Multiple resistance in equine cyathostomins: a case study from military establishments in Rio Grande do Sul, Brazil (original) (raw)
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First report of anthelmintic resistance of equine cyathostomins in Cuba
Veterinary Parasitology: Regional Studies and Reports, 2018
Anthelmintic resistance in equine cyathostomins has been described worldwide, with resistance to the benzimidazole class being particularly widespread. The status of anthelmintic efficacy in Cuba has been virtually unknown due to the lack of equine labelled products. One recent report documented suboptimal efficacy levels of extra-label albendazole products against cyathostomins, but it remains unknown to which extent benzimidazole resistance exists in the population. The aim of the present study was to evaluate the anthelmintic efficacy of two benzimidazole products labelled for equines, fenbendazole and oxibendazole. A fecal egg count reduction test (FECRT) was carried out on 132 horses aged 4 months to 18 years in 14 herds, belonging to six provinces. Ten herds exhibited signs of resistance to at least one of the benzimidazoles (mean FECRT < 90%). Overall, oxibendazole exhibited higher efficacy than fenbendazole (p = 0.0062), and higher efficacy levels were found in horses never dewormed before compared to those treated within 3-12 months prior to the study (p = 0.0015). Pre-treatment larval cultures revealed the presence of large strongyles and cyathostomin larvae in all herds, while only cyathostomin larvae were detected post treatment. The present work is the first report of anthelmintic resistance in equine cyathostomins in Cuba, and suggests pre-selection for resistant strains by extra-label use of albendazole on the studied farms.
Lack of Cyathostomin sp. reduction after anthelmintic treatment in horses in Brazil
Veterinary Parasitology, 2013
The increase of anthelmintic resistance in the last years in the nematode population of veterinary importance has become a major concern. The objective of the present study was to evaluate the efficacy of the main anthelmintic drugs available in the market against small strongyles of horses in Brazil. A total of 498 horses from 11 horse farms, located in the states of Paraná, São Paulo, Rio de Janeiro and Minas Gerais, in Brazil, were treated with ivermectin, moxidectin, pyrantel and fenbendazole, orally at their recommended doses. The fecal egg count reduction test (FECRT) was used to determine the product's efficacy and fecal culture was used to determine the parasite genus. Reduction on anthelmintic efficacy was found for fenbendazole in all horse farms (11/11), pyrantel in five yards (5/11) and ivermectin had low efficacy in one of the yards studied (1/11). Multidrug resistance of up to 3 drugs classes was found in one of the tested farms (1/11). Cyathostomin were the most prevalent parasite. The results showed that resistance to fenbendazole is widespread; the efficacy of pyrantel is in a critical situation. Although the macrocyclic lactones compounds still showed high efficacy on most farms, suspected resistance to macrocyclic lactones is of great concern.
Veterinary parasitology, 2004
A larval development assay (LDA, DrenchRite) was evaluated to determine the effectiveness of this method in detecting anthelmintic resistance in cyathostomin nematodes of horses. A total of 15 horse farms from Georgia and South Carolina (USA) and Population S ponies from the University of Kentucky (USA) were included in this study. Nematode eggs were extracted from pooled fecal samples and placed into the wells of a DrenchRite plate for testing against thiabendazole (TBZ), levamisole (LEV) and 2 ivermectin (IVM) analogs (IVM-1, IVM-2). After a 7-day incubation larvae in each well were counted and data were analyzed by logistic regression. Resistance status of each farm for different drugs was determined in a separate study using a fecal egg count reduction test. LDA were performed on the 15 farms once, however, the Population S cyathostomins were assayed on 3 separate occasions to estimate the consistency of results between assays. Mean TBZ LC50 for oxibendazole resistant, suspected...
2000
The occu rrence of anthelmintic resistance to benzimidazoles and avermectin in cyathostome nematodes in New Zealand horses was investigated using a larval development assay (LOA) to conduct a small su rvey. For the benzimidazoles the analogue, thiabendazole was used and for avermectin the analogues, ivermectin and ivermectin aglycone were used in the LOA. The normal ra nge of LOso values was estimated by assaying eggs from Kaimanawa fe ral horses (n = 22) for each analogue used. From these the mean LOso values + 2xstandard deviation was taken as the upper limit of normal. The survey involved domestic horses (n = 47) from several locations around New Zealand. For ivermectin and ivermectin aglycone 12% had LOso values higher than normal with resistance factors up to 5.3 and 6.8 respectively. This represents horses from three separate farms. For the benzimidazoles 43% of domestic horses had higher than normal LOso values with resistance factors up to 4.8. These results suggest that some nematodes in these domestic horses had an increased tolerance to avermectins and as well as to benzimidazoles. Two studies were conducted to assess the efficacy of a combination of abamectin (0.2mg/kg), oxibendazole (1 Omg/kg) and bithionol {5mg/kg or 7mg.kg). In the first study bithionol was included at 5mg/kg and in the second study it was included at 7mg/kg. These studies showed the efficacy of the combination was >98% against adult luminal stages of S. vulgaris, S. edentatus, cyathostomes, migratory stages of S. edentatus and third instar stages of Gasterophilus intestinalis. Efficacy against mucosal stages of cyathostomes (about 64%) and arterial stages of S. vulgaris (71 %) was poor. Inclusion of bithionol at 7mg/kg achieved an efficacy of 100% against A. perfoliata whereas at Smg/kg the efficacy was only 84.6%. In these studies the following species were identified: two species of Strongylus (S. vulgaris and S. edentatus); three species of Triodontophorus (T. serratus, T. minor• and T. tenuicollis) ; and twelve species of cyathostomes (Cyathostomum coronatum, Cya th ostomum labiatum, Cya thostomum catinatum, Cylicocyclus nassatus, Cylicocyclus leptostomus, Cylicocyclus radia tus, Cylicocyclus insigne, Cylicostephanus poculatus, Cylicostephanus minutus, Cylicostephanus calicatus, Cylicostephanus longibursatus and Cylicostephanus goldi). ii ACKNOWLEDGEMENTS I am grateful and especially indebted to my chief supervisor, Dr. Bill Pomroy, for his scholastic guidance, continuous encouragement, va luable suggestions, constructive criticism, keen interest, patience and tolerance as well as friendly behavior during my study and the preparation of thesis. I wou ld like to thank to Dr. Tony Charleston for his humour, willing assistance, va luable suggestion and helpful advice throughout the work which inspired and stimulated me during this study. I am grateful to the Virbac Laboratories Limited (NZ), for providing me with the opportunity, facilities, financial and technical support to undertake this study. In
Resistance to benzimidazole and macrocyclic lactone anthelmintics in cattle nematodes in Argentina
Veterinary Parasitology, 2004
In April 2003, persistent scouring and ill-thrift that was reported in calves form an intensive beef rearing operation in central Argentina despite treatments with benzimidazole and ivermectin. In order to conduct a controlled faecal egg count reduction test on this herd, 40 calves 5-8-months-old were selected on the basis that they had a nematode eggs per gram (epg) of faeces count greater than 150. Animals were divided into four groups (1-4) of 10 calves. Calves of groups 1-3 were treated, respectively, with subcutaneous injection of ivermectin (200 mcg/kg), ricobendazole (4 mg/kg) and levamisole (7.5 mg/kg), while calves of group 4 remained as untreated controls. The egg count reductions carried out 10 days later were lower than 15% in calves treated with ivermectin and ricobendazole, but 100% in animals receiving levamisole. Pooled post-treatment faecal cultures showed larval percentages of 92 and 95 for Haemonchus and 8 and 5 for Cooperia in the faeces of calves treated with ivermectin and ricobendazole, respectively. This is the first reported case of Haemonchus parasiting cattle showing simultaneous resistance to avermectins and benzimidazole type anthelmintics.
Anthelmintic resistance in important parasites of horses: Does it really matter?
Veterinary Parasitology, 2014
Parascaris equorum and cyathostomins are currently considered the most important parasites of horses and have traditionally been controlled with anthelmintics belonging to three drug classes: benzimidazoles, the tetrahydropyrimidine pyrantel, and macrocyclic lactones. Unfortunately, resistance to benzimidazoles, and to a lesser extent pyrantel, is widespread in cyathostomins around the world. Furthermore, resistance to macrocyclic lactones appears to be in the early stages of development in cyathostomins in multiple locations. In contrast, P. equorum populations have remained susceptible to the three anthelmintic drug classes for a considerably longer period of time. However, over the last 10 years, resistance to macrocyclic lactones has been described in multiple countries. In contrast, resistance to pyrantel has only been described in the USA; resistance to benzimidazoles has yet to be reported. Despite the large number of reports of anthelmintic resistance in both cyathostomins and P. equorum, there are presently no reports that definitively link anthelmintic resistance with clinical problems in horses. However, that generally appears to be due to a publication bias toward well managed horse farms and the lack of appropriate diagnostic methods for rapidly quantifying anthelmintic resistance in these parasites. Management-based, and other, reasons likely responsible for this apparent anomaly are also discussed. Finally, future research priorities in this area, identified from a discussion at the 9th International Conference on Equine Infectious Diseases, are summarized.
Larval development assay for detection of anthelmintic resistance in cyathostomins of Swedish horses
Veterinary parasitology, 2005
The aim of this study was to investigate the suitability of a larval development assay (LDA) for the determination of anthelmintic resistance in cyathostomin nematode populations of the horse. In addition, comparison of results between geographic regions, types of horse establishment, and the use of anthelmintics in Sweden, was established. Seventy horse herds from different parts of Sweden were sampled, and strongyle eggs from the faeces of 54 of those were investigated by an LDA (DrenchRite). The following anthelmintics were tested: thiabendazole (TBZ), levamisole (LEV), ivermectin monosaccharide (IVM-MS), ivermectin aglycone (IVM-AG) and pyrantel (PYR). The LC50 values for TBZ and LEV were generally lower than those previously reported in other LDA studies on horse nematodes. This could be related to the infrequent use of these compounds for the past 20 years in Sweden. In this study, there was a great variation within and between assay plates that could not be explained. Still t...
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.
Veterinaria México OA, 2016
Sheep production requires the constant assessment of parasitic burden and the efficacy of existing treatments for proper management. In this study, the administration of five different treatments was evaluated for the reduction of the percentage of eggs per gram of feces (EPG) shed by gastrointestinal nematodes (GIN) from sheep on three different sheep-breeding farms in Mexico (Texcoco, Estado de Mexico; Hueytamalco, Puebla; and Tlaltizapán de Zapata, Morelos). In these farms, ivermectin and benzimidazole derivatives had been routinely administered for two consecutive years. To determine whether drugs with different pharmacological properties decreased GIN fecal egg excretion, the treatments closantel (CLOS), albendazole (ABZ) and fenbendazole (FBZ) were administered alone and in combinations of CLOS + ABZ and CLOS + FBZ, to five groups of sheep, with an additional untreated control group on each farm (n = 28 per flock). Anthelmintic resistance was determined using Fecal Egg Count Reduction Tests (FECRT) as recommended in the guidelines of the World Association for the Advancement of Veterinary Parasitology. Fecal samples were collected 14 and 21 days after treatment. The anthelmintic resistance status was determined based on the reduction in the fecal egg count arithmetic mean and 95 % confidence limits. According to the FECRT, resistance developed to CLOS, ABZ, FBZ and CLOS + FBZ because the mean percentage of EPG reduction was ≤ 95 % with a lower confidence limit of ≤ 90 %. By contrast, nematode susceptibility was confirmed for the CLOS + ABZ combination, as it reduced the percentage of GIN fecal egg output by 96.46 ± 3.04 % (day 14) and 96.88 ± 3.04 % (day 21). Based on the morphometric identification of larvae, Haemonchus spp., Cooperia spp. and Teladorsagia spp. were the most abundant genera on all farms before the administration of these five treatments. In conclusion, the use of the anthelmintic combination of closantel plus albendazole may reduce the development of anthelmintic resistance in gastrointestinal nematodes.