The effect of climate, season, and treatment intensity on anthelmintic resistance in cyathostomins: A modelling exercise.
Abstract: Anthelmintic resistance is widespread in equine cyathostomin populations across the world, and with no new anthelmintic drug classes in the pharmaceutical pipeline, the equine industry is forced to abandon traditional parasite control regimens. Current recommendations aim at reducing treatment intensity and identifying high strongylid egg shedders in a targeted treatment approach. But, virtually nothing is known about the effectiveness of these recommendations, nor their applicability to different climatic regions, making it challenging to tailor sustainable recommendations for equine parasite control. This study made use of a computer model of the entire cyathostomin life-cycle to evaluate the influence of climate and seasonality on the development of anthelmintic resistance in cyathostomin parasites. Furthermore, the study evaluated the impact of recommended programs involving selective anthelmintic therapy on delaying anthelmintic resistance development. All simulations evaluated the use of a single anthelmintic (i.e., ivermectin) over the course of 40 model years. The study made use of weather station data representing four different climatic zones: a cold humid continental climate, a temperate oceanic climate, a cold semi-arid climate, and a humid subtropical climate. Initially, the impact of time of the year was evaluated when a single anthelmintic treatment was administered once a year in any of the twelve months. The next simulations evaluated the impact of treatment intensities varying between 2 and 6 treatments per year. And finally, we evaluated treatment schedules consisting of a combination of strategic treatments administered to all horses and additional treatments administered to horses exceeding a predetermined fecal egg count threshold. Month of treatment had a large effect on resistance development in colder climates, but little or no impact in subtropical and tropical climates. Resistance development was affected by treatment intensity, but was also strongly affected by climate. Selective therapy delayed resistance development in all modelled scenarios, but, again, this effect was climate dependent with the largest delays observed in the colder climates. This study is the first to demonstrate the value of cyathostomin parasite refugia in managing anthelmintic resistance, and also that climate and seasonality are important. This modelling exercise has allowed an illustration of concepts believed to play important roles in anthelmintic resistance in equine cyathostomins, but has also identified knowledge gaps and new questions to address in future studies.
Copyright © 2019 Elsevier B.V. All rights reserved.
Publication Date: 2019-04-07 PubMed ID: 31079830DOI: 10.1016/j.vetpar.2019.04.003Google Scholar: Lookup
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Summary
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The research explores how climate, season, and treatment intensity affect anthelmintic resistance in cyathostomins, a type of parasitic worm affecting horses. Using computer modelling, the research evaluated the effectiveness of different parasite control recommendations in various climates and how these factors contribute to anthelmintic resistance.
Anthelmintic Resistance in Cyathostomins
- The problem of anthelmintic resistance in cyathostomins is widespread across the equine population globally. This has resulted in a change in current equine parasite control measures, with a shift away from heavy treatment routines.
- However, there is limited knowledge about how effective these new methods are and how suitable they are for different climates.
Modelling Exercise
- The research utilised computer modelling of biological processes in order to assist in understanding the development of resistance in cyathostomins based on different variables like climate, season, and treatment intensity.
- The utilised model allowed for simulations of various scenarios involving different treatment programs, climates and seasonal impacts over a 40-year period.
Impact of Climate and Treatment Intensity
- The computer simulations showed that colder climates and the timing of treatments had a significant impact on the development of resistance. This was not the case in subtropical and tropical climates, where timing had little or no impact.
- The intensity of treatment also played a significant role in resistance development, with higher treatment frequencies resulting in quicker development of resistance.
Role of Selective Therapy
- Programs that involve selective therapy, where only individuals exceeding a certain threshold of parasite infection are treated, were shown to slow down the development of resistance.
- However, the extent to which this effect is realized is also climate dependent, with the most significant delays in resistance development occurring in colder climates.
Understanding Anthelmintic Resistance
- This research provides the first evidence that maintaining a population of susceptible cyathostomin parasites, known as ‘refugia’, is beneficial in managing the development of anthelmintic resistance.
- The inclusion of climate and seasonality in the assessment of resistance development provides a more nuanced understanding and proves their importance in determining resistance development.
- The study further identifies areas of future research to address the remaining gaps in knowledge regarding anthelmintic resistance in cyathostomins.
Cite This Article
APA
Nielsen MK, Sauermann CW, Leathwick DM.
(2019).
The effect of climate, season, and treatment intensity on anthelmintic resistance in cyathostomins: A modelling exercise.
Vet Parasitol, 269, 7-12.
https://doi.org/10.1016/j.vetpar.2019.04.003 Publication
Researcher Affiliations
- M.H. Gluck Equine Research Center, Department of Veterinary Science, University of Kentucky, Lexington, KY, USA. Electronic address: martin.nielsen@uky.edu.
- AgResearch Grasslands, Private Bag 11008, Palmerston North, 4442, New Zealand.
- AgResearch Grasslands, Private Bag 11008, Palmerston North, 4442, New Zealand.
MeSH Terms
- Animals
- Anthelmintics / pharmacology
- Climate
- Computer Simulation
- Drug Resistance
- Horse Diseases / drug therapy
- Horse Diseases / parasitology
- Horses
- Ivermectin / pharmacology
- Refugium
- Seasons
- Strongyle Infections, Equine / drug therapy
- Strongyle Infections, Equine / parasitology
- Strongyloidea / drug effects
- Weather
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