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 Trypano soma congolense rechallenge infection in five trypanosusceptible Boran cattle. Early in the infection (week 2), in the absence of any detect able parasitaemia, a drop in the number of nucleated marrow cells was recorded. This was accompanied by a marked but transient decrease in t he 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 decline d and remained below preinfection levels throughout the infection. The BFU-E remained below preinfection levels until the end of the experim ent. 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 p luripotential stem cell level early in the infection (week 2). The ery throcyte indices, i.e. mean corpuscular volume (MCV) and mean corpuscu lar haemoglobin concentration (MCHC), were unchanged until week 10 pos tinfection. Two animals became severely anaemic; one was euthanised at week 8 and one treated at week 9. The three remaining animals develop ed chronic anaemia with mean packed cell volume (PCV) fluctuating arou nd 18%-19% between weeks 11 and 14. Low parasitaemia levels were recor ded during that period. A CFU-E peak above preinfection levels was not ed at week 12 and BFU-E appeared in the peripheral blood culture of tw o animals between weeks 11 and 14. A progressive rise in MCV associate d with a gradual decrease in MCHC also characterised that period. A re turn to near preinfection levels was recorded for the numbers of all t hree progenitors three weeks after trypanocidal treatment followed by a full recovery five months after treatment. Although ineffective haem opoiesis has been suggested to contribute to the anaemia of bovine try panosomiasis, this is the first demonstration of a negative effect on erythroid development in cultures of bone marrow of trypanosome-infect ed cattle.