Isolation of Trypanosoma theileri from the blood of two cows, one leukotic, one exhibiting lymphocytosis.

Trypanosoma theileri was isolated by the blood culture method from a leukotic cow in extremis. The parasite could be maintained along with leukocytes with weekly changes of culture medium up to 6 months. In connection with a subsequent transmission experiment a cow, not inoculated with trypanosomes but kept in the same shelter as the inoculated one, commenced to be positive for T. theileri in its blood cultures. This cow had a long history of lymphocytosis but showed no signs of leukosis when slaughtered. The significance of the findings is discussed from the point of view of false positive diagnosis of bovine leukosis and the possible role of trypanosome in the etiology of leukosis.