Parasite dynamics in untreated horses through one calendar year

Prevalence and risk factors of gastrointestinal helminths infection in Brazilian horses: A retrospective study of a 12-year (2008-2019) diagnostic data

Understanding gastrointestinal parasite distribution is crucial for effective control programs in horses. This study reports the prevalence of helminth infections in horses and selected risk factors (i.e., breed, age, climate, season) by analyzing 19,276 fecal samples from the Laboratory of Veterinary Clinical Parasitology, in Curitiba, Southern Brazil. The analyses were carried out from 2008 to 2019, coming from 153 stud farms located in 60 municipalities of nine Brazilian states. The parasite prevalence was 73.3%, with 72.1% present in the adult population and 80.6% in young horses. Strongyles were present in 100% horse farms. Strongyles had a prevalence of 72.1% with a mean FEC of 453.53 (+/- 717.6). Parascaris spp. had a prevalence of 5.8% and a FEC of 17.11 (+/- 149.2). The tropical wet/monsoon climate (Am) showed the lowest FEC for strongyles and Parascaris spp. when compared to the other climates. In the logistic regression analysis, young horses exhibited 4.6 times higher odds ratio (OR) (3.9-5.5) of Parascaris spp. and 1.2 (1.1-1.4) times higher OR of strongyles egg shedding when compared to adults (P < 0.001). Summer presented a higher risk for Parascaris spp. and Strongyles eggs when compared to the other seasons (P < 0.001). Mangalarga Marchador, Criollo, and Crossbred breeds were identified with higher OR of Parascaris spp. egg shedding than Thoroughbred. The extensive prevalence of strongyles across ages, seasons, breeds, and climates alerts for the risk of clinical manifestations in equines raised on pastures designing optimal health management and parasite control strategies worldwide.

Welfare assessment of Thoroughbred horses naturally infected with gastrointestinal parasites in Southern Brazil: Quantifying the host-parasite relationship

Horse welfare assessment (HWA) does not account for individual or herd parasite infection. This study investigated the connection between HWA and individual parasite fecal egg count (FEC) in 90 Thoroughbred horses. All horses were naturally infected with gastrointestinal parasites and were evaluated for individual welfare indicators and FEC monthly, for 12 months. Horses were divided into three groups of 30 mares, 30 foals aged between 13 and 16 months (G2013), and 30 foals aged between two months and one year (G2014). A horse welfare protocol was developed and 1024 assessments were carried out by five trained assessors. FEC ranged from 0 to 5,760 with 98.8 % showing small strongyle eggs. Body condition scores were ideal in 94.4 % of the evaluations (n = 967), and 95.8 % of all horses had good clinical and behavioral indicators. Despite the variation in FEC, the data found no significant association between FEC and the behavioral indicators. The study suggests that FEC alone should not be used as a determinant of welfare when animals are managed with good nutritional and health management practices.

US-wide equine strongylid egg count data demonstrate seasonal and regional trends

Equine strongylid parasites are ubiquitous around the world and are main targets of parasite control programmes. In recent years, automated fecal egg counting systems based on image analysis have become available allowing for collection and analysis of large-scale egg count data. This study aimed to evaluate equine strongylid fecal egg count (FEC) data generated with an automated system over three years in the US with specific attention to seasonal and regional trends in egg count magnitude and sampling activity. Five US regions were defined; North East, South East, North Central, South Central and West. The data set included state, region and zip code for each FEC. The number of FECs falling in each of the following categories were recorded: (1) 0 eggs per gram (EPG), (2) 1 ⩽ 200 EPG, (3) 201 ⩽ 500 EPG and (4) >500 EPG. The data included 58 329 FECs. A fixed effects model was constructed fitting the number of samples analysed per month, year and region, and a mixed effects model was constructed to fit the number of FECs falling in each of the 4 egg count categories defined above. The overall proportion of horses responsible for 80% of the total FEC output was 18.1%, and this was consistent across years, months and all regions except West, where the proportion was closer to 12%. Statistical analyses showed significant seasonal trends and regional differences of sampling frequency and FEC category. The data demonstrated that veterinarians tended to follow a biphasic pattern when monitoring strongylid FECs in horses, regardless of location.

Validation of a serum ELISA test for cyathostomin infection in equines

Cyathostomins are ubiquitous equine nematodes. Infection can result in larval cyathostominosis due to mass larval emergence. Although faecal egg count (FEC) tests provide estimates of egg shedding, these correlate poorly with burden and provide no information on mucosal/luminal larvae. Previous studies describe a serum IgG(T)-based ELISA (CT3) that exhibits utility for detection of mucosal/luminal cyathostomins. Here, this ELISA is optimised/validated for commercial application using sera from horses for which burden data were available. Optimisation included addition of total IgG-based calibrators to provide standard curves for quantification of antigen-specific IgG(T) used to generate a CT3-specific 'serum score' for each horse. Validation dataset results were then used to assess the optimised test's performance and select serum score cut-off values for diagnosis of burdens above 1000, 5000 and 10,000 cyathostomins. The test demonstrated excellent performance (Receiver Operating Characteristic Area Under the Curve values >0.9) in diagnosing infection, with >90% sensitivity and >70% specificity at the selected serum score cut-off values. CT3-specific serum IgG(T) profiles in equines in different settings were assessed to provide information for commercial test use. These studies demonstrated maternal transfer of CT3-specific IgG(T) in colostrum to newborns, levels of which declined before increasing as foals consumed contaminated pasture. Studies in geographically distinct populations demonstrated that the proportion of horses that reported as test positive at a 14.37 CT3 serum score (1000-cyathostomin threshold) was associated with parasite transmission risk. Based on the results, inclusion criteria for commercial use were developed. Logistic regression models were developed to predict probabilities that burdens of individuals are above defined thresholds based on the reported serum score. The models performed at a similar level to the serum score cut-off approach. In conclusion, the CT3 test provides an option for veterinarians to obtain evidence of low cyathostomin burdens that do not require anthelmintic treatment and to support diagnosis of infection.

Comparison of the Automated OvaCyte Telenostic Faecal Analyser versus the McMaster and Mini-FLOTAC Techniques in the Estimation of Helminth Faecal Egg Counts in Equine

Gastrointestinal helminth parasites continue to be a significant threat to the health of equine. OvaCyte Telenostic (OCT) (Telenostic Ltd., Kilkenny, Ireland) has developed an automated digital microscope utilising Artificial Intelligence to identify and count the clinically important helminth species in equine, bovine, and ovine host species. In this paper, the performance of the OCT analyser was evaluated for the detection and counting of equine helminth species parasites and its performance compared to the currently accepted benchmark methods of faecal egg counts being the McMaster and the Mini-FLOTAC techniques. A pairwise comparison of tests was assessed based on the correlation of egg counts and Cohen's kappa agreement statistics for dichotomized outcomes. Bayesian latent class analysis was used to estimate the sensitivity and specificity of all three techniques in the absence of a gold standard for four helminth parasites (strongyles, Anoplocephala spp., Parascaris spp. and Strongyloides westeri). Based on the analysis of 783 equine faecal samples, we found a high level (ρ ≥ 0.94) of correlation between each pairwise comparison of techniques for strongyle egg counts. Cohen's kappa agreement between techniques was high for strongyles and S. westeri, moderate for Parascaris spp., and low for Anoplocephala spp. All three techniques had a high sensitivity and specificity (>0.90) for strongyles. Across helminth parasites, the sensitivity of the OCT was the highest of the three techniques evaluated for strongyles (0.98 v 0.96 and 0.94), Anoplocephala spp. (0.86 v 0.44 and 0.46) and Parascaris spp. (0.96 v 0.83 and 0.96); but lowest for S. westeri (0.74 v 0.88 and 0.88), compared to McMaster and Mini-FLOTAC, respectively. In terms of specificity, OCT was the lowest in two species (Parascaris spp. 0.96, Anoplocephala spp. 0.95). In conclusion, OCT has a sensitivity and specificity statistically similar to both McMaster and Mini-FLOTAC, and had a higher correlation with Mini-FLOTAC. The OCT point of care faecal analyser offers improved workflow, test turn-around time and does not require trained laboratory personnel to operate or interpret the results.

First report of four rare strongylid species infecting endangered Przewalski's horses (Equus ferus przewalskii) in Xinjiang, China

BACKGROUND

The Przewalski's horse (Equus ferus przewalskii) is the only surviving wild horse species in the world. A significant population of Przewalski's horses resides in Xinjiang, China. Parasitosis poses a considerable threat to the conservation of this endangered species. Yet, there is limited information on the nematode parasites that infect these species. To deepen our understanding of parasitic fauna affecting wild horses, we identified the intestinal nematodes of Przewalski's horses in Xinjiang and added new barcode sequences to a public database.

METHODS

Between 2018 and 2021, nematodes were collected from 104 dewormed Przewalski's horses in Xinjiang. Each nematode was morphologically identified to the species level, and selected species underwent DNA extraction. The extracted DNA was used for molecular identification through the internal transcribed spacer 2 (ITS2) genetic marker.

RESULTS

A total of 3758 strongylids were identified. To the best of our knowledge, this is the first study to identify four specific parasitic nematodes (Oesophagodontus robustus, Bidentostomum ivashkini, Skrjabinodentus caragandicus, Petrovinema skrjabini) and to obtain the ITS2 genetic marker for P. skrjabini.

CONCLUSIONS

The ITS2 genetic marker for P. skrjabini enriches our understanding of the genetic characteristics of this species and expands the body of knowledge on parasitic nematodes. Our findings extend the known host range of four strongylid species, thereby improving our understanding of the relationship between Przewalski's horses and strongylids. This, in turn, aids in the enhanced conservation of this endangered species. This study introduces new instances of parasitic infections in wild animals and offers the DNA sequence of P. skrjabini as a valuable resource for molecular techniques in nematode diagnosis among wildlife.

Parascaris spp. eggs shedding patterns in juvenile horses

Parascaris spp. infect foals worldwide and foals typically shed eggs in the feces from about three to six months of age, upon which natural immunity is incurred. High levels of anthelmintic resistance of Parascaris spp. are a global concern, and further understanding egg shedding patterns and fecal egg counting (FEC) data variability is of high importance. The aims of this study were to monitor Parascaris spp. egg shedding in untreated foals during 12-23 weeks of age, estimate sources of data variability, and assess precision of two ascarid FEC techniques. Fecal samples were collected weekly from 11 foals born in 2022, from May through November (29 weeks). Six subsamples were extracted from each weekly sample to determine 30 FECs between two techniques: a McMaster technique and an Automated Egg Counting System (AECS). Mixed linear modeling was carried out with age, sex, birth month, seasonality, spring- or summer-born foals, and egg counting technique as explanatory variables. Ascarid FECs were associated with age (p < 0.001), seasonality (p < 0.001), and technique (p < 0.001). The McMaster technique was more precise with a mean coefficient of variation (CV) of 34.57% and a 95% confidence interval (CI) of 30.80%- 38.30% compared to the CV for the AECS, which was 42.22% (CI: 37.70%-46.70%). Seasonality accounted for the highest proportion of variance (PV) of all covariates, but differences in PVs for covariates existed between techniques with foal age and subsample contributing more variance to the McMaster, and individual foal and seasonality contributing more to the AECS. Subsamples and replicate counts accounted for less than 1% of the total data variance. The results highlighted substantial differences in PVs between the two techniques at the subsample (AECS: 57.14%; McMaster: 77.51%) and replicate count levels (AECS: 42.86%; McMaster: 22.49%). While differences in precision were observed between the two FEC techniques, they were negligible in the data set, as the overwhelming majority of the data variability in ascarid FECs was attributed to individual foal, seasonality, and foal age.

Occurrence and control of equine strongyle nematode infections in Prince Edward Island, Canada

Widespread overuse of anthelmintics has produced a growing population of intestinal parasites resistant to control measures. A paradigm shift in equine parasite control is warranted to prevent continued resistance development and maintain equine health. Small strongyles, which are ubiquitous in horses, are currently the most important intestinal parasites of adult horses. Sustainable management programs consider the variation in egg shedding by individual horses, and varied risks associated with age, use, density, climate, and environment. To develop regional recommendations for Prince Edward Island (PEI), Canada, it is important to first characterize strongyle egg shedding patterns and parasite management practices in use. Study objectives were to conduct a cross-sectional observational survey and risk factor analysis of parasite control programs, strongyle egg shedding and Strongylus vulgaris serology. A total of 339 horses from 40 PEI farms were sampled. Mean farm size was 8 horses and ranged from 2 to 30. Mean horse age was 11.6 years (Std. Dev. =7.2) and ranged from 2 months to 32 years. Mean fecal egg count (FEC) was 322 eggs per gram (EPG) (Std. Dev. =648). On average, 32% (Std. Dev. =16%) of horses shed 80% of strongyle eggs across 32 eligible farms. When considering all horses (n = 313) as one large herd, 18.7% of horses shed 80% of strongyle eggs. Use of FEC was identified in 4.6% of horses at 15% (n = 6) of PEI farms. Reported deworming intervals included 37.4% (n = 123) every 2-3 months and 58% (n = 191) every 3-4 months. Positive S. vulgaris titers were identified in 60% of horses (n = 200). Univariate analysis revealed that months since last deworming, age, and body condition score (BCS) were associated with strongyle shedding. The estimated odds of being in the high FEC category (>500 EPG) was 1.4 (95% CI, 1.1-1.8) times higher when last deworming increased by one month. Under-conditioned (BCS <4.5) horses had 3.6 (95% CI, 1.2-10.6) times odds of being in the higher FEC category than over-conditioned horses. Non-racing horses had 5.4 times odds of having a positive S. vulgaris titer than racehorses. This cross-sectional observational study is the first to report on the occurrence, risk factors and control of equine strongyle nematode infections in PEI, Canada. We conclude that the 80:20 rule can be used to develop control recommendations in PEI. Very few farms in PEI currently use FEC to guide parasite management. These findings provide a basis for future client education and investigations aimed at providing region specific recommendations.

Epidemiological study on factors influencing the occurrence of helminth eggs in horses in Germany based on sent-in diagnostic samples

Gastrointestinal nematodes are ubiquitous parasites of grazing equines with Parascaris spp., and strongyles being the most relevant ones regarding the prevalence and potential disease severity. Despite their importance, epidemiological data regarding the presence and egg-shedding intensities of these parasites are scarce. Data from 1067 horse samples collected on German horse farms initially to compare diagnostic methods were used for epidemiological analyses. Due to its higher sensitivity, presence/absence data were based on a combined sedimentation/flotation technique while faecal egg counts were based on Mini-FLOTAC. For strongyles, 46.5% of the samples were positive and the median egg-shedding intensity was 40 (range 5-2590). In multivariate analyses, prevalence and egg-shedding intensity were significantly influenced by season, age group and sample type. The drug used for the last treatment and the number of foals on the yard only affected prevalence while the number of horses on the yard and sex were only significant for egg-shedding intensity. For Parascaris spp., a prevalence of 4.6% and a median egg-shedding intensity of 0 (range 5-905) were observed. In multivariate analyses, the age group, the time since the last anthelmintic treatment, presence and number of foals had significant effects on ascarid prevalence whereas egg-shedding intensity was significantly influenced by age group and season only. Parascaris occurred only on yards with foals, but with an increasing number of foals, Parascaris egg-shedding intensity decreased. Prevalence and egg-shedding intensity were influenced by different but partially overlapping variables for Parascaris and strongyles.

Species interactions, stability, and resilience of the gut microbiota - Helminth assemblage in horses

The nature and strength of interactions entertained among helminths and their host gut microbiota remain largely unexplored. Using 40 naturally infected Welsh ponies, we tracked the gut microbiota-cyathostomin temporal dynamics and stability before and following anthelmintic treatment and the associated host blood transcriptomic response. High shedders harbored 14 species of cyathostomins, dominated by Cylicocyclus nassatus. They exhibited a highly diverse and temporal dynamic gut microbiota, with butyrate-producing Clostridia likely driving the ecosystem steadiness and host tolerance toward cyathostomins infection. However, anthelmintic administration sharply bent the microbial community. It disrupted the ecosystem stability and the time-dependent network of interactions, affecting longer term microbial resilience. These observations highlight how anthelmintic treatments alter the triangular relationship of parasite, host, and gut microbiota and open new perspectives for adding nutritional intervention to current parasite management strategies.

Molecular diagnostics for gastrointestinal helminths in equids: Past, present and future

This review is aimed to (i) appraise the literature on the use of molecular techniques for the detection, quantification and differentiation of gastrointestinal helminths (GIH) of equids, (ii) identify the knowledge gaps and, (iii) discuss diagnostic prospects in equine parasitology. Following the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines for systematic reviews, we retrieved 54 studies (horses: 50/54; donkeys and zebras: 4/54) from four databases. Polymerase chain reaction (PCR) was employed in all of the studies whereas PCR amplicons were sequenced in only 18 of them. Other techniques used (including modifications of PCR) were reverse line blot, quantitative (q)PCR, restriction fragment length polymorphism, nested-PCR, PCR-directed next-generation sequencing, Southern blotting, single strand conformation polymorphism, PCR-enzyme linked immunosorbent assay, matrix-assisted laser desorption/ionisation-time of flight and random amplification of polymorphic DNA. Most of the studies (53/54) used nuclear ribosomal RNA (including the internal transcribed spacers, intergenic spacer, 5.8 S, 18 S, 28 S and 12 S) as target loci while cytochrome c oxidase subunit 1 and random genomic regions were targeted in only three and one studies, respectively. Overall, to date, the majority of molecular studies have focused on the diagnosis and identification of GIHs of equids (i.e. species of Anoplocephala, Craterostomum, cyathostomins, Oesophagodontus, Parascaris, Strongylus, Strongyloides and Triodontophorus), with a recent shift towards investigations on anthelmintic resistance and the use of high-throughput nemabiome metabarcoding. With the increasing reports of anthelmintic resistance in equid GIHs, it is crucial to develop and apply techniques such as advanced metabarcoding for surveillance of parasite populations in order to gain detailed insights into their diversity and sustainable control. To the best of our knowledge, this is the first systematic review that evaluates molecular investigations published on the diagnosis and quantification of equid GIHs and provides useful insights into important knowledge gaps and future research directions in equid molecular parasitology.

Equine strongylids: Ivermectin efficacy and fecal egg shedding patterns

Equine cyathostomins are ubiquitous in grazing horses around the world and a main target in parasite control programs. Anthelmintic resistance has been reported with increasing frequency in these parasites over the past decades, and recent findings of fulminant resistance to the macrocyclic lactone class have raised severe concerns. This study aimed to evaluate ivermectin efficacy in cohorts of yearlings and mares present on four different farms in Central Kentucky. Strongylid egg counts were determined with an automated egg counting system, and the percent fecal egg count reduction (FECR) was calculated using a hierarchical Bayesian analysis. Novel principles were used for classification of groups to either no signs of anthelmintic resistance, evidence of resistance, or inconclusive. Furthermore, an epidemiological analysis was conducted evaluating the possible influence of pregnancy status, time of foaling, and year of arrival on mare strongylid egg shedding levels. A total of 102 yearlings and 247 mares were enrolled in the study. Evidence of ivermectin resistance was documented in one group of yearlings with a mean FECR of 91.2% and a 95% credible interval of 84.0-95.8. The results from one mare group and one additional yearling group were deemed inconclusive, whereas the remaining five groups displayed no evidence of ivermectin resistance. Strongylid shedding in the mares was not positively associated with any of the evaluated factors. This study is the first to demonstrate ivermectin resistance in US bred horses, and the findings emphasize the need for routine monitoring of anthelmintic efficacy on horse farms.