Worms – what’s new: some recent developments in worm control in ruminants and camelids

Worms are economically important, being the number one disease in sheep in Australia, and number two (after bloat) in cattle in southern temperate regions of Australia (possibly number one if liver fluke is included). Faecal worm egg counting (WEC) is still the standard diagnostic tool, with useful adjuncts such as the lectin binding assay and the Haemonchus Dipstick Test being tested and deployed in recent years. There has been a shift away from prescriptive, calendar-based strategic worm control programs for sheep to modified strategic programs with an increased emphasis on integrated parasite management and treatments based on worm egg count monitoring rather than visual assessment or the calendar. Use of effective combinations and drench rotation are recommended. Monitoring of drench efficacy by way of post-drench WEC in small and large ruminants and alpaca is recommended. Resistance has worsened during the last 10 years with macrocyclic lactones (MLs) in particular being affected. The prevalence of sheep/goat worm resistance to the MLs is quite high in certain areas. Resistance has been identified as a significant issue in cattle worms in New Zealand, and it appears to be an emerging issue in Australia as well. Two new drench groups have appeared on the horizon in the last two years. One, the AADs (aminoacetonitrile derivatives), represented by monepantel (Zolvix® (Pfizer)) was recently launched in Australia, about 1.5 years after the world launch in New Zealand. Another, the spiroindoles (represented by derquantel, marketed in combination with abamectin as Startect® (Pfizer)), was released in NZ in July 2010. In the past in Australia, first reports of resistance to new drench groups have typically appeared just five years or so after the launch of the new chemicals. Taking measures to manage resistance will hopefully ensure that resistance does not develop so rapidly in the case of the AADs and spiroindoles.