Suspected ivermectin resistance in a south-east Queensland Parascaris equorum population.

Background: There have been several international reports of macrocyclic lactone (ML)-resistant Parascaris equorum over the past decade, but the resistance status of Australian P. equorum populations is largely unknown. A case of apparent reduced efficacy of ivermectin against P. equorum in Australia was investigated.

Results: A faecal egg count reduction test carried out on a group of weanling foals in south-east Queensland showed the efficacy of ivermectin to be 65%.

Conclusions: The case highlights the need to review current worm control strategies, especially for young horses.