Submitted to: Microscopy Society of America Proceedings
Publication Type: Abstract Only
Publication Acceptance Date: 4/28/1997
Publication Date: N/A
Citation: Interpretive Summary:
Technical Abstract: Relatively benign, mildly pathogenic strains of bovine Theileria, an intraerythrocytic protozoan parasite, have been reported in many parts of the world including the United States. The Theileria found in the US has not been specifically speciated; however, it has been referred to as T. mutans-like. Although cattle in the US infected with these Theileria spp. usually have a circulating parasitemia of less than 1% and are asymptomatic, recently an animal suffering from severe anemia was admitted to the Large Animal Clinic at Texas A&M University with a circulating parasitemia of over 50%. Parasites in Giemsa stained blood films were pleomorphic in shape, with some parasites apparently connected to the erythrocyte membrane by structures which appeared similar to the bar structure found within eland erythrocytes parasitized by T. taurotragi. Examination by TEM revealed that parasitized erythrocytes contained parasites which possessed cytoplasmic extensions and an interaction between the parasite and the erythrocyte membrane which involved invaginations of the erythrocyte membrane that appeared to be surrounded by parasite cytoplasm. In semi-thick sections (400 nm as opposed to 70 nm for thin sections) the parasite cytoplasm surrounding the erythrocyte membrane invagination was connected to the main body of the parasite by a cytoplasmic extension. The parasite-erythrocyte membrane interaction was similar to that described at the ultrastructural level for T. taurotragi, except that in the latter case parasite membranes taking part in the interaction were reported to be on the exterior of the erythrocyte forming what was referred to as a vesicular structure which may serve as a "metabolic window."