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CHRONIC monocytic leukaemia (CMoL) is characterised by the proliferation of mature monocytes that predominate in the peripheral blood ( Monteith and Cole 1995 ). CMoL is frequently indolent, with a persistent monocytosis that is unresponsive to therapeutic agents (Messick 2000). In human beings, the disease has an asymptomatic period of evolution before becoming clinically evident. Initially, cytopenia of one or more blood cell types is observed, followed by pronounced splenomegaly and then marked peripheral blood monocytosis with bone marrow infiltration. Occasionally, hepatomegaly and lymph node enlargement are evident ( Bearman and others 1981 ).
CMoL is rare in human beings ( Bearman and others 1981 ), and is seldom recognised in domestic animals ( Valli and others 2002 ). In previously reported cases, dogs presented with normocytic normochromic anaemia, marked leucocytosis and thrombocytopenia, but the description of many cells as monoblasts and the presence of atypical mononuclear cells with a monocytoid appearance, noted on examination of a peripheral blood smear, do not allow a definitive diagnosis of CMoL to be made ( Mackey and others 1975 ). At the time of the report by Mackey and others (1975) , certain diagnostic tools such as flow cytometry were not available, and so a definitive diagnosis of CMoL could not be reached. This short communication describes the clinicopathological features of a dog diagnosed with CMoL on the basis of clinical, haematological and flow cytometric findings.
An 11-year-old neutered male crossbred dog was presented to a private veterinary clinic with signs of apathy, shivering and pale mucous membranes. On physical examination, there were no signs of hepatomegaly, splenomegaly or enlarged lymph nodes. A complete blood cell count (CBC) performed by the referring veterinarian showed severe anaemia (haematocrit 19·4 per cent, reference range 37 to 55 per cent; haemoglobin 64 g/l, reference range 120 to 180 g/l), a severe leucocytosis (43·2 x 109 cells/l, reference range 6 x 109 to 17 x 109 cells/l) with atypical cells, and a normal platelet count (450 x 109 platelets/l, reference range 150 x 109 to 550 x 109 cells/l). PCR assays for Ehrlichia canis , Leishmania species and Mycoplasma haemocanis were negative. On the basis of the large number of atypical cells seen on blood...