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Veterinary parasitology2011; 185(1); 45-56; doi: 10.1016/j.vetpar.2011.10.011

Statistical and biological considerations in evaluating drug efficacy in equine strongyle parasites using fecal egg count data.

Abstract: Anthelmintic resistance (AR) is a serious problem for the control of equine gastrointestinal nematodes, particularly in the cyathostomins. The fecal egg count reduction test (FECRT) is the most common method for diagnosing AR and serves as the practical gold standard. However, accurate quantification of resistance and especially accurate diagnosis of emerging resistance to avermectin/milbemycin (A/M) drugs, is hampered by a lack of accepted standards for study design, data analysis, and data interpretation. In order to develop rational evidence-based standards for diagnosis of resistance, one must first take into account the numerous sources of variability, both biological and technical, that affect the measurement of fecal egg counts (FECs). Though usually ignored, these issues can greatly impact the observed efficacy. Thus, to accurately diagnose resistance on the basis of FECRT data, it is important to reduce levels of variability through improved study design, and then deal with inherent variability that cannot be removed, by performing thorough and proper statistical analysis. In this paper we discuss these issues in detail, and provide an explanation of the statistical models and methods that are most appropriate for analyzing these types of data. We also provide several examples using data from laboratory, field, and simulation experiments illustrating the benefits of these approaches.
Copyright © 2011 Elsevier B.V. All rights reserved.
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Publication Date: 2011-10-18 PubMed ID: 22119386DOI: 10.1016/j.vetpar.2011.10.011Google Scholar: Lookup
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Summary

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This research article focuses on the need for standardizing techniques in diagnosing anthelmintic resistance (AR) in equine gastrointestinal parasites, specifically the cyathostomins, using fecal egg count reduction tests (FECRT). The authors discuss the statistical models and methods best suited for this kind of data analysis, in order to guide future research accuracy and application.

Problems in Diagnosing Anthelmintic Resistance (AR)

  • The paper begins by discussing the importance of AR in the health care of horses and the problems it poses to gastrointestinal nematodes control, especially in a specific type of these nematodes, the cyathostomins.
  • Most commonly, diagnosis of this resistance is done using FECRT. This method, however, is not without flaws and inconsistencies due to a lack of accepted standards in study design, data analysis and data interpretation.

Nature of Variability in Fecal Egg Counts

  • The authors point out that for creating evidenced-based standards, it’s important to consider the variability of fecal egg counts (FECs) – both biological and technical.
  • The parameters often overlooked but have a crucial impact on observed efficacy of the drugs being evaluated are examined in this study.

Improving Resistance Diagnosis Through Study Design and Statistical Analysis

  • A suggestion is made to reduce variability levels through an enhancement in the study design and to use proper statistical analysis to manage the inherent variability that can’t be eliminated.
  • The paper elaborates on the statistical models and techniques that are appropriate for this kind of analysis, thus, providing future studies a guide on how to analyze similar data.

Examples Illustrating the Proposed Approach

  • Moreover, the text offers several examples drawn from laboratory, field, and simulation experiments to illustrate the benefits of implementing these approaches in research on FECRT data analysis.

Cite This Article

APA
Vidyashankar AN, Hanlon BM, Kaplan RM. (2011). Statistical and biological considerations in evaluating drug efficacy in equine strongyle parasites using fecal egg count data. Vet Parasitol, 185(1), 45-56. https://doi.org/10.1016/j.vetpar.2011.10.011

Publication

Veterinary parasitology
ISSN: 1873-2550
NlmUniqueID: 7602745
Country: Netherlands
Language: English
Volume: 185
Issue: 1
Pages: 45-56

Researcher Affiliations

Vidyashankar, A N
  • Department of Statistics, Volgenau School of Engineering, George Mason University, Fairfax, VA 22030, USA. avidyash@gmu.edu
Hanlon, B M
    Kaplan, R M

      MeSH Terms

      • Animals
      • Anthelmintics / pharmacology
      • Anthelmintics / therapeutic use
      • Data Interpretation, Statistical
      • Drug Resistance
      • Feces / parasitology
      • Horses
      • Parasite Egg Count / standards
      • Parasite Egg Count / veterinary
      • Strongyle Infections, Equine / diagnosis
      • Strongyle Infections, Equine / drug therapy
      • Strongyle Infections, Equine / parasitology
      • Strongyloidea / drug effects

      Citations

      This article has been cited 11 times.
      1. Jamshidpour R, Nabavi R, Moadab H, Rezaie F, Chale AC, Sargison N. Evaluation of Benzimidazole Resistance in Equine Cyathostomins in the Kermanshah Province of Iran Using Coprological Analysis and Allele-Specific PCR. Iran J Parasitol 2025 Jul-Sep;20(3):389-399.
        doi: 10.18502/ijpa.v20i3.19614pubmed: 41181201google scholar: lookup
      2. Fakheri A, Esmaeilnejad B, Akbari H, Molaei R. In vitro evaluation of anthelmintic activity of biocompatibile carbon quantum dot nanocomposite against egg and larval stages of equine strongyles. BMC Vet Res 2025 Jan 22;21(1):32.
        doi: 10.1186/s12917-025-04494-5pubmed: 39844158google scholar: lookup
      3. Boelow H, Krücken J, Thomas E, Mirams G, von Samson-Himmelstjerna G. Comparison of FECPAK(G2), a modified Mini-FLOTAC technique and combined sedimentation and flotation for the coproscopic examination of helminth eggs in horses. Parasit Vectors 2022 May 12;15(1):166.
        doi: 10.1186/s13071-022-05266-ypubmed: 35549990google scholar: lookup
      4. Mickiewicz M, Czopowicz M, Moroz A, Potărniche AV, Szaluś-Jordanow O, Spinu M, Górski P, Markowska-Daniel I, Várady M, Kaba J. Prevalence of anthelmintic resistance of gastrointestinal nematodes in Polish goat herds assessed by the larval development test. BMC Vet Res 2021 Jan 7;17(1):19.
        doi: 10.1186/s12917-020-02721-9pubmed: 33413368google scholar: lookup
      5. Fairweather I, Brennan GP, Hanna REB, Robinson MW, Skuce PJ. Drug resistance in liver flukes. Int J Parasitol Drugs Drug Resist 2020 Apr;12:39-59.
        doi: 10.1016/j.ijpddr.2019.11.003pubmed: 32179499google scholar: lookup
      6. Wang C, Torgerson PR, Kaplan RM, George MM, Furrer R. Modelling anthelmintic resistance by extending eggCounts package to allow individual efficacy. Int J Parasitol Drugs Drug Resist 2018 Dec;8(3):386-393.
        doi: 10.1016/j.ijpddr.2018.07.003pubmed: 30103206google scholar: lookup
      7. Misuno E, Clark CR, Anderson SL, Jenkins E, Wagner B, Dembek K, Petrie L. Characteristics of parasitic egg shedding over a 1-year period in foals and their dams in 2 farms in central Saskatchewan. Can Vet J 2018 Mar;59(3):284-292.
        pubmed: 29599559
      8. Vidyashankar AN, Jimenez Castro PD, Kaplan RM. A statistical approach for evaluating the effectiveness of heartworm preventive drugs: what does 100% efficacy really mean?. Parasit Vectors 2017 Nov 9;10(Suppl 2):516.
        doi: 10.1186/s13071-017-2440-xpubmed: 29143648google scholar: lookup
      9. Love JW, Kelly LA, Lester HE, Nanjiani I, Taylor MA, Robertson C. Investigating anthelmintic efficacy against gastrointestinal nematodes in cattle by considering appropriate probability distributions for faecal egg count data. Int J Parasitol Drugs Drug Resist 2017 Apr;7(1):71-82.
        doi: 10.1016/j.ijpddr.2017.01.002pubmed: 28161555google scholar: lookup
      10. Ahmed AM, Sebastiano SR, Sweeney T, Hanrahan JP, Glynn A, Keane OM, Mukhopadhya A, Thornton K, Good B. Breed differences in humoral and cellular responses of lambs to experimental infection with the gastrointestinal nematode Teladorsagia circumcincta. Vet Res 2015 Feb 17;46:8.
        doi: 10.1186/s13567-014-0137-0pubmed: 25827901google scholar: lookup
      11. Matthews JB. Anthelmintic resistance in equine nematodes. Int J Parasitol Drugs Drug Resist 2014 Dec;4(3):310-5.
        doi: 10.1016/j.ijpddr.2014.10.003pubmed: 25516842google scholar: lookup
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