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Nielsen MK, Steuer AE, Anderson HP, Gavriliuc S, Carpenter AB, Redman EM, Gilleard JS, Reinemeyer CR, Poissant J. Shortened egg reappearance periods of equine cyathostomins following ivermectin or moxidectin treatment: morphological and molecular investigation of efficacy and species composition. Int J Parasitol 2022; 52:787-798. [PMID: 36244428 DOI: 10.1016/j.ijpara.2022.09.003] [Citation(s) in RCA: 18] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/01/2022] [Revised: 09/02/2022] [Accepted: 09/04/2022] [Indexed: 11/05/2022]
Abstract
Macrocyclic lactones have been the most widely used drugs for equine parasite control during the past four decades. Unlike ivermectin, moxidectin exhibits efficacy against encysted cyathostomin larvae, and is reported to have persistent efficacy with substantially longer egg reappearance periods. However, shortened egg reappearance periods have been reported recently for both macrocyclic lactones, and these findings have raised several questions: (i) are egg reappearance period patterns different after ivermectin or moxidectin treatment? (ii) Are shortened egg reappearance periods associated with certain cyathostomin species or stages? (iii) How does moxidectin's larvicidal efficacy affect egg reappearance period? To address these questions, 36 horses at pasture, aged 2-5 years old, were randomly allocated to three treatment groups: 1, moxidectin; 2, ivermectin; and 3, untreated control. Strongylid fecal egg counts were measured on a weekly basis, and the egg reappearance period was 5 weeks for both compounds. Strongylid worm counts were determined for all horses: 18 were necropsied at 2 weeks post-treatment (PT), and the remaining 18 at 5 weeks PT. Worms were identified to species morphologically and by internal transcribed spacer-2 (ITS-2) rDNA metabarcoding. Moxidectin and ivermectin were 99.9% and 99.7% efficacious against adults at 2 weeks post treatment, whereas the respective efficacies against luminal L4s were 84.3% and 69.7%. At 5 weeks PT, adulticidal efficacy was 88.3% and 57.6% for moxidectin and ivermectin, respectively, while the efficacy against luminal L4s was 0% for both drugs. Moxidectin reduced early L3 counts by 18.1% and 8.0% at 2 or 5 weeks, while the efficacies against late L3s and mucosal L4s were 60.4% and 21.2% at the same intervals, respectively. The luminal L4s surviving ivermectin treatment were predominantly Cylicocyclus (Cyc.) insigne. The ITS-2 rDNA metabarcoding was in good agreement with morphologic species estimates but suggested differential activity between moxidectin and ivermectin for several species, most notably Cyc. insigne and Cylicocyclus nassatus. This study was a comprehensive investigation of current macrocyclic lactone efficacy patterns and provided important insight into potential mechanisms behind shortened egg reappearance periods.
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Affiliation(s)
- Martin K Nielsen
- M.H. Gluck Equine Research Center, Department of Veterinary Science, University of Kentucky, Lexington, KY, USA.
| | - Ashley E Steuer
- M.H. Gluck Equine Research Center, Department of Veterinary Science, University of Kentucky, Lexington, KY, USA
| | - Haley P Anderson
- M.H. Gluck Equine Research Center, Department of Veterinary Science, University of Kentucky, Lexington, KY, USA
| | - Stefan Gavriliuc
- Department of Ecosystem and Public Health, University of Calgary, Calgary, Alberta, Canada
| | - Alyssa B Carpenter
- M.H. Gluck Equine Research Center, Department of Veterinary Science, University of Kentucky, Lexington, KY, USA
| | - Elizabeth M Redman
- Department of Comparative Biology and Experimental Medicine, University of Calgary, Calgary, Alberta, Canada
| | - John S Gilleard
- Department of Comparative Biology and Experimental Medicine, University of Calgary, Calgary, Alberta, Canada
| | | | - Jocelyn Poissant
- Department of Ecosystem and Public Health, University of Calgary, Calgary, Alberta, Canada
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Anthelmintic resistance in equine nematodes: Current status and emerging trends. Int J Parasitol Drugs Drug Resist 2022; 20:76-88. [PMID: 36342004 PMCID: PMC9630620 DOI: 10.1016/j.ijpddr.2022.10.005] [Citation(s) in RCA: 31] [Impact Index Per Article: 15.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/05/2022] [Revised: 10/19/2022] [Accepted: 10/20/2022] [Indexed: 11/06/2022]
Abstract
Anthelmintic resistance is reported in equine nematodes with increasing frequency in recent years, and no new anthelmintic classes have been introduced during the past 40 years. This manuscript reviews published literature describing anthelmintic resistance in cyathostomins, Parascaris spp., and Oxyuris equi with special emphasis on larvicidal efficacy against encysted cyathostomin larvae and strongylid egg reappearance periods (ERP). Resistance to benzimidazoles and pyrimidines is highly prevalent in cyathostomin populations around the world, and macrocyclic lactone resistance has been documented in cyathostomins in recent years as well. Two recent studies have documented resistance to the larvicidal regimen of fenbendazole, whereas the larvicidal efficacy of moxidectin is variable, but with no evidence of a reduction from historic levels. In the 1990s, ERP estimates were 8-10 and 12-16 weeks for ivermectin and moxidectin, respectively, while several studies published after year 2000 found ERPs to be 5 weeks for both compounds. This is a clear change in anthelmintic performance, but it remains unclear if this is due to development of anthelmintic resistance or selection for other biological traits leading to a quicker resumption of strongylid egg shedding following anthelmintic treatment. Macrocyclic lactone resistance is common in Parascaris spp. around the world, but recent reports suggests that resistance to the two other classes should be monitored as well. Finally, O. equi has been reported resistant to ivermectin and moxidectin in countries representing four continents. In conclusion, multi-drug resistance is becoming the norm in managed cyathostomin populations around the world, and a similar pattern may be emerging in Parascaris spp. More work is required to understand the mechanisms behind the shortened ERPs, and researchers and veterinarians around the world are encouraged to routinely monitor anthelmintic efficacy against equine nematodes.
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Abbas G, Ghafar A, Hurley J, Bauquier J, Beasley A, Wilkes EJA, Jacobson C, El-Hage C, Cudmore L, Carrigan P, Tennent-Brown B, Gauci CG, Nielsen MK, Hughes KJ, Beveridge I, Jabbar A. Cyathostomin resistance to moxidectin and combinations of anthelmintics in Australian horses. Parasit Vectors 2021; 14:597. [PMID: 34863271 PMCID: PMC8645149 DOI: 10.1186/s13071-021-05103-8] [Citation(s) in RCA: 24] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/17/2021] [Accepted: 11/17/2021] [Indexed: 11/25/2022] Open
Abstract
Background Cyathostomins are the most important and common parasitic nematodes of horses, with > 50 species known to occur worldwide. The frequent and indiscriminate use of anthelmintics has resulted in the development of anthelmintic resistance (AR) in horse nematodes. In this study we assessed the efficacy of commonly used anthelmintics against cyathostomins in Australian thoroughbred horses. Methods Two drug efficacy trials per farm were conducted on two thoroughbred horse farms in the state of Victoria, Australia. In the first trial, the horses on Farm A were treated with single and combinations of anthelmintics, including oxfendazole (OFZ), abamectin (ABM), abamectin and morantel (ABM + MOR), moxidectin (MOX) and oxfendazole and pyrantel (OFZ + PYR), at the recommended doses, whereas the horses on Farm B only received MOX, at the recommended dose. The faecal egg count reduction test (FECRT) was used to determine the efficacy and egg reappearance period (ERP) of anthelmintics. Based on the results of the first trial, the efficacies of MOX and a combination of ABM + MOR were reassessed to confirm their activities against cyathostomins. Results Of the five anthelmintic products tested on Farm A, resistance against OFZ, ABM and OFZ + PYR was found, with efficacies of − 41% (− 195% lower confidence limit [LCL]), 73% (60% LCL) and 82% (66% LCL) at 2 weeks post-treatment, respectively. The FECRT showed high efficacies of MOX and ABM + MOR (100%) at 2 week post-treatment and shortened ERPs for these anthelmintics (ABM + MOR: 4 weeks; MOX: 5 weeks). Resistance to MOX was found on Farm B, with a reduced efficacy of 90% (70% LCL) and 89% (82% LCL) at 2 weeks post-treatment in trials one and two, respectively. Conclusions This study provides the first evidence of MOX- and multidrug-resistant (ABM and combinations of anthelmintics) cyathostomins in Australia and indicates the need for continuous surveillance of the efficacy of currently effective anthelmintics and large-scale investigations to assess the ERP for various anthelmintics. Graphical Abstract ![]()
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Affiliation(s)
- Ghazanfar Abbas
- Melbourne Veterinary School, Faculty of Veterinary and Agricultural Sciences, The University of Melbourne, Werribee, VIC, Australia
| | - Abdul Ghafar
- Melbourne Veterinary School, Faculty of Veterinary and Agricultural Sciences, The University of Melbourne, Werribee, VIC, Australia
| | | | - Jenni Bauquier
- Melbourne Veterinary School, Faculty of Veterinary and Agricultural Sciences, The University of Melbourne, Werribee, VIC, Australia
| | - Anne Beasley
- School of Agriculture and Food Sciences, University of Queensland, Gatton, QLD, Australia
| | - Edwina J A Wilkes
- School of Animal and Veterinary Sciences, Charles Sturt University, Wagga Wagga, NSW, Australia
| | - Caroline Jacobson
- Centre for Animal Production and Health, Murdoch University, Murdoch, WA, Australia
| | - Charles El-Hage
- Melbourne Veterinary School, Faculty of Veterinary and Agricultural Sciences, The University of Melbourne, Werribee, VIC, Australia
| | | | | | - Brett Tennent-Brown
- Melbourne Veterinary School, Faculty of Veterinary and Agricultural Sciences, The University of Melbourne, Werribee, VIC, Australia
| | - Charles G Gauci
- Melbourne Veterinary School, Faculty of Veterinary and Agricultural Sciences, The University of Melbourne, Werribee, VIC, Australia
| | - Martin K Nielsen
- Department of Veterinary Science, M.H. Gluck Equine Research Center, University of Kentucky, Lexington, KY, USA
| | - Kristopher J Hughes
- School of Animal and Veterinary Sciences, Charles Sturt University, Wagga Wagga, NSW, Australia
| | - Ian Beveridge
- Melbourne Veterinary School, Faculty of Veterinary and Agricultural Sciences, The University of Melbourne, Werribee, VIC, Australia
| | - Abdul Jabbar
- Melbourne Veterinary School, Faculty of Veterinary and Agricultural Sciences, The University of Melbourne, Werribee, VIC, Australia.
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Lester HE, Morgan ER, Hodgkinson JE, Matthews JB. Analysis of Strongyle Egg Shedding Consistency in Horses and Factors That Affect It. J Equine Vet Sci 2018. [DOI: 10.1016/j.jevs.2017.04.006] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/19/2022]
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Bellaw JL, Krebs K, Reinemeyer CR, Norris JK, Scare JA, Pagano S, Nielsen MK. Anthelmintic therapy of equine cyathostomin nematodes - larvicidal efficacy, egg reappearance period, and drug resistance. Int J Parasitol 2017; 48:97-105. [PMID: 29050919 DOI: 10.1016/j.ijpara.2017.08.009] [Citation(s) in RCA: 43] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/22/2017] [Revised: 08/01/2017] [Accepted: 08/05/2017] [Indexed: 10/18/2022]
Abstract
Cyathostomins are ubiquitous in grazing horses across the world, and anthelmintic resistance has been reported with increasing levels over past decades. The aims of the present study were (i) to investigate the efficacy against encysted larval stages of moxidectin (0.4 mg/kg) and fenbendazole (10 mg/kg daily for five consecutive days) and compare these regimens at 2 and 5 weeks post-treatment, (ii) to investigate individual cyathostomin species associated with shortened egg reappearance periods, and (iii) to document species exhibiting decreased susceptibility to the evaluated compounds. Thirty-six ponies were allocated to treatment groups with half euthanatized 2 weeks post-treatment, and the remainder necropsied after 5 weeks. Luminal and mucosal worm counts were conducted and strongyle egg counts were determined at weekly intervals. At 2 weeks, mean reductions of early L3s were 50.4% and 73.8% for fenbendazole and moxidectin, respectively. At 5 weeks, the respective efficacies were 51.3% and 71.8%. Two week efficacies against late L3s and L4s (LL3s/L4s) were 70.8% and 74.6% for fenbendazole and moxidectin, respectively, whereas very low numbers were found in all three groups at 5 weeks. None of the mucosal counts were significantly different between treatment groups. Fenbendazole and moxidectin reduced luminal worm counts by 93.2% and 98.3% at 2 weeks following administration, with moxidectin group adult counts being significantly lower than the other two groups (P < 0.0001). Both treatment groups had increased counts 3 weeks later (P = 0.0415). A moxidectin ERP of 4 weeks was associated with surviving luminal L4s, and adult species contributing to this were Cyathostomum catinatum, Cylicostephanus longibursatus, Cylicocyclus ashworthi and Cylicocyclus nassatus. This study documented (i) larvicidal efficacy of fenbendazole much lower than historical standards, (ii) survival of luminal immatures (L4) following moxidectin administration, and (iii) new information about cyathostomin species associated with these phenomena.
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Affiliation(s)
- Jennifer L Bellaw
- M.H. Gluck Equine Research Center, Department of Veterinary Science, University of Kentucky, Lexington, KY, USA
| | - Kristen Krebs
- M.H. Gluck Equine Research Center, Department of Veterinary Science, University of Kentucky, Lexington, KY, USA
| | - Craig R Reinemeyer
- East Tennessee Clinical Research, 80 Copper Ridge Farm Road, Rockwood, TN 37854, USA
| | - Jamie K Norris
- M.H. Gluck Equine Research Center, Department of Veterinary Science, University of Kentucky, Lexington, KY, USA
| | - Jessica A Scare
- M.H. Gluck Equine Research Center, Department of Veterinary Science, University of Kentucky, Lexington, KY, USA
| | - Stefanie Pagano
- M.H. Gluck Equine Research Center, Department of Veterinary Science, University of Kentucky, Lexington, KY, USA
| | - Martin K Nielsen
- M.H. Gluck Equine Research Center, Department of Veterinary Science, University of Kentucky, Lexington, KY, USA.
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A survey of macrocyclic lactone efficacy in Australian cyathostomin populations. VETERINARY PARASITOLOGY- REGIONAL STUDIES AND REPORTS 2017; 8:127-132. [DOI: 10.1016/j.vprsr.2017.03.009] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/11/2016] [Revised: 12/16/2016] [Accepted: 03/20/2017] [Indexed: 11/18/2022]
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Comparison of the larvicidal efficacies of moxidectin or a five-day regimen of fenbendazole in horses harboring cyathostomin populations resistant to the adulticidal dosage of fenbendazole. Vet Parasitol 2015; 214:100-7. [DOI: 10.1016/j.vetpar.2015.10.003] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/02/2015] [Revised: 09/29/2015] [Accepted: 10/03/2015] [Indexed: 11/20/2022]
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Scott I, Bishop RM, Pomroy WE. Anthelmintic resistance in equine helminth parasites - a growing issue for horse owners and veterinarians in New Zealand? N Z Vet J 2015; 63:188-98. [PMID: 25608588 DOI: 10.1080/00480169.2014.987840] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/24/2022]
Abstract
There is growing concern that given the high frequency with which anthelmintics are being administered to many horses, anthelmintic resistance amongst equine helminth populations will be an increasing problem, rendering many of the currently available products unusable with little prospect of new products becoming available, at least in the near future. Worldwide, much reliance has been placed on the macrocyclic lactone (ML) group of anthelmintics, but resistance has been reported to these products as well as to the two other major anthelmintic classes used in this species, the benzimidazoles (BZ) and the tetrahydropyrimidines (e.g. pyrantel). In New Zealand, resistance has been reported to the ML and BZ groups, but not yet to pyrantel. As an alternative to interval-based anthelmintic regimens, the highly overdispersed nature of parasite populations in horses can be utilised to decide whether treatment is required, based on whether or not animals exceed a predetermined level of shedding of parasite eggs. If well managed, such a targeted and selective approach can be utilised to eliminate the majority of egg output whilst still providing a refuge for susceptible parasites to persist. Such a system would require that an adequate standard of monitoring be in place and cognisance needs to be taken of parasites or their lifecycle stages that cannot be diagnosed by routine methods. At the same time, using anthelmintics with high levels of efficacy, avoiding practices such as under-dosing, as well as utilising non-chemical means of parasite control when possible, e.g. regular removal of faeces from pasture, should all be considered. Combinations of anthelmintics, specifically of anthelmintics that target the same or a similar spectrum of parasite species, should play an important role in parasite control in horses. As well as providing arguably the highest levels of efficacy, combinations may also slow the rate at which anthelmintic resistance develops.
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Affiliation(s)
- I Scott
- a Infectious Diseases and Public Health Group , Institute of Veterinary, Animal and Biomedical Sciences, Massey University , Private Bag 11222, Palmerston North , New Zealand
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Lester H, Spanton J, Stratford C, Bartley D, Morgan E, Hodgkinson J, Coumbe K, Mair T, Swan B, Lemon G, Cookson R, Matthews J. Anthelmintic efficacy against cyathostomins in horses in Southern England. Vet Parasitol 2013; 197:189-96. [DOI: 10.1016/j.vetpar.2013.06.009] [Citation(s) in RCA: 69] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/05/2013] [Revised: 05/28/2013] [Accepted: 06/01/2013] [Indexed: 11/16/2022]
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Stratford CH, Lester HE, Pickles KJ, McGorum BC, Matthews JB. An investigation of anthelmintic efficacy against strongyles on equine yards in Scotland. Equine Vet J 2013; 46:17-24. [DOI: 10.1111/evj.12079] [Citation(s) in RCA: 35] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/21/2012] [Accepted: 01/27/2013] [Indexed: 10/27/2022]
Affiliation(s)
- C. H. Stratford
- Royal (Dick) School of Veterinary Studies and Roslin Institute; University of Edinburgh; UK
| | - H. E. Lester
- Disease Control; Moredun Research Institute; Edinburgh UK
| | - K. J. Pickles
- Department of Veterinary Medicine and Epidemiology; University of California, Davis; USA
| | - B. C. McGorum
- Royal (Dick) School of Veterinary Studies and Roslin Institute; University of Edinburgh; UK
| | - J. B. Matthews
- Disease Control; Moredun Research Institute; Edinburgh UK
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Molento MB, Nielsen MK, Kaplan RM. Resistance to avermectin/milbemycin anthelmintics in equine cyathostomins - current situation. Vet Parasitol 2011; 185:16-24. [PMID: 22047763 DOI: 10.1016/j.vetpar.2011.10.013] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/16/2022]
Abstract
Avermectins and milbemycins (AM) are potent compounds against all major nematode parasites, but their continuous usage has led to the development of widespread resistance in many of the important species of ruminant and equine parasites. The exception to this has been the cyathostomins, where AM resistance was recently first reported only after decades of drug exposure. Data from a Brazilian study suggests that AM resistance has developed in cyathostomins and reports of shortened egg reappearance periods after ivermectin treatment have been published recently from USA and Germany. Thus, AM resistance in cyathostomins is an emerging worldwide concern, but there is only limited amount data on the extent of this problem. To limit the development and spread of AM-resistant cyathostomins the equine industry must implement new strategies for worm control, and the veterinary parasitology community must develop and validate improved protocols for detecting anthelmintic resistance in the field.
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Affiliation(s)
- Marcelo Beltrão Molento
- Laboratory of Parasitic Diseases, Department of Veterinary Medicine, Federal University of Parana, Curitiba, PR, Brazil.
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STRATFORD CH, McGORUM BC, PICKLES KJ, MATTHEWS JB. An update on cyathostomins: Anthelmintic resistance and diagnostic tools. Equine Vet J 2011:133-9. [DOI: 10.1111/j.2042-3306.2011.00397.x] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
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Abbott JB, Mellor DJ, Love S. Assessment of serum protein electrophoresis for monitoring therapy of naturally acquired equine cyathostomin infections. Vet Parasitol 2007; 147:110-7. [PMID: 17462826 DOI: 10.1016/j.vetpar.2007.03.020] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/29/2006] [Revised: 03/16/2007] [Accepted: 03/19/2007] [Indexed: 11/28/2022]
Abstract
Serum protein electrophoresis (SPE) has previously been suggested as a means of assessing cyathostomin burdens in horses, although SPE used for that purpose is supported by little evidence. This clinical research report describes a study that objectively evaluated the use of SPE on a population of 38 horses following the administration of different anthelmintics. The population was subdivided into three groups, Groups F, M and P: 7.5 mg/kg bwt fenbendazole was administered to Group F on day -12; on day 0 0.4 mg/kg bwt moxidectin was administered to Group M and 19 mg/kg bwt pyrantel was administered to Group P. Faecal worm egg counts were obtained on days -14, 0 and 10. Groups M and P acted as controls for the Group F faecal egg count reduction test (FECRT) in which a high level of benzimidazole resistance was demonstrated. Group F was then used as a control group for the FECRT for both Groups P and M. A high anthelmintic efficacy of moxidectin and pyrantel was detected. SPE was performed on venous blood collected on days 0, 10, 30, 56 and 80. As the cyathostomins infecting the horses had been shown to be highly resistant to fenbendazole, Group F then served as a control group for comparison of any changes in protein fractions. Serum proteins did not vary significantly between groups on any of the sampling dates. No significant changes in serum proteins were observed in any group and no patterns were apparent on qualitative assessment of SPE profiles. SPE was therefore concluded to be an insensitive tool for the monitoring of cyathostomin treatment in horses in a clinical environment.
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Affiliation(s)
- J B Abbott
- Division of Companion Animal Sciences, Institute of Comparative Medicine, Faculty of Veterinary Medicine, University of Glasgow Veterinary School, Bearsden Road, Glasgow G61 1QH, UK.
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