Risk factors for high endoparasitic burden and the efficiency of a single anthelmintic treatment of Danish horses

Strongyle faecal egg counts in Swiss horses: A retrospective analysis after the introduction of a selective treatment strategy

The standard parasite management of horses based on regular anthelmintic treatments, now practiced for decades has resulted in a worrying expansion of resistant helminth populations, which may considerably impair control on the farm level. The aim of the present study was to obtain a retrospective (year 2010 - 2016) nationwide analysis of faecal egg count (FEC) data from the Swiss adult horse population, related to horse age and geographic region. Thirteen labs provided a total of 16,387 FEC data of horses aged four to 39 years (average: 13.6 years). The annual number of performed FEC tests increased from 38 to 4,939 within the observation period. Independent of the annual sample size the yearly patterns of the FEC were very similar. Seventy-eight percent (n = 12,840) of the samples were negative and 90 % (n = 14,720) showed a FEC below 200 strongyle eggs per gram (EPG) of faeces. The annual mean strongyle FEC ranged between 60 and 88 EPG with a total mean of 75 EPG. Horses aged 4-7 years showed a significantly (p < 0.00001) higher mean FEC compared with the other age groups, differences were not significant among the older horses. Based on ZIP codes, samples were allocated by 70.0 %, 6.0 % and 0.2 % to the German-, French- and Italian-speaking regions of Switzerland, respectively. With 222 EPG the mean FEC in the French part of Switzerland was significantly higher (p < 0.05) than in the German-speaking region (60 EPG). Eggs of Parascaris spp., anoplocephalids and Strongyloides westeri were found in 0.36 %, 0.32 % and 0.01 % of the samples, respectively. Based on 3,813 questionnaire feedbacks from owners in 2017 covering a total of 12,689 horses, sixty-eight percent (n = 8,476) were dewormed without diagnosis, two percent (n = 240) were not dewormed at all, whereas for 30 % (n = 3,721) the selective anthelmintic treatment (SAT) concept was applied. The SAT implementation rate differed significantly (p < 0.0005) between regions, with 33 %, 20 % and 25 % for the German-, French- and Italian-speaking areas, respectively. The rate of horses spending 16-24 h on pasture per day was significantly higher in the French-speaking region compared to the German-speaking part of Switzerland (p < 0.0001). In addition, pasture hygiene was practiced at a significantly lower rate in the French-speaking part compared to the German- and Italian-speaking regions (both p < 0.0001). Overall, the shift towards the SAT-concept represents a very promising development with respect to mitigating the further spread of anthelmintic resistance.

Estimating the Prevalence and Factors Affecting the Shedding of Helminth Eggs in Irish Equine Populations

Gastrointestinal helminths are ubiquitous in horse populations across the world. Intensive anthelmintic treatments have succeeded in controlling some of the pathogenic effects of these parasites. However, the success of anthelmintic drugs has been threatened by the development of widespread resistance to those most commonly used. To develop improved control strategies, information on helminth distribution patterns is needed, which can be obtained by identifying animals regarded as high egg shedders and taking age, gender, and other risk factors into account. The aim of this study was to determine the prevalence of helminth infection in the Irish equine population using faecal egg counts and to evaluate the effects of risk factors on these faecal egg counts. For the 2700 horses that were included in the study, the prevalence of gastrointestinal helminth infection was 52.40%, 4.22%, 2.59%, and 0.89% for strongyle species, Parascaris spp., Anoplocephala spp., and Strongyloides westeri, respectively. Overall, strongyle faecal egg counts from 159 farms averaged 250.22 eggs per gram. Both age and season had significant effects on strongyle egg shedding. In conclusion, this study revealed high prevalence of strongyle worm infection in horses on Irish farms, which highlights the need to optimize and develop good management practices and strategic deworming.

Seasonality and Dynamics of Gastrointestinal Helminths in Grazing Horses

The prevalence of helminths in horses may vary, depending on climatic factors and host susceptibility. The objective of this study was to evaluate the seasonal dynamics of helminth infection in grazing horses, from October 2015 to September 2016. In total, 104 crossbred horses of different age groups, males and females in a single herd, participated in this study. Individual fecal samples were collected every 28 days for counting of eggs per gram of feces (EPG) and fecal cultures. The horses were evaluated individually for weight, body condition score (BCS) and clinical status. Climatic information relating to the farm was also collected. The categories most affected by helminths were foals and senior horses, with EPG averages of 1271.9 and 1186.5, respectively. The EPG averages for all animal categories together, in the four seasons were: 1042.1 spring; 1508.9 summer; 817.8 autumn; and 571.1 winter. Through the body condition evaluation, it was seen that senior animals presented the lowest BCS in all seasons. It was concluded that the season in which these animals were most affected by helminth infections was the summer and that the most susceptible categories were foals and senior horses.

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.

The Effects of Seasonality and Group Size on Fecal Egg Counts in Wild Przewalski's Horses (Equus Ferus Przewalskii, Poljakov, 1881) in The Chernobyl Exclusion Zone, Ukraine During 2014 - 2018

The aim of this study was to investigate the difference in Fecal Egg Counts (FEC) with regard to group size, age, sex and body condition of wild free-roaming Przewalski's horses in the Chernobyl Exclusion Zone (Ukraine), across different seasons, over a five-year period (2014 - 2018). We hypothesized that horses from larger group sizes would have higher faecal egg counts (FECs). The relationship between FECs and the year and season of sample collection, and age, sex and group size of the horses was analyzed. Generalized linear model using positive strongylid FEC`s as a variable response, was used to investigate the differences in FECs between the groups. Nematode (Strondylidae, Parascaris spp., Habronematidae) and cestode (Anoplocephalidae) eggs were also identified. Stronglyids were the most prevalent helminth egg, and had the highest FECs. The model for egg counts of strongylids showed that season and group size of horses were statistically significant. Presence of strongylid eggs was not dependent on age and sex of horses. We suggest that this could be a result of parasite transmission between individuals and groups in places were animals aggregate around water sources or collective farms. Results obtained in this current study broaden the knowledge of gastrointestinal parasites in free-roaming horses under wild natural conditions.

Characteristics of parasitic egg shedding over a 1-year period in foals and their dams in 2 farms in central Saskatchewan

The goals of this study were to report the seasonal shedding patterns of strongyle and Parascaris spp. eggs in repeated fecal samples for mares (n = 38) and foals (n = 39), and to evaluate the efficacy of ivermectin treatment in mares from 2 selected horse breeding farms in central Saskatchewan. Median strongyle fecal egg counts (FEC) peaked in July and August in adult horses. The farms differed significantly (P = 0.0005) in regard to strongyle shedding categories (< 200; 200 to 500; and > 500 eggs/g) over time, but for each individual horse (both farms combined) these categories did not differ over time (P = 0.13) on samples collected in grazing season. When evaluating 3 samples collected fall, summer and fall in 2 consecutive grazing seasons, 94% of horses that shed < 200 eggs/g on 2 initial samples, remained in the same category on the third sample. Mares on each farm didn't differ statistically in shedding categories when comparing September samples from 2 consecutive years (Farm A: P = 0.56, Farm B: P = 0.06). Peak strongyle shedding occurred late fall in the first year of life for foals on Farm A, and in July in the second year of life for foals on Farm B. Parascaris spp. FEC were greatest in foals ≤ 6 months of age, with peak observed when foals were 5 to 6 months old. Ivermectin was 100% effective at reducing strongyle FEC 2 weeks after treatment in adult horses. Horses in Saskatchewan had relatively high strongyle shedding levels, which were significantly different between the farms, and high prevalence of Oxyuris equi. Strongyle shedding consistency was observed for FECs collected from mares in grazing season (July to September).

Parasitological survey of Polish primitive horses (Equus caballus gmelini Ant.): influence of age, sex and management strategies on the parasite community

An extensive analysis of the relationship between age, sex, and different types of management strategies relative to the gastrointestinal parasite community of Polish primitive horses was performed on 124 horses maintained in nine farms from four regions of Poland. The horses (96 females and 28 males) were housed in three types of management strategies: stabled (ST), free-ranging (FR) and semi-free (SF). These horses also were divided into three age groups: <3 years, 3 – 10 years and >10 years old. The gastrointestinal parasites were collected following deworming of all horses with anthelmintics containing the macrocyclic lactones and praziquantel. Totally, 66,192 parasite specimens were collected and identified. The analysis of dependence of horse infection with intestinal nematodes using sex, age and management strategies demonstrated that females had significantly heavier infections of strongylids. Young horses (<3 years old) had higher infections of Parascaris equorum and Strongyloides westeri. Free ranging horses were more infected with strongylids, Oxyuris equi and Gasterophilus intestinalis. Thirty-five nematode species, one cestode and one species of the botfly larvae of Gasterophilus were found. Diagnostic deworming examination revealed presence of Parascaris equorum in 27.4 %, Oxyuris equi in 38.7 %, Habronema muscae in 16.9 %, Anoplocephala perfoliata in 42.7 % and Gasterophilus intestinalis in 46.8% in the Polish primitive horses examined. Strongyloides westeri presence was confirmed only by fecal samples examination; threadworms were not observed in these horses after deworming. In the strongylid community, 31 species (6 of subfamily Strongylinae and 25 of Cyathostominae) were found. Significant differences in prevalence of separate strongylid species, or their proportions in the communities were not observed between females and males, or between age groups (p > 0.05). The highest species diversity (n=30 or 31) was observed in the FR horses, the lowest (n=15) – in ST horses. The FR horses had higher prevalence and proportion of large strongyles in the community, in comparison to SF or ST horses (p < 0.05).

Helminth egg excretion with regard to age, gender and management practices on UK Thoroughbred studs

Few studies have described the combined effect of age, gender, management and control programmes on helminth prevalence and egg shedding in grazing equines. Here, fecal samples collected from 1221 Thoroughbred horses, residing at 22 studs in the UK, were analysed. The distribution of strongyle eggs amongst individuals in relation to age, gender and management practices was investigated. Fecal worm egg counts (FWECs), described as the number of eggs per gramme (epg) of feces, were determined using a modification of the salt flotation method. The FWEC prevalence (mean%) of strongyles, Parascaris equorum, tapeworm spp. and Strongyloides westeri was 56, 9, 4 and 8%, respectively. Strongyle, P. equorum, tapeworm spp. and S. westeri infections were detected on 22 (100%), 11 (50%), 9 (41%) and 8 (36%) of studs, respectively. Within all age and gender categories, strongyle FWECs were highly over-dispersed (arithmetic mean = 95 epg, aggregation parameter k=0·111) amongst horses. Animal age, last anthelmintic type administered and management practices (for example, group rotation on grazing) most strongly influenced strongyle prevalence and level of egg shedding (P < 0·05). Overall, 11% of equines (range: 234–2565 epg) were responsible for excreting 80% of the strongyle eggs detected on FWEC analysis. The results confirm that the judicious application of targeted treatments has potential to control equine strongyle populations by protecting individual horses from high burdens, whilst promoting refugia for anthelmintic susceptible genotypes.

Intrinsic Factors Influencing the Infection by Helminth Parasites in Horses under an Oceanic Climate Area (NW Spain)

A coprological survey to determine the influence of some intrinsic factors (breed, age, and sex) on the infection by helminth parasites in equine livestock (n = 418) under an oceanic climate area (NW Spain) was conducted. Faecal samples were individually collected and analyzed by the coprological techniques. The main strongylid genera identified were Trichonema and Cyalocephalus spp (small strongyles) and Strongylus and Triodontophorus (large strongyles). The prevalence of gastrointestinal nematode was 89% (95% CI 86, 92) and 1% cestoda (0, 2). The percentage of horses with strongyloid parasites was 89% (86, 92), 11% (8, 14) for Parascaris, and 3% (1, 5) for Oxyuris. The highest prevalence for ascariosis was observed in the youngest horses (<3 years), for oxyurosis in the >10 years animals, and for strongylosis in the 3-10 years ones. Females were significantly more parasitized than males. A negative correlation between the age and the egg-excretion of ascarids and strongyles was recorded. The autochthonous and the English Pure Blood horses were the most parasitized. We concluded that the infections by helminths, especially the strongyloids, are significantly common in the region, so that greater importance should be given to this situation.