A systematic review and meta-analysis on the current status of anthelmintic resistance in equine nematodes: A global perspective

BACKGROUND

The intensive application of anthelmintics in equine has led to considerable resistance in cyathostomins and Parascaris equorum. It has been well documented that benzimidazole (BZ) and pyrantel resistance is widespread in cyathostomins and Parascaris equorum. Since no new classes of anthelmintic have been introduced in the last 40 years, it is critical to be aware of the current risk factors of anthelmintic application to avoid further resistance.

OBJECTIVE

To review the factors affecting the level of anthelmintics resistance in equine around the world, type of anthelmintics, mode of application, dosage, nematode species, and location of anthelmintics application were evaluated and summarized.

DESIGN/PROCEDURE

A systematic review and meta-analyses following the PRISMA Framework were conducted to identify, evaluate, and synthesize primary literature reporting the efficacy of anthelmintic drugs in equines. Information on the bibliographic data, anthelmintic drugs, animals, continents, parasite genera, type of anthelmintics, and dosage was collected. Nonparametric tests (Kruskal-Wallis and Mann-Whitney) were used in SPSS (v.27) to investigate the association between variables. Factors that have a significant impact on efficacy have been subjected to binary logistic regression. Six meta-analyses were conducted in Microsoft Excel (2021) to qualify current resistance issues of the three major anthelmintics classes.

RESULTS

The final database was composed of 60 articles published between 1994 and 2022 with a total of 11835 animals. Anthelmintic class as well as anthelmintic active principle selection did have a significant effect on resistance (P < 0.01), whilst no correlation of the type of anthelmintics, mode of application, and dosage with efficacy were found. Anthelmintics resistance in ascarid was significantly more severe than in strongyle (P < 0.01). Macrocyclic lactone (ML) class and the benzimidazole and probenzimidazole (BP) class have the lowest efficacy against ascarid and strongyle, respectively (67.83% and 69.85%). The effect of location (by continent) also had a significant influence on the resistance of the ML class (P < 0.01). The resistance of the BP class which is the most prevalently applied was demonstrated in all six continents. Binary logistic regression revealed that parasite genera and drug class independently influenced the presence of drug resistance. The forest plots included in this study did not show a significant difference over time.

CONCLUSION

Current evidence indicated that anthelmintics resistance of ML and BP class were common in ascarid and strongyle. A combination of anthelmintics may reduce anthelmintics resistance, but multi-drug resistance may be a concern. Customerised anthelmintics strategy could help reduce resistance.

Understanding anthelmintic resistance in livestock using "omics" approaches

Widespread and improper use of various anthelmintics, genetic, and epidemiological factors has resulted in anthelmintic-resistant (AR) helminth populations in livestock. This is currently quite common globally in different livestock animals including sheep, goats, and cattle to gastrointestinal nematode (GIN) infections. Therefore, the mechanisms underlying AR in parasitic worm species have been the subject of ample research to tackle this challenge. Current and emerging technologies in the disciplines of genomics, transcriptomics, metabolomics, and proteomics in livestock species have advanced the understanding of the intricate molecular AR mechanisms in many major parasites. The technologies have improved the identification of possible biomarkers of resistant parasites, the ability to find actual causative genes, regulatory networks, and pathways of parasites governing the AR development including the dynamics of helminth infection and host-parasite infections. In this review, various "omics"-driven technologies including genome scan, candidate gene, quantitative trait loci, transcriptomic, proteomic, and metabolomic approaches have been described to understand AR of parasites of veterinary importance. Also, challenges and future prospects of these "omics" approaches are also discussed.

Awareness and control measures for gastrointestinal parasites in donkeys in Maseru district, Lesotho

Parasitic infection is one of the major problems in equines which negatively influence their health. It hinders working performance of equines. This study was conducted to evaluate donkey owners' knowledge and control measures on prevalence of gastrointestinal parasites (GIPs) in three agro-ecological zones (AEZs) of Maseru district. A total of 144 donkey owners were selected for individual interviews through a stratified random sampling. Descriptive statistics and chi-square tests were used to analyze data. The significance (p <0.05) of different AEZs was tested using a post-hoc cell-wise adjusted standardized residual analysis. Majority of donkey owners were familiar with the GIPs especially nematodes as it seemed to be the most occurring, but there was no significant effect (p > 0.05) across the AEZs. The adult donkeys were mostly susceptible to different GIPs according to respondents and severe infection was experienced in summer and winter. Donkeys were dewormed seasonally using anthelmintics with inappropriate weighing instruments to establish the dosage, however, chi-square test pointed out the significance (p = 0.004) effect between types of medication used across the AEZs. Donkeys were kept in non-roofed stables that were not cleaned regularly hence, these compromised their welfare. However, communal grazing shared by different livestock species was the main source of animal feeding though it was found to be the major source of GIPs. Therefore, there is a need to equip them on the proper skills to improve on their management practices and the behaviour of parasites in different areas. This will help donkey owners adhere to appropriate control and prevention strategies.

Anthelmintic resistance in equine nematodes: Current status and emerging trends

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.

Feasibility of selective anthelmintic therapy to horses in tropical conditions: the Cuban scenario

For the past several decades, selective anthelmintic therapy (SAT) has been recommended in temperate climate countries for controlling gastrointestinal parasites in horses. However, the feasibility of this approach in tropical climates remains unknown, given the very different parasite transmission patterns and a larger representation of working equids. The aim of this study was to evaluate the bio-economic feasibility of SAT in horses kept under tropical conditions of Camagüey, Cuba. Fecal egg counts were determined from 794 adult horses and used for evaluating three different putative treatment thresholds; > 500 strongylid eggs per gram of feces (EPG); > 1000 EPG; and treatments yielding > 80% of the total herd egg output. These scenarios were evaluated under three treatment frequencies (every 2, 6, and 12 months). The bio-economic feasibility of these nine possible selective anthelmintic therapy scenarios was evaluated taking into account the cost of parasitological tests, and the mean cost of anthelmintic treatment in Camagüey. The majority (96.7%) of the samples tested were positive for strongyle eggs, with a mean of 1549 EPG. The percentage of horses exceeding the cut-off points at the nine scenarios varied between 40.1 and 93.8%. All owners surveyed used extra-label anthelmintic product in their horses on a routine basis. The economic analysis demonstrated that selective therapy generally was much more costly than deworming the entire herd without determining egg counts. However, we consider that the deworming every 6 months of the horses that expel 80% of the eggs in the herd allows a reduction of the treatment intensity without increasing costs, and it can be considered as a viable selective deworming scheme under similar conditions.