Dr. Orla Keane:

Different situations can apply to different parasites and different drugs. For the stomach worms, for example, which is where resistance is probably most widespread, resistance arose internationally within less than a decade of every new drug coming on the market. In Ireland, the first report of resistance was in 1992 and the first report of ivermectin resistance was probably in approximately 2015. These products had been around for quite some time at that point, but one of the issues is that once resistance arises, it can spread quite quickly. This is where an effective biosecurity protocol is essential. When there are no effective drugs it is very difficult to implement a good biosecurity protocol.