Anthelmintic efficacy on Parascaris equorum in foals on Swedish studs.
BACKGROUND
In the last few years stud farms have experienced increasing problems with Parascaris equorum infections in foals despite intensive deworming programs. This has led to the question as to whether the anthelmintic drugs used against this parasite are failing. This study aimed to investigate the efficacy of ivermectin, fenbendazole and pyrantel on the faecal output of ascarid eggs of foals.


METHODS
A Faecal Egg Count Reduction Test (FECRT) was performed on nine large studs in Sweden. Anthelmintic drugs were given orally and faecal samples were examined for ascarid eggs on the day of deworming and 14 days later. Faecal Egg Count Reductions (FECRs) were calculated on arithmetic means of transformed individual FECRs and on arithmetic means of individual FECRs.


RESULTS
Seventy-nine (48%) out of a total of 165 foals sampled were positive for P. equorum eggs before deworming and 66 of these met the criteria for being used in the efficacy assessment. It was shown that there was no, or very low activity of ivermectin on the output of ascarid eggs in the majority of the foals, whereas for fenbendazole and pyrantel it was >90%.


CONCLUSIONS
Ivermectin resistance was shown in 5 out of 6 farms. Therefore, ivermectin should not be the drug of choice in the control of P. equorum infections in foals. According to the results of this study, fenbendazole or pyrantel are still effective and should be used against this parasite.
Lind
Eva Osterman
EO
National Veterinary Institute, Department of Virology, Immunobiology and Parasitology, Section for Parasitological Diagnostics, SE-751 89 Uppsala, Sweden. eva.osterman-lind@sva.se
Christensson
Dan
D
D000818:Animals; D000871:Anthelmintics / Q000627:therapeutic use*; D017191:Ascaridida Infections / Q000188:drug therapy / Q000662:veterinary*; D001199:Ascaridoidea; D005243:Feces / Q000469:parasitology; D006734:Horse Diseases / Q000188:drug therapy*; D006736:Horses; D008297:Male; D010270:Parasite Egg Count / Q000662:veterinary; D013548:Sweden; D016896:Treatment Outcome
D000871:Anthelmintics