Drug Resistance in Equine Parasites: An Emerging Global Problem

Patterns of Equine Small Strongyle Species Infection after Ivermectin Intervention in Thailand: Egg Reappearance Period and Nemabiome Metabarcoding Approach

The indiscriminate use of anthelmintics to control parasitic nematodes in horses has led to the emergence of anthelmintic resistance worldwide. However, there are no data available on using ivermectin for treating strongyle infections within domesticated horses in Thailand. Therefore, this study aimed to use the fecal egg count reduction (FECR) test to determine the strongylid egg reappearance period (ERP). Additionally, the nemabiome metabarcoding approach is incorporated to study patterns of strongyle species infection following ivermectin treatment. The study results indicate that, although ivermectin effectively eliminated adult strongyle parasites within two weeks post-treatment, the ERP was shortened to 6 weeks post-treatment with a mean FECR of 70.4% (95% CI 46.1-84.0). This potentially indicates a recent change in drug performance. In addition, nemabiome metabarcoding revealed that strongyle species have different levels of susceptibility in response to anthelmintic drugs. The reduction in ERP was associated with the early reappearance of specific species, dominated by Cylicostephanus longibursatus and Cylicocyclus nassatus, indicating the lower susceptibility of these species. In contrast, Poteriostomum imparidentatum, Triodontophorus nipponicus, and Triodontophorus serratus were not found post-treatment, indicating the high level of susceptibility of these species. This information is vital for comprehending the factors contributing to the emergence of resistance and for devising strategies to manage and control strongyle infections in horses.

CANTERing towards more sustainable helminth control

Victoria Colgate of Equine Infectious Disease Surveillance introduces CANTER, a voluntary pan-industry initiative that is aiming to inspire behaviour change among horse owners and promote a more sustainable approach to controlling parasites in their animals.

Moringa oleifera as a Natural Alternative for the Control of Gastrointestinal Parasites in Equines: A Review

Studies have shown a wide variety of parasites that infect horses, causing major gastrointestinal damage that can lead to death, and although the main method of control has been synthetic anthelmintics, there are parasites that have developed resistance to these drugs. For generations, plants have been used throughout the world as a cure or treatment for countless diseases and their symptoms, as is the case of Moringa oleifera, a plant native to the western region. In all its organs, mainly in leaves, M. oleifera presents a diversity of bioactive compounds, including flavonoids, tannins, phenolic acids, saponins, and vitamins, which provide antioxidant power to the plant. The compounds with the greatest antiparasitic activity are tannins and saponins, and they affect both the larvae and the oocytes of various equine gastrointestinal parasites. Therefore, M. oleifera is a promising source for the natural control of gastrointestinal parasites in horses.

Study on Gastrointestinal Nematodes of Equines in and around Bekoji, South Eastern Ethiopia

Parasitic infections can cause a variety of respiratory, intestinal, and other problems in horses, as well as contribute to some performance issues. A cross-sectional study was undertaken in and around Bekoji, South Eastern Ethiopia, from November 2020 to June 2021 to identify species and evaluate the prevalence of gastrointestinal parasites in donkeys and horses, using direct fecal smear, floatation methods, and larval cultures. In this study, the overall prevalence of gastrointestinal nematode parasites was 94.5% (363 out of 384), with donkeys accounting for 95.8% and horses accounting for 90.5%. The coprological study indicated that an overall prevalence of gastrointestinal nematode parasites was 87%, 8.3%, 2.5%, 1.4%, and 0.8% for mixed parasite infection, nonmigratory strongylids, migratory strongylids, Parascaris equorum, and Oxyuris equi, respectively. Among mixed infections, nonmigratory strongylids+migratory strongylids (51.5%) occurred most frequently. The odds of male horses being infected by GIT nematodes were 1.59 times higher than male donkeys. Horses which have poor body condition were 2.94 times more infected than donkeys. The odds of old-aged donkeys were 3.11 times more infected than horses. A statistically significant difference (p < 0.05) was observed in the prevalence of gastrointestinal nematodes with species and body conditions of the animals. However, no statistically significant difference (p > 0.05) was seen in the prevalence of gastrointestinal nematode parasites between the sex and age of the Equidae. The mean fecal egg count of nematodes revealed that horses (1364.4 ± 483.5) had a more severe infection than donkeys with a statistically significant difference (p < 0.05). The current study determined there was a high prevalence of gastrointestinal nematode parasites in Equidae. Regular deworming, improved housing and nutrition management systems, increased animal owner awareness, and prevention techniques should all be undertaken to minimize the disease's economic burden in the area.

Gastrointestinal Strongyles Egg Excretion in Relation to Age, Gender, and Management of Horses in Italy

Simple Summary

Horses worldwide are plagued by gastrointestinal parasites that can lead to severe health problems. The occurrence and intensity of these worm infections vary based on the geographical location, season, and animal management strategies applied. One of these strategies is to monitor the parasite situation in different parts of the world. This research investigates the abundance, proportions, and risk factors of strongyle egg shedding of horses in Italy. Overall, the results showed that approximately 40% of all horses in Italy shed strongyle eggs and that almost 90% of stables have at least one infected animal. In addition, most parasite eggs are found in just a small fraction of the horse population, confirming the need for improved parasite control strategies.

Abstract

Current equine helminth control strategies play a key role in strongyle epidemiology and anthelmintic resistance and have led to the recommendation for new treatment plans, which include diagnostic and efficacy surveillance. Assessing the equine strongyle distribution patterns would thus be useful and this study describes the strongyle prevalence in the equine population in Italy through coprological analysis and coproculture. In addition, individual data on each animal were collected in order to identify risk factors associated with strongyle egg shedding. Of the total number of stables investigated, 86.4% were found to have at least one positive animal and a 39.5% prevalence of strongyle egg shedding with a mean eggs per gram (EPG) of 245. A total of 80% of the total recorded EPG was shed from 12.8% of positive horses, thus confirming the need for new targeted intervention strategies. Significant differences in parasite prevalence were found based on season, sex, geographical distribution, management and rearing system, and breed. Significantly lower EPG values were found in horses that had received anthelmintic treatment, and macrocyclic lactones (MLs) were the most effective. Lastly, although large strongyles are more pathogenic, horses in Italy are mainly burdened by small strongyles, which pose an important animal health risk requiring continuous parasitological monitoring.

Anthelmintic activity of crude powder and crude aqueous extract of Trachyspermum ammi on gastrointestinal nematodes in donkey (Equus asinus): An in vivo study

ETHNOPHARMACOLOGICAL RELEVANCE

Trachyspermum ammi has been used traditionally as a popular ethnobotanical plant in human and animal parasitic infestations. Few scientific studies have been conducted on in vitro anthelmintic activity of T. ammi against various helminths and there is no study on its in vivo/in vitro anthelmintic properties against equine helminths.

AIM OF THE STUDY

The present study aimed to evaluate in vivo anthelmintic activity of crude powder (CP) and crude aqueous extract (CAE) of T. ammi seeds against gastrointestinal nematodes in the donkey.

MATERIALS AND METHODS

Thirty donkeys, naturally and severely infected with Strongyle-type nematodes, were randomly divided into six groups and administered orally with graded doses of CP and CAE at single dose as follow: Two groups were treated with 1 and 3 gkg^-1 body weight of CP, two groups were treated with CAE at the equivalent dose rate 1 and 3 gkg^-1 bw of CP and one group was treated with 200 μgkg^-1 bw of Ivermectin 0.2% (Positive Control). One group received no medication (Negative Control). Efficacy was determined by faecal egg count reduction (FECR) test. The faecal samples were taken from the donkeys on days 7, 14 and 28 post-treatments (PT) and the egg per gram (EPG) of faeces was determined for each animal. FECR for donkeys treated with CP, CAE, and Ivermectin 0.2% was calculated on days 7, 14, and 28 PT. In the present study, CAE was analyzed using gas chromatography-mass spectrometry (GC-MS) to determine CAE chemical components. High-performance liquid chromatography (HPLC) using a marker (thymol) was applied to confirm the existence of thymol as an active principle.

RESULTS

Based on the FECR findings, the maximum FECR (71.2%) was observed in the group treated with CAE₃ on day 14 PT, while it was 66.2% for CP₃ on the same day. The effects of different treatments (P < 0.001), time (P < 0.001) and their interactions (P < 0.05) on EPG showed a significant difference. A dose-dependent response in the anthelmintic activity of CP and CAE was observed. GC-MS analysis indicated that thymol was the major component of CAE (Area = 45.01%) with the respective peak at retention times (Rt) 10.41 min. On HPLC analysis of CAE, thymol was found to be the major constituent of CAE (Area = 58.76%) with the same Rt at 13.233 min.

CONCLUSION

The present study indicated that both CP and CAE of T. ammi had the dose-dependent anthelmintic effects. Due to the development of drug resistance against synthetic anti-helminthics, T. ammi seems to be a promising alternative for the treatment and prevention of helminths in livestock.

Anthelmintic resistance and novel control options in equine gastrointestinal nematodes

Control of equine nematodes has relied on benzimidazoles (BZs), tetrahydropyrimidines and macrocyclic lactones. The intensive use of anthelmintics has led to the development of anthelmintic resistance (AR) in equine cyathostomins and Parascaris equorum. Field studies indicate that BZ and pyrantel resistance is widespread in cyathostomins and there are also increasing reports of resistance to macrocyclic lactones in cyathostomins and P. equorum. The unavailability of reliable laboratory-based techniques for detecting resistance further augments the problem of nematode control in horses. The only reliable test used in horses is the fecal egg count reduction test; therefore, more focus should be given to develop and validate improved methodologies for diagnosing AR at an early stage, as well as determining the mechanisms involved in resistance development. Therefore, equine industry and researchers should devise and implement new strategies for equine worm control, such as the use of bioactive pastures or novel feed additives, and control should increasingly incorporate alternative and evidence-based parasite control strategies to limit the development of AR. This review describes the history and prevalence of AR in equine nematodes, along with recent advances in developing resistance diagnostic tests and worm control strategies in horses, as well as giving some perspective on recent research into novel control strategies.

Identifying anti-Toxocara IgG antibodies in horses of Mexico

ABSTRACT Both the presence of owned dogs and stray dogs allows the spread of Toxocara, a parasite whose eggs can be found in soil, water and food. Animals, including horses, serve as definitive and paratenic hosts. In México, where consumption of horse meat is common, Toxocara is a zoonotic parasite. The aim of this study was to identify the presence of anti-Toxocara antibodies in work horses and horses intended for human consumption by ELISA. ELISA was chosen for analysis as paratenic hosts do not shed Toxocara eggs in their feces. Blood samples were collected from a total of 188 horses, 94 of which were work horses and 94 horses from the slaughter house. Samples were analyzed by ELISA, and the general equine seroprevalence was found to be 44.6% (n = 188). Adult horses for slaughter had a 61.7% greater presence of anti-Toxocara antibodies (p = 0.006). Toxocara IgG antibodies were found in horses, confirming that horses are paratenic hosts and possible sources of infection for other animals and people.

Anthelmintic Resistance of Strongyle Nematodes to Ivermectin and Fenbendazole on Cart Horses in Gondar, Northwest Ethiopia

A study was conducted from November 2015 to April 2016 to determine fenbendazole and ivermectin resistance status of intestinal nematodes of cart horses in Gondar, Northwest Ethiopia. Forty-five strongyle infected animals were used for this study. The animals were randomly allocated into three groups (15 horses per group). Group I was treated with fenbendazole and Group II with ivermectin and Group III was left untreated. Faecal samples were collected from each cart horse before and after treatment. Accordingly, the reduction in the mean fecal egg count at fourteen days of treatment for ivermectin and fenbendazole was 97.25% and 79.4%, respectively. It was significantly different in net egg count between treatment and control groups after treatment. From the study, resistance level was determined for fenbendazole and suspected for ivermectin. In addition, a questionnaire survey was also conducted on 90 selected cart owners to assess their perception on anthelmintics. In the survey, the most available drugs in the study area used by the owners were fenbendazole and ivermectin. Most respondents have no knowledge about drug management techniques. Hence, animal health extension services to create awareness regarding anthelmintic management that plays a key role in reducing the anthelmintic resistance parasites.

Anthelmintics efficacy against intestinal strongyles in horses of Sardinia, Italy

Intestinal strongyles (IS) are the most important parasites of equids, due to their high prevalence worldwide, pathogenicity and the spread of drug-resistant populations. Despite the large number of horses bred in Sardinia Island, Italy, no data are available on the efficacy of anthelmintic compounds in the control of horse strongylosis. Therefore the aim of the present study was to evaluate the efficacy of five commercial anthelmintic formulations containing fenbendazole (FBZ), pyrantel (PYR), moxidectin (MOX) and two ivermectin formulations (IVM1 and IVM2) against IS in Sardinia by performing a fecal egg count reduction test (FECRT) and investigating the egg reappearance period (ERP) after treatment. In total, 74 horses from 7 farms were examined. Coprocultures performed for individual fecal samples collected at the day of the treatment revealed that cyathostomins were the predominant parasitic species (98.6%). The FECR for all horses belonging to the treatment groups after two weeks was ≥ 95% with a 95% C.I. > 90%. The expected ERP did not decrease in any of the treatment group as FECR values < 90% were found at D60 for FBZ, at D90 for PYR and IVM1, at D150 for IVM2. All horses treated with MOX showed FECRT > 90% for the entire duration of the trial until D150. The results of the present survey indicate that drug-resistant cyathostomin populations are not present in the examined horse population, contrariwise to what observed in other Italian and European regions. The reasons and implications of these results are discussed.

Anthelmintic resistance in equine helminth parasites - a growing issue for horse owners and veterinarians in New Zealand?

There is growing concern that given the high frequency with which anthelmintics are being administered to many horses, anthelmintic resistance amongst equine helminth populations will be an increasing problem, rendering many of the currently available products unusable with little prospect of new products becoming available, at least in the near future. Worldwide, much reliance has been placed on the macrocyclic lactone (ML) group of anthelmintics, but resistance has been reported to these products as well as to the two other major anthelmintic classes used in this species, the benzimidazoles (BZ) and the tetrahydropyrimidines (e.g. pyrantel). In New Zealand, resistance has been reported to the ML and BZ groups, but not yet to pyrantel. As an alternative to interval-based anthelmintic regimens, the highly overdispersed nature of parasite populations in horses can be utilised to decide whether treatment is required, based on whether or not animals exceed a predetermined level of shedding of parasite eggs. If well managed, such a targeted and selective approach can be utilised to eliminate the majority of egg output whilst still providing a refuge for susceptible parasites to persist. Such a system would require that an adequate standard of monitoring be in place and cognisance needs to be taken of parasites or their lifecycle stages that cannot be diagnosed by routine methods. At the same time, using anthelmintics with high levels of efficacy, avoiding practices such as under-dosing, as well as utilising non-chemical means of parasite control when possible, e.g. regular removal of faeces from pasture, should all be considered. Combinations of anthelmintics, specifically of anthelmintics that target the same or a similar spectrum of parasite species, should play an important role in parasite control in horses. As well as providing arguably the highest levels of efficacy, combinations may also slow the rate at which anthelmintic resistance develops.

Structure of the trehalose-6-phosphate phosphatase from Brugia malayi reveals key design principles for anthelmintic drugs

Parasitic nematodes are responsible for devastating illnesses that plague many of the world's poorest populations indigenous to the tropical areas of developing nations. Among these diseases is lymphatic filariasis, a major cause of permanent and long-term disability. Proteins essential to nematodes that do not have mammalian counterparts represent targets for therapeutic inhibitor discovery. One promising target is trehalose-6-phosphate phosphatase (T6PP) from Brugia malayi. In the model nematode Caenorhabditis elegans, T6PP is essential for survival due to the toxic effect(s) of the accumulation of trehalose 6-phosphate. T6PP has also been shown to be essential in Mycobacterium tuberculosis. We determined the X-ray crystal structure of T6PP from B. malayi. The protein structure revealed a stabilizing N-terminal MIT-like domain and a catalytic C-terminal C2B-type HAD phosphatase fold. Structure-guided mutagenesis, combined with kinetic analyses using a designed competitive inhibitor, trehalose 6-sulfate, identified five residues important for binding and catalysis. This structure-function analysis along with computational mapping provided the basis for the proposed model of the T6PP-trehalose 6-phosphate complex. The model indicates a substrate-binding mode wherein shape complementarity and van der Waals interactions drive recognition. The mode of binding is in sharp contrast to the homolog sucrose-6-phosphate phosphatase where extensive hydrogen-bond interactions are made to the substrate. Together these results suggest that high-affinity inhibitors will be bi-dentate, taking advantage of substrate-like binding to the phosphoryl-binding pocket while simultaneously utilizing non-native binding to the trehalose pocket. The conservation of the key residues that enforce the shape of the substrate pocket in T6PP enzymes suggest that development of broad-range anthelmintic and antibacterial therapeutics employing this platform may be possible.

Here, we describe the structure of trehalose-6-phosphate phosphatase (T6PP) from Brugia malayi. This enzyme is essential to the organism; deletion of the gene encoding T6PP results in toxic accumulation of trehalose 6-phosphate. Structure-guided mutagenesis coupled with kinetic analyses revealed residues important for binding and catalysis. The model for substrate binding suggests a binding mode in which shape complementarity plays a major role. Conservation of binding residues among T6PP orthologs present in pathogenic nematodes and bacteria favors T6PP as a suitable target for broad-range anthelmintic and antibacterial drug design.

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.

A questionnaire study of equine gastrointestinal parasite control in Scotland

REASONS FOR PERFORMING STUDY

Anthelmintic resistance in equine gastrointestinal nematodes is a threat to equine health and welfare. Detailed knowledge of anthelmintic use and parasite control methods is a prerequisite to identification of potential risk factors for resistance.

OBJECTIVES

To identify parasite control practices employed by equine owners in Scotland and investigate management factors associated with anthelmintic resistance.

STUDY DESIGN

Questionnaire study of equine parasite control in Scotland.

METHODS

Questionnaires were available electronically, distributed at a conference and mailed to clients. Key areas explored included general background, grazing management, anthelmintic treatment practices and use of diagnostic tests.

RESULTS

A total of 193 responses detailing information on parasite control programmes of 993 equids were analysed. Moxidectin (MOX) and ivermectin or related combination products were the most commonly administered anthelmintics in the preceding 12 months. Treatments licensed for use against cyathostomin encysted larvae and tapeworms were administered by 80% and 90% of respondents, respectively. This was often achieved through indiscriminate use of MOX and MOX-praziquantel products. Faecal egg count (FEC) analysis had been performed on 62% of yards and regular use of FECs reduced annual anthelmintic treatment frequency. Veterinarians had the greatest influence on control practices. While 40% of respondents believed that they practised targeted dosing, this was not associated with delaying treatment beyond the egg reappearance period of the anthelmintic used.

CONCLUSIONS

Responses indicated increasing veterinary involvement and use of FECs. The majority of respondents administered anthelmintics licensed against cyathostomin encysted larvae and tapeworms. However, responses suggested that owners did not understand the definition of 'targeted' dosing regimens.

POTENTIAL RELEVANCE

The high frequency of MOX use represents a potential risk factor for macrocyclic lactone resistance. As veterinarians were the most influential factor in anthelmintic choice, awareness of macrocyclic lactone resistance and potential risk factors for its development and spread should be incorporated into client advice.

Anthelmintic tolerance in free-living and facultative parasitic isolates of Halicephalobus (Panagrolaimidae)

Studies on anthelmintic resistance in equine parasites do not include facultative parasites. Halicephalobus gingivalis is a free-living bacterivorous nematode and a known facultative parasite of horses with a strong indication of some form of tolerance to common anthelmintic drugs. This research presents the results of an in vitro study on the anthelmintic tolerance of several isolates of Halicephalobus to thiabendazole and ivermectin using an adaptation of the Micro-Agar Larval Development Test hereby focusing on egg hatching and larval development. Panagrellus redivivus and Panagrolaimus superbus were included as a positive control. The results generally show that the anthelmintic tolerance of Halicephalobus to both thiabendazole and ivermectin was considerably higher than that of the closely related Panagrolaimidae and, compared to other studies, than that of obligatory equine parasites. Our results further reveal a remarkable trend of increasing tolerance from fully free-living isolates towards horse-associated isolates. In vitro anthelmintic testing with free-living and facultative parasitic nematodes offers the advantage of observing drug effect on the complete life cycle as opposed to obligatory parasites that can only be followed until the third larval stage. We therefore propose Halicephalobus gingivalis as an experimental tool to deepen our understanding of the biology of anthelmintic tolerance.

Equine anthelmintics: survey of the patterns of use, beliefs and attitudes among horse owners in the UK

An online survey was conducted to establish horse owners' beliefs, attitudes and practices relating to the use of anthelmintic drugs. Out of a total of 574 respondents, 89 per cent described themselves as 'leisure riders', most of whom took part in a variety of activities including eventing, show jumping, dressage, hunter trials, hunting, driving, endurance and showing. Overall, respondents were generally aware and concerned about the issue of anthelmintic resistance. Less than 60 per cent of all respondents were comfortable with their existing anthelmintic programme, and 25 per cent would like to reduce the use of anthelmintics in their horses. Of all the respondents, 47 per cent used livery, and 49 per cent of those reported that the livery imposed a common anthelmintic programme for horses kept on the premises; 45 per cent of these respondents were not entirely happy with the livery yard's programme. Less than 50 per cent of all respondents included 'veterinary surgeon' among their sources of advice on worming.