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Erratum to: Comparison of calculation methods used for the determination of anthelmintic resistance in sheep in a temperate continental climate

Falzon, L. C., van Leeuwen, J., Menzies, P. I., Jones-Bitton, A., Sears, W., Jansen, J. T., Peregrine, A. S.
Parasitology research 2015 v.114 no.4 pp. 1631-1643
climate, detection limit, farms, fecal egg count, fenbendazole, gastrointestinal nematodes, ivermectin, levamisole, researchers, sheep, statistical models
This study compared results obtained with five different fecal egg count reduction (FECR) calculation methods for defining resistance to ivermectin, fenbendazole, and levamisole in gastrointestinal nematodes of sheep in a temperate continental climate: FECR₁and FECR₂used pre-and posttreatment fecal egg count (FEC) means from both treated and control animals, but FECR₁used arithmetic means, whereas FECR₂used geometric means; FECR₃used arithmetic means for pre- and posttreatment FECs from treated animals only; FECR₄was calculated using only arithmetic means for posttreatment FECs from treated and control animals; and FECR₅was calculated using mean FEC estimates from a general linear mixed model. The classification of farm anthelmintic resistance (AR) status varied, depending on which FECR calculation method was used and whether a bias correction term (BCT, i.e., half the minimum detection limit) was added to the zeroes or not. Overall, agreement between all methods was higher when a BCT was used, particularly when levels of resistance were low. FECR₄showed the highest agreement with all the other FECR methods. We therefore recommend that small ruminant clinicians use the FECR₄formula with a BCT for AR determination, as this would reduce the cost of the FECRT, while still minimizing bias and allowing for comparisons between different farms. For researchers, we recommend the use of FECR₁or FECR₂, as the inclusion of both pre- and posttreatment FECs and use of randomly allocated animals in treatment and control groups makes these methods mathematically more likely to estimate the true anthelmintic efficacy.