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Martin K. Nielsen - One of the best experts on this subject based on the ideXlab platform.
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Reduced efficacy of ivermectin and moxidectin against Parascaris spp. in foals from Argentina
Veterinary parasitology regional studies and reports, 2020Co-Authors: Laura Gabriela Cooper, Martin K. Nielsen, Gabriel Caffe, Julieta Cerutti, O. S. AnzianiAbstract:Macrocyclic lactones are the most widely used drugs for the control of gastrointestinal nematodes of horses in Argentina. Ivermectin and moxidectin are used as broad spectrum anthelmintics and although there are several international reports on the resistance of Parascaris spp., the resistance status of the local nematode population is largely unknow. This report informs a case of suboptimal efficacy to both drugs to control Parascaris spp in foals in central Argentina. In February 2018, routine fecal parasite egg counts showed a moderate-high number of Parascaris spp eggs (mean = 680 eggs per gram of feces) in foals treated approximately one month before with moxidectin. Upon suspicion of resistance of this parasite to the macrocyclic lactones, 24 of these animals were selected for a fecal egg count reduction test (FECRT). Twelve foals were treated with ivermectin and the remaining 12 animals with moxidectin. Two weeks after treatment, the FECRT was 48.1% and 34.8% for moxidectin and ivermectin respectively (25% of the animals increased the number of eggs in feces after treatment). Five days later, the administration of fenbendazole resulted in a FECRT = 100%. The monitoring of the status of susceptibility or resistance in each establishment is critical for the design of control programs based on rational and sustainable use of anthelmintics.
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Ascarids exposed: a method for in vitro drug exposure and gene expression analysis of anthelmintic naïve Parascaris spp
Parasitology, 2020Co-Authors: J.a. Scare, Pouya Dini, Jamie K. Norris, A.e. Steuer, K. Scoggin, H.s. Gravatte, Daniel K. Howe, Paul Slusarewicz, Martin K. NielsenAbstract:Ascarid parasites infect a variety of hosts and regular anthelmintic treatment is recommended for all species. Parascaris spp. is the only ascarid species with widespread anthelmintic resistance, which allows for the study of resistance mechanisms. The purpose of this study was to establish an in vitro drug exposure protocol for adult anthelmintic-naive Parascaris spp. and report a preliminary transcriptomic analysis in response to drug exposure. Live worms were harvested from foal necropsies and maintained in RPMI-1640 at 37 °C. Serial dilutions of oxibendazole (OBZ) and ivermectin (IVM) were prepared for in vitro drug exposure, and worm viability was monitored over time. In a second drug trial, worms were used for transcriptomic analysis. The final drug concentrations employed were OBZ at 40.1 μm (10 μg mL-1) and IVM at 1.1 μm (1 μg mL-1) for 24 and 3 h, respectively. The RNA-seq analysis revealed numerous differentially expressed genes, with some being potentially related to drug detoxification and regulatory mechanisms. This report provides a method for in vitro drug exposure and the phenotypic responses for Parascaris spp., which could be extrapolated to other ascarid parasites. Finally, it also provides preliminary transcriptomic data following drug exposure as a reference point for future studies of Parascaris spp.
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Risk factors for equine intestinal parasite infections and reduced efficacy of pyrantel embonate against Parascaris sp.
Veterinary Parasitology, 2019Co-Authors: Katja Hautala, Oili Kauppinen, Martin K. Nielsen, Antti Sukura, Anu Näreaho, Päivi J. Rajala-schultzAbstract:Abstract Gastrointestinal parasites, Parascaris sp. and strongyles, are common in young horses worldwide and control of these parasites is challenged by increasing anthelmintic resistance. Our aim was to identify risk factors for these infections as well as to assess the efficacy of fenbendazole (dose 7.5 mg/kg) and pyrantel embonate (dose 19 mg/kg) against Parascaris sp. We also evaluated association between owner observed symptoms and patent infections with these parasites. Fecal samples were collected from 367 young horses in Finland and a questionnaire study was conducted. Fecal egg counts were performed by Mini-FLOTAC® method. Univariable logistic regression models using patent infection status (Yes/No), separately for Parascaris sp. and strongyle infections as an outcome were run initially to screen potential risk factors collected by the questionnaire. After the initial screening, multiple logistic regression models were constructed and run to account for correlated data structure, risk factors and potential confounders simultaneously. Two significant risk factors for a patent Parascaris sp. infection were found: breeding farm size (p = 0.028) and frequency of horse movements (p = 0.010). Horses originating from large breeding farms were more likely (OR = 2.47, 95% confidence interval (CI) 1.10–5.51) to shed Parascaris sp. eggs upon relocation to training stables compared to horses originating from small breeding farms. Horses living in farms with frequent horse movements to other premises had higher odds (OR = 3.56, 95% CI: 1.35–9.39) of a patent Parascaris sp. infection compared to farms with less frequent horse movements. Risk factors for patent strongyle infection included age (p
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Anthelmintic efficacy of single active and combination products against commonly occurring parasites in foals
Veterinary Parasitology, 2019Co-Authors: L.h. Morris, Stephen Colgan, Dave M. Leathwick, Martin K. NielsenAbstract:Abstract Parasite control in foals is complicated by the concurrent presence of biologically diverse parasites with differing levels of anthelmintic resistance. Several combination anthelmintic products are available for use in horses, but information on their efficacies against important equine parasites is scarce. Two trials were performed in New Zealand during 2008 and 2011 on four different farms with substantially different anthelmintic treatment histories. The first trial evaluated the efficacy of an ivermectin/praziquantel/oxibendazole combination, a single active oxibendazole, and a single-active macrocyclic lactone (ML) in 49 foals located on three farms. The second trial evaluated two combination anthelmintic products and three single-active ML products and enrolled a total of 110 foals on three farms. Foals in the second trial were allocated to one of six anthelmintic treatment groups; oxfendazole/pyrantel embonate, pyrantel embonate/ivermectin/praziquantel, ivermectin/praziquantel, abamectin/praziquantel, moxidectin/praziquantel, and a placebo-treated control. In both trials, foals were monitored monthly prior to treatment, and fecal egg counts (FECs) of Parascaris spp., strongylid, and Strongyloides westeri were determined. A “rolling enrolment” process was implemented whereby foals were systematically allocated to a treatment group and treated with the corresponding anthelmintic following the first appearance of Parascaris spp. eggs in the faeces. A generalised linear model was used to evaluate the effect of farm and treatment on Day14 FEC (ln) for each parasite. Three different FECR calculation methods were employed as follows; i) FECR(T) pre and post treatment ii) FECR (C) in the treated group compared with control, and iii) FECR (P) pre- and post- treatment in the treated and control groups. Across both trials, treatment with ML single active products failed to achieve >95% reduction in Parascaris spp. FEC on two of three farms. The pyrantel embonate/oxfendazole and ivermectin/ praziquantel/oxibendazole combinations demonstrated full efficacy against Parascaris spp. This is in contrast to the anti-strongylid efficacies determined, where the pyrantel embonate/oxfendazole combination and single active oxibendazole had reduced efficacy on one farm, while the macrocyclic lactones generally had good efficacy. Strongyloides egg counts were sporadic in both trials, and allowed limited insight into anthelmintic efficacy. The study illustrated the importance of keeping an untreated or placebo-treated control group in studies evaluating anti-Parascaris efficacy and it demonstrated the utility of a rolling enrolment procedure, where foals are enrolled over the course of a defined period of time. Furthermore, the study demonstrated the value of a farm specific FECR monitoring programme and the complexity of parasite control in foals, where combination anthelmintic products can be employed to target multiple species of parasites.
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Long live the worms: methods for maintaining and assessing the viability of intestinal stages of Parascaris spp. in vitro.
Parasitology, 2018Co-Authors: J.a. Scare, A.e. Steuer, Paul Slusarewicz, C. L. Shaffer, Angela Mousley, Martin K. NielsenAbstract:In vitro maintenance of helminth parasites enables a variety of molecular, pharmaceutical and immunological analyses. Currently, the nutritional and environmental in vitro requirements of the equine ascarid parasite, Parascaris spp., have not been determined. Additionally, an objective method for assessing viability of Parascaris spp. intestinal stages does not exist. The purpose of this study was to ascertain the in vitro requirements of intestinal stages of Parascaris spp., and to develop a viability assessment method. A total of 1045 worms were maintained in a total of 212 cultures. Worms obtained from naturally infected foals at necropsy were immediately placed in culture flasks containing 200 mL of culture media. A variety of media types, nutrient supplementation and environmental conditions were examined. A motility-based scoring system was used to assess worm viability. Worms maintained in Roswell Park Memorial Institute-1640 had significantly better viability than any other media (P < 0.0001) and all media types supplemented with any of the nutrients examined (P < 0.0001). The use of a platform rocker also significantly improved viability (P = 0.0305). This is the first study to examine the requirements for maintaining Parascaris spp. intestinal stages in vitro and to evaluate their viability based on movement using an objective scoring system.
Eva Tydén - One of the best experts on this subject based on the ideXlab platform.
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Transcriptional responses in Parascaris univalens after in vitro exposure to ivermectin, pyrantel citrate and thiabendazole.
Parasites & vectors, 2020Co-Authors: Frida Martin, Johan Höglund, Tomas F. Bergström, Oskar Karlsson Lindsjö, Faruk Dube, Matthías Eydal, Eva TydénAbstract:BACKGROUND Parascaris univalens is a pathogenic parasite of foals and yearlings worldwide. In recent years, Parascaris spp. worms have developed resistance to several of the commonly used anthelmintics, though currently the mechanisms behind this development are unknown. The aim of this study was to investigate the transcriptional responses in adult P. univalens worms after in vitro exposure to different concentrations of three anthelmintic drugs, focusing on drug targets and drug metabolising pathways. METHODS Adult worms were collected from the intestines of two foals at slaughter. The foals were naturally infected and had never been treated with anthelmintics. Worms were incubated in cell culture media containing different concentrations of either ivermectin (10-9 M, 10-11 M, 10-13 M), pyrantel citrate (10-6 M, 10-8 M, 10-10 M), thiabendazole (10-5 M, 10-7 M, 10-9 M) or without anthelmintics (control) at 37 °C for 24 h. After incubation, the viability of the worms was assessed and RNA extracted from the anterior region of 36 worms and sequenced on an Illumina NovaSeq 6000 system. RESULTS All worms were alive at the end of the incubation but showed varying degrees of viability depending on the drug and concentration used. Differential expression (Padj
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Resistance to pyrantel embonate and efficacy of fenbendazole in Parascaris univalens on Swedish stud farms.
Veterinary parasitology, 2018Co-Authors: Frida Martin, Johan Höglund, Tomas F. Bergström, Oskar Karlsson Lindsjö, Eva TydénAbstract:Abstract The aims of this study were to determine the species of Parascaris present in foals in Sweden and to establish whether anthelmintic resistance to pyrantel and fenbendazole is present on Swedish stud farms. Ascarid eggs collected from different regions in Sweden were karyotyped and were all identified as Parascaris univalens, characterized by one chromosomal pair. Faecal egg count reduction tests were performed on a total of 142 foals on 9 farms between September 2016 and May 2017. Healthy foals with at least 150 eggs per gram faeces (EPG) were included in the study and treated with oral pastes of pyrantel embonate or fenbendazole according to manufacturer instructions. The efficacy of the drugs was calculated by a Bayesian model using the R package “eggCounts”. In accordance with the American Association of Equine Practitioners, parasites were classified as resistant to pyrantel if the reduction in EPG was ≤ 85% and to fenbendazole if the observed efficacy was ≤ 90%. Four of eleven groups treated with pyrantel had an observed efficacy of ≤ 85%, and as many as 43% of the foals treated with pyrantel excreted eggs 10–16 days after treatment. In contrast, one of the six groups treated with fenbendazole had an observed efficacy of ≤ 90%, and only 6% of all foals were excreting eggs 10–16 days after treatment. Since resistance to ivermectin has earlier been shown to be widespread in Parascaris spp. in Sweden it is likely that multiresistant populations are present on Swedish stud farms. This is the first study showing the existence of pyrantel-resistant Parascaris spp. in Europe, and the first ever study where anthelmintic resistance has been shown in P. univalens.
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differential expression of β tubulin isotypes in different life stages of Parascaris spp after exposure to thiabendazole
Molecular and Biochemical Parasitology, 2016Co-Authors: Eva Tydén, Moa Skarin, Mikael Anderssonfranko, Matilda Sjoblom, Johan HöglundAbstract:Anthelmintic resistance (AR) to macrocyclic lactones (ML) has been described in Parascaris of horses world-wide. In contrast, benzimidazoles (BZ) are still effective, although reduced efficacy to this drug class was recently reported. The mode of action of BZ is binding to β-tubulin, which prevents polymerisation of microtubules. In this study, β-tubulin gene expression of isotypes 1 and 2 was investigated at seven time points (0, 6, 24, 72, 96 and 120 h) during embryogenesis and in adult worms. In addition, an in ovo larval developmental test was developed to study β-tubulin gene expression of both isotypes in parasacaris eggs after exposure to different concentrations of thiabendazole (TBZ) for five days at 25 °C. A strong pattern of differential expression of β-tubulin and isotype 1 was observed in all stages, while isotype 2 expression was mainly found at an early phase of the embryogenesis. For isotype 1, a 5-fold increase was observed during the first 48 h, but gene expression gradually decreased after 72, 96 and 120 h. Isotype 2 was only expressed during the first 24h, followed by a 130-fold decrease at (time points) 72, 96 and 120 h. The in ovo larval developmental test, in which we exposed initially unembryonated eggs to increased concentrations of TBZ, did affect isotype 1 gene expression but not isotype 2. This assumes that each isotype has specific functions in different life stages. This is in agreement with the 'multi-tubulin' hypothesis, which states that different tubulin isotypes are required for specialised microtubule functions. Isotype 1 is the most likely drug target for BZs, as isotype 2 was only expressed at very low levels later in development. Increasing concentrations of TBZ altered β-tubulin isotype 1 gene expression after exposure of the eggs for five days, but this was not seen for isotype 2.
Frida Martin - One of the best experts on this subject based on the ideXlab platform.
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Transcriptional responses in Parascaris univalens after in vitro exposure to ivermectin, pyrantel citrate and thiabendazole.
Parasites & vectors, 2020Co-Authors: Frida Martin, Johan Höglund, Tomas F. Bergström, Oskar Karlsson Lindsjö, Faruk Dube, Matthías Eydal, Eva TydénAbstract:BACKGROUND Parascaris univalens is a pathogenic parasite of foals and yearlings worldwide. In recent years, Parascaris spp. worms have developed resistance to several of the commonly used anthelmintics, though currently the mechanisms behind this development are unknown. The aim of this study was to investigate the transcriptional responses in adult P. univalens worms after in vitro exposure to different concentrations of three anthelmintic drugs, focusing on drug targets and drug metabolising pathways. METHODS Adult worms were collected from the intestines of two foals at slaughter. The foals were naturally infected and had never been treated with anthelmintics. Worms were incubated in cell culture media containing different concentrations of either ivermectin (10-9 M, 10-11 M, 10-13 M), pyrantel citrate (10-6 M, 10-8 M, 10-10 M), thiabendazole (10-5 M, 10-7 M, 10-9 M) or without anthelmintics (control) at 37 °C for 24 h. After incubation, the viability of the worms was assessed and RNA extracted from the anterior region of 36 worms and sequenced on an Illumina NovaSeq 6000 system. RESULTS All worms were alive at the end of the incubation but showed varying degrees of viability depending on the drug and concentration used. Differential expression (Padj
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Resistance to pyrantel embonate and efficacy of fenbendazole in Parascaris univalens on Swedish stud farms.
Veterinary parasitology, 2018Co-Authors: Frida Martin, Johan Höglund, Tomas F. Bergström, Oskar Karlsson Lindsjö, Eva TydénAbstract:Abstract The aims of this study were to determine the species of Parascaris present in foals in Sweden and to establish whether anthelmintic resistance to pyrantel and fenbendazole is present on Swedish stud farms. Ascarid eggs collected from different regions in Sweden were karyotyped and were all identified as Parascaris univalens, characterized by one chromosomal pair. Faecal egg count reduction tests were performed on a total of 142 foals on 9 farms between September 2016 and May 2017. Healthy foals with at least 150 eggs per gram faeces (EPG) were included in the study and treated with oral pastes of pyrantel embonate or fenbendazole according to manufacturer instructions. The efficacy of the drugs was calculated by a Bayesian model using the R package “eggCounts”. In accordance with the American Association of Equine Practitioners, parasites were classified as resistant to pyrantel if the reduction in EPG was ≤ 85% and to fenbendazole if the observed efficacy was ≤ 90%. Four of eleven groups treated with pyrantel had an observed efficacy of ≤ 85%, and as many as 43% of the foals treated with pyrantel excreted eggs 10–16 days after treatment. In contrast, one of the six groups treated with fenbendazole had an observed efficacy of ≤ 90%, and only 6% of all foals were excreting eggs 10–16 days after treatment. Since resistance to ivermectin has earlier been shown to be widespread in Parascaris spp. in Sweden it is likely that multiresistant populations are present on Swedish stud farms. This is the first study showing the existence of pyrantel-resistant Parascaris spp. in Europe, and the first ever study where anthelmintic resistance has been shown in P. univalens.
Johan Höglund - One of the best experts on this subject based on the ideXlab platform.
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Transcriptional responses in Parascaris univalens after in vitro exposure to ivermectin, pyrantel citrate and thiabendazole.
Parasites & vectors, 2020Co-Authors: Frida Martin, Johan Höglund, Tomas F. Bergström, Oskar Karlsson Lindsjö, Faruk Dube, Matthías Eydal, Eva TydénAbstract:BACKGROUND Parascaris univalens is a pathogenic parasite of foals and yearlings worldwide. In recent years, Parascaris spp. worms have developed resistance to several of the commonly used anthelmintics, though currently the mechanisms behind this development are unknown. The aim of this study was to investigate the transcriptional responses in adult P. univalens worms after in vitro exposure to different concentrations of three anthelmintic drugs, focusing on drug targets and drug metabolising pathways. METHODS Adult worms were collected from the intestines of two foals at slaughter. The foals were naturally infected and had never been treated with anthelmintics. Worms were incubated in cell culture media containing different concentrations of either ivermectin (10-9 M, 10-11 M, 10-13 M), pyrantel citrate (10-6 M, 10-8 M, 10-10 M), thiabendazole (10-5 M, 10-7 M, 10-9 M) or without anthelmintics (control) at 37 °C for 24 h. After incubation, the viability of the worms was assessed and RNA extracted from the anterior region of 36 worms and sequenced on an Illumina NovaSeq 6000 system. RESULTS All worms were alive at the end of the incubation but showed varying degrees of viability depending on the drug and concentration used. Differential expression (Padj
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Resistance to pyrantel embonate and efficacy of fenbendazole in Parascaris univalens on Swedish stud farms.
Veterinary parasitology, 2018Co-Authors: Frida Martin, Johan Höglund, Tomas F. Bergström, Oskar Karlsson Lindsjö, Eva TydénAbstract:Abstract The aims of this study were to determine the species of Parascaris present in foals in Sweden and to establish whether anthelmintic resistance to pyrantel and fenbendazole is present on Swedish stud farms. Ascarid eggs collected from different regions in Sweden were karyotyped and were all identified as Parascaris univalens, characterized by one chromosomal pair. Faecal egg count reduction tests were performed on a total of 142 foals on 9 farms between September 2016 and May 2017. Healthy foals with at least 150 eggs per gram faeces (EPG) were included in the study and treated with oral pastes of pyrantel embonate or fenbendazole according to manufacturer instructions. The efficacy of the drugs was calculated by a Bayesian model using the R package “eggCounts”. In accordance with the American Association of Equine Practitioners, parasites were classified as resistant to pyrantel if the reduction in EPG was ≤ 85% and to fenbendazole if the observed efficacy was ≤ 90%. Four of eleven groups treated with pyrantel had an observed efficacy of ≤ 85%, and as many as 43% of the foals treated with pyrantel excreted eggs 10–16 days after treatment. In contrast, one of the six groups treated with fenbendazole had an observed efficacy of ≤ 90%, and only 6% of all foals were excreting eggs 10–16 days after treatment. Since resistance to ivermectin has earlier been shown to be widespread in Parascaris spp. in Sweden it is likely that multiresistant populations are present on Swedish stud farms. This is the first study showing the existence of pyrantel-resistant Parascaris spp. in Europe, and the first ever study where anthelmintic resistance has been shown in P. univalens.
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differential expression of β tubulin isotypes in different life stages of Parascaris spp after exposure to thiabendazole
Molecular and Biochemical Parasitology, 2016Co-Authors: Eva Tydén, Moa Skarin, Mikael Anderssonfranko, Matilda Sjoblom, Johan HöglundAbstract:Anthelmintic resistance (AR) to macrocyclic lactones (ML) has been described in Parascaris of horses world-wide. In contrast, benzimidazoles (BZ) are still effective, although reduced efficacy to this drug class was recently reported. The mode of action of BZ is binding to β-tubulin, which prevents polymerisation of microtubules. In this study, β-tubulin gene expression of isotypes 1 and 2 was investigated at seven time points (0, 6, 24, 72, 96 and 120 h) during embryogenesis and in adult worms. In addition, an in ovo larval developmental test was developed to study β-tubulin gene expression of both isotypes in parasacaris eggs after exposure to different concentrations of thiabendazole (TBZ) for five days at 25 °C. A strong pattern of differential expression of β-tubulin and isotype 1 was observed in all stages, while isotype 2 expression was mainly found at an early phase of the embryogenesis. For isotype 1, a 5-fold increase was observed during the first 48 h, but gene expression gradually decreased after 72, 96 and 120 h. Isotype 2 was only expressed during the first 24h, followed by a 130-fold decrease at (time points) 72, 96 and 120 h. The in ovo larval developmental test, in which we exposed initially unembryonated eggs to increased concentrations of TBZ, did affect isotype 1 gene expression but not isotype 2. This assumes that each isotype has specific functions in different life stages. This is in agreement with the 'multi-tubulin' hypothesis, which states that different tubulin isotypes are required for specialised microtubule functions. Isotype 1 is the most likely drug target for BZs, as isotype 2 was only expressed at very low levels later in development. Increasing concentrations of TBZ altered β-tubulin isotype 1 gene expression after exposure of the eggs for five days, but this was not seen for isotype 2.
Tomas F. Bergström - One of the best experts on this subject based on the ideXlab platform.
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Transcriptional responses in Parascaris univalens after in vitro exposure to ivermectin, pyrantel citrate and thiabendazole.
Parasites & vectors, 2020Co-Authors: Frida Martin, Johan Höglund, Tomas F. Bergström, Oskar Karlsson Lindsjö, Faruk Dube, Matthías Eydal, Eva TydénAbstract:BACKGROUND Parascaris univalens is a pathogenic parasite of foals and yearlings worldwide. In recent years, Parascaris spp. worms have developed resistance to several of the commonly used anthelmintics, though currently the mechanisms behind this development are unknown. The aim of this study was to investigate the transcriptional responses in adult P. univalens worms after in vitro exposure to different concentrations of three anthelmintic drugs, focusing on drug targets and drug metabolising pathways. METHODS Adult worms were collected from the intestines of two foals at slaughter. The foals were naturally infected and had never been treated with anthelmintics. Worms were incubated in cell culture media containing different concentrations of either ivermectin (10-9 M, 10-11 M, 10-13 M), pyrantel citrate (10-6 M, 10-8 M, 10-10 M), thiabendazole (10-5 M, 10-7 M, 10-9 M) or without anthelmintics (control) at 37 °C for 24 h. After incubation, the viability of the worms was assessed and RNA extracted from the anterior region of 36 worms and sequenced on an Illumina NovaSeq 6000 system. RESULTS All worms were alive at the end of the incubation but showed varying degrees of viability depending on the drug and concentration used. Differential expression (Padj
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Resistance to pyrantel embonate and efficacy of fenbendazole in Parascaris univalens on Swedish stud farms.
Veterinary parasitology, 2018Co-Authors: Frida Martin, Johan Höglund, Tomas F. Bergström, Oskar Karlsson Lindsjö, Eva TydénAbstract:Abstract The aims of this study were to determine the species of Parascaris present in foals in Sweden and to establish whether anthelmintic resistance to pyrantel and fenbendazole is present on Swedish stud farms. Ascarid eggs collected from different regions in Sweden were karyotyped and were all identified as Parascaris univalens, characterized by one chromosomal pair. Faecal egg count reduction tests were performed on a total of 142 foals on 9 farms between September 2016 and May 2017. Healthy foals with at least 150 eggs per gram faeces (EPG) were included in the study and treated with oral pastes of pyrantel embonate or fenbendazole according to manufacturer instructions. The efficacy of the drugs was calculated by a Bayesian model using the R package “eggCounts”. In accordance with the American Association of Equine Practitioners, parasites were classified as resistant to pyrantel if the reduction in EPG was ≤ 85% and to fenbendazole if the observed efficacy was ≤ 90%. Four of eleven groups treated with pyrantel had an observed efficacy of ≤ 85%, and as many as 43% of the foals treated with pyrantel excreted eggs 10–16 days after treatment. In contrast, one of the six groups treated with fenbendazole had an observed efficacy of ≤ 90%, and only 6% of all foals were excreting eggs 10–16 days after treatment. Since resistance to ivermectin has earlier been shown to be widespread in Parascaris spp. in Sweden it is likely that multiresistant populations are present on Swedish stud farms. This is the first study showing the existence of pyrantel-resistant Parascaris spp. in Europe, and the first ever study where anthelmintic resistance has been shown in P. univalens.
