Theileriosis in a Missouri beef herd caused by Theileria buffeli: Case report, herd investigation, ultrastructure, phylogenetic analysis, and experimental transmission

A 6-year-old Simmental cow infected with Theileria buffeli had a clinical d isease characterized by theilerial parasitemia, macrocytic normochromic ane mia with acanthocytosis and spherocytosis, lymphoid hyperplasia (lymphocyto sis, edematous lymphadenomegaly), dysproteinemia, evidence of liver disease , and a low serum antibody titer against T. buffeli. The cow was in a herd in which all cattle originated in Missouri; 22/75 (29%) of cattle had a the ilerial parasitemia and 26/75 (35%) had titers to T. buffeli of greater tha n or equal to 1:160. Classification of the Missouri bovine organism as T. b uffeli was based on DNA sequencing and comparison to sequences for T. buffe li and Theileria sp. type A obtained from GenBank. Intraerythrocytic veils and piroplasms were seen during transmission electron microscopy. The organ ism was successfully transmitted to two splenectomized calves, which develo ped mild anemias while parasitemic. Blood from the second calf was used as the source of T. buffeli antigen for an indirect immunofluorescence antibod y test. Theilerial isolates from a Missouri white-tailed deer were also seq uenced and resembled Theileria sp. types F and G and were not consistent wi th the bovine organism.