<span style="font-family: arial,helvetica;">The infection of Yankassa rams with three important trypanosome species affecting livestock, namely, <em>Trypanosoma congolense, T. vivax and T. brucei </em>produced both acute and chronic fatal conditions. Chronic infections were induced in the three infections by the application of subcurative doses of diaminazene aceturate (Berenil&reg;). Pathological changes in the infected animals included splenomegaly and hepatomegaly which were more pronounced in acute than in chronic <em>T. congolense</em> infection. However, these changes were more severe in chronic than in acute <em>T. vivax</em> infection. While splenomegaly was more pronounced in chronic <em>T. brucei </em>infection than in acute, hepatomegaly and lymphadenopathy were more severe in acute than in the chronic condition. The increases in size of the spleen, lymph nodes and liver were associated with congestion, increases in cell density related to increased immunological reactions in the spleen and lymph nodes as well as increase in numbers, size and activity of the phagocytic cells in these organs.</span>

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The cytogenic origin of canine transmissible venereal tumor (CTVT) still remains unknown. Resulting from paucity of information on the histiocytic phenotypic features and behaviours of CTVT, this study was undertaken to show some uncommon cytomorphological features of CTVT and its immunoreactivity with S-100 protein. Nine cases of CTVT were investigated (6 females and 3 males) using nine fine needle aspirates for cytology and four biopsy samples for histopathology and immunohistochemistry. Cytology revealed CTVT cells with pale basophilic, fine granular cytoplasm and distinct intra-nuclear (3/9) and intra-cytoplasmic (9/9) vacuolations. Erythrophagocytosis by a giant binucleated CTVT cell in one dog and nuclear budding in 2 dogs were observed. Histopathology showed loose sheets and cords of uniformly round to ovoid cells with slight indistinct eosinophilic cytoplasm and a tendency towards glandular as well as syncytial formation. Nuclei were large and round with a single centrally placed nucleolus. The mitotic index was high. Immunohistochemistry of the four biopsy samples revealed negative immunoreactivity to pan-cytokeratin, actin and desmin but positive immunoreactivity with vimetin and S-100 proteins. This is the first report in which CTVT showed erythrophagocytosis, nuclear budding and positive immunoreactivity to S-100 protein. Based on these cytomorphological and immunohistochemical features, we conclude that CTVT is of histiocytic/dendritic origin.

Trois chiens ont été infectés par une souche ILRAD 1797 de Trypanosoma brucei par voie sous-cutanée. Une anémie hémolytique a été provoquée artificiellement chez deux autres chiens par phlébotomie, traitement thermique et réinjection de sang, alors que deux autres chiens ont servi de témoin. Les animaux infectés ont manifesté une panleucopénie et une thrombocytopénie, alors que les chiens atteints d'une anémie hémolytique provoqué artificiellement ont présenté une leucocytose et une thrombocytose. Ces résultats laissent supposer l'existence d'un facteur d'aplasie médullaire dans le plasma des chiens infectés à T. brucei, d'autant plus que la production leucocytaire a été affectée.