Anthelmintic resistance in equine parasites – detection, potential clinical relevance and implications for control.
Abstract: During the past two decades anthelmintic resistance in equine parasites has been found in the group of small strongyle species (cyathostomins) and in the ascarid species Parascaris equorum. The ubiquitous nature and possible severe consequences of disease with these nematodes make them the prime targets of current worm control programmes. Traditional control strategies mainly rely on the strategic application of anthelmintics, currently represented by three major drug classes: benzimidazoles (BZ), the tetrahydropyrimidine pyrantel (PYR) and macrocyclic lactones (ML). Following decades of routine and frequent anthelmintic applications, many cyathostomin populations on horse farms in industrialised countries must be considered as resistant to BZ anthelmintics. However, to date no published cases of cyathostomin disease specifically associated with anthelmintic resistance were reported. Possibly this is due to the generally subclinical and unspecific symptoms associated with cyathostomin infections. Nevertheless, exclusive reliance on the ML drug class may increase the threat of clinical disease due to drug-resistant cyathostomins. More recently, P. equorum has been reported as having developed resistance against ivermectin and moxidectin, two representatives of the ML-class. These anthelmintics are currently the most frequently used drug class in horses. This nematode species is mainly found in foals and in younger horses due to the development of immunity following exposure to infection. Infection with P. equorum can result in clinically drastic consequences such as obstruction and/or penetration of the small intestine, the latter usually leading to death. In conclusion, on horse farms the efficacy of anthelmintic treatments should be examined routinely for each drug class. Several factors can influence the rate at which anthelmintic resistance develops; high frequency of treatment being one of the most important. Modern control strategies should therefore attempt to significantly reduce anthelmintic treatments. Several pasture and farm management practices found to be negatively associated with nematode and anthelmintic resistance prevalence will be discussed in the review presented here.
Copyright © 2011 Elsevier B.V. All rights reserved.
Publication Date: 2011-10-18 PubMed ID: 22100141DOI: 10.1016/j.vetpar.2011.10.010Google Scholar: Lookup
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Summary
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This article discusses the growing resistance to de-worming drugs among horse parasites and suggests improved treatment strategies and farm management methods for more effective control of the issue.
Understanding Anthelmintic Resistance
- The research looks at the increasing occurrence of anthelmintic resistance in equine parasites over the past twenty years. Anthelmintic drugs are those used for treating worm infestations.
- The species of parasites that have shown this resistance are the group of small strongyle species (also known as cyathostomins) and Parascaris equorum, an ascarid species. These nematodes are widespread and can cause severe diseases, making them the primary targets of worm control programmes.
Current Control Strategies and their Limitations
- The most common control strategies rely on the strategic use of anthelmintics, represented by three major drug classes: benzimidazoles (BZ), the tetrahydropyrimidine pyrantel (PYR), and macrocyclic lactones (ML).
- Cyathostomin populations in horse farms in industrialised countries have developed a resistance to BZ drugs due to routine and frequent application over the years. Yet, the disease related to cyathostomins and associated with resistance aren’t reported, likely due to the subclinical and nonspecific symptoms involved in the infections.
- Over-reliance on ML drugs can increase the chances of disease caused by drug-resistant cyathostomins.
- Parascaris equorum has shown resistance development against two ML-class drugs, ivermectin and moxidectin, which are widely used in horses, mainly in foals and younger horses. Infections with P. equorum can lead to serious clinical consequences like obstruction or penetration of the small intestine, the latter often causing death.
Proposed Steps for Addressing the Problem
- The authors suggest that the efficacy of anthelmintic treatments on horse farms need to be examined regularly for each of the drug classes.
- The authors identify that the high frequency of treatment is one of the key factors escalating the development of anthelmintic resistance. Thus, modern control strategies should aim to significantly reduce the frequency of anthelmintic treatments.
- The article also discusses certain pasture and farm management practices that have a negative influence on the prevalence of nematode and anthelmintic resistance. Addressing these through improved farm management might help control the resistance issue.
Cite This Article
APA
von Samson-Himmelstjerna G.
(2011).
Anthelmintic resistance in equine parasites – detection, potential clinical relevance and implications for control.
Vet Parasitol, 185(1), 2-8.
https://doi.org/10.1016/j.vetpar.2011.10.010 Publication
Researcher Affiliations
- Institute for Parasitology and Tropical Veterinary Medicine, Freie Universität Berlin, Königsweg 67, 14163 Berlin, Germany. gvsamson@vetmed.fu-berlin.de
MeSH Terms
- Animals
- Anthelmintics / pharmacology
- Anthelmintics / therapeutic use
- Drug Resistance
- Horse Diseases / diagnosis
- Horse Diseases / drug therapy
- Horse Diseases / parasitology
- Horse Diseases / prevention & control
- Horses
- Nematoda / drug effects
- Nematode Infections / diagnosis
- Nematode Infections / drug therapy
- Nematode Infections / prevention & control
- Nematode Infections / veterinary
Citations
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