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Novel insights in the faecal egg count reduction test for monitoring drug efficacy against gastrointestinal nematodes of veterinary importance

Bruno Levecke UGent, RJ Dobson, N Speybroeck, Jozef Vercruysse UGent and Johannes Charlier UGent (2012) VETERINARY PARASITOLOGY. 188(3-4). p.391-396
abstract
The faecal egg count reduction test (FECRT) is the method of choice to monitor anthelmintic efficacy against gastro-intestinal nematodes in livestock. Guidelines on how to conduct a FECRT are made available by the World Association for the Advancement of Veterinary Parasitology (WAAVP). Since the publication of these guidelines in the early 1990s, some limitations have been noted, including (i) the ignorance of host-parasite interactions that depend on animal and parasite species, (ii) their feasibility under field conditions, (iii) appropriateness of study design, and (iv) the high detection limit of the recommended faecal egg count (FEC) method. Therefore, the objective of the present study was to empirically assess the impact of the level of excretion and aggregation of FEC, sample size and detection limit of the FEC method on the sensitivity and specificity of the FECRT to detect reduced efficacy (<90% or <95%) and to develop recommendations for surveys on anthelmintic resistance. A simulation study was performed in which the FECRT (based on the arithmetic mean of grouped FEC of the same animals before and after drug administration) was conducted under varying conditions of mean FEC, aggregation of FEC (inversely correlated with k), sample size, detection limit and 'true' drug efficacies. Classification trees were built to explore the impact of the above factors on the sensitivity and specificity of detecting a truly reduced efficacy. For a reduced-efficacy threshold of 90%, most combinations resulted in a reliable detection of reduced and normal efficacy. For the reduced-efficacy threshold of 95% however, unreliable FECRT results were found when sample sizes <15 were combined with highly aggregated FEC (k = 0.25) and detection limits >= 5 EPG or when combined with detection limits >= 15 EPG. Overall, an increase in sample size and mean preDA FEC, and a decrease in detection limit improved the diagnostic accuracy. FECRT remained inconclusive under any evaluated condition for drug efficacies ranging from 87.5% to 92.5% for a reduced-efficacy-threshold of 90% and from 92.5% to 97.5% for a threshold of 95%. The results highlight that (i) the interpretation of this FECRT is affected by a complex interplay of factors, including the level of excretion and aggregation of FEC and (ii) the diagnostic value of FECRT to detect small reductions in efficacy is limited. This study, therefore, provides a framework allowing researchers to adapt their study design according to a wide range of field conditions, while ensuring a good diagnostic performance of the FECRT.
Please use this url to cite or link to this publication:
author
organization
year
type
journalArticle (original)
publication status
published
subject
keyword
Anthelmintic resistance, Monte Carlo simulation, Monitoring programmes, Faecal egg count reduction test, Anthelmintic efficacy, Classification trees, ANTHELMINTIC EFFICACY, INTERNATIONAL HARMONIZATION, RESISTANCE, AGGREGATION, INFECTIONS, GUIDELINES, DIAGNOSIS, HELMINTHS, PARASITES, SHEEP
journal title
VETERINARY PARASITOLOGY
Vet. Parasitol.
volume
188
issue
3-4
pages
391 - 396
Web of Science type
Article
Web of Science id
000307802600026
JCR category
VETERINARY SCIENCES
JCR impact factor
2.381 (2012)
JCR rank
6/142 (2012)
JCR quartile
1 (2012)
ISSN
0304-4017
DOI
10.1016/j.vetpar.2012.03.020
language
English
UGent publication?
yes
classification
A1
copyright statement
I have transferred the copyright for this publication to the publisher
id
3032861
handle
http://hdl.handle.net/1854/LU-3032861
date created
2012-10-22 15:49:57
date last changed
2012-10-23 10:24:58
@article{3032861,
  abstract     = {The faecal egg count reduction test (FECRT) is the method of choice to monitor anthelmintic efficacy against gastro-intestinal nematodes in livestock. Guidelines on how to conduct a FECRT are made available by the World Association for the Advancement of Veterinary Parasitology (WAAVP). Since the publication of these guidelines in the early 1990s, some limitations have been noted, including (i) the ignorance of host-parasite interactions that depend on animal and parasite species, (ii) their feasibility under field conditions, (iii) appropriateness of study design, and (iv) the high detection limit of the recommended faecal egg count (FEC) method. Therefore, the objective of the present study was to empirically assess the impact of the level of excretion and aggregation of FEC, sample size and detection limit of the FEC method on the sensitivity and specificity of the FECRT to detect reduced efficacy ({\textlangle}90\% or {\textlangle}95\%) and to develop recommendations for surveys on anthelmintic resistance. A simulation study was performed in which the FECRT (based on the arithmetic mean of grouped FEC of the same animals before and after drug administration) was conducted under varying conditions of mean FEC, aggregation of FEC (inversely correlated with k), sample size, detection limit and 'true' drug efficacies. Classification trees were built to explore the impact of the above factors on the sensitivity and specificity of detecting a truly reduced efficacy. For a reduced-efficacy threshold of 90\%, most combinations resulted in a reliable detection of reduced and normal efficacy. For the reduced-efficacy threshold of 95\% however, unreliable FECRT results were found when sample sizes {\textlangle}15 were combined with highly aggregated FEC (k = 0.25) and detection limits {\textrangle}= 5 EPG or when combined with detection limits {\textrangle}= 15 EPG. Overall, an increase in sample size and mean preDA FEC, and a decrease in detection limit improved the diagnostic accuracy. FECRT remained inconclusive under any evaluated condition for drug efficacies ranging from 87.5\% to 92.5\% for a reduced-efficacy-threshold of 90\% and from 92.5\% to 97.5\% for a threshold of 95\%. The results highlight that (i) the interpretation of this FECRT is affected by a complex interplay of factors, including the level of excretion and aggregation of FEC and (ii) the diagnostic value of FECRT to detect small reductions in efficacy is limited. This study, therefore, provides a framework allowing researchers to adapt their study design according to a wide range of field conditions, while ensuring a good diagnostic performance of the FECRT.},
  author       = {Levecke, Bruno and Dobson, RJ and Speybroeck, N and Vercruysse, Jozef and Charlier, Johannes},
  issn         = {0304-4017},
  journal      = {VETERINARY PARASITOLOGY},
  keyword      = {Anthelmintic resistance,Monte Carlo simulation,Monitoring programmes,Faecal egg count reduction test,Anthelmintic efficacy,Classification trees,ANTHELMINTIC EFFICACY,INTERNATIONAL HARMONIZATION,RESISTANCE,AGGREGATION,INFECTIONS,GUIDELINES,DIAGNOSIS,HELMINTHS,PARASITES,SHEEP},
  language     = {eng},
  number       = {3-4},
  pages        = {391--396},
  title        = {Novel insights in the faecal egg count reduction test for monitoring drug efficacy against gastrointestinal nematodes of veterinary importance},
  url          = {http://dx.doi.org/10.1016/j.vetpar.2012.03.020},
  volume       = {188},
  year         = {2012},
}

Chicago
Levecke, Bruno, RJ Dobson, N Speybroeck, Jozef Vercruysse, and Johannes Charlier. 2012. “Novel Insights in the Faecal Egg Count Reduction Test for Monitoring Drug Efficacy Against Gastrointestinal Nematodes of Veterinary Importance.” Veterinary Parasitology 188 (3-4): 391–396.
APA
Levecke, B., Dobson, R., Speybroeck, N., Vercruysse, J., & Charlier, J. (2012). Novel insights in the faecal egg count reduction test for monitoring drug efficacy against gastrointestinal nematodes of veterinary importance. VETERINARY PARASITOLOGY, 188(3-4), 391–396.
Vancouver
1.
Levecke B, Dobson R, Speybroeck N, Vercruysse J, Charlier J. Novel insights in the faecal egg count reduction test for monitoring drug efficacy against gastrointestinal nematodes of veterinary importance. VETERINARY PARASITOLOGY. 2012;188(3-4):391–6.
MLA
Levecke, Bruno, RJ Dobson, N Speybroeck, et al. “Novel Insights in the Faecal Egg Count Reduction Test for Monitoring Drug Efficacy Against Gastrointestinal Nematodes of Veterinary Importance.” VETERINARY PARASITOLOGY 188.3-4 (2012): 391–396. Print.