent antibody test with monoclonal antibodies against piroplasms only piroplasms showed a highly specific fluorescence. Electron microscopy revealed that bar-structures were vesicular in structure, surrounded by a double membrane connected to the host cell membrane.