Geometric means provide a biased efficacy result when conducting a faecal egg count reduction test (FECRT)

Dobson, R.J.; Sangster, Nicholas C.; Besier, R.B.; Woodgate, Robert

doi:10.1016/j.vetpar.2008.12.007

Cited by 94 publications

(63 citation statements)

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“…The FECRT can be performed by means of an overall count of strongyle eggs (Strongylida) or individual counts of parasitic genera through fecal culture (MCKENNA, 1997). Albeit very common, there are several limitations inherent to the interactions between host, parasite and the environment (LEVECKE et al, 2012), and there are variations in the calculation formula , in the need for control groups (MCKENNA, 2013(MCKENNA, , 2014, and in use of arithmetic (COLES et al, , 2006 or geometric means (SMOTHERS et al, 1999;DOBSON et al, 2009) in the calculation. According to Falzon et al (2014), the various methods to calculate FECRT are influenced by the level of AHR and if a bias correction is used in the formula, so it is important to analyze each case.…”

Section: Diagnostic Methods Employed In Brazil To Detect Ahr In Smallmentioning

confidence: 99%

Overview of anthelmintic resistance of gastrointestinal nematodes of small ruminants in Brazil

Salgado

Santos

2016

Rev. Bras. Parasitol. Vet.

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Frequent and inappropriate use of all classes of antiparasitic drugs in small ruminants has led to failures in their effectiveness, culminating in a global problem of anthelmintic resistance. Brazil stands out as one of the world's leaders in publications about anthelmintic resistance, and for having the most numerous reports of this resistance in small ruminants in the Americas. These studies have involved mainly the fecal egg count reduction test (FECRT) and its correlation with field management practices. In vivo effectiveness testing is conducted in areas where livestock is of greater economic significance, e.g., in the South (sheep) and Northeast (goats), or is important for research and economic centers, such as the Southeast (sheep). The most widely studied species is sheep, for which the widest range of drugs is also evaluated. Despite significant advances achieved in molecular research, laboratory analyses should include knowledge about the reality in the field so that they can become feasible for the producer. Moreover, molecular studies can be underpinned by the analysis of field studies, such as the maintenance of antiparasitic effectiveness over time and the mechanisms involved in this process.Keywords: Small ruminants, anthelmintic resistance, sheep, goat, gastrointestinal nematodes. ResumoO uso frequente e inapropriado de todas as classes de antiparasitários em pequenos ruminantes levou a falhas de eficácia, culminando na problemática global de resistência anti-helmíntica. O Brasil destaca-se como sendo um dos pioneiros nas publicações com resistência anti-helmíntica no mundo e por ter o maior número de relatos em pequenos ruminantes na América. Essas pesquisas envolvem principalmente o teste da redução da contagem de ovos nas fezes (TRCOF) e sua correlação com as práticas de manejo utilizadas no campo. Os estudos de testes de eficácia in vivo localizam-se em áreas onde há maior importância dos rebanhos como nas Regiões Sul (ovinos) e Nordeste (caprinos), ou com importância em polos de pesquisa e econômicos, como a região Sudeste (ovinos). Ovina é a espécie mais estudada e com maior gama de drogas avaliadas. Mesmo com grande avanço em pesquisas moleculares, as análises laboratoriais devem envolver o conhecimento da realidade do campo para que possam se tornar viáveis ao produtor. Além disso, a análise dos estudos de campo pode nortear estudos moleculares como, por exemplo, a manutenção da eficácia das drogas ao longo dos anos e os mecanismos envolvidos em tal processo.

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Section: Diagnostic Methods Employed In Brazil To Detect Ahr In Smallmentioning

confidence: 99%

Overview of anthelmintic resistance of gastrointestinal nematodes of small ruminants in Brazil

Salgado

Santos

2016

Rev. Bras. Parasitol. Vet.

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“…and the choice of constant can effect the results. In addition the use of logarithmic transformation can result in bias when conducting a faecal egg count reduction test (Dobson et al, 2009). The issue of over-dispersion of egg counts between animals can be more rigorously analysed by using appropriate statistical techniques that embrace the skewed statistical distributions observed.…”

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

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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“…However, to determine the resistant populations, we followed Dobson et al, 2009 andVercruysse et al, 2002.…”

Section: Discussionmentioning

confidence: 99%

“…The damages these parasites cause include impaired growth, reduction in gain weight or weight loss, reduced milk production and, in more severe cases, death. Heavy reliance on the chemical control of this parasite, allied to the constant observation of its resistance to anthelmintics, represents a serious obstacle to production (WALLER, 1997;GILL, 1999;WOLSTENHOLME et al, 2004;FLEMING et al, 2006;LECOVÁ et al, 2014). An aggravating factor of this situation is the high cost involved in the development of new molecules with anthelmintic activity, which results in low availability of different chemical groups for the treatment of worm infections (PRICHARD, 1994).…”

Section: Introductionmentioning

confidence: 99%

“…The only commercially available representative of this group, monepantel, was first released in New Zealand in 2009(HOSKING et al, 2010, and reached the Brazilian market in 2012. Several characteristics of this product, such as low toxicity and broad spectrum efficacy against sheep gastrointestinal nematodes, made monepantel an excellent choice for the treatment of sheep flocks (KAMINSKY et al, 2008(KAMINSKY et al, , 2011.…”

Section: Introductionmentioning

confidence: 99%

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Haemonchus contortus resistance to monepantel in sheep: fecal egg count reduction tests and randomized controlled trials

Martins

Bergamasco

Felippelli

et al. 2017

SCA

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Worm infections are a major cause of economic losses in sheep farming, and their control depends essentially on anthelmintic drugs. After decades without the discovery of new drug types, a new class of anthelmintics, called aminoacetonitrile derivatives, represented by monepantel, was released on the market. In order to evaluate a report of low efficacy of monepantel on a sheep farm in the municipality of Taiúva, state of São Paulo, Brazil, fecal egg count reduction and critical tests were performed on a Haemonchus contortus strain collected from this farm. To this end, ten animals were experimentally infected with 5000 H. contortus third-stage larvae, and these animals were divided into two groups, control and treated, according to the treatment with monepantel. The parameters evaluated were reduction in fecal egg counts on post-treatment days (PTD) 0, 2, 4, 7 and 14, and the therapeutic efficacy at the end of this period. Egg count reduction was observed starting on PTD 2, with a maximum reduction of 32.89% recorded on PTD 14. The critical test revealed 24.65% efficacy, indicating resistance to the active ingredient monepantel. The ineffectiveness of monepantel may be associated with the excessive use of the anthelmintic, which the farmer administered at intervals of less than one month, without technical guidance or a defined criterion. Given that the anthelmintic was used on this farm for less than one year, according to the farmer, it can be inferred that H. contortus develops resistance to monepantel in a few generations if the product is used incorrectly. ResumoVerminoses são uma das principais causas de prejuízo econômico na ovinocultura, cujo controle depende essencialmente de fármacos anti-helmínticos. Depois de décadas sem o surgimento de novos grupos químicos de fármacos, uma nova classe de anti-helmínticos, os derivados da aminoacetonitrila, representados pelo monepantel, foram lançados no mercado. Com o objetivo de avaliar um relato de baixa eficácia do monepantel em uma propriedade produtora de ovinos do município de Taiúva, estado de São Paulo, foi realizado um teste de redução de contagem de ovos e um teste crítico em uma linhagem de Haemonchus contortus obtida da propriedade. Dez animais foram infectados experimentalmente com 5000 larvas de terceiro estágio do isolado de Haemonchus contortus, e estes animais foram divididos em dois grupos, controle e tratados, em dependência do tratamento com monepantel. Foram avaliados a redução de ovos nas fezes nos dias 0, 2, 4, 7 e 14 pós-tratamento e a eficácia terapêutica ao final do período. A redução da contagem de ovos foi observada a partir do 2 o dia pós-tratamento (DPT), com redução máxima, de 32,89%, registrada no 14º DPT. O teste crítico revelou eficácia de apenas 24,65%, evidenciando resistência ao princípio ativo. A ineficácia do monepantel pode estar associada a utilização do vermífugo de forma massiva, uma vez que o produtor administrava o produto em intervalos inferiores a um mês, sem orientação técnica ou critério definido. Dado que...

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Geometric means provide a biased efficacy result when conducting a faecal egg count reduction test (FECRT)

Cited by 94 publications

References 12 publications

Overview of anthelmintic resistance of gastrointestinal nematodes of small ruminants in Brazil

Overview of anthelmintic resistance of gastrointestinal nematodes of small ruminants in Brazil

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

Haemonchus contortus resistance to monepantel in sheep: fecal egg count reduction tests and randomized controlled trials

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