In order to compare the prophylactic effect provided by a
poly(D,L-lactide) sustained-release device (SRD) containing
isometamidium (
ISMM) with that provided by the classical
intramuscular injection of the
drug, a field trial was carried out at the Madina Diassa Ranch in Mali. One- to 3-year-old N'Dama cattle were randomly divided into three groups. The first group (n = 42) was treated with
ISMM at a dose of 1 mg/kg of
body weight, the second group (n = 44) received the same dose of the
drug via an SRD, which was subcutaneously implanted in the shoulder region, and the third group (n = 36) was kept as an untreated control group. All animals were treated with
diminazene aceturate (7 mg/kg of
body weight) 2 weeks before the start of the experiment and were tested monthly by the buffy coat technique for a period of 8 months. Glossina morsitans submorsitans was the most important tsetse species, with apparent densities (number of catches/trap/day) varying between 11.9 and 38.7 over the experimental period. Eight months
after treatment the cumulative
infection rates were 27.7, 58.5, and 77.4% in the group with the SRD implant, the group receiving the
intramuscular injection, and the control group, respectively. Statistical analysis showed that the incidence of
trypanosomiasis was significantly lower (P = 0.006) in the group which received
ISMM via the SRD than in the one which was treated with
ISMM intramuscularly.