Comparison of two assays, a faecal egg count reduction test (FECRT) and a coproantigen reduction test (CRT), for the diagnosis of resistance to triclabendazole in Fasciola hepatica in sheep

A sheep trial was performed to evaluate two diagnostic assays, a faecal egg count reduction test (FECRT) and a coproantigen reduction test (CRT), for the diagnosis of resistance of Fasciola hepatica to triclabendazole (TCBZ). The FECRT defines successful TCBZ treatment as a 95% or greater reduction in fluke faecal egg counts (FECs) at 14 days post-treatment (dpt). The CRT defines effective TCBZ treatment as faeces negative for Fasciola coproantigens at 14dpt, as measured by the commercial BIO K201 coproantigen ELISA (Bio-X Diagnostics, Jemelle, Belgium). Forty-nine indoor-reared sheep were split into four trial groups and each sheep was infected with 200 metacercariae of 1 of 4 F. hepatica isolates, previously described as susceptible (Cullompton and Fairhurst) and resistant (Leon and Oberon) to TCBZ action, respectively. TCBZ treatment was administered at 12 weeks post-infection (wpi) to one sub-group in each infected sheep group, and these sheep were culled at 4 weeks post-treatment (wpt). Untreated sheep sub-groups, were culled at a parallel time-point, that is, at 16wpi. Necropsy was performed to confirm treatment efficacy. Individual faecal samples were collected twice-weekly throughout the trial period, sub-sampled and examined by a standardised egg sedimentation protocol and by the BIO K201 ELISA. Results supported the use of both the FECRT and the CRT for the diagnosis of resistance of F. hepatica to TCBZ. In addition, the study confirmed the TCBZ susceptibility of the Cullompton and Fairhurst F. hepatica isolates and the TCBZ resistance of the Oberon F. hepatica isolate. However, the Leon F. hepatica isolate was found to be susceptible, rather than resistant, to TCBZ action.     

Comparative use of faecal egg count reduction test,egg hatch assay and beta-tubulin codon 200 genotyping in small strongyles (cyathostominae) before and after benzimidazole treatment

A survey on benzimidazole (BZ) resistance in small strongyles was performed on three farms in the tenth region in Chile. Samples from a total of 100 horses were tested using the faecal egg count reduction test (FECRT), the egg hatch assay (EHA) and an allele-specific PCR for the detection of beta-tubulin isotype 1 genes coding for phenylalanine (phe) or tyrosine (tyr) at codon 200. In the past, BZ-type drugs have been used within anthelmintic campaigns on all the three farms. This has predictably led to a high degree of BZ resistance at the Valdivia and Ri?ihue farms and to a lesser degree at the Frutillar farm, as demonstrated by all the three tests. The FECRT indicated resistance in every farm by faecal egg count reductions (FECR) of 27% (S.D. +/- 33), 26.5% (S.D. +/- 26.9) and 83.9% (S.D. +/- 22.8) for the Valdivia, Ri?ihue and Frutillar farms, respectively. With the EHA, the following mean LD(50) values were found before and after treatment with fenbendazole (FBZ): 0.093, 0.141 and 0.066 microg TBZ/ml and 0.149, 0.158 and 0.091 microg TBZ/ml, respectively, for the Valdivia, Ri?ihue and Frutillar samples. The corresponding LD(96) values were 0.222, 0.263 and 0.188 microg TBZ/ml before treatment and 0.316, 0.322 and 0.221 microg TBZ/ml after treatment, indicating BZ resistance in all the cases. Genotyping was performed on more than 1700 single larvae, at least 10 per faecal sample, for 98 pre- and 66 post-treatment samples. Despite a general trend toward higher percentages of phe/tyr and tyr/tyr individuals following treatment, no statistically significant difference was found between these two and the phe/phe genotype percentages. However, a significantly negative correlation was detected between the LD(50) values and the phe/phe percentages and there was a positive correlation between the FECRT results and the phe/phe percentages. Thus, there seems to be a difference in the significance of the codon 200 polymorphism in the mechanisms of BZ resistance in small strongyles of the horse and sheep trichostrongyles.