Pathological Studies on Aleukemic Case of Bovine Leukosis

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Abstract
Eleven (11.7%) of 94 cows affected with the adult type of bovine leukosis were diagnosed as aleukemic cases by the hematological diagnositic key of the European Community (EC). Atypical mononuclear cells (AtMC) amounted to 143-450/cmm (1.5-3.6%) in the peripheral blood of 3 of the 11 cows. These findings were indistinguishable from those of healthy cattle. Although no persistent lymphocytosis was observed in the other 8 cows, AtMC amounted to 891-2912/cmm (9.5-28.0%). Histopathological and ultrastructural studies on tumorous lesions and cells in the aleukemic cows revealed no essential differences from those on leukemic leukosis. A common finding of aleukemic leukosis obtained was practically no proliferative lesions of neoplastic cells in the spleen. One of the 3 cows, without showing an increase in AtMC in the peripheral blood was considered to be in the early stage of disease. In it tumorous lesions were detected in some of the lymph and hemolymph nodes. Fairly marked tumorous lesions were found in the visceral organs of the other 2 cows. Neoplastic cells were were located dispersedly in the dilated sinus of most of the lymph nodes in the 3 cows. There might be enough room in the sinus for neoplastic cells to proliferate in the lymph nodes and to obstruct the AtMC flow into the peripheral circulation. The necessity of careful observation of the blood smear for an accurate diagnosis of aleukemic bovine leukosis by the hematological diagnostic key of EC is discussed.

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