Platelet aggregation inhibition in Trypanosoma vivax infection of sheep

We have investigated in vitro platelet aggregation in platelet rich plasma from Trypanosoma vivax infected and control sheep using the dual channel Payton Aggregometer. Final concentrations of the following inducing agents were used: 1.2 um ADP, 6.2 ug collagen, 1.2 ug ristocetin and 1 u thrombin. These showed that there was a significantly reduced aggregation of platelets from infected sheep (13.4 +/- 1.1 pc at week 3 post infection when compared with control sheep PRP 95.0 +/- 1.0pc; P less than 0.001) using ADP. Similar differences were also obtained with other inducing agents. Preliminary 14C-5HT uptake and release studies showed that there was difference in the uptake of label between platelets from infected (18.6pc) and control (28.4pc) sheep. However, when release was inducted, comparable results were obtained for both infected and control sheep platelets. It is concluded that the degree of aggregation inhibiting varies directly with the level of parasitaemia.