Trypanosoma theileri Laveran, 1902, in Wyoming cattle

Trypanosoma theileri Laveran, 1902, a cosmopolitan blood parasite of cattle, was found in 86 of 377 Wyoming cattle. Acute infection was experimentally produced in 22 cattle, with blood stream trypanosomes reaching peaks (up to 8,00/ml) in the first 2 weeks of infection. Infection subsided after 3 to 4 weeks. In studies of animals with chronic infection, the parasites reappeared in the blood 4 to 6 months after initial exposure and again at 8 months. Morphologically, three trypomastigote forms were seen: short-thin forms, long-thin forms, and long-broad forms. It is considered that the first two types derived from the last. Comparisons of bloodstream trypomastigotes were made with chicken embryo culture forms, and it was concluded that identification and description of trypanosomes from cattle can be made only by examination of bloodstream stages.