KINETICS OF HEMATOPOIETIC PROGENITOR CELLS DURING A TRYPANOSOMA-CONGOLENSE RECHALLENGE INFECTION IN BORAN CATTLE

In a preliminary study, using clonogenic assays, the in vitro kinetics of committed haemopoietic progenitors were monitored during a Trypanosoma congolense rechallenge infection in five trypanosusceptible Boran cattle. Early in the infection (week 2), in the absence of any detectable parasitaemia, a drop in the number of nucleated marrow cells was recorded. This was accompanied by a marked but transient decrease in the levels of the colony-forming units-erythroid (CFU-E) followed by a partial recovery by weeks 3-4 after infection. The burst-forming units-erythroid (BFU-E) and the colony-forming units-granulocyte macrophage (CFU-GM) also significantly decreased between weeks 2 and 4. After a transient rise at weeks 3-5 postinfection, the CFU-GM steadily declined and remained below preinfection levels throughout the infection. The BFU-E remained below preinfection levels until the end of the experiment. The drop in nucleated marrow cells associated with the decreased numbers of CFU-E, BFU-E and CFU-GM was suggestive of a defect at the pluripotential stem cell level early in the infection (week 2). The erythrocyte indices, i.e. mean corpuscular volume (MCV) and mean corpuscular haemoglobin concentration (MCHC), were unchanged until week 10 postinfection. Two animals became severely anaemic; one was euthanised at week 8 and one treated at week 9. The three remaining animals developed chronic anaemia with mean packed cell volume (PCV) fluctuating around 18%-19% between weeks 11 and 14. Low parasitaemia levels were recorded during that period. A CFU-E peak above preinfection levels was noted at week 12 and BFU-E appeared in the peripheral blood culture of two animals between weeks 11 and 14. A progressive rise in MCV associated with a gradual decrease in MCHC also characterised that period. A return to near preinfection levels was recorded for the numbers of all three progenitors three weeks after trypanocidal treatment followed by a full recovery five months after treatment. Although ineffective haemopoiesis has been suggested to contribute to the anaemia of bovine trypanosomiasis, this is the first demonstration of a negative effect on erythroid development in cultures of bone marrow of trypanosome-infected cattle.