Development of an egg hatch assay for the detection of anthelmintic resistance to albendazole in Fasciola hepatica isolated from sheep

The aim of this study was to develop an egg hatch assay (EHA) to detect the resistance of Fasciola hepatica to albendazole (ABZ). With this purpose, two different F. hepatica isolates were tested: (i) susceptible (Shrewsbury/South Gloucester strain) to ABZ (SA); (ii) resistant to ABZ (RA). A commercial formulation of ABZ (Sinvermin®) diluted in dimethyl sulfoxide (DMSO) was used at concentrations of 0.0002, 0.002, 0.02, 0.2, and 2 μg/ml. In the SA isolates, eggs from feces exposed to ABZ at the three highest concentrations showed significantly lower hatching percentages than the control well (P < 0.01); also for the two highest concentrations, the percentage of development was significantly lower than the control (P < 0.01). However, in the RA isolate, no differences among treatments and control were found in the percentage of hatched or developed eggs. On the other hand, the EHA was conducted over a 15 day period following treatment with ABZ for sheep infected by the RA isolate. On day 7 post-treatment (pt), no differences among treatments and controls were observed. On day 15 pt, the development and hatching rates exposed to the highest ABZ concentration were lower than at lower concentrations, suggesting susceptibility. The ovicidal effect of ABZ and the potential use of EHA to differentiate between ABZ susceptible and resistant isolates are confirmed in the current study. However, the use of this technique should be confirmed with a higher number of isolates.