Equine parasites: diagnosis and control - a current perspective

Total Failure of Fenbendazole to Control Strongylid Infections in Czech Horse Operations

The control of strongylid infections has become challenging globally for equine practitioners due to the development of anthelmintic resistance. Comprehensive information on anthelmintic resistance in the Czech Republic, however, is still lacking. This study monitored the current efficacy of fenbendazole, pyrantel embonate, ivermectin and moxidectin. Forty-eight of 71 operations met the criteria (≥6 horses with ≥200 eggs per gram), with 969 fecal egg count reduction tests performed. Anthelmintic resistance was evaluated on an operation level based on fecal egg count reduction (FECR) and the lower limit of the 95% credible interval (LLCI) using Bayesian hierarchical models. General anthelmintic efficacy across all operations was assessed by posterior FECRs and the occurrence of sub-zero efficacies. Ivermectin and moxidectin demonstrated excellent efficacy (FECR 99.8–100%; 99.4–100 LLCI) in 45 and 23 operations, respectively, pyrantel embonate demonstrated sufficient efficacy in 15 operations and resistance was suspected in seven operations (FECR 88.1–99.1%; 72.5–98.5 LLCI). Fenbendazole, however, was not effective in a single operation (FECR 19.1–77.8%; 8.1–50.1 LLCI) out of 18. Fenbendazole had the highest probability of sub-zero efficacy (29.1%), i.e., post-treatment fecal egg counts exceeded the pre-treatment counts. Our data indicate an increase in the development of anthelmintic resistance, resulting in total failure of fenbendazole and a reduced efficacy of pyrantel embonate. Introducing advanced approaches of parasite control in the Czech Republic to slow the spread of anthelmintic resistance is thus needed.

Diagnostic performance of McMaster, Wisconsin, and automated egg counting techniques for enumeration of equine strongyle eggs in fecal samples

Fecal egg counts are the cornerstone of equine parasite control programs. Previous work led to the development of an automated, image-analysis-based parasite egg counting system. The system has been further developed to include an automated reagent dispenser unit and a custom camera (CC) unit that generates higher resolution images, as well as a particle shape analysis (PSA) algorithm and machine learning (ML) algorithm. The first aim of this study was to conduct a comprehensive comparison of method precision between the original smartphone (SP) unit with the PSA algorithm, CC/PSA, CC/ML, and the traditional McMaster (MM) and Wisconsin (MW) manual techniques. Additionally, a Bayesian analysis was performed to estimate and compare sensitivity and specificity of all five methods. Feces were collected from horses, screened with triplicate Mini-FLOTAC counts, and placed into five categories: negative (no eggs seen), > 0 - ≤ 200 eggs per gram (EPG), > 200 - ≤ 500 EPG, > 500 - ≤ 1000 EPG, and > 1000 EPG. Ten replicates per horse were analyzed for each technique. Technical variability for samples > 200 EPG was significantly higher for MM than CC/PSA and CC/ML (p <  0.0001). Biological variability for samples> 0 was numerically highest for CC/PSA, but with samples > 200 EPG, MM had a significantly lower CV than MW (p =  0.001), MW had a significantly lower CV than CC/PSA (p <  0.0001), CC/ML had a significantly lower CV than both MW and SP/PSA (p <  0.0001, p =  0.0003), and CC/PSA had a significantly lower CV than CC/SP (p =  0.0115). Sensitivity was> 98 % for all five methods with no significant differences. Specificity, however, was significantly the highest for CC/PSA, followed numerically by SP/PSA, MM, CC/ML, and finally MW. Overall, the automated counting system is a promising new development in equine parasitology. Continued refinement to the counting algorithms will help improve precision and specificity, while additional research in areas such as egg loss, analyst variability at the counting step, and accuracy will help create a complete picture of its impact as a new fecal egg count method.

The importance of anthelmintic efficacy monitoring: results of an outreach effort

Anthelmintic resistance in equine cyathostomin parasites is widespread. A surveillance-based parasite control program using fecal egg counts (FECs) and fecal egg count reduction tests (FECRTs) to decrease anthelmintic use and monitor treatment efficacy is recommended. The purpose of this study was to examine shifts in equine parasite control program management practices via a short course presented by the Penn State Extension, and to highlight how data collected from these programs is useful for monitoring anthelmintic efficacy on a large scale. Horse owners were enrolled after participating in a short course and filled out questionnaire surveys about their parasite management programs pre and post study, horse information, and farm information. FECs were performed at three time points, and horses above a 300 strongyle eggs per gram cut-off were treated with pyrantel pamoate, fenbendazole, or ivermectin. Two weeks post-treatment, FECRTs were performed to determine treatment efficacy, which included 29 farms with 513 individual treatments. Prior to the study, only 30.6% of farms used FECs, but after the study, 97.3% of farms said they would use FECs in the future. Horses were given an average of 4.1 anthelmintic treatments per year before the study, and post study 89.2% of farms were able to reduce the number of anthelmintic treatments used. Fenbendazole was effective on zero farms, pyrantel pamoate on 7.4% of farms, and ivermectin on 92.9% of farms. This outreach project helped generate information about anthelmintic efficacy levels, causing a shift in practices on participating farms, and collected useful anthelmintic resistance data.

Adaptation of a 96-well plate larval migration inhibition test for measuring the sensitivity of cyathostomins to macrocyclic lactone anthelmintics

The use of macrocyclic lactone drugs for control of equine cyathostomins is threatened by increasing levels of resistance. Detection of changes in drug sensitivity is important for effective and sustainable management of cyathostomins, however, at present such detection relies on the use of the faecal egg count reduction test, which is known to be an insensitive method. The present study therefore aimed to examine the use of a 96-well plate larval migration inhibition test for detection of resistance to macrocyclic lactone drugs in cyathostomins. We optimised conditions for migration of larvae, and examined the effects of larval storage time on drug dose responses. The modified test was able to define the sensitivity of cyathostomin isolates to ivermectin and eprinomectin in terms of dose response curves, and IC₅₀ and IC₉₅ values. The IC₉₅ showed much greater consistency than the IC₅₀ with larvae that had been stored for different periods prior to the test. Comparisons between two isolates, which had both been defined previously as susceptible using faecal egg count reduction tests, showed more variation at the IC₅₀ compared to the IC₉₅. Limitations of the test included the degree of variation in control-well migration despite optimisation of migration incubation conditions, and the need to incorporate a method to determine the species composition of the larval populations to account for possible species differences in drug sensitivity among cyathostomins. Validation of the technique on reference susceptible and resistant isolates of known species composition is still required.

Searching for ivermectin resistance in a Strongylidae population of horses stabled in Poland

BACKGROUND

There are no available studies describing the possible resistance of strongyles to ivermectin in horses in Poland. One hundred seventy three horses from nine stud farms from South-Western Poland were studied. The effectiveness of ivermectin was studied on the 14th day after ivermectin administration using the fecal egg count reduction test, and a long-term observation of the egg reappearance period was carried out. The fecal study was carried out using a modified McMaster method, which typically detects 20 eggs per gram of stool. The results were subjected to statistical analysis that enabled quantification of the eggs in the stool samples.

RESULTS

The study revealed high efficacy of ivermectin on the 14th day after administration without a shortening of the egg reappearance period.

CONCLUSION

The results indicate that strongyles resistance to ivermectin in Poland is not a serious problem.

Strongyle egg reappearance period after moxidectin treatment and its relationship with management factors in UK equine populations

Parasitic nematodes, particularly cyathostomins, are ubiquitous in grazing horses world-wide. Considerable burdens of cyathostomin larvae can encyst in the large intestinal wall. The most recommended treatment against these pathogenic stages is moxidectin. Information is required on how effective moxidectin is against cyathostomin populations in different regions. The objectives here were to determine the efficacy of moxidectin treatment and estimate the strongyle egg reappearance period (ERP) after treatment in several equine populations, to confirm the type of strongyle nematodes present and to identify other (i.e. management) factors associated with shortened ERP. Eight yards were recruited and moxidectin in combination with praziquantel administered to all horses (n=261). Faecal egg count (FEC) analysis was performed at weeks 0, 2, 6, 10 and 12 after treatment to determine efficacy and ERP. The ERP was estimated using two previously published methods. Morphological identification of cultured third stage larvae from the sample population was compared to a Strongylus vulgaris-specific end-point PCR to examine the presence of S. vulgaris in samples before and after treatment. Strongyle egg shedding patterns were also compared to worm management practices at each site. At 2 weeks post-treatment, moxidectin was highly effective (faecal egg count reduction range, 99.9-100%). The strongyle ERP ranged from 6 weeks to >12 weeks depending on the calculation method applied. Only cyathostomin larvae were detected by morphological identification. The results from the coprocultures and PCR showed that S. vulgaris was absent before and after treatment. Analysis revealed that regular faecal removal from pasture was associated with lower average FEC and lower prevalence of egg shedding.

Prevalence and intensity of gastro-intestinal helminths in horses in the Sudano-Guinean climatic zone of Cameroon

Background:

It is important to understand the biology and health impact of parasites affecting horses in the Western highlands of Cameroon.

Aim:

to evaluate the prevalence and intensity of infection of gastrointestinal helminths in these animals.

Materials and Methods:

A total of 894 horses (367 males and 527 females), and aged ≤1 to ≥7 years old were examined. A parasitological investigation of faeces was carried out using two techniques: concentration method of Full Born Willis (flotation in saturated solution of sodium chloride) and Mc Master Technique.

Results and conclusions:

From the results the overall prevalence was 100%. Nine species of nematode (Parascaris equorum, Oxyuris equi, Habronema sp., Strongyloides westeri, Dictyocaulus arnfieldi, Trichostrongylus axei, Cyathostome sp., Triodontophorus sp., Strongylus sp.) were identified with the prevalence of 18.48%, 16.94%, 2.99%, 6.05%, 5.22%, 7.75%, 12.49%, 1.09%, and 22.26%, respectively, and one species of cestode (Anoplocephala magna) with a prevalence of 6.73%. Strongylus sp. had the highest mean intensity of infection (1270±942) in female horses. Poly-parasitic infections (92.28%) were more common than mono-parasitic infections (7.72%).