A collective outbreak of an infection character- ized with anemia occurred among imported Jersey cows in Okayama Prefecture.A type of Trypanosoma was isolated from 2 cows involved in the outbreak. From its morphological and other characteristics, this type was identified as Trypanosoma theileri or some closely related type.
The virulent blood of naturally infected cows was inoculated to mice, guinea pigs, and rabbits with negative results. Artificial infection was successful in Jersey cows, in the circulating blood of which appeared trypanosomata.
The isolated trypanosoma was easily propagated in N. N. N. media and kept by passage until the 17th generation.
At autopsy, naturally infected fatal cases revealed hemorrhagic changes in the lymph nodes, skin, mucous membranes, subcutaneous tissue and intestinal tract, and the swelling of the spleen and liver. Artificially infected cows presented the swelling of the spleen, liver, and lymph nodes.
Histologically, remarkable activation of the reticulo-endothelial system, hemosiderosis of the liver, kidney, and lymph nodes, increase of phasrna cells in the spleen and lymph nodes, local, lymphocytic, interstitial nephritis, and congestive spleen were observed.
As the virulent blood contained a relatively large number of small piroplasmata as well as trypanosomata, these findings might have been caused by the pathogenicity produced by synergy of the two kinds of protozoa which are generally considered to be not so highly pathogenic. If the pathology of pure infection of either protozoa is clarified, the etiological analysis of mixed infection in the present cases will be feasible.
