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Pathogens (Basel, Switzerland)2025; 14(9); 898; doi: 10.3390/pathogens14090898

Independent Development of Resistance to Main Classes of Anthelmintics by Gastrointestinal Nematodes of Ruminants and Horses.

Abstract: Resistance to anthelmintics in gastrointestinal nematodes (GINs) is highly prevalent, as these parasites have been treated with anthelmintics for decades in ruminants and horses. Anthelmintics belong to different classes, each with a different mode of action. The most used are benzimidazoles and macrocyclic lactones and, to a lesser extent, levamisole and pyrantel in herbivores, as estimated from the literature. Combining these classes should be effective in controlling GIN. However, several farmers' practices tend to promote GIN resistance. Therefore, it is unclear whether the use of anthelmintic associations is a sustainable solution for controlling resistance in natural conditions. It is not easy to establish the association of anthelmintic resistances on farms since rarely several anthelmintics and their combinations are used on a single farm. Composed probability calculations were employed when literature data indicated the presence of resistance (to benzimidazoles, levamisole, or macrocyclic lactones) in several ruminant GIN cases. The efficacy of different anthelmintics (benzimidazoles, pyrantel, or macrocyclic lactones) was evaluated in terms of the correlation between faecal nematode egg counts in horses in the available literature. No associations of anthelmintic resistance were found between the different classes of anthelmintics in either ruminants or horses. However, the association between anthelmintic resistance in GIN may appear in the long term. It is presumed that combining drugs may reduce the development of resistance and allow better control of infection on farms where resistance is already established to a low level.
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Publication Date: 2025-09-05 PubMed ID: 41011797PubMed Central: PMC12473072DOI: 10.3390/pathogens14090898Google Scholar: Lookup
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  • Journal Article

Summary

This research summary has been generated with artificial intelligence and may contain errors and omissions. Refer to the original study to confirm details provided. Submit correction.

Overview

  • This research investigates the development of resistance in gastrointestinal nematodes (GINs) to different classes of anthelmintic drugs used in ruminants and horses.
  • The study explores whether resistance to multiple drug classes arises independently and discusses the implications for controlling these parasitic infections on farms.

Background

  • Gastrointestinal nematodes are parasitic worms infecting the digestive systems of ruminants (like cattle, sheep) and horses.
  • To manage these parasites, various classes of anthelmintic drugs have been used for decades, including:
    • Benzimidazoles (most common)
    • Macrocyclic lactones (very commonly used)
    • Levamisole (used less frequently)
    • Pyrantel (used less frequently)
  • Each drug class works through a different mechanism to kill or paralyze nematodes.
  • Repeated use of these drugs has led to resistance developing in nematode populations worldwide.

Aims and Challenges

  • The study aims to understand whether resistance to each drug class develops independently or as combined resistance to multiple classes on farms.
  • One challenge is that farms rarely use multiple anthelmintics or their combinations simultaneously, which makes monitoring combined resistance difficult.
  • There is a question about whether using combinations of anthelmintics is a sustainable strategy for managing resistance.

Methodology

  • The researchers analyzed data from existing literature:
    • Looking at reported cases of resistance to benzimidazoles, levamisole, and macrocyclic lactones in ruminants.
    • Using composed probability calculations to estimate the likelihood of combined resistance occurring.
    • Evaluating drug efficacy in horses by analyzing the correlation between fecal nematode egg counts after treatment with benzimidazoles, pyrantel, or macrocyclic lactones.

Key Findings

  • No clear evidence was found that resistance to multiple classes of anthelmintics is directly associated or linked in either ruminants or horses.
  • This suggests that resistance to each drug class tends to develop independently rather than simultaneously.
  • The data hint that combined resistance might eventually emerge in the long term, especially if drug use practices continue unchanged.

Implications and Recommendations

  • Combining anthelmintic drugs from different classes may help delay the development of resistance.
  • Using drug combinations could also improve control of nematode infections on farms where low-level resistance is already present.
  • Farmers’ current practices, which often favor repeated or single-drug use, might be accelerating resistance development.
  • Therefore, strategic use of drug combinations alongside integrated parasite management could be a better approach to sustain effectiveness.

Conclusion

  • This research highlights that resistance to major anthelmintic classes in GINs appears to develop independently rather than as a linked occurrence.
  • However, vigilance is necessary as resistance patterns may change over time with continued drug pressure.
  • The findings support the idea that anthelmintic combination therapy could be a useful part of resistance management plans on farms.

Cite This Article

APA
Cabaret J. (2025). Independent Development of Resistance to Main Classes of Anthelmintics by Gastrointestinal Nematodes of Ruminants and Horses. Pathogens, 14(9), 898. https://doi.org/10.3390/pathogens14090898

Publication

Pathogens (Basel, Switzerland)
ISSN: 2076-0817
NlmUniqueID: 101596317
Country: Switzerland
Language: English
Volume: 14
Issue: 9
PII: 898

Researcher Affiliations

Cabaret, Jacques
  • Institut National de la Recherche Agronomique et Environnement (INRAE), F. Rabelais University Tours, UMR 1282, 37380 Nouzilly, France.

MeSH Terms

  • Animals
  • Horses
  • Anthelmintics / pharmacology
  • Anthelmintics / therapeutic use
  • Nematoda / drug effects
  • Nematode Infections / veterinary
  • Nematode Infections / drug therapy
  • Nematode Infections / parasitology
  • Drug Resistance
  • Horse Diseases / parasitology
  • Horse Diseases / drug therapy
  • Ruminants / parasitology
  • Gastrointestinal Diseases / parasitology
  • Gastrointestinal Diseases / veterinary
  • Gastrointestinal Diseases / drug therapy
  • Parasite Egg Count
  • Feces / parasitology

Conflict of Interest Statement

The author declares no conflicts of interest.

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