Peer-reviewed veterinary case report
Reduced efficacy of ivermectin and moxidectin against Parascaris spp. in foals from Argentina.
- Journal:
- Veterinary parasitology, regional studies and reports
- Year:
- 2020
- Authors:
- Cooper, Laura G et al.
- Affiliation:
- Facultad Ciencias Agropecuarias
- Species:
- horse
Plain-English summary
In Argentina, ivermectin and moxidectin are commonly used medications to treat intestinal worms in horses, but there are concerns about how effective they are against a specific type of worm called Parascaris. In a case from February 2018, foals that had been treated with moxidectin about a month earlier still had a high number of Parascaris eggs in their feces. To investigate this, 24 foals were divided into two groups, with one group receiving ivermectin and the other moxidectin. After two weeks, the effectiveness of moxidectin was only about 48%, while ivermectin was even lower at 34%, and some foals actually had more eggs after treatment. However, when fenbendazole was given five days later, it completely cleared the worms. This suggests that the Parascaris worms in these foals are resistant to ivermectin and moxidectin, but fenbendazole was effective.
Abstract
Macrocyclic lactones are the most widely used drugs for the control of gastrointestinal nematodes of horses in Argentina. Ivermectin and moxidectin are used as broad spectrum anthelmintics and although there are several international reports on the resistance of Parascaris spp., the resistance status of the local nematode population is largely unknow. This report informs a case of suboptimal efficacy to both drugs to control Parascaris spp in foals in central Argentina. In February 2018, routine fecal parasite egg counts showed a moderate-high number of Parascaris spp eggs (mean = 680 eggs per gram of feces) in foals treated approximately one month before with moxidectin. Upon suspicion of resistance of this parasite to the macrocyclic lactones, 24 of these animals were selected for a fecal egg count reduction test (FECRT). Twelve foals were treated with ivermectin and the remaining 12 animals with moxidectin. Two weeks after treatment, the FECRT was 48.1% and 34.8% for moxidectin and ivermectin respectively (25% of the animals increased the number of eggs in feces after treatment). Five days later, the administration of fenbendazole resulted in a FECRT = 100%. The monitoring of the status of susceptibility or resistance in each establishment is critical for the design of control programs based on rational and sustainable use of anthelmintics.
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Search related cases →Original publication: https://pubmed.ncbi.nlm.nih.gov/32448542/