The contribution of simple random sampling to observed variations in faecal egg counts

Torgerson, Paul R.; Paul, Michaela; Lewis, Fraser

doi:10.1016/j.vetpar.2012.03.043

Cited by 48 publications

(29 citation statements)

References 17 publications

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“…Only counting eggs in the gridded area appears to account for this aggregation at higher levels of egg densities; the number of eggs present at lower densities, however, was still underestimated. Therefore, although counting of the entire chamber rather than solely the gridded area is considered to improve precision due to the reduced dilution factor (Torgerson et al, 2012), the greater degree of measurement error seen in the present study clearly outweigh this benefit and supports the approach recommended by FECPAK to count the number of eggs under one or both gridded areas rather than the full chamber (Coles, 2003).…”

Section: Discussionsupporting

confidence: 60%

“…This may reflect the fact that the minimum detection limit is 5 epg with the Mini-FLOTAC compared to 30 epg with FECPAK grids. Torgerson et al (2012) previously identified that applying a larger multiplication factor to raw FECs, as is necessary with the FECPAK, leads to a greater inflation of variation (reduced precision) in the final FEC. Underestimated FECs observed at the lower egg densities of 10 and 50 epg are expected with the FECPAK grid counts as the minimum detection limit is 30 epg.…”

Section: Discussionmentioning

confidence: 99%

See 1 more Smart Citation

A comparison of the FECPAK and Mini-FLOTAC faecal egg counting techniques

Godber

Phythian

Bosco

et al. 2015

Veterinary Parasitology

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Section: Discussionsupporting

confidence: 60%

Section: Discussionmentioning

confidence: 99%

A comparison of the FECPAK and Mini-FLOTAC faecal egg counting techniques

Godber

Phythian

Bosco

et al. 2015

Veterinary Parasitology

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“…before or after treatment. In a previous studies in the northeast of Spain, Cooperia oncophora was not the most prevalent GIN in cattle, representing the 9.6-19.7% of species (Almería et al, 1996); on the other hand, the present study in herds was carried out mainly between autumn and winter, when mean In horses, there is a lack of consensus on study design, data analysis and data to evaluate AR based on a FEC reduction test (Torgerson et al, 2012;Vidyashankar et al, 2012). In the present study, susceptibility was defined as a reduction of FEC higher than 90% for BZ and PYR, and 95% for MLs.…”

Section: Discussionmentioning

confidence: 68%

Resistance of gastrointestinal nematodes to the most commonly used anthelmintics in sheep, cattle and horses in Spain

Martínez‐Valladares

Geurden

Bartram

et al. 2015

Veterinary Parasitology

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The objective of this study was to evaluate the status of anthelmintic resistance (AR) in ruminants and horses in Spain. The efficacy of commonly used macrocyclic lactones (MLs) - ivermectin (IVM) and moxidectin (MOX) - was measured in sheep, cattle and horses. In addition, albendazole (ABZ) and levamisole (LEV) were evaluated in sheep and oxibendazole (OXI) and pyrantel (PYR) in horses. Efficacy was evaluated based on the difference between the arithmetic mean pre- and post-treatment faecal egg count (in cattle and horses), or compared to an untreated control group (in sheep). AR was present when the percentage reduction in egg count was <95% and the lower 95% confidence interval (CI) was <90%; if only one of these two criteria was met, the finding was recorded as suspected AR (SAR). In horses, AR-PYR and OXI was considered when the percentage reduction in egg count was ≤ 90% and the lower 95% CI was ≤ 80%. For each animal species, at least 10 study sites were selected. AR to at least one of the drugs was detected in all 10 sheep flocks; the main parasite identified after treatment was Teladorsagia circumcincta. Moreover, in 5 flocks multidrug resistance was identified, on 4 farms to drugs from different families, on one farm to both MOX and IVM and on another farm to all drugs tested. In cattle, the efficacy of both MOX and IVM was 100% on 4 and 3 farms, respectively, and therefore 60% of these farms were considered to have AR or SAR to both MLs. The most frequent parasite identified after treatment was Trichostrongylus spp., although Ostertagia ostertagi was also identified after treatment on one farm. In contrast to ruminants, the 4 drugs evaluated in horses were highly efficacious against strongyles, with efficacies for the MLs and OXI between 95 and 100% and between 94 and 100% for PYR, although 3 herds were SAR against PYR. In conclusion, AR to at least one of the commonly used drugs was identified on all sheep flocks investigated in the northwest of Spain. The occurrence of AR to MLs in cattle was higher than expected but consistent with what was observed in sheep. In horses, all currently used drugs were confirmed as effective against strongyles.

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“…It would be wrong to conclude there are no parasite eggs in the faeces as even quite substantial positive real counts can result in zero eggs being observed on the McMaster slide due to Poisson errors. For a fuller explanation see Torgerson et al (2012)). For example, with a dilution factor of 50, even if the true egg count is 100 epg, there is still a probability of 13.5% of observing zero eggs.…”

Section: Discussionmentioning

confidence: 99%

“…The random distribution of eggs within a faecal sample will conform to a Poisson process and thus repeat calculations of eggs per gram from the same faecal sample will be subject to Poisson errors (Torgerson et al, 2012). Therefore there is inevitable variability in evaluating faecal egg counts even with a highly precise laboratory technique due to this random variation.…”

Section: Introductionmentioning

confidence: 99%

Evaluating faecal egg count reduction using a specifically designed package “eggCounts” in R and a user friendly web interface

Torgerson

Paul

Furrer

2014

International Journal for Parasitology

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107

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The seemingly straightforward task of analysing faecal egg counts resulting from laboratory procedures such as the McMaster technique has, in reality, a number of complexities. These include Poisson errors in the counting technique which result from eggs being randomly distributed in well mixed faecal samples. In addition, counts between animals in a single experimental or observational group are nearly always over-dispersed. We describe the R package "eggCounts" that we have developed that incorporates both sampling error and over-dispersion between animals to calculate the true egg counts in samples of faeces, the probability distribution of the true counts and summary statistics such as the 95% uncertainty intervals. Based on a hierarchical Bayesian framework, the software will also rigorously estimate the percentage reduction of faecal egg counts and the 95% uncertainty intervals of data generated by a faecal egg count reduction test. We have also developed a user friendly web interface that can be used by those with limited knowledge of the R statistical computing environment. We illustrate the package with three simulated data sets of faecal egg count reduction experiments. Evaluating faecal egg count reduction using a specifically designed package "eggCounts" in R and AbstractThe seemingly straightforward task of analysing faecal egg counts resulting from laboratory procedures such as the McMaster technique has, in reality, a number of complexities. These include Poisson errors in the counting technique which result from eggs being randomly distributed in well mixed faecal samples. In addition, counts between animals in a single experimental or observational group are nearly always over-dispersed. We describe the R package "eggCounts" that we have developed that incorporates both sampling error and over-dispersion between animals to calculate the true egg counts in samples of faeces, the probability distribution of the true counts and summary statistics such as the 95% uncertainty intervals. Based on a hierarchical Bayesian framework, the software will also rigorously estimate the percentage reduction of faecal egg counts and the 95% uncertainty intervals of data generated by a faecal egg count reduction test. We have also developed a user friendly web interface that can be used by those with limited knowledge of the R statistical computing environment. We illustrate the package with three simulated data sets of faecal egg count reduction experiments.

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The contribution of simple random sampling to observed variations in faecal egg counts

Cited by 48 publications

References 17 publications

A comparison of the FECPAK and Mini-FLOTAC faecal egg counting techniques

A comparison of the FECPAK and Mini-FLOTAC faecal egg counting techniques

Resistance of gastrointestinal nematodes to the most commonly used anthelmintics in sheep, cattle and horses in Spain

Evaluating faecal egg count reduction using a specifically designed package “eggCounts” in R and a user friendly web interface

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