Presence Of Anthelmintic Resistance Research Articles

Anthelmintic resistance of horse strongyle nematodes to ivermectin in São Paulo state, Brazil

The indiscriminate use of drugs to control gastrointestinal helminths in horses can lead to serious consequences for the animals, which represents a growing problem for health, animal welfare and productivity. Therefore, the present study aimed to evaluate the anthelmintic efficacy of ivermectin in naturally infected horses in the western region of the state of São Paulo. From May 2021 to April 2022, 123 naturally infected adult horses in 12 equine breeding farms (7 to 14 animals per farm) were evaluated with the fecal egg count reduction test. The horses had not been treated with anthelmintic drugs for at least 60 days before the start of the study. The animals were treated with ivermectin (0.2 mg/kg; Eqvalan®, Merial) administered orally according to recommended dosage by the manufacturer. Individual fecal samples were collected directly from the rectal ampulla and used to determine the eggs per gram of feces (EPG) and perform coproculture for identification of larvae on the day of anthelmintic treatment (D0) and 14 days later (D14). The fecal egg count reduction (FECR) on each property was calculated using the program Shiny-egg Counts R version 3.6.1, and the presence of anthelmintic resistance was confirmed when the FECR percentage was less than 95%, and when the lower confidence limit [LCI] was less than 90%. The pre-treatment average EPG count in the 12 properties was 991. In five properties the FECR was lower than 90%; in three properties between 90% and 95%; and in four properties equal to or greater than 95% after treatment with ivermectin. The occurrence of cyathostomins with resistance to ivermectin was recorded in the majority of the farms.

Anthelmintic resistance and common worm control practices in sheep farms in Flanders, Belgium.

In contrast to many other European countries, no data were available on the presence of anthelmintic resistance in gastrointestinal nematodes in sheep in Belgium. A faecal egg count reduction test was performed in 26 sheep flocks in Flanders, Northern Belgium. Results indicated widespread resistance against benzimidazoles (albendazole, fenbendazole and mebendazole), with treatment failure on all 8 farms investigated. Haemonchus contortus and Teladorsagia circumcincta were the predominant species after treatment failure. Amino acid substitutions associated with benzimidazole resistance were detected at the codon positions 167 (8%) and 200 (92%) of the isotype-1 beta tubulin gene in H. contortus, codon positions 198 (47%) and 200 (43%) in T. circumcincta and position 200 (100%) in T. colubriformis. Resistance against macrocyclic lactones (ivermectin, doramectin and moxidectin) was recorded on 7 out of 20 flocks, mainly in H. contortus and T. circumcincta. Treatment failure was also observed for closantel (in combination with mebendazole) and for monepantel, on one farm each. Trichostrongylus spp. were implicated with resistance against monepantel. A questionnaire survey on farm management and worm control measures indicated that worm control was often not sustainable. Ewes and lambs were treated frequently (on average 2.6 and 3.2 times per year), mostly without weighing. Only few sheep farmers (9%) regularly used faecal egg counts to monitor worm infections. Despite the FECRT showing otherwise, most of the farmers perceived the efficacy of anthelmintics as very good (30%) or good (54%).

Risk factors for equine intestinal parasite infections and reduced efficacy of pyrantel embonate against Parascaris sp.

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 < 0.001) and season (p = 0.017). Horses were less likely (OR = 0.27, 95% CI: 0.10 - 0.66) to shed strongylid eggs during the spring compared to the winter. Horses excreting over 200 ascarid eggs per gram were included in the anthelmintic efficacy trial. A mean FECR less than 90% was interpreted as presence of anthelmintic resistance. The mean FECR was 98.5% (95% CI: 95.8–100) and 68.0% (95% CI: 52.7–83.3) in the fenbendazole (n = 31) and pyrantel (n = 26) treatment groups, respectively. In conclusion, we identified two new risk factors for patent Parascaris sp. infection; breeding farm size and frequency of horse movements. Reduced efficacy of pyrantel against Parascaris sp. was observed for the second time in Europe. A relatively high Parascaris sp. prevalence in yearlings (34%) and two-year-olds (20%) was observed, which has not been reported earlier. An association between symptoms and a patent Parascaris sp. infection was observed in foals.

Field trial assessment of ivermectin pharmacokinetics and efficacy against susceptible and resistant nematode populations in cattle

The study compared the pharmacokinetic (PK) behaviour and anthelmintic efficacy against susceptible and resistant nematodes following subcutaneous (SC) and oral administration of ivermectin (IVM) to cattle. Six commercial farms were involved: Farms 1 and 2 (IVM-susceptible nematode population) and Farms 3, 4, 5 and 6 (IVM-resistant nematode population). On each farm, forty-five calves naturally infected with gastrointestinal (GI) nematodes were randomly allocated into three groups (n = 15): untreated control, IVM SC administration, and IVM oral administration (both at 0.2 mg/kg). PK assessment (plasma and faeces) was performed on Farm 1. Efficacy was determined by Faecal Egg Count Reduction Test. IVM systemic availability upon SC administration (421 ± 70.3 ng·d/mL) was higher (P < 0.05) compared to the oral treatment (132 ± 31.3 ng·d/mL). However, higher (P < 0.05) faecal IVM concentrations were observed following oral treatment (9896 ± 1931 ng·d/mL) compared to SC administration (4760 ± 924 ng·d/mL). Similar (91–93%) IVM efficacy was observed on Farms 1 and 2 by both routes. Efficacy against resistant nematodes was slightly higher on Farms 3 and 4 after the oral (63 and 82%, respectively) compared to the SC (36 and 68%, respectively) treatment. However, there was complete therapeutic failure (0% efficacy) on Farm 5 and a very low response on Farm 6 (40 and 41% for SC and oral administration, respectively). Although larger faecal concentrations following IVM oral administration may increase drug exposure of GI adult worms, this does not always improve efficacy against resistant nematodes. The potential therapeutic advantages of oral treatments should be cautiously assessed, especially in presence of anthelmintic resistance.

Anthelmintic resistance in grazing beef cattle in central and northeastern areas of Argentina - An update.

The presence of anthelmintic resistance in Argentina has experienced a marked increase in cattle, with numerous reports showing levels of resistance of different parasite genera to different chemical groups. The aim of this study is to update comprehensively the situation of anthelmintic resistance to the different chemical groups in the most important areas of cattle production in Argentina. The study involved the determination of anthelmintic resistance in 62 cattle farms in 7 provinces using the faecal egg count reductions test. The results showed a marked increase of anthelmintic resistance compared to previous reports; the main resistant genera were Cooperia and Haemonchus to ivermectin, Ostertagia and Cooperia to ricobendazole, and Haemonchus to fenbendazole. There was also a distinct difference in clinical efficacies between subcutaneous ricobendazole and oral fenbendazole in favour of the latter, probably attributed to the administration route. Levamisole has showed high efficacy and broad antiparasitic spectrum. Anthelmintic resistance is widely and firmly established in grazing cattle production systems in the country; the diagnosis of resistance must be done in every particular farm in order to design a sustainable parasite control based on anthelmintics use.

In vivo and In vitro Efficacy of Albendazole Against Canine Ancylostomosis: A Possible Presence of Anthelmintic Resistance in Nigerian Local Breed of Dogs

In vivo and In vitro Efficacy of Albendazole Against Canine Ancylostomosis: A Possible Presence of Anthelmintic Resistance in Nigerian Local Breed of Dogs

Gastrointestinal nematodes and anthelmintic resistance in Danish goat herds.

The prevalence of gastrointestinal parasites in Danish goats and the presence of anthelmintic resistance (AR) in 10 selected herds were investigated during April–September 2012. All Danish herds (n = 137) with 10 or more adult goats were invited to participate, and of these 27 herds met the inclusion criterion of more than 10 young kids never treated with anthelmintics. Questionnaire data on management were collected, and faecal samples from 252 kids were analysed by the McMaster technique. From all herds with a mean faecal egg count (FEC) above 300 eggs per g of faeces, pooled samples were stained with peanut agglutinin (PNA) for specific detection of Haemonchus contortus. Strongyle eggs were detected with an individual prevalence of 69%, including Nematodirus battus (3.6%) and other Nematodirus species (15.0%). Eimeria spp. were observed in 99.6% of the kids. H. contortus was found in 11 of 12 (92%) tested herds. Anthelmintics were used in 89% of the herds with mean treatment frequencies of 0.96 and 0.89 treatments per year for kids and adults, respectively. In 2011, new animals were introduced into 44% of the herds of which 25% practised quarantine anthelmintic treatments. In 10 herds the presence of AR was analysed by egg hatch assay and FEC reduction tests using ivermectin (0.3 mg/kg) or fenbendazole (10.0 mg/kg). AR against both fenbendazole and ivermectin was detected in seven herds; AR against fenbendazole in one herd, and AR against ivermectin in another herd. In conclusion, resistance to the most commonly used anthelmintics is widespread in larger goat herds throughout Denmark.

An investigation of anthelmintic efficacy against strongyles on equine yards in Scotland

Cyathostomins comprise 50 helminth species, considered the most problematic equine endoparasites. Three classes of anthelmintic are currently licensed for their control, namely the benzimidazoles (fenbendazole), tetrahydropyrimidines (pyrantel) and macrocyclic lactones (ivermectin and moxidectin). Anthelmintic resistance in cyathostomins is common. With no new classes expected in the near future, it is essential to determine the efficacy of the available anthelmintics to inform future control programmes. To determine the efficacy of all 3 anthelmintic classes against strongyles in equids on livery yards in east and central Scotland. Anthelmintic efficacy testing using the faecal egg count reduction test (FECRT). FECRTs were performed on equids with initial strongyle faecal egg counts (FECs) of ≥50 eggs per gram. Efficacy was determined by comparing pretreatment (Day 0) and 14 days post treatment (Day 14) FECs. The following chemicals were tested: fenbendazole, pyrantel, ivermectin and moxidectin. Group arithmetic mean FECR of >90% for fenbendazole and pyrantel, and >95% for ivermectin and moxidectin, represented efficacy, whereas lower mean FECR indicated potential resistance. A total of 447 FECRTs were performed on 15 yards, as follows (the numbers in parentheses represent the number of yards each anthelmintic was tested on): 55 equids (7 yards) fenbendazole, 111 (8 yards) pyrantel, 163 (13 yards) ivermectin and 118 (10 yards) moxidectin. Fenbendazole resistance was documented on all yards (range of mean FECR, 15.8-83.4%), whereas pyrantel (90.4-99.6%), ivermectin (99.5-100%) and moxidectin (99.4-100%) treatment had acceptable efficacy. Reduced efficacy of fenbendazole was widespread, whereas >90% efficacy was found after pyrantel, and >95% efficacy after ivermectin and moxidectin. Overall, efficacies were higher than reported previously in Europe and the USA, potentially reflecting differences in management and anthelmintic use on the yards surveyed. The use of fenbendazole for strongyle control in Scotland should be questioned. Targeted use of pyrantel should be encouraged to reduce reliance on macrocyclic lactones. Further work to correlate management practices with the presence of anthelmintic resistance is warranted.

Managing anthelmintic resistance: Untreated adult ewes as a source of unselected parasites, and their role in reducing parasite populations

AIMS: To test the hypotheses that when untreated adult ewes are rotationally grazed (follow behind) on pastures after lambs receiving routine anthelmintic treatments, the ewes can function as a source of unselected parasites in refugia, capable of slowing the development of anthelmintic resistance, and suppress the build-up of parasites resulting from the development of anthelmintic resistance. METHODS: Firstly, the potential of untreated adult ewes to slow the development of anthelmintic resistance, and to suppress parasite populations under differing levels of anthelmintic efficacy, was investigated using a simulation model. Secondly, a field trial with three replicates of each treatment compared two grazing systems (lambs only vs lambs followed by ewes) and two types of anthelmintic, viz albendazole (ALB), to which resistance was present (faecal nematode egg count reduction (FECR)=57–59%) and ivermectin plus levamisole (IL), to which resistance was absent (FECR=97–99%), in a factorial treatment structure. Parasite populations were monitored using faecal nematode egg counts (FEC), faecal larval cultures, pasture larval sampling, and slaughter of tracer lambs. Animal performance was measured using liveweight, dag score, body condition score, and fleece weights. RESULTS: Model simulations indicated that parasites cycling in the untreated ewes could slow the development of resistance being selected for by the anthelmintic treatments given to lambs and this could occur without a nett increase in larval numbers on pasture. Further, as worm control in the lambs declined with increasing levels of anthelmintic resistance the ewes increasingly functioned as nett removers of parasite larvae, effectively reducing parasite population size. In the field trial, untreated adult ewes contributed to pasture infestations of most parasite species, but not Nematodirus spp. Parasite species on pasture and infecting lambs changed when ewes were present, but larval populations on pasture in the autumn were no greater than when lambs grazed alone. In the presence of anthelmintic resistance, parasite populations were reduced when ewes grazed in rotation with lambs, implicating the ewes as nett removers of parasite challenge. CONCLUSIONS: Untreated adult ewes were a source of unselected genotypes, capable of slowing the development of anthelmintic resistance in most, but not all, parasite species. Further, the potential of adult ewes to remove from pasture more parasite larvae than they contribute through faecal contamination indicates a potentially useful role in suppressing parasite populations, particularly when worm control in lambs is less effective as a result of anthelmintic resistance.

Anthelmintic resistance and management of nematode parasites on beef cattle-rearing farms in the North Island of New Zealand

AIM: To provide information on current farmers’ opinions and farming practices thought to be related to anthelmintic resistance, and to test for associations between the presence of anthelmintic resistance and management practices on beef cattle- rearing farms in the North Island of New Zealand. METHODS: A study using an interview-based questionnaire about management of internal parasites was conducted on 62 beef cattle-rearing farms in the North Island of New Zealand, using case-control analyses to test for associations between management practices and the presence or absence of resistance to ivermectin or albendazole. Resistance was inferred from faecal nematode egg count (FEC) reduction (FECR) tests (FECRTs) when there was <90% reduction in FEC 7-10 days after treatment of calves <12 months of age. RESULTS: Of the 59 farmers who completed the questionnaire, most (n=40) ranked parasites highly, and at about the same level as quality and quantity of feed, as important production-limiting factors for their enterprises. In contrast, anthelmintic resistance was not perceived to be a problem on 13 farms, and its importance was rated low on 24, moderate on 15, and high on only six farms. Despite all farms having planned parasite control programmes, there was heavy reliance on clinical signs of parasitism to determine frequency of treatments. About one in three farmers with beef breeder cows routinely treated their calves at marking, one in five treated mixed-age cows, and almost half treated rising 2-year-old cows before calving. One in four farmers used anthelmintics on calves on 8–12 occasions in their first year of life. Co-grazing with other species was rare, but follow-on grazing within 3 months after older cattle or sheep was common. On most farms, grazing cattle was restricted to part of the farm, a finding with implications for parasite control and persistence of larvae in refugia. Macrocyclic lactone (ML) anthelmintics or their combinations with other action families were currently, and for the past 5 years, used more frequently than benzimidazoles and levamisole, and benzimidazole-levami- sole combinations. The prevalence of resistance to ivermectin was high (82%) and no plausible model of associations could be constructed from the data. The prevalence of resistance to albendazole was 60%, and the risk of resistance increased as the number of rising 1-year-old cattle present mid-winter increased, and decreased as the number of breeding cows >2 years old present mid-winter increased. CONCLUSION: It is clear that in practice anthelmintic resistance is a secondary consideration to obtaining productivity advantages from the use of anthelmintics in beef cattle. Farmers’ opinions were divided on many issues and the overall impres- sion was of confused and diverse thinking regarding the principles of the use of anthelmintics. The overall outlook regarding anthelmintic resistance in cattle is bleak unless the need for integrated and long-term research activities is acted upon soon.

New worming guidelines: Quarantine anthelmintic treatments

aimed at slowing the rate of development of anthelmintic resistance within UK sheep flocks (UK Vet 11 (3), 59-64, 2006) and the importance of monitoring for the presence of anthelmintic resistance (UK Vet 11 (4), 50-55, 2006) have been discussed in recent editions of UK Vet. It is also important to avoid bringing in significant numbers of resistant nematodes with introduced sheep or goats. In the absence of any sensitive, rapid and accurate diagnostic test for anthelmintic resistant nematodes in individual sheep, all introduced sheep and goats should be assumed to be sources of multiple anthelmintic resistance. All introduced sheep and goats should, therefore, be treated with an effective anthelmintic on arrival and yarded or housed for 48 hours to ensure that any viable nematode parasite eggs have been voided before they are turned onto pastures which might be grazed by sheep within the next six months. Ideally, introduced sheep should then be turned onto likely contaminated pasture, so that any resistant nematode parasites that survive anthelmintic treatment only make up a very small proportion of the otherwise susceptible population in refugia (UK Vet 11 (3), 59-64, 2006). Entry of stray sheep or goats should be prevented and basic biosecurity should be imposed to ensure that sheep or goat faeces are not brought onto the farm.

The productivity of Merino flocks in South-Eastern Australia in the presence of anthelmintic resistance

Nematodes resistant to the benzimidazoles and levamisole anthelminitics have been present in many sheep flocks in South-Eastern (SE) Australia for over 20 years. We examined the productivity and profitability of six self-replacing Merino flocks, in which resistance to these anthelmintics had been confirmed for over 10 years. The profitability of three farms increased considerably over this period following progressive adoption of known determinants of profitability, namely the optimum application of fertilisers, increased stocking rates and improved sheep genotype. The remaining three flocks maintained their physical production and profitability, with two of these considerably increasing the scale of their enterprise. This suggests that anthelmintic resistance needs to be kept in perspective and tackled as just one part of whole farm management.

Economic evaluation of three anthelmintic strategies for lamb flocks affected by benzimidazole-resistant nematodes.

To compare the profitability of three anthelmintic strategies in growing lambs in flocks with nematodes resistant to benzimidazole anthelmintics. A partial-budgeting analysis was carried out by means of a stochastic simulation model, which allows inputs to be described as distributions rather than as fixed values, and hence permits variation between farms to be considered in the analysis. The results show that control of nematode parasites by use of an effective anthelmintic provides the highest net returns, yielding a margin over ineffectively treated lambs of A$114 per 100 lambs on average. Suppressive treatment based on the administration of two controlled-release capsules and monthly with moxidectin resulted in an average loss of A$131 per 100 lambs in comparison with animals treated with an ineffective anthelmintic. Analysis of the results from capsule-treated lambs did not take into account the unmeasured benefits associated with less contamination of pastures. Sensitivity analysis using a stochastic model indicates that apart from the effect of treatment on weight gain variation in carcase price greatly influences the profitability of all the parasite control programs examined. The results suggest that it is economically important for farmers to adjust their strategy in the presence of anthelmintic resistance. But as a result of uncertainty in the factors influencing economic return, the expected economic benefit is likely to vary substantially.