PROPHYLACTIC EFFECTS OF ISOMETAMIDIUM-SUSTAINED AND ETHIDIUM-SUSTAINED RELEASE DEVICES AGAINST TRYPANOSOMA-CONGOLENSE IN CATTLE

Two successive experiments were carried out in which three cows were t reated by intramuscular injection of either 0.5 mg/kg isometamidium or 1 mg/kg ethidium and compared with another group of three cows which received a subcutaneously implanted sustained release device (SRD) con taining the same dose of drug. The prophylactic effect of both drug fo rmulations was evaluated by exposing the animals at monthly intervals to Glossina morsitans morsitans infected with Trypanosoma congolense. The average protection period using the isometamidium- and the ethidiu m-SRD was extended by a factor of 3.2 and 2.8, respectively in compari son with the intramuscular injection of the drugs. In the analysis of isometamidium concentrations in the serum of the animals using a compe titive drug-ELISA the drugs remained present for much longer periods i n the sera of the implanted animals than in those of the intramuscular ly treated cattle. The animals were still protected, however, a long t ime after the disappearance of detectable drug levels in the serum. No difference in drug sensitivity could be observed, when breakthrough i solates were compared from animals which received the ethidium-SRD and those treated intramuscularly, although a slight loss of sensitivity occurred in the breakthrough isolates as compared to the parent trypan osome population. (C) 1997 Elsevier Science B.V.