Preliminary Analysis of the Results of Selective Therapy Against Strongyles in Pasturing Horses

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.

Egg reappearance periods of anthelmintics against equine cyathostomins: The state of play revisited

Cyathostomins are the most common and highly prevalent parasites of horses worldwide. Historically, the control of cyathostomins has mainly relied on the routine use of anthelmintic products. Increasing reports on anthelmintic resistance (AR) in cyathostomins are concerning. A potential method proposed for detecting emerging AR in cyathostomins has been estimating the egg reappearance period (ERP). This paper reviews the data available for the ERP of cyathostomins against the three major classes of anthelmintics, macrocyclic lactones, tetrahydropyrimidines, and benzimidazoles. Published peer-reviewed original research articles were obtained from three databases (PubMed, CAB Direct and Web of Science) and were evaluated for their inclusion in a systematic review. Subsets of articles were then subjected to a review of ERP data. A total of 54 (of 134) studies published between 1972 and 2022 met the criteria for inclusion in the systematic review. Until the beginning of 2022, there was no agreed definition of the ERP; eight definitions of ERP were identified in the literature, complicating the comparison between studies. Additionally, potential risk factors for the shortening of the ERP, including previous anthelmintic use and climate, were frequently not described. Reports of shortened ERP for moxidectin and ivermectin are frequent: 20 studies that used comparable ERP definitions reported shortened moxidectin and ivermectin ERPs of 35 and 28 days, respectively. It is unclear whether the ERPs of these anthelmintics reduced to such levels are due to the development of AR or some biological factors related to horses, cyathostomin species, and/or the environment. The ERPs for other anthelmintics, such as fenbendazole and pyrantel, were frequently not reported due to established resistance against these drugs. Future research in horses is required to understand the mechanism(s) behind the shortening of ERP for cyathostomins. Based on this systematic review, we propose recommendations for future ERP studies.

Anthelmintic efficacy in strongyles of horses in Northern Minas Gerais, Brazil

The intensive use of anthelmintics has resulted in resistant parasite populations in horses. The objective of this trial was to evaluate the anthelmintic efficacies of the anthelmintics fenbendazole, ivermectin and abamectin in 24 horse farms in Northern Minas Gerais. Egg counts per gram of faeces (EPG) were performed individually in 619 animals. Animals presenting EPG counts greater than or equal to 150 were used in the tests on faecal egg count reduction (FECR), totalling 436 equines. These animals received the anthelmintics, fenbendazole, ivermectin, and abamectin. Faeces were collected 14 days after the administration of anthelmintics to perform the EPG. Pre- and post-treatment EPG counts were used to calculate the FECR for each anthelmintic group, and faecal culture was used to identificy of the strongyles. The resistance status was evaluated based on the FECR and LCL95%. Fenbendazole was effective in 11 (45.8%) of the horse farms. Ivermectin was effective in 17 (77.3%) and abamectin in 17 (74%) of the farms; side-resistance was detected in 3 (12.5%) of the farms. Intestinal strongyle resistance to anthelmintics was observed in 14 (58.3%) of the farms. Cyathostomin larvae were found in 100% of the farms, Strongylus vulgaris in 13 (54.2%), and S. equinus in 3 (12.5%). Only cyathostomins larvae were detected post-treatment with ivermectin and abamectin.

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.

Gastrointestinal Parasitism in Miranda Donkeys: Epidemiology and Selective Control of Strongyles Infection in the Northeast of Portugal

Simple Summary

In the northeast of Portugal, the Association for the Study and Protection of Donkeys (AEPGA) works to recuperate the autochthonous Miranda do Douro donkey breed. Donkeys living in the three rehabilitation centers of the association have been assessed since 2005 with regards to the parasite control, since parasitism is an important issue affecting their health. Firstly, a strategic approach was implemented for parasite control, but over the years, a lack of anthelmintic efficacy over cyathostomins was observed. Thus, a different strategy was designed, using a targeted selective treatment (TST), and the effects of this approach were studied through the evaluation of parasite dynamics in the animals. Generally, it was observed that TST promoted a rational use of resources, as well as a reduction of parasite prevalence, although with a reduction of parasite biodiversity.

Abstract

In Portugal, equine parasitism in pasture animals is characterized by high parasitic burden and high helminthic biodiversity; both factors are potentially pathogenic for their hosts. The decrease in the number of donkeys over the last years in Portugal, their importance in rural lowland and mountain ecosystems and pastures and the scarce information regarding their parasitism led to this research, which aimed to evaluate the parasitological status of a Miranda donkey breed population, a native breed mainly located in the northeast of Portugal. This study provides better knowledge of their gastrointestinal parasitism, particularly strongyles, and the assessment of a targeted selective treatment (TST) as an alternative control approach of their parasitism. A longitudinal observational study was developed during a period of five years in a population of 62 Miranda donkeys. At first, strategic deworming of these animals was performed every semester, but this was progressively replaced by a TST approach according to the levels of Eggs per Gram (EPG). This new deworming strategy was conducted in association with a regular parasitological monitoring of the animals every three months, being dewormed with ivermectin when egg shedding was higher than 500 EPG. Over the study period, a decrease of the annual prevalence rate of infection by gastrointestinal strongyles was observed, from 35.5% to 19.4%, as well as a negative binomial distribution of parasitic strongyles in donkeys submitted to selective anthelminthic control. The prevalence rate of infection was higher in females (39.5%), in individuals under four years (46.7%) and in those presenting a lower body condition (40.8%). The egg output was higher in animals younger than four years (589.3 EPG) than in those older than 10 years (533.6 EPG) (p < 0.05). However, no differences were observed according to sex during the study period. Results from this study allowed to note the influence of swampy pastures and of the weather changes in the epidemiology of strongylosis in Miranda donkeys. Moreover, it was possible to establish the annual epidemiological curve of strongyle egg shedding, with June being the month with the highest EPG, December having the lowest EPG and March and September showing intermediate numbers. Overall, a lower biodiversity of gastrointestinal parasites was observed. Cyathostomum sensu lato was the most prevalent genus and Strongylus vulgaris was the most observed large strongyle of the Strongylidae family. Trichostrongylus axei and Parascaris sp. were other nematodes with a minor frequency. The higher prevalence of strongyles at the beginning of the study showed a progressive decrease throughout the research period, and also for parasite biodiversity. Therefore, a targeted selective treatment seems to be a rational anthelminthic control approach in Miranda donkey strongyle infection and in other gastrointestinal parasites, since it reduces the antiparasitic treatments, the parasite’ prevalence and the EPG level. However, a loss of parasite biodiversity was noted at the end of the study period, as Cyathostominae were the only isolated strongyles. This can be a challenging situation in the long run, taking the ability of these nematodes to adapt easily to any deworming program, meaning that fecal EPG monitoring should be kept as a rule to a rational parasite control program.

Implementation of Biological Control to the Integrated Control of Strongyle Infection among Wild Captive Equids in a Zoological Park

The integrated control of strongyles was assayed for a period of three years in wild equids (zebras, European donkeys, and African wild asses) captive in a zoo and infected by strongyles. During three years control of parasites consisted of deworming with ivermectin + praziquantel; equids also received every two days commercial nutritional pellets containing a blend of 10⁴ - 10⁵ spores of the fungi Mucor circinelloides + Duddingtonia flagrans per kg meal. Coprological analyses were done monthly to establish the counts of eggs of strongyles per gram of feces (EPG). The reductions in the fecal egg counts (FECR) and in the positive horses (PHR) were calculated fifteen days after deworming; the egg reappearance period (ERP) and the time elapsed from the previous deworming (TPD) were also recorded. Four anthelmintic treatments were administered during the assay, three times throughout the first 2 yrs, and another treatment during the last one. FECR values of 96-100% and 75-100% for the PHR were recorded. The ERP oscillated between eight and twenty-eight weeks, and the TPD ranged from four to eighteen months, increasing to the end of the trial. No side effects were observed in any of the equids. It is concluded that integrated control of strongyles among equids captive in a zoo can be developed by anthelmintic deworming together with the administration of pellets manufactured with spores of parasiticide fungi every two days.

A combined effort to avoid strongyle infection in horses in an oceanic climate region: rotational grazing and parasiticidal fungi

Background

An approach to preventing strongyle infection in horses was tested, comprising rotational pasturing and the administration of spores of two parasiticidal fungi, Mucor circinelloides and Duddingtonia flagrans.

Methods

Twenty-two adult Spanish Sport Horses were dewormed with ivermectin (1 mg pour-on/kg body weight) and then randomly divided into three groups. G-1 was maintained with continuous grazing, and G-2 and G-3 were kept on a four-paddock rotation system. Commercial pelleted feed (2.5 kg/horse) was supplied to G-1 and G-2 twice a week; horses in G-3 received pellets containing 2 × 10⁶ spores/kg of each fungus. Fecal samples were analyzed by the flotation method to estimate the reduction in the fecal egg counts (FECR), the percentage of horses shedding eggs (PHR), and the egg reappearance period (ERP).

Results

Third-stage larvae were identified in fecal pats as Cyathostomum (sensu lato) types A, C and D, Gyalocephalus capitatus, Triodontophorus serratus, Poteriosthomum spp., Strongylus vulgaris and S. edentatus. Two weeks after treatment, the FECR values were 100% in G-1, 96% in G-2 and 99% in G-3; the PHR values were 100% in G-1, 75% in G-2 and 88% in G-3. A strongyle ERP of 6 weeks was observed in G-1, ERP of 10 weeks was observed in G-2, and ERP of 16 weeks was observed in G-3. The counts of eggs per gram of feces (EPG) were > 300 EPG in G-1 and G-2 but remained below 250 EPG in G-3 throughout the observation period of 12 months.

Conclusions

These results suggest that horse strongyle infection could be decreased by combining rotational pasturing with feeding pellets containing the spores of parasiticidal fungi.

Feeding horses with industrially manufactured pellets with fungal spores to promote nematode integrated control

The usefulness of pellets industrially manufactured with spores of parasiticide fungi as a contribution to integrated nematode control was assessed in grazing horses throughout sixteen months. Two groups of 7 Pura Raza Galega autochthonous horses (G-T and G-P) were dewormed pour-on (1mg Ivermectin/kg bw) at the beginning of the trial, and other group (G-C) remained untreated. The G-P was provided daily with commercial pellets to which was added a mixture of fungal spores during the industrial manufacturing (2×10⁶ spores of Mucor circinelloides and same dose of Duddingtonia flagrans/kg), and G-T and G-C received pellets without spores. The efficacy of the parasiticidal strategy was assessed by estimating the reduction in the faecal egg counts (FECR) and in the number of horses shedding eggs in the faeces (PHR), and also the egg reappearance periods (ERP). Blood analyses were performed to identify the changes in the red and white cell patterns. To ascertain if horses developed an IgG humoral response against the fungi, antigenic products collected from M. circinelloides and D. flagrans were exposed to the horse sera by using an ELISA. The faecal elimination of eggs of Parascaris equorum and strongyles ceased 2 weeks after treatment in G-T and G-P, thus the values of FECR and PHR were 100%. No P. equorum-eggs were detected later, and the strongyle egg reappearance period was 28 weeks in G-P, and 8 weeks in G-T. Strongyle egg-output values remained lower than 300 eggs per gram of faeces in the G-P, whereas numbers between 330 and 772 in G-C and G-T were recorded. Normal values for the erythrocytes, haemoglobin and haematocrit in horses consuming pellets with spores were recorded, and lower than normal in the other groups. Sensitization of horses to the fungal species was disproven. It is concluded that feeding horses with pellets industrially manufactured with fungal spores represents a very useful tool to implement an integrated control of helminths affecting horses. This strategy allows a decrease in their risk of infection, aids in reducing the frequency of anthelmintic treatment.

Screening for anthelmintic resistance in equid strongyles (Nematoda) in Romania

Resistance to anthelmintic medication of equid strongyles is a worldwide phenomenon and for this reason systematic investigations of resistant parasite populations are necessary. The purpose of the present study was to investigate the presence and distribution of equid strongyles resistant to the anthelmintics used in Romania, as well as the pre-treatment and post-treatment prevalence of species of strongylid nematodes. The Faecal Egg Count Reduction Test was performed between 2010 and 2013 on a total number of 588 horses and 23 donkeys from 26 locations (subgroups). Animals of the first group (I) consisting of subgroups no. 1-11 were treated with Albendazole (ABZ), those of the second group (II) consisting of subgroups no. 12-23 with Fenbendazole (FBZ), while Ivermectin (IVM) was used on animals of the third group (III) consisting of subgroups no. 24-26. Resistant strongyles have been found in 82% (average lower limit of the 95% confidence interval, LCL95%, was 65) of the total equids from the group treated with ABZ. In the group of horses treated with FBZ, resistant strongyles were identified in 75% of the subgroups (LCL95% = 44). No resistant strongyles have been identified in IVM-treated horse groups (LCL95% = 98). The pre-treatment prevalence of the species of the Strongylinae Müller, 1780 was 22%, whereas that with nematodes of the subfamily Cyathostominae Molin, 1861 78%. Post-treatment reduction of strongyline nematodes was observed (5%), which demonstrates the sensitivity of large strongyles to common anthelmintics. The post-treatment prevalence of cyathostomes was of 95%, which proves their resistance, especially to ABZ- and FBZ-based anthelmintics.

The effectiveness of faecal removal methods of pasture management to control the cyathostomin burden of donkeys

BACKGROUND

The level of anthelmintic resistance within some cyathostomin parasite populations has increased to the level where sole reliance on anthelmintic-based control protocols is not possible. Management-based nematode control methods, including removal of faeces from pasture, are widely recommended for use in association with a reduction in anthelmintic use to reduce selection pressure for drug resistance; however, very little work has been performed to quantitatively assess the effectiveness of such methods.

METHODS

We analysed data obtained from 345 donkeys at The Donkey Sanctuary (Devon, UK), managed under three different pasture management techniques, to investigate the effectiveness of faeces removal in strongyle control in equids. The management groups were as follows: no removal of faeces from pasture, manual, twice-weekly removal of faeces from pasture and automatic, twice-weekly removal of faeces from pasture (using a mechanical pasture sweeper). From turn-out onto pasture in May, monthly faecal egg counts were obtained for each donkey and the dataset subjected to an auto regressive moving average model.

RESULTS

There was little to no difference in faecal egg counts between the two methods of faecal removal; both resulted in significantly improved cyathostomin control compared to the results obtained from the donkeys that grazed pasture from which there was no faecal removal.

CONCLUSIONS

This study represents a valuable and unique assessment of the effectiveness of the removal of equine faeces from pasture, and provides an evidence base from which to advocate twice-weekly removal of faeces from pasture as an adjunct for equid nematode control. Widespread adoption of this practice could substantially reduce anthelmintic usage, and hence reduce selection pressure for nematode resistance to the currently effective anthelmintic products.