No evidence for synergy between nitroxynil and triclabendazole against juvenile, 4-week-old, triclabendazole-resistant Fasciola hepatica in sheep.

摘要

Triclabendazole is currently the only single flukicide with licensed efficacy claims against all parasitic stages of Fasciola hepatica, including young immature flukes; it has been widely used in sheep and cattle for more than 30 years. Triclabendazole resistance was first confirmed in 1995 in Australia and since then has been reported in many other countries. Previous studies have shown synergy between triclabendazole and other flukicides against triclabendazoleresistant (TCBZ-R) liver fluke isolates. A study was conducted in sheep to investigate whether synergy exists between nitroxynil and triclabendazole, when administered at their recommended doses, in the treatment of early, immature (4-week-old) TCBZ-R F. hepatica infections. Lambs (68) were allocated by live weight to six groups and each animal was dosed with either 250 triclabendazole-susceptible (TCBZ-S) metacercariae (Groups 1 and 3) or 250 TCBZ-R metacercariae (Groups 2, 4, 5 and 6). Treatments were administered 28 days after infection. Groups 3 and 4 were dosed with triclabendazole (10 mg/kg); Group 5 with nitroxynil (10 mg/kg), Group 6 with triclabendazole (10 mg/kg) plus nitroxynil (10 mg/kg); Groups 1 and 2 were not treated with a flukicide. The livers of two lambs from each group were examined post-mortem 48 hours after treatment; the remaining lambs were submitted for necropsy eight weeks post-treatment (12 weeks post-infection) to determine efficacy. Amongst groups infected with TCBZ-R metacercariae, there were no significant differences (P<0.001) in the numbers of fluke recovered 12 weeks post-infection, irrespective of treatment. The mean number of flukes recovered at 12 weeks in Groups 2, 4, 5 and 6 was 53, 63, 43 and 51, respectively. There was no evidence from this study that, at their recommended dosages, triclabendazole alone, nitroxynil alone or a combined treatment with triclabendazole plus nitroxynil were effective in eliminating infections with 4-week-old TCBZ-R F. hepatica in sheep.