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Rapid selection for ivermectin resistance in Haemonchus contortus.
G C Coles1, A C Rhodes, A J Wolstenholme
1Department of Clinical Veterinary Science, University of Bristol, Langford House, Bristol BS40 5DU, UK. gerald.c.coles@bristol.ac.uk
Veterinary Parasitology
|April 23, 2005
Summary
Researchers found that Haemonchus contortus, a parasite in lambs, quickly developed resistance to ivermectin. This highlights how easily parasite resistance can emerge with intense drug pressure.
Area of Science:
- Veterinary Parasitology
- Anthelmintic Resistance
- Sheep Health
Background:
- Haemonchus contortus is a significant gastrointestinal nematode affecting sheep globally.
- Ivermectin is a widely used broad-spectrum anthelmintic for controlling parasitic infections in livestock.
- The emergence of anthelmintic resistance poses a major threat to animal health and agricultural productivity.
Purpose of the Study:
- To investigate the speed and ease of developing ivermectin resistance in Haemonchus contortus.
- To assess the impact of repeated high-dose ivermectin treatment on parasite susceptibility.
- To evaluate the potential for rapid selection of resistant parasite populations.
Main Methods:
- Lambs were infected with Haemonchus contortus isolates from the UK and USA.
- Parasite populations were subjected to increasing doses of ivermectin over three successive generations.
- Eggs from surviving infections were cultured, and larvae were used to establish the next generation.
Main Results:
- Haemonchus contortus populations demonstrated resistance to 0.2 mg/kg of ivermectin after three generations of selection.
- The study confirmed rapid selection of ivermectin resistance under high drug pressure.
- Both British and American isolates showed a similar capacity for developing resistance.
Conclusions:
- Ivermectin resistance in Haemonchus contortus can be rapidly selected when high-dose pressure is applied.
- The findings underscore the critical need for judicious use of anthelmintics to mitigate resistance.
- Sustainable parasite control strategies must incorporate resistance management principles.