Diagnosis of albendazole resistance in fasciola hepatica

Abstract

The increasing widespread development of drug resistance in the liver fluke Fasciola hepatica has motivated the need for alternative diagnostic tools. The work reported here describes the validation of an egg hatch test (EHT) as an in vitro technique to detect albendazole (ABZ) resistance in F. hepatica. The validation includes the intra-assay, inter-assay and intra-herd variations, and the comparison of results obtained after performing the EHT and a controlled efficacy test. Additionally, the development of the protocol included the adjustment of different critical factors to improve the simplicity of the assay. The greatest uniformity between results within the assay and over time until 8 weeks after gallbladder eggs collection (the deadline proposed for egg analysis), was obtained after incubation with an ABZ concentration of 0.5 µM. The length of exposure to ABZ was shown to be critical, as prolonged (15 days) ABZ incubation led to a reversal of drug resistance. There was a close agreement between the outcome of the EHT and that obtained for the in vivo assays. Moreover, the same level of resistance was observed when eggs and faeces were collected from animals of four (4) different farms and analyzed with both the EHT and the faecal egg count reduction test. A 0.5 µM drug level is confirmed as the discriminating concentration to predict ABZ resistance by the EHT in F. hepatica.