Bone marrow response to acute and chronic Trypanosoma congolense infectionin multimammate rats (Mastomys coucha)

The femoral bone marrow of multimammate rats (n = 90), aged 3 8 weeks, expe rimentally infected with different doses of Trypanosoma congolense was exam ined by light and electron microscopy. Some animals died from trypanosomosi s, but groups of 10 were killed at 4 8, 9-16, 20 24, 30, 40, 50 and 60 days post-infection (dpi). In the acute stage of infection (4 8 dpi) the bone m arrow invariably showed a striking increase in erythropoiesis, characterize d by an increase in the number of mitotic figures and erythroblastic island s and by a marked decrease in the myeloid:erythroid cell ratio. Later in th e infection, erythropoietic activity decreased, while erythrophagoctosis, g ranulopoiesis, megakaryopoiesis and plasma cell population increased. In ch ronic infection (16 60 dpi), erythropoietic activity decreased, while intra - and extra-vascular erythrophagocytosis greatly increased. There was also an increase in the bone marrow stroma cells. Exercise erythrophagocytosis b y these cells led to the formation of myelin figures and cytoplasmic teleph agolysosomes. Degeneration and necrosis of neutrophils lining the adluminal surfaces of the blood sinuses were observed. It is concluded that in the a cute stage of the infection, the bone marrow is responsive to the anaemia a nd that in the chronic stage, dyserythropoiesis and increased erythrophagoc ytosis by the expanded and activated cells of the mononuclear phagocytic sy stem play an important role in the production of anaemia. (C) 2001 Harcourt Publishers Ltd.