Activity of Duddingtonia flagrans on Trichostrongylus colubriformis larvae in goat feces and interaction with a benzimidazole treatment

Due to the high level of anthelmintic resistance in goat nematode populations in France, there is an obvious need to develop alternative strategies to control parasitic infections in grazing animals. The purpose of this work was first to assess the efficacy of the nematode trapping fungus Duddingtonia flagrans on the development of infective larvae of Trichostrongylus colubriformis in feces. Eighteen culled strongyle free dairy goats were experimentally infected with 7500 infective larvae of a T. colubriformis benzimidazole resistant strain. Half of the animals received an oral dose of 5 × 105 D. flagrans chlamydospores/ kg body weight (BW) during 9 days whereas the remaining was kept as controls. From the 6th day of administration onwards, coproscopical examinations as well as standard coprocultures incubated 13 days at 26 ◦C were performed on all the animals. The reduction in developing T. colubriformis larvae due to activity by D. flagrans ranged from 86 to 96% compared to control. The second objectivewas to determine an eventual interaction in the feces between the growth and the trapping activity of D. flagrans and the presence of benzimidazole (BZD) compounds, some of which having a high antifungal activity. In a first experiment, the growth of D. flagrans spores was measured on Sabouraud medium with increasing concentrations of thiabendazole (TBZ, 1–200 g/ml) or albendazole (ABZ, 1–10 g/ml) added. In a second experiment, the activity of D. flagrans against BZD resistant T. colubriformis larvae was assessed in feces with TBZ solution added (final concentration of 100 g TBZ/g of feces) compared to controls without TBZ or without D. flagrans spores. Finally, the larval development of BZD resistant T. colubriformis in feces was compared from goats fed or not fed D. flagrans chlamydospores (5×105/kg BW) and either treated or not with TBZ (50 mg/kg BW) or ABZ (5 mg/kg BW). The results clearly indicated a very high fungicidal activity of TBZ against D. flagrans on Sabouraud medium from 10 g/ml whereas no antagonistic activity could be measured for ABZ because of solvent toxicity. When adding directly TBZ upon the feces or when collecting feces 24 h or 36 h after drenching the animals (TBZ or ABZ), the effect of these drugs on the activity of D. flagrans could not have been assessed because of the absence of larval development due to the BZD compounds. These results showed that the level of BZD compounds in feces immediately after drenching was probably so high that a nearly total inhibition of larval development occurred even when aresistant strain is concerned. Ninety-six hours after drenching, the full predatory activity of D. flagrans was displayed again, indicating that no long term inhibition due to BZD residues could be suspected. © 2004 Elsevier B.V. All rights reserved