Evaluation of benzimidazole resistance status in Ascaridia galli

The occurance of Ascaridia galli has increased since the EU ban on battery cages. Reliance on anthelmintic drugs against A. galli in laying hens increases the risk for development of resistance in the abcense of systematic monitoring tools. In this study susceptability of A. galli to benzimidazole (BZ) was investigated using faecal egg count reduction test (FECRT), in ovo larval development test (LDT) and genetic markers (mutations at codons 167, 198 and 200 of ß-tubulin gene). Six flocks (F1-F6) of a commercial laying hen farm were recruited. The F1/F4 were treated with flubendazole at 22, 27 and 36 weeks post placement (wpp). The F2/F5 were treated at 27 wpp while F3/F6 were not treated. The FECR was calculated by analyzing faeces from 15 randomly selected hens (F1, F2, F4 and F5) before and 10 days after treatment. The liquid-based LDT was performed on parasite eggs isolated from pooled samples collected at 43 wpp from all flocks. LC50 and LC99 were calculated using a non-linear regression model. Twenty adult worms were collected at 45 wpp from each flock for DNA extraction and sequencing of the ß-tubulin gene. In all flocks, irrespective of the number of exposures to FBZ, the percentage FECR were above 95% with lower confidence intervals above 90%. No significant difference was observed (p> 0.05) among obtained LC50 (F1/F4 and F2/F5 vs. F3/F6) in the LDT. However, LC50 and LC99 were higher than suggested values for declaration of resistance in other nematode species. No variation was observed in codon positions known to be involved in BZ resistance. Overall, our results indicated lack of evidence of resistance to BZ in A. galli. More research is needed to confirm these results and to further optimize the existing tools for detection and monitoring of AR in A. galli.