Impact of ivermectin-resistant gastrointestinal nematodes in feedlot cattle in Argentina (original) (raw)
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Parasites & Vectors, 2014
Background: Anthelmintic resistance (AR) is an increasing problem for the ruminant livestock sector worldwide. However, the extent of the problem is still relatively unknown, especially for parasitic nematodes of cattle. The effect of ivermectin (IVM) (Ivomec inj.®, Merial) was investigated in Swedish isolates of gastrointestinal nematode (GIN) populations showing signs of AR in the field to further characterise the AR status by a range of in vivo and in vitro methods. Methods: Three groups, each of 11 calves, were infected with an equal mixture of third stage larvae (L3) of Cooperia oncophora and Ostertagia ostertagi. Group A was inoculated with an IVM-susceptible laboratory isolate and groups B and C with isolates originating from 'resistant' cattle farms. Faecal egg counts (FEC) were monitored from 0 to 45 days post infection (d.p.i.), and L3 were harvested continuously for larval migration inhibition testing (LMIT) and species-specific PCR (ITS2). At 31 d.p.i., one calf from each group was necropsied and adult worms were recovered pre-treatment. At 35 d.p.i., calves from all groups were injected with IVM at the recommended dose (0.2 mg/kg bodyweight). At 45 d.p.i., another two animals from each group were sacrificed and established gastrointestinal worms were collected and counted.
Anthelmintic resistance in cattle nematode in the western Pampeana Region of Argentina
Veterinary Parasitology, 2007
During the past three years there have been several reports of cattle anthelmintic resistance (AR) in Argentina. Twenty-five cattle herds in the west fattening area of the Pampeana Region were surveyed to assess the prevalence of AR and the species of nematode involved. The survey involved fattening and cow-calf systems with a mean of 6760 bovines. Resistance was determined in vivo by a faecal egg count reduction test (FECRT). Efficacies from the World Association for the Advancement of Veterinary Parasitology (WAAVP) formula were compared with those obtained from the Abbott formula. Sixty 6-12-month-old calves were selected from each property and divided into four groups, namely, IVM (ivermectin, 0.2 mg/kg), BZD (fenbendazole, 5 mg/kg or albendazole 7.5 mg/kg), LVM (levamisole, 7.5 mg/kg) and Control (untreated group). Nematode larvae were identified by four pooled faecal cultures for each group. Cooperia and Ostertagia were the predominant nematode larvae in pre-treatment cultures. The mean FECRT efficacies for IVM, BZD and LVM were 81.0 AE 21%, 93.3 AE 8% and 97.6 AE 4%, respectively. AR was detected in 16 (64%) herds. IVM resistance was present in 15 herds and BZD resistance in eight herds (32%). Resistance to both ivermectin and fenbendazole was present in seven herds. LVM resistance was not detected. Cooperia was the predominant post-treatment nematode in all the herds with IVM resistance. In one herd with IVM resistance, Ostertagia counts were slightly increased over pretreatment counts. Ostertagia was the prevalent post-treatment genera in herds with BZD resistance. A high level of resistance to ivermectin was recorded in this fattening region of Argentina. Also several herds with resistance to benzimidazole were observed. These results show the importance of AR in Argentinian cattle production. High correlation between WAAVP and Abbott formulae was observed. However, under some uncertain diagnosis, both formulae could be applied as complementary to help result interpretations.
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.
Veterinary Parasitology, 2005
The objective was to examine the coincidence in the prevalence of benzimidazole (Bz) resistance in smallholder goat herds, as determined by three average-based and two individually-based faecal egg count reduction (FECR) tests. Nineteen smallholder goat herds with more than 30 animals were selected from 84 herds in Yucatan. Animals shedding 150 eggs/g of faeces (EPG) on day zero were randomly divided into two groups. The control group did not receive treatment and the treated group received fenbendazole (10 mg/kg body weight per os). Feed was withdrawn for 16 h before treatment. Ten days after treatment, both groups were sampled to determine their FEC. Faecal cultures and identification of infective larvae were performed for estimating the proportions of genera of gastrointestinal nematodes (GIN) present. Presence of resistant GIN was determined with three different average-based FECR (FECR 1 , FECR 2 and FECR 3 ) and two individually-based FECR (iFECR 1 and iFECR 2 ). The prevalence of herds with Bz resistant nematodes (and 95% confidence interval (95% CI)) was calculated using each formula. Coincidence among formulae was estimated with Kappa values. The prevalence (AE95% CI) of Bz resistance calculated with FECR 1 (57.89 AE 22.20) had a high coincidence with iFECR 1 and iFECR 2 (Kappa values of 0.86 and 0.79, respectively). The prevalence with FECR 2 (31.58 AE 20.90) and FECR 3 (21.05 AE 18.33) had a low coincidence with FECR 1 (Kappa < 0.50). Trichostrongylids found on Bz resistant farms were mainly Haemonchus spp., however, some Trichostrongylus spp. and Oesophagostomum spp. were found too. The high coincidence between the standard average-based FECR 1 and the individually based formulae is encouraging and may suggest that either formula could be applied to smallholder farmers. Further laboratory studies are needed to confirm the resistance status in the herds. #
The effect of anthelmintic resistance on the productivity in feedlot cattle
Veterinary parasitology, 2014
The aim of this study was to evaluate, in a commercial feedlot, the effect of different anthelmintic drugs on the productivity of naturally infected calves from a cow-calf operation, where resistance to ivermectin (IVM) has been previously detected. The study began with the random selection of 80 calves whose weight was 132 ± 12 kg. Four groups were made: IVM, ricobendazole (RBZ), ricobendazole plus levamisol (RBZ + LEV) and a control group (CG) without treatment. On days 0, 21, 42, 70, 98 and 126, manual collection of fecal matter and individual weight were registered. Mixed SAS procedure was used for statistical analysis. The percentages of fecal egg count reduction test (FECRT) calculated 21 days post treatment (PT) were 18%, 96% and 100% for the IVM, RBZ and RBZ + LEV groups, respectively. Body weight (± SEM) at the end of the trial was 266 kg (± 0.9), 269 kg (± 1.1), 276 kg (± 1.3), 280 kg (± 1.9) for CG, IVM, RBZ and RBZ + LEV groups, respectively. The effect on live weight wa...
Revista Brasileira de Parasitologia Veterinária, 2014
Risk factors for anthelmintic resistance (AR) on bovine ranches were studied. Data were derived from a survey made to 50 ranch owners, who had conducted a faecal egg-count-reduction test. The questionnaire contained descriptors of bovine ranch management and nematode control. A case-control design study was undertaken and AR cases were present in 26 herds. Associations between the binary outcome variable (AR versus not AR) and risk factors recorded in the questionnaire were evaluated. Variables associated with the presence of AR at P< 0.15 and/or odds ratio (OR) > 2 were subjected to a multivariable logistic regression model. The main effects contributing to general AR (avermectin AVM and/or benzimidazole) in the final model were total number of annual treatments (OR 7.68; 95% CI 2.4 to 28.3) and use of more than 75% of AVM in the past (OR= 18.6; 95% CI 1.3 to 97.3), whereas for AVM resistance alone were total number of AVM annual treatments (OR= 11.5; 95% CI 2.9 to 45.5) and ...
Parasitology International, 2014
Two high doses of ivermectin (630 μg/kg and 700 μg/kg) that are sold commercially in Brazil were evaluated in dose-and-slaughter trials with 144 naturally nematode-infected cattle from eight regions within the states of Minas Gerias, São Paulo and Rio Grande do Sul in Brazil. Treatment groups were based on fecal egg counts 1, 2, and 3 days before treatment; all animals studied had a minimum egg count of at least 500 eggs per gram of feces (EPG). Post-mortem analyses were conducted on day 14. The highest levels of resistance to ivermectin were found for Haemonchus placei, Cooperia punctata and Oesophagostomum radiatum; all populations of H. placei were resistant to the 630 μg/kg dose, and 67% were resistant to 700 μg/kg; 86% of C. punctata were resistant to the 630 μg/kg dose, and 33% were resistant to 700 μg/kg. A combined analysis revealed that 57% of O. radiatum were resistant to the lower dose of ivermectin. H. placei, C. punctata and O. radiatum, in order, were the nematode populations with the highest indices of resistance, whereas Trichostrongylus axei was the most susceptible to 630 and 700 μg/kg dosages of ivermectin. The results of helminthic resistance to ivermectin for different populations of H. placei and C. punctata described in the present study support previous literature data, in which a small decrease in the average parasitic burden of C. punctata and a consequent increase of H. placei were observed in cattle from the Southeast, South and Center-West regions of Brazil.
Veterinarski Arhiv
Frequent and indiscriminate use of anthelmintic drugs has led to anthelmintic resistance in animals. Different in vivo and in vitro tests have been employed to detect anthelmintic resistance. Among the in vivo tests, faecal egg count reduction test (FECRT) can best be used to evaluate anthelmintic effi cacy in commercial flocks and herds. In the present study, a total 40 animals, aged 12-24 months, were randomly divided into four groups of 10 goats each. All the 40 goats selected had egg counts of more than 500 eggs per gram (epg). Among these,Group I was kept as untreated control, while Groups II, III and IV were treated with fenbandazole at a dosage rate of 5mg/kg body weight orally, levamisole at a dosage rate of 7.5 mg/kg body weight orally and ivermectin at a dosage rate of 0.2 mg/kg body weight by subcutaneous injection, respectively. Faecal samples from the selected animals were collected on day 0 and day 14 post treatment. EPG was determined from each collected faecal sample a...