The efficacy of ivermectin, pyrantel and fenbendazole against Parascaris equorum infection in foals on farms in Australia

Occurrence of fenbendazole resistance in Parascaris spp. on breeding farms in Sweden

Anthelmintic resistance is an increasing problem in many gastrointestinal parasites of grazing animals. Among these, the equine roundworm, Parascaris spp., has developed wide-spread resistance to macrocyclic lactones over the past decades. Additionally, there are recent observations of emerging treatment failure of both tetrahydropyrimidine and fenbendazole. Therefore, the aims of this study were to further investigate the occurrence of fenbendazole resistance on breeding farms and to explore potential management-related risk factors associated with resistance in Parascaris spp. in Sweden. Eleven farms with 92 foals positive for Parascaris spp. were included in a faecal egg count reduction test during the years 2021-2023. According to the clinical protocol of the guidelines of the World Association for the Advancement of Veterinary Parasitology, fenbendazole resistance was present on four farms with efficacies varying from 45 % to 96 %. Having previously reported reduced efficacy on one of these farms, we can now confirm that fenbendazole resistance in Parascaris spp. has established. Farms with more than 40 yearly born foals had a significantly higher probability of having resistant Parascaris spp. Populations compared with smaller farms, (generalized linear model (GLM), t = 70.39, p < 0.001). In addition, there was a correlation between the number of foals on the farm and the frequency of yearly treatments showing that farms with < 20 foals were notably inclined to administer treatments twice during the first year (GLM, t=2.76, p < 0.05) in contrast to larger farms with > 40 foals that were using more frequent treatment intervals. In conclusion, this study confirms the establishment of fenbendazole resistance in Parascaris spp. populations on Swedish stud farms with the number of foals on the farm identified as a risk factor for development of anthelmintic resistance.

BEVA primary care clinical guidelines: Equine parasite control

BACKGROUND

There is a lack of consensus on how best to balance our need to minimise the risk of parasite-associated disease in the individual horse, with the need to limit the use of anthelmintics in the population to preserve their efficacy through delaying further development of resistance.

OBJECTIVES

To develop evidence-based guidelines utilising a modified GRADE framework.

METHODS

A panel of veterinary scientists with relevant expertise and experience was convened. Relevant research questions were identified and developed with associated search terms being defined. Evidence in the veterinary literature was evaluated using the GRADE evidence-to-decision framework. Literature searches were performed utilising CAB abstracts and PubMed. Where there was insufficient evidence to answer the research question the panel developed practical guidance based on their collective knowledge and experience.

RESULTS

Search results are presented, and recommendation or practical guidance were made in response to 37 clinically relevant questions relating to the use of anthelmintics in horses.

MAIN LIMITATIONS

There was insufficient evidence to answer many of the questions with any degree of certainty and practical guidance frequently had to be based upon extrapolation of relevant information and the panel members' collective experience and opinions.

CONCLUSIONS

Equine parasite control practices and current recommendations have a weak evidence base. These guidelines highlight changes in equine parasite control that should be considered to reduce the threat of parasite-associated disease and delay the development of further anthelmintic resistance.

A national survey of anthelmintic resistance in ascarid and strongylid nematodes in Australian Thoroughbred horses

This study quantified the extent of anthelmintic resistance (AR) in ascarid and strongylid nematodes against commonly used anthelmintics in Australian Thoroughbred horses. Faecal egg count reduction tests (FECRTs, n = 86) and egg reappearance period (ERP) tests were conducted on 22 farms across Australia. Faecal egg counts (FECs) were determined using the modified McMaster technique, and percent faecal egg count reduction (%FECR) was calculated using the Bayesian hierarchical model and hybrid Frequentist/Bayesian analysis method. The results were interpreted using old (published in 1992) and new (2023) research guidelines of the World Association for the Advancement of Veterinary Parasitology (WAAVP). The species composition of strongylid nematodes was detected utilising a DNA-metabarcoding method using pre- and post-treatment samples. Resistance was observed in strongylid nematodes to commonly used single-active and combination anthelmintics, including ivermectin (IVM %FECR range: 82%-92%; 95% lower credible interval (LCI) range: 80%-90%), abamectin (ABM: 73%-92%; 65%-88%), moxidectin (MOX: 89%-91%; 84%-89%), oxfendazole (OFZ: 0%-56%; 0%-31%) and its combination with pyrantel (OFZ + PYR: 0%-82%; 0%-78%). Resistance in Parascaris spp. was observed to IVM (10%-43%; 0%-36%), ABM (0%; 0%) and MOX (0%; 0%). When the new thresholds recommended by the WAAVP were used, AR was detected in six additional FECRTs for strongylids and three more tests for Parascaris spp., introducing resistance to OFZ and OFZ + PYR in the latter. Shortened ERPs (4-6 weeks) of strongylids were observed in 31 FECRTs in which AR was not detected at 2 weeks post-treatment for all the anthelmintics tested. Among cyathostomins, Cylicocyclus nassatus, Cylicostephanus longibursatus and Coronocyclus coronatus were the most prevalent species at 2 weeks post-treatment, whereas the main species appearing at five weeks following treatments with macrocyclic lactones were Cylicocyclus nassatus, Cylicostephanus longibursatus and Cylicocyclus ashworthi. After treatment with OFZ + PYR, the latter three, plus Coronocyclus coronatus and Cyathostomum catinatum, were detected at 5 weeks post-treatment. Overall, the study highlights the prevalence of AR in both ascarids and strongylid nematodes against commonly used anthelmintic products to control worms in Australian horses. The results indicate that ML combination products provided acceptable efficacy at 2 weeks. However, ERP calculations suggest that products work less effectively than previously measured. It is suggested to regularly monitor the efficacy of the anthelmintics and consider changing the worm control practices to better manage worms and AR in Australian horses.

Worm control practices used by Thoroughbred horse managers in Australia: A national survey

This study assessed worm control practices used by Australian Thoroughbred farm managers with an online questionnaire survey. The questionnaire comprised 52 questions (close-ended: 44; open-ended: 8) about farm demography and general husbandry practices, farm managers' knowledge of gastrointestinal nematodes (GIN) and their importance, diagnosis, worm control strategies and anthelmintics, anthelmintic resistance (AR) and grazing management. Following the pilot survey, the link for the questionnaire survey was sent to all (n = 657) registered members of the Thoroughbred Breeders Australia on 12th April 2020. The response rate for the questionnaire was 18.5% (122 of 675). The farm managers reported a good understanding of GIN and their importance in different age groups of horses as most respondents (70% of 122) perceived worm-related illness to be more important in young (i.e., foals, weanlings and yearlings) than adult (> 3 years old) horses. Although most respondents (93%, 113 of 122) used anthelmintics prophylactically to control GIN, only 15% (18 of 122) observed worm-related illness in their horses. Just under 40% of respondents were performing faecal egg counts, with less than 20% using the results of faecal egg counts to guide deworming decisions. The interval-based deworming strategy was the most common method (≥55% of 122 respondents) to control GIN in all age groups of horses. Macrocyclic lactones were the first choice of anthelmintics for all age groups of horses. Although the majority of respondents (88%, 107 of 122) perceived resistance in GIN against commonly used anthelmintics as an important issue in managing worms in horses, only 29% assessed the efficacy of anthelmintics and 91% (111 of 122) were unaware of AR on their properties. Grazing management practices, such as manure removal, were more frequently performed on smaller paddocks (<0.20 ha: 58%) than on larger paddocks (>0.20 ha: 18%). Multiple correspondence analyses showed that the likelihood of suboptimal worm control practices on small farms (n = ≤50 horses) was greater than that of medium (n = 51-100) and large (n = >100) farms. This study provides insights into the demography of Thoroughbred farms in Australia, husbandry practices used by stud managers and their knowledge about worms, control options and AR concerns, thereby paving the way for taking any initiatives to address the problem of AR in GIN of Australian Thoroughbred horses.

Anthelmintic and Hepatoprotective Activities of the Green-Synthesized Zinc Oxide Nanoparticles Against Parascaris equorum Infection in Rats

MAIN CONCLUSIONS

Green-synthesized zinc oxide nanoparticle is a promising treatment modality against parasitic infection through its powerful anthelmintic, antioxidant, healing promotion, and anti-inflammation effects.

BACKGROUND

Nanoparticles have many properties, depending on their size, shape, and morphology, allowing them to interact with microorganisms, plants, and animals.

OBJECTIVES

Investigation of the therapeutic effects of green-synthesized zinc oxide nanoparticles (ZnO NPs) on Parascaris equorum infection in rats.

METHODS

Thirty-six rats were divided into two divisions: the first division is noninfected groups were allocated into three groups. Group 1: Control, group 2: ZnO NPs (30 mg/kg), and group 3: ZnO NPs (60 mg/kg). The second division is infected groups were allocated into three groups. Group 1: vehicle, group 2: ZnO NPs (30 mg/kg), and group 3: ZnO NPs (60 mg/kg).

FINDINGS

Ten days post-infection, two larvae per gram of liver tissue were present in the vehicle group compared to the control group. No larvae were recovered from ZnO NPs (30 mg/kg), and one larva/g.tissue from ZnO NPs (60 mg/kg)-treated groups compared to untreated infected animals. Green-synthesized ZnO NPs caused a significant decrease in liver functions, low-density lipoprotein (LDL), cholesterol, triglycerides, malondialdehyde (MDA), and nitric oxide (NO). While it caused a significant increase in hemoglobin (HB), high-density lipoprotein (HDL), butyrylcholinesterase (BCHE), glutathione (GSH), catalase (CAT), and glutathione S-transferase (GST) in infected treated rats. The histological inflammation and fibroplasia scores showed a significant enhancement during the treatment with ZnO NPs (30, 60 mg/kg) compared to the infected untreated animals that scored the highest pathological destruction score. Immunohistochemical markers of NF-κB showed a significant decrease during the treatment with ZnO NPs (30, 60 mg/kg) compared to the infected untreated animals.

Anthelmintic and therapeutic effects of the biogenic zinc oxide nanoparticles against acute kidney injury induced by Parascaris equorum Infection in rats

Complications of parasite infections, especially kidney disease, have been linked to poorer outcomes. Acute kidney damage, glomerulonephritis, and tubular dysfunction are the most prevalent renal consequences of Parascaris equorum infection. The purpose of this study was to determine the pharmacological effects of green-produced zinc oxide nanoparticles (ZnO NPs) on P. equorum infection in male Wistar rats. Thirty-six male rats were divided into two groups of 18 each: infected and non-infected. Both groups were separated into three subgroups, each of which received distilled water, 30 mg/kg ZnO NPs, and 60 mg/kg ZnO NPs. After 10 days of ZnO NPs administration, four larvae per gram of kidney tissue were present in the untreated infected group. While, no larvae were present in ZnO NPs (30 mg/kg) treated group, and one larva/g.tissue was present in ZnO NPs (60 mg/kg) treated group compared to untreated infected animals. P. equorum infected rats had increased kidney biomarkers (creatinine, urea, uric acid), malondialdehyde, and nitric oxide, with a significant decrease in their antioxidant systems. On the other hand, infected treated rats with green-produced zinc oxide nanoparticles had a substantial drop in creatinine, urea, uric acid, malondialdehyde, and nitric oxide, as well as a significant rise in their antioxidant systems. P. equorum infection in rats caused severe degenerative and necrotic renal tissues. On the other hand, there were no detectable histopathological alterations in rats treated with ZnO NPs (30, 60 mg/kg) as compared to the infected untreated animals. When compared to infected untreated mice, immunohistochemical examination of nuclear factor-kappa B showed a significant decrease during treatment with ZnO NPs (30, 60 mg/kg). Green-produced zinc oxide nanoparticles are a viable therapeutic strategy for Parascaris equorum infection due to their potent anthelmintic activity, including a significant decrease in larval burden in infected treated rats.

A systematic review and meta-analysis on the current status of anthelmintic resistance in equine nematodes: A global perspective

BACKGROUND

The intensive application of anthelmintics in equine has led to considerable resistance in cyathostomins and Parascaris equorum. It has been well documented that benzimidazole (BZ) and pyrantel resistance is widespread in cyathostomins and Parascaris equorum. Since no new classes of anthelmintic have been introduced in the last 40 years, it is critical to be aware of the current risk factors of anthelmintic application to avoid further resistance.

OBJECTIVE

To review the factors affecting the level of anthelmintics resistance in equine around the world, type of anthelmintics, mode of application, dosage, nematode species, and location of anthelmintics application were evaluated and summarized.

DESIGN/PROCEDURE

A systematic review and meta-analyses following the PRISMA Framework were conducted to identify, evaluate, and synthesize primary literature reporting the efficacy of anthelmintic drugs in equines. Information on the bibliographic data, anthelmintic drugs, animals, continents, parasite genera, type of anthelmintics, and dosage was collected. Nonparametric tests (Kruskal-Wallis and Mann-Whitney) were used in SPSS (v.27) to investigate the association between variables. Factors that have a significant impact on efficacy have been subjected to binary logistic regression. Six meta-analyses were conducted in Microsoft Excel (2021) to qualify current resistance issues of the three major anthelmintics classes.

RESULTS

The final database was composed of 60 articles published between 1994 and 2022 with a total of 11835 animals. Anthelmintic class as well as anthelmintic active principle selection did have a significant effect on resistance (P < 0.01), whilst no correlation of the type of anthelmintics, mode of application, and dosage with efficacy were found. Anthelmintics resistance in ascarid was significantly more severe than in strongyle (P < 0.01). Macrocyclic lactone (ML) class and the benzimidazole and probenzimidazole (BP) class have the lowest efficacy against ascarid and strongyle, respectively (67.83% and 69.85%). The effect of location (by continent) also had a significant influence on the resistance of the ML class (P < 0.01). The resistance of the BP class which is the most prevalently applied was demonstrated in all six continents. Binary logistic regression revealed that parasite genera and drug class independently influenced the presence of drug resistance. The forest plots included in this study did not show a significant difference over time.

CONCLUSION

Current evidence indicated that anthelmintics resistance of ML and BP class were common in ascarid and strongyle. A combination of anthelmintics may reduce anthelmintics resistance, but multi-drug resistance may be a concern. Customerised anthelmintics strategy could help reduce resistance.

Understanding temporal and spatial distribution of intestinal nematodes of horses using faecal egg counts and DNA metabarcoding

This study reports the spatial and temporal distribution of ascarid and strongylid nematodes in Thoroughbred horses by age category across different climatic zones in Australia over an 18-month period. Faecal samples (n = 2046) from individual horses were analysed using the modified McMaster technique for faecal egg counts (FECs). Strongylids were identified using PCR-directed next-generation sequencing of the second internal transcribed spacer (ITS-2) of the nuclear ribosomal DNA. Yearlings had the highest prevalence (82%) of strongyle eggs followed by weanlings (79%), foals (58%), wet mares (49%) and dry mares (46%). For Parascaris spp., foals had the highest prevalence (35%) followed by weanlings (21%) and yearlings (10%). The highest mean FECs for Parascaris spp. were observed in foals (525 eggs per gram [EPG] of faeces) while those for strongyles were in yearlings (962 EPG). Among horses that were classified as adults at the time of sampling, 77% (860 of 1119) of mares were low (i.e., <250 EPG) strongyle egg-shedders. Mean strongyle FEC counts were highest in the Mediterranean (818 EPG) followed by summer (599 EPG), winter (442 EPG), and non-seasonal (413 EPG) rainfall zones. Twenty-six nematode species were detected, with Cylicostephanus longibursatus (26.5%), Cylicocyclus nassatus (23.7%) and Coronocyclus coronatus (20.5%) being the most frequently detected species. Their richness and relative abundance varied with horse age, season and climatic zone. In addition, Strongylus equinus and Triodontophorus spp. (T. brevicauda and T. serratus) were also detected. This comprehensive study elucidates spatial (climatic zone) and temporal (i.e., seasonal) trends in prevalence and burdens of intestinal nematodes in Australian horses using non-invasive conventional and molecular methods. The information presented in this study is crucial for developing integrated management strategies to control horse parasites in farmed horses.

Impaired efficacy of fenbendazole and ivermectin against intestinal nematodes in adult horses in Iran

This study aimed to evaluate the efficacy of fenbendazole and ivermectin on strongyles and Parascaris sp. infecting adult riding horses in three regions with different climates. During 2021 and 2022 fecal specimens were randomly collected from 483 horses older than three years in 31 equestrian clubs in Hamedan (n = 217), Yazd (n = 146) and Tabriz cities (n = 120). Eggs were counted by McMaster technique, and the strongyle larvae were identified using coproculture, PCR and sequencing. Horses with strongyles and Parascaris egg counts ≥150 were enrolled in fecal egg count reduction (FECR) examination following treatment with ivermectin or fenbendazole. In total, 26.5% of examined horses were positive with at least one parasite. Infection rates varied in three cities i.e., 25.8% in Hamedan, 28.8% in Yazd, 25% in Tabriz. Fifty-seven horses had FECR measured. FECR below <90% was observed for IVM-strongyle in two horses in Tabriz, for FBZ-strongyle in two horses in Tabriz and two horses in Hamedan, for IVM-Parascaris in one horse in all three cities, and for FBZ-Parascaris in one horse in Yazd. Furthermore, FECR 90-100% was observed in IVM-Parascaris and FBZ -Parascaris groups in Tabriz. Data herein presented demonstrate different degrees of resistance of strongyles and Parascaris infecting horses in Iran against both ivermectin and fenbendazole. Since non-principled use of anthelminthics is common among horse owners, urgency of test-and-treatment strategy should be educated and implemented by policy-making organizations. Evaluating efficacy of different anthelminthics and choosing the most effective treatment in each region is suggested.

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.

Assessment of worm control practices recommended by equine veterinarians in Australia

This study aimed to assess Australian veterinarians' knowledge, perceptions and treatment strategies for worm control in horses with an online questionnaire. The questionnaire comprised 64 questions covering various aspects of: (i) veterinary practice; (ii) the veterinarian's knowledge of gastrointestinal nematodes (GINs) and the importance of parasites in different age groups of horses; (iii) the diagnosis and control of worms; (iv) anthelmintics and anthelmintic resistance (AR); (v) grazing management; and (vi) the means of communication and the discussion between veterinarians and their clients regarding worm control. Following a pilot survey, a link for the questionnaire survey was sent to all (n = 1,148) registered members of Equine Veterinarians Australia in April 2020. The response rate for the questionnaire was 10% (118 of 1,148). The findings of this study illustrate veterinarians' good understanding of aspects of equine parasites, including control. However, respondents mainly recommended frequent, interval-based prophylactic deworming in young horses, and only 40% (96 of 239) diagnosed GIN infections based on faecal egg count (FEC) results in all age groups of horses. Furthermore, only 27% (88 of 330) of the respondents made deworming decisions based on FECs. Most of the respondents recommended macrocyclic lactones (MLs) for all age groups of horses (71%, 481 of 677), and the most frequently used method to calculate the dose of anthelmintics was by estimating the weight of animals visually (53%, 63 of 118). Although the majority of respondents (97%, 115 of 118) perceived AR to be a critical issue in managing worms in horses, 58% (67 of 118) of them were unaware of the status of AR on their clients' properties. Forty-two percent (50 of 118) of the respondents perceived the presence of AR in worms, including pinworms (16%), strongylins (15%), species of Draschia and Habronema (6%), Strongyloides westeri (2%) and tapeworms (1%). Twenty-seven percent (32 of 118) of the respondents rarely discussed equine worm control practices with their clients. This study provides insights into the perception and worm control practices recommended by Australian veterinarians to manage equine parasites. The findings highlight the importance of continued education and awareness of AR, and the use of non-chemical methods as well as consideration of the legislation of prescription-only use of anthelmintics based on FECs to achieve sustainable control of GINs in Australian horses.

Prevalence and diversity of ascarid and strongylid nematodes in Australian Thoroughbred horses using next-generation sequencing and bioinformatic tools

The study presents the results of a cross-sectional survey to describe the epidemiology of ascarid and strongylid nematodes in horses, the impact of diverse climatic conditions on parasite diversity and the levels of faecal egg shedding in different age groups of managed Thoroughbred horses. Individual faecal samples (n = 1377) collected from 62 Thoroughbred farms across four climatic zones in Australia were analysed using the modified McMaster technique for faecal egg counts (FECs) and strongylid nematodes were identified utilising PCR-directed next-generation sequencing (NGS) of the second internal transcribed spacer of the nuclear ribosomal DNA (ITS-2). Across all age groups, the prevalence of ascarid and strongylid nematodes was 12% (95% confidence interval 10-14%) and 72% (70-74%), respectively. Based on strongylid FECs, yearlings had the highest prevalence (89%) followed by weanlings (83%), foals (79%), wet mares (61%), dry mares (59%) and stallions (54%). However, for Parascaris spp., foals had the highest prevalence (46%) followed by weanlings (32%) and yearlings (13%). The highest mean FECs for Parascaris spp. were observed in foals (418 eggs per gram [EPG] of faeces) while those for strongylids were in yearlings (1002 EPG). Of the adult horses (mares and stallions), 67% (489 of 729) and 11% (77 of 729) were low (i.e., ≤250 EPG) and moderate (i.e., 251-500 EPG) strongylid egg-shedders, respectively. Strongylid egg shedding varied across climatic zones, with the highest mean FECs in the summer rainfall (723 EPG) followed by non-seasonal rainfall (629 EPG), winter rainfall (613 EPG), and Mediterranean (606 EPG) rainfall zones. Twenty-three nematode species were detected using NGS, with Cylicostephanus longibursatus (28%), Cylicocyclus nassatus (23%) and Coronocyclus coronatus (23%), being the most abundant species. Three species of Strongylus (i.e., S. vulgaris, S. equinus and S. edentatus) were also detected. The nemabiome composition, species richness and relative abundance varied within horse age and between climatic zones. These empirical findings provide a comprehensive understanding of the prevalence of parasites within horse populations and the multifaceted factors that influence their occurrence, thereby allowing for the formulation of tailored strategies aimed at parasite control in domestic horses.

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.

Evidence of resistance to ivermectin in the gastrointestinal nematodes of horses from Mexican southeast

Gastrointestinal nematodes (GIN) are a major impediment to breeding and exploitation of horses. Traditional control of GIN has generated resistance to main anthelmintics, including ivermectin. An analysis of five ranches with a history of IVM use was done to determine the efficacy and resistance of GIN to IVM treatment in horses from the Mexican southeast. Predesigned questionnaires were applied to collect information on previous treatment protocols. The fecal egg count reduction test (FECRT) was applied to determine resistance. Before IVM application, a McMaster test was used to diagnose GIN infection in horses, and feces cultures were done to identify L3 larvae for Strongylida eggs. Pre-treatment samples showed that 72.7% (80/110) of horses were GIN positive, with cyathostomins being the most frequent (91.8%), followed by Oxyuris equi (7.0%), Parascaris equorum (1.0%), and Strongylus vulgaris (0.2%). Based on the results, the horses at each ranch were divided in control (CG) and experimental (EG) groups with similar eggs per gram of feces (EPG). The EG (40/80) was dewormed with IVM (0.2 mg/kg orally) and the CG (40/80) remained untreated. After 14 days, EPG were measured, and feces cultures were done again to identify L3 larvae. After treatment of EG, 40% (16/40) of horses were positive, the most frequently identified GIN were cyathostomins (98.6%), followed by P. equorum (1.0%) and S. vulgaris (0.2%). Three of the five ranches were classified as resistant, according to the FECRT, with a percentage of reduction from 53 to 68%, all of which used IVM ≥4 times annually. This is the first evidence of resistance in cyathostomins to IVM treatment in horses from the Mexican southeast, adding to the current problem of anthelmintic resistance in equine GIN.

Occurrence and risk factors associated with gastrointestinal parasitism in horses reared in different systems

To facilitate exploration of the immense range of gastrointestinal parasites in horses and the impact of parasitism on equine health, the present study aimed to evaluate the occurrence and risk factors associated with these infections in horses reared in different management systems in the state of Santa Catarina, Brazil. Samples were collected from 208 horses: 91 from extensive, 64 from semi-extensive, and 53 from intensive rearing systems. The identified helminths included those of the Strongylida order (80.29%), Parascaris equorum (3.36%), Oxyuris equi (4.33%), and Anoplocephala spp. (1.92%). By analyzing the coproculture results to differentiate among Strongylida order parasites, species such as Strongylus vulgaris, S. edentatus, S. equinus, Triodontophorus spp., and Trichostrongylus axei, in addition to members of the Cyathostominae subfamily, which include Gyalocephalus capitatus and Poteriostomum spp., were identified. The only positive sample of protozoa was that of Cryptosporidium spp. (13%). Regarding the rearing system, animals in the extensive system had a higher proportion of infected horses and a higher chance of infection than those in the other systems. For the variable co-grazing with cattle, only cyathostomins showed a significant difference with relatively low infection risk in co-grazing. Overall, the present study demonstrated a high occurrence of equine gastrointestinal parasites, especially those of the Strongylida order, with emphasis on small strongylids. In addition, analyzing factors associated with infection showed that management variables are important for controlling parasitism in horses.

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.

Investigation of the Efficacy of Pyrantel Pamoate, Mebendazole, Albendazole, and Ivermectin against Baylisascaris schroederi in Captive Giant Pandas

Baylisascaris schroederi is one of the main health risks threatening both wild and captive giant pandas. The administration of anthelmintics is a common method to effectively control B. schroederi infection, but there is a notable risk of anthelmintic resistance (AR) after long-term, constant use of anthelmintics. Four anthelmintics-pyrantel pamoate (PYR), mebendazole (MBZ), albendazole (ABZ), and ivermectin (IVM)-were each administered separately at intervals of 2 months to 22 enrolled giant pandas. The fecal egg count reduction (FECR) proportions were calculated by both the Markov chain Monte Carlo (MCMC) Bayesian mathematical model and the arithmetic mean. AR was assessed based on the criteria recommended by the World Association for the Advancement of Veterinary Parasitology (WAAVP). The estimated prevalence of B. schroederi infection was 34.1%. After treatment with PYR, MBZ, ABZ, and IVM, it was determined that MBZ, ABZ, and IVM were efficacious against B. schroederi, while nematodes were suspected to be resistant to PYR according to the fecal egg count reduction (FECR) proportions.

The microbial community associated with Parascaris spp. infecting juvenile horses

Background

Parasitic nematodes, including large roundworms colloquially known as ascarids, affect the health and well-being of livestock animals worldwide. The equine ascarids, Parascaris spp., are important parasites of juvenile horses and the first ascarids to develop widespread anthelmintic resistance. The microbiota has been shown to be an important factor in the fitness of many organisms, including parasitic nematodes, where endosymbiotic Wolbachia have been exploited for treatment of filariasis in humans.

Methods

This study used short-read 16S rRNA sequences and Illumina sequencing to characterize and compare microbiota of whole worm small intestinal stages and microbiota of male and female intestines and gonads. Diversity metrics including alpha and beta diversity, and the differential abundance analyses DESeq2, ANCOM-BC, corncob, and metagenomeSeq were used for comparisons.

Results

Alpha and beta diversity of whole worm microbiota did not differ significantly between groups, but Simpson alpha diversity was significantly different between female intestine (FI) and male gonad (MG) (P= 0.0018), and Shannon alpha diversity was significantly different between female and male gonads (P = 0.0130), FI and horse jejunum (HJ) (P = 0.0383), and FI and MG (P= 0.0001). Beta diversity (Fig. 2B) was significantly different between female and male gonads (P = 0.0006), male intestine (MI) and FG (P = 0.0093), and MG and FI (P = 0.0041). When comparing organs, Veillonella was differentially abundant for DESeq2 and ANCOM-BC (p < 0.0001), corncob (P = 0.0008), and metagenomeSeq (P = 0.0118), and Sarcina was differentially abundant across four methods (P < 0.0001). Finally, the microbiota of all individual Parascaris spp. specimens were compared to establish shared microbiota between groups.

Conclusions

Overall, this study provided important information regarding the Parascaris spp. microbiota and provides a first step towards determining whether the microbiota may be a viable target for future parasite control options.

Graphical abstract

Supplementary Information

The online version contains supplementary material available at 10.1186/s13071-022-05533-y.

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.

The equine ascarids: resuscitating historic model organisms for modern purposes

The equine ascarids, Parascaris spp., are important nematode parasites of juvenile horses and were historically model organisms in the field of cell biology, leading to many important discoveries, and are used for the study of chromatin diminution. In veterinary parasitology, Parascaris spp. are important not only because they can cause clinical disease in young horses but also because they are the only ascarid parasites to have developed widespread anthelmintic resistance. Despite this, much of the general biology and mechanisms of anthelmintic resistance are poorly understood. This review condenses known basic biological information and knowledge on the mechanisms of anthelmintic resistance in Parascaris spp., highlighting the importance of foundational research programs. Although two variants of this parasite were recognized based on the number of chromosomes in the 1870s and suggested to be two species in 1890, one of these, P. univalens, appears to have been largely forgotten in the veterinary scientific literature over the past 100 years. We describe how this omission has had a century-long effect on nomenclature and data analysis in the field, highlighting the importance of proper specimen identification in public repositories. A summary of important basic biology, including life cycle, in vitro maintenance, and immunology, is given, and areas of future research for the improvement of knowledge and development of new systems are given. Finally, the limited knowledge regarding anthelmintic resistance in Parascaris spp. is summarized, along with caution regarding assumptions that resistance mechanisms can be applied across clades.

In Silico Docking of Nematode β-Tubulins With Benzimidazoles Points to Gene Expression and Orthologue Variation as Factors in Anthelmintic Resistance

The efficacy of benzimidazole anthelmintics can vary depending on the target parasite, with Ascaris nematodes being highly responsive, and whipworms being less responsive. Anthelmintic resistance has become widespread, particularly in strongyle nematodes such as Haemonchus contortus in ruminants, and resistance has recently been detected in hookworms of humans and dogs. Past work has shown that there are multiple β-tubulin isotypes in helminths, yet only a few of these contribute to benzimidazole interactions and resistance. The β-tubulin isotypes of ascarids and soil-transmitted helminths were identified by mining available genome data, and phylogenetic analysis showed that the ascarids share a similar repertoire of seven β-tubulin isotypes. Strongyles also have a consistent pattern of four β-tubulin isotypes. In contrast, the whipworms only have two isotypes, with one of these clustering more basally and distinct from any other group. Key β-tubulin isotypes selected based on previous studies were the focus of in silico molecular docking simulations to look at the interactions with benzimidazoles. These showed that all β-tubulins had similar interactions with benzimidazoles and maintained the key bond with residue E198 in all species, indicating similar mechanisms of action. However, the interaction was stronger and more consistent in the strongyles and whipworms than it was in the ascarids. Alteration of β-tubulin isotypes with the common resistance-associated mutations originally identified in H. contortus resulted in similar interaction modeling for all species. In conclusion, ascarids, strongyles, and whipworms all have their own unique repertoire of β-tubulins, which could explain why benzimidazole resistance and susceptibility varies between these groups of parasites. These data complement recent work that has highlighted the roles of essential residues in benzimidazole drug binding and shows that there is a separation between strongyle parasites that frequently develop resistance and ascarid parasites, which have been much less prone to developing resistance.

Ivermectin-induced gene expression changes in adult Parascaris univalens and Caenorhabditis elegans: a comparative approach to study anthelminthic metabolism and resistance in vitro

Background

The nematode Parascaris univalens is one of the most prevalent parasitic pathogens infecting horses but anthelmintic resistance undermines treatment approaches. The molecular mechanisms underlying drug activity and resistance remain poorly understood in this parasite since experimental in vitro models are lacking. The aim of this study was to evaluate the use of Caenorhabditis elegans as a model for P. univalens drug metabolism/resistance studies by a comparative gene expression approach after in vitro exposure to the anthelmintic drug ivermectin (IVM).

Methods

Twelve adult P. univalens worms in groups of three were exposed to ivermectin (IVM, 10^–13 M, 10^–11 M, 10^–9 M) or left unexposed for 24 h at 37 °C, and total RNA, extracted from the anterior end of the worms, was sequenced using Illumina NovaSeq. Differentially expressed genes (DEGs) involved in metabolism, transportation, or gene expression with annotated Caernorhabditis elegans orthologues were identified as candidate genes to be involved in IVM metabolism/resistance. Similarly, groups of 300 adult C. elegans worms were exposed to IVM (10^–9 M, 10^–8 M and 10^–7 M) or left unexposed for 4 h at 20 °C. Quantitative RT-PCR of RNA extracted from the C. elegans worm pools was used to compare against the expression of selected P. univalens candidate genes after drug treatment.

Results

After IVM exposure, 1085 DEGs were found in adult P. univalens worms but the relative gene expression changes were small and large variabilities were found between different worms. Fifteen of the DEGs were chosen for further characterization in C. elegans after comparative bioinformatics analyses. Candidate genes, including the putative drug target lgc-37, responded to IVM in P. univalens, but marginal to no responses were observed in C. elegans despite dose-dependent behavioral effects observed in C. elegans after IVM exposure. Thus, the overlap in IVM-induced gene expression in this small set of genes was minor in adult worms of the two nematode species.

Conclusion

This is the first time to our knowledge that a comparative gene expression approach has evaluated C. elegans as a model to understand IVM metabolism/resistance in P. univalens. Genes in P. univalens adults that responded to IVM treatment were identified. However, identifying conserved genes in P. univalens and C. elegans involved in IVM metabolism/resistance by comparing gene expression of candidate genes proved challenging. The approach appears promising but was limited by the number of genes studied (n = 15). Future studies comparing a larger number of genes between the two species may result in identification of additional candidate genes involved in drug metabolism and/or resistance.

Graphical Abstract

Supplementary Information

The online version contains supplementary material available at 10.1186/s13071-022-05260-4.

Absence of Polymorphisms in Codons 167, 198 and 200 of All Seven β-tubulin Isotypes of Benzimidazole Susceptible and Resistant Parascaris spp. Specimens from Australia

Benzimidazoles resistance is widespread in strongyle parasitic nematodes and associated with polym orphisms in the codons 167, 198 and 200 of isotype 1 β-tubulin (tbb-1). In ascarids, benzimidazole (BZ) resistance has rarely been reported and in none of these cases were any of these polymorphisms detected. Here, available genome and transcriptome data from WormBase ParaSite were used to compare the complete β-tubulin reservoirs of Parascaris univalens, Ascaris suum and Ascaris lumbricoides. Adult Parascaris spp. specimens collected in Australia from horses after BZ treatment (susceptible, n = 13) or surviving BZ treatment and collected after ivermectin treatment (resistant, n = 10) were genotyped regarding codons 167, 198 and 200 using Sanger sequencing. Phylogenetic analyses clearly showed that there are no one-to-one ascarid orthologs of strongyle tbb-1 genes. In the reference genomes, as well as phenotypically susceptible and resistant Parascaris spp. from Australia, six out of seven β-tubulin genes showed a BZ-susceptible genotype (F167, E198, F200). The only exception were the testis-specific β-tubulin D genes from all three ascarid species that encode tyrosine at codon 200. This was observed independently of the BZ-susceptibility phenotype of Parascaris spp. These data suggest that different mechanisms lead to BZ resistance in ascarid and strongyle nematodes.

Exploring the β-tubulin gene family in a benzimidazole-resistant Parascaris univalens population

Benzimidazole (BZ) drugs are frequently used to treat infections with the equine ascarid Parascaris univalens due to increasing resistance to macrocyclic lactones and pyrantel. Benzimidazole resistance is rare in ascarids in contrast to strongyle parasites where this resistance is widespread. In strongyles, single nucleotide polymorphisms (SNPs) at codons 167, 198 and 200 in a β-tubulin gene have been correlated to BZ resistance, but little is known about the β-tubulin genes and their possible involvement in BZ resistance in P. univalens and other ascarids. Previously two β-tubulin genes have been identified in P. univalens. In this study, we present five additional β-tubulin genes as well as the phylogenetic relationship of all seven genes to β-tubulins of other clade III and V nematodes. In addition, the efficacy of fenbendazole for treatment of P. univalens on a Swedish stud farm was studied in 2019 and 2020 using faecal egg count reduction test. Reductions varied from 73% to 88%, indicating the presence of a resistant P. univalens population on the farm. The emergence of BZ resistance emphasizes the need for development of molecular markers for rapid and more sensitive detection of resistant populations. We therefore investigated whether possible SNPs at positions 167, 198 or 200 in any of the β-tubulin genes could be used to distinguish between resistant and susceptible P. univalens populations. Amplicon sequencing covering the mutation sites 167, 198 and 200 in all seven β-tubulin genes revealed an absence of SNPs in both resistant and susceptible populations, suggesting that the mechanism behind BZ resistance in ascarids is different from that in strongyle nematodes and the search for a molecular marker for BZ resistance in P. univalens needs to continue.

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First case of fenbendazole resistance in Parascaris univalens in Europe.

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The P. univalens β-tubulin family contains seven genes.

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P. univalens β-tubulin genes cluster with β-tubulins from other clade V nematodes.

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No resistance associated SNPs were identified in P. univalens β-tubulin genes.

Very low intraspecific sequence variation in selected nuclear and mitochondrial Parascaris univalens genes

Equines were over decades considered to be infected by two morphologically virtually indistinguishable ascarid species, Parascaris univalens and Parascaris equorum. Reliable species discrimination is only possible using enzyme isoelectric focussing and karyotyping with P. univalens having one and P. equorum two chromosome pairs. However, presumably the complexity of both methods prevented their routine use in nearly all previous studies about prevalence and drug resistance of Parascaris spp. These have barely been performed on the species level although most studies stated presence of one or the other species. Recently, only P. univalens has been identified by karyotyping and the last published study identifying P. equorum dates back to 1989. In order to improve species-specific detection, molecular markers are required. Here, partial 12S rRNA, cytochrome oxidase I (COI) and complete internal transcribed spacer (ITS)-1 and - 2 sequences were obtained from 24 karyotyped Parascaris specimens from Poland and 6 German specimens (not karyotyped) and used in phylogenetic analyses with orthologous sequences from GenBank. All karyotyped specimens were identified as P. univalens. In the phylogenetic analysis, they formed very homogenous clusters for all target genes and in a multi-locus analysis. Within this cluster, almost all sequences from GenBank were also included, no matter if they had been assigned to P. univalens or P. equorum. However, a small number of P. univalens ITS and COI sequences originating from donkeys from a single farm in China formed a highly supported sister cluster suggesting that they might represent another Parascaris genotype or species. Our data also strongly suggest that nearly all ITS and COI sequences previously deposited in GenBank and assigned to P. equorum actually represent P. univalens. The fact that significantly different sequences can be found in Parascaris spp. suggests that PCR-based species diagnosis will be possible once molecular markers have been identified for P. equorum from karyotyped specimens.

Constitutive and differential expression of transport protein genes in Parascaris univalens larvae and adult tissues after in vitro exposure to anthelmintic drugs

The equine roundworm Parascaris univalens has developed resistance to the three anthelmintic substances most commonly used in horses. The mechanisms responsible for resistance are believed to be multi-genic, and transport proteins such as the P-glycoprotein (Pgp) family have been suggested to be involved in resistance in several parasites including P. univlaens. To facilitate further research into the mechanisms behind drug metabolism and resistance development in P. univalens we aimed to develop an in vitro model based on larvae. We developed a fast and easy protocol for hatching P. univalens larvae for in vitro studies, resulting in a hatching rate of 92 %. The expression of transport protein genes pgp-2, pgp-9, pgp-11.1, pgp-16.1 and major facilitator superfamily (MFS) genes PgR006_g137 and PgR015_g078 were studied in hatched larvae exposed to the anthelmintic drugs ivermecin (IVM) 10^-9 M, pyrantel citrate (PYR) 10^-6 M and thiabendazole (TBZ) 10^-5 M for 24 h. In comparison, the expression of these transport protein genes was studied in the anterior end and intestinal tissues of adult worms in vitro exposed to IVM, TBZ and PYR, at the same concentrations as larvae, for 3 h, 10 h and 24 h. Larval exposure to sub-lethal doses of IVM for 24 h did not affect the expression levels of any of the investigated genes, however larvae exposed to PYR and TBZ for 24 h showed significantly increased expression of pgp-9. In vitro drug exposure of adult worms did not result in any significant increases in expression of transport protein genes. Comparisons of constitutive expression between larvae and adult worm tissues showed that pgp-9, pgp-11.1, pgp-16.1 and MFS gene PgR015_g078 were expressed at lower levels in larvae than in adult tissues, while pgp-2 and MFS gene PgR006_g137 had similar expression levels in larvae and adult worms. All investigated transport protein genes were expressed at higher rates in the intestine than in the anterior end of adult worms, except pgp-11.1 where the expression was similar between the two tissues. This high constitutive expression in the intestine suggests that this is an important site for xenobiotic efflux in P. univalens. Despite the fact that the results of this study show differences in expression of transport protein genes between larvae and adult tissues, we believe that the larval assay system described here will be an important tool for further research into the molecular mechanisms behind anthelmintic resistance development and for other in vitro studies.

Antiprotozoal and anthelmintic activity of zinc oxide nanoparticles

Nanomaterials represent a wide alternative for the treatment of several diseases that affect both human and animal health. The use of these materials mainly involves trying to solve the problem of resistance that pathogenic organisms acquire to conventional drugs. A well-studied example that represents a potential component for biomedical applications is the use of zinc oxide (ZnO) nanoparticles (NPs). Its antimicrobial function is related, especially the ability to generate/induce ROS that affects the homeostasis of the pathogen in question. Protozoa and helminths that harm human health and the economic performance of animals have already been exposed to this type of nanoparticle. Thus, through this review, our goal is to discuss the state-of-the-art effect of ZnO NPs on these parasites.

Parascaris spp. eggs in horses of Italy: a large-scale epidemiological analysis of the egg excretion and conditioning factors

Background

Equine ascariosis, caused by Parascaris spp., is a worldwide endoparasitic disease affecting young horses in particular. Despite the great number of horses reared in Italy, large-scale epidemiological surveys dealing with ascariosis prevalence in the country are not reported in the current literature. For this reason, the present survey aims to describe, for the first time, the spread and infestation of Parascaris spp. in a large population of Italian horses (6896 animals) using faecal egg counts, and further to identify risk factors associated with ascarid egg shedding.

Methods

Individual rectal faecal samples collected during routine veterinary examinations were used and Parascaris spp. prevalence was tested against the animal’s age, sex, housing conditions, geographic provenance as well as the respective sampling season.

Results

Among the examined stables, 35.8% showed at least one horse to be positive for Parascaris spp. eggs and an overall prevalence of 6.3% was found. Ascariosis rates tended to decrease significantly with age and, proportionally, 80.0% of the recorded Parascaris spp. eggs were found in 0.7% of the examined animals. Statistically significant differences among prevalence rates were found between the different geographic areas of provenance and prevalence was found to be higher in horses reared outdoors compared to those raised indoors. Analysis of data based on sex and season did not show any significant differences. Despite the lower prevalence found compared to other European countries, ascariosis was concluded to represent a significant health challenge for horses reared in Italy, especially foals. Age (foals and yearlings) and outdoor rearing were identified to be significant risk factors for Parascaris spp. egg shedding. Furthermore, the relevance of the infected horses over 6 years of age should not be underestimated as these represent a significant source of contamination for younger animals.

Conclusions

The development of improved treatment protocols based on regular faecal examination combined with follow-up assessment of the efficacy of integrated action plans would prove beneficial in regard to animal health and anthelmintic resistance reduction in the field.

Graphic Abstract

First Report of Resistance to Ivermectin in Parascaris univalens in Iceland

Horses in Iceland have been isolated for more than 1,000 yr but still harbor a similar range of gastrointestinal parasites as do horses across the world. The long isolation of the horses and their parasites presumably means that no resistance genes have been introduced into the Parascaris spp. population. It is therefore of particular interest to investigate the efficacy of ivermectin on Parascaris spp. infecting Icelandic foals. Potential treatment failure of ivermectin in Iceland will add substantial new information on how resistance can arise independently. This study aimed to determine the efficacy of subcutaneous injection of ivermectin for the treatment of Parascaris spp. infection in foals and to identify the Parascaris species present in the west and north of Iceland. A fecal egg count reduction (FECR) test (FECRT) was performed on 50 foals from 8 farms, including an untreated control group of 6 foals, from September to November 2019. The foals were between 3 and 5 mo of age at the start of the study and had not previously been treated with anthelmintic drugs. Each foal was treated subcutaneously with off-label use of Ivomec® injection 10 mg/ml or Noromectin® 1% at a dose of 0.2 mg/kg. The FECR for each farm was calculated in 2 ways, by the eggCounts package in R and by the Presidente formula (FECRT). Both calculation methods resulted in efficacy levels between 0% and 80.78%, indicating ivermectin resistance on all farms. We also confirmed, by karyotyping, that the species of equine ascarid present in the west and north of Iceland is Parascaris univalens. This study provides evidence for treatment failure of ivermectin against P. univalens infection in foals. Since Icelandic horses have been isolated on the island for more than 1,000 yr, this implies that resistance alleles have developed independently in the Icelandic Parascaris population. The actual clinical impact of ivermectin resistance is unknown but another drug of choice should be considered to treat Parascaris infection in foals in Iceland.

The P-glycoprotein repertoire of the equine parasitic nematode Parascaris univalens

P-glycoproteins (Pgp) have been proposed as contributors to the widespread macrocyclic lactone (ML) resistance in several nematode species including a major pathogen of foals, Parascaris univalens. Using new and available RNA-seq data, ten different genomic loci encoding Pgps were identified and characterized by transcriptome-guided RT-PCRs and Sanger sequencing. Phylogenetic analysis revealed an ascarid-specific Pgp lineage, Pgp-18, as well as two paralogues of Pgp-11 and Pgp-16. Comparative gene expression analyses in P. univalens and Caenorhabditis elegans show that the intestine is the major site of expression but individual gene expression patterns were not conserved between the two nematodes. In P. univalens, PunPgp-9, PunPgp-11.1 and PunPgp-16.2 consistently exhibited the highest expression level in two independent transcriptome data sets. Using RNA-Seq, no significant upregulation of any Pgp was detected following in vitro incubation of adult P. univalens with ivermectin suggesting that drug-induced upregulation is not the mechanism of Pgp-mediated ML resistance. Expression and functional analyses of PunPgp-2 and PunPgp-9 in Saccharomyces cerevisiae provide evidence for an interaction with ketoconazole and ivermectin, but not thiabendazole. Overall, this study established reliable reference gene models with significantly improved annotation for the P. univalens Pgp repertoire and provides a foundation for a better understanding of Pgp-mediated anthelmintic resistance.

Transcriptional responses in Parascaris univalens after in vitro exposure to ivermectin, pyrantel citrate and thiabendazole

Background

Parascaris univalens is a pathogenic parasite of foals and yearlings worldwide. In recent years, Parascaris spp. worms have developed resistance to several of the commonly used anthelmintics, though currently the mechanisms behind this development are unknown. The aim of this study was to investigate the transcriptional responses in adult P. univalens worms after in vitro exposure to different concentrations of three anthelmintic drugs, focusing on drug targets and drug metabolising pathways.

Methods

Adult worms were collected from the intestines of two foals at slaughter. The foals were naturally infected and had never been treated with anthelmintics. Worms were incubated in cell culture media containing different concentrations of either ivermectin (10⁻⁹ M, 10⁻¹¹ M, 10⁻¹³ M), pyrantel citrate (10⁻⁶ M, 10⁻⁸ M, 10⁻¹⁰ M), thiabendazole (10⁻⁵ M, 10⁻⁷ M, 10⁻⁹ M) or without anthelmintics (control) at 37 °C for 24 h. After incubation, the viability of the worms was assessed and RNA extracted from the anterior region of 36 worms and sequenced on an Illumina NovaSeq 6000 system.

Results

All worms were alive at the end of the incubation but showed varying degrees of viability depending on the drug and concentration used. Differential expression (Padj < 0.05 and log2 fold change ≥ 1 or ≤ − 1) analysis showed similarities and differences in the transcriptional response after exposure to the different drug classes. Candidate genes upregulated or downregulated in drug exposed worms include members of the phase I metabolic pathway short-chain dehydrogenase/reductase superfamily (SDR), flavin containing monooxygenase superfamily (FMO) and cytochrome P450-family (CYP), as well as members of the membrane transporters major facilitator superfamily (MFS) and solute carrier superfamily (SLC). Generally, different targets of the anthelmintics used were found to be upregulated and downregulated in an unspecific pattern after drug exposure, apart from the GABA receptor subunit lgc-37, which was upregulated only in worms exposed to 10⁻⁹ M of ivermectin.

Conclusions

To our knowledge, this is the first time the expression of lgc-37 and members of the FMO, SDR, MFS and SLC superfamilies have been described in P. univalens and future work should be focused on characterising these candidate genes to further explore their potential involvement in drug metabolism and anthelmintic resistance.

Reduced efficacy of ivermectin and moxidectin against Parascaris spp. in foals from Argentina

Macrocyclic lactones are the most widely used drugs for the control of gastrointestinal nematodes of horses in Argentina. Ivermectin and moxidectin are used as broad spectrum anthelmintics and although there are several international reports on the resistance of Parascaris spp., the resistance status of the local nematode population is largely unknow. This report informs a case of suboptimal efficacy to both drugs to control Parascaris spp in foals in central Argentina. In February 2018, routine fecal parasite egg counts showed a moderate-high number of Parascaris spp eggs (mean = 680 eggs per gram of feces) in foals treated approximately one month before with moxidectin. Upon suspicion of resistance of this parasite to the macrocyclic lactones, 24 of these animals were selected for a fecal egg count reduction test (FECRT). Twelve foals were treated with ivermectin and the remaining 12 animals with moxidectin. Two weeks after treatment, the FECRT was 48.1% and 34.8% for moxidectin and ivermectin respectively (25% of the animals increased the number of eggs in feces after treatment). Five days later, the administration of fenbendazole resulted in a FECRT = 100%. The monitoring of the status of susceptibility or resistance in each establishment is critical for the design of control programs based on rational and sustainable use of anthelmintics.

Ascarids exposed: a method for in vitro drug exposure and gene expression analysis of anthelmintic naïve Parascaris spp

Ascarid parasites infect a variety of hosts and regular anthelmintic treatment is recommended for all species. Parascaris spp. is the only ascarid species with widespread anthelmintic resistance, which allows for the study of resistance mechanisms. The purpose of this study was to establish an in vitro drug exposure protocol for adult anthelmintic-naïve Parascaris spp. and report a preliminary transcriptomic analysis in response to drug exposure. Live worms were harvested from foal necropsies and maintained in RPMI-1640 at 37 °C. Serial dilutions of oxibendazole (OBZ) and ivermectin (IVM) were prepared for in vitro drug exposure, and worm viability was monitored over time. In a second drug trial, worms were used for transcriptomic analysis. The final drug concentrations employed were OBZ at 40.1 μm (10 μg mL-1) and IVM at 1.1 μm (1 μg mL-1) for 24 and 3 h, respectively. The RNA-seq analysis revealed numerous differentially expressed genes, with some being potentially related to drug detoxification and regulatory mechanisms. This report provides a method for in vitro drug exposure and the phenotypic responses for Parascaris spp., which could be extrapolated to other ascarid parasites. Finally, it also provides preliminary transcriptomic data following drug exposure as a reference point for future studies of Parascaris spp.

A questionnaire study of parasite control in Thoroughbred and Standardbred horses in Australia

BACKGROUND

Information regarding parasite control practices currently used on Thoroughbred and Standardbred studs in Australia is lacking. Anthelmintic resistance (AR) is a global problem which has implications for equine health and welfare.

OBJECTIVES

To identify parasite control practices currently used on horse studs in Australia and investigate the frequency of use of management factors that have been associated with the likelihood of promoting or delaying AR.

STUDY DESIGN

Questionnaire study of equine parasite control on Thoroughbred and Standardbred studs in Australia.

METHODS

An online questionnaire was emailed to 300 studs in Australia. Information obtained included property details, grazing management, anthelmintic use, non-chemotherapeutic parasite control practices, use of faecal egg counts (FECs) and perceptions of AR.

RESULTS

Seventy-five completed questionnaires were received (25% response rate). Macrocyclic lactones (MLs) were the most commonly administered anthelmintics in mares and foals and less than 5% of respondents used targeted treatment regimens. The implementation of pasture hygiene practices was variable. The majority of respondents (97%) considered AR to be important; however, few respondents were aware of the use of FEC reduction tests for monitoring of drug efficacy.

MAIN LIMITATIONS

The potential for nonresponse bias was the main limitation of this study.

CONCLUSIONS

Parasite control strategies on Australian stud farms remain over-reliant on anthelmintic use. The frequent use of MLs is of concern for the increased selection pressure for AR. There is a lack of awareness of the importance of non-chemotherapeutic strategies in integrated approaches to parasite control aimed at delaying the development of AR. This study highlights the need for greater veterinary involvement in the implementation of more sustainable parasite control practices with greater emphasis placed on surveillance through FEC testing.

Equine helminth prevalence and management practices on Australian properties as shown by coprological survey and written questionnaire

Context Parasite control is an essential part of a broader equine health-management strategy and is often completely administered by the horse owner, with little or no supporting evidence on which to base decisions. Practical and sound advice relies on knowledge of the resident parasite species, the anthelmintic resistance status of important species, and the strategies currently being utilised by owners and managers of horses. Much of this farm-level information is lacking in the Australian literature. Aims The present study aimed to gather both farm- and horse-level prevalence data for four important equine helminth species and to gather information on the current worm-management practices conducted on Australian horse farms. Methods We conducted a coprological survey of cyathostomins, Strongylus vulgaris, Parascaris spp. and equine tapeworm on 102 horse properties, using a combination of classical and molecular parasitological methods, including a tapeworm polymerase chain reaction developed as part of the study. A questionnaire canvasing horse owners on internal parasite-control practices was also distributed. Key results Cyathostomin were present on all farms surveyed and S. vulgaris, despite being considered rare, was present on 7.8% (95% CI: 3.9–15.0) of farms. The prevalence of Parascaris spp. and equine tapeworm was 33.3% (95% CI: 19.6–50.6) and 3.9% (95% CI: 1.5–10.1) respectively. Questionnaire responses showed that the majority (85.0%) of horse owners administer anthelmintics at regular intervals of 12 weeks or less, and only 2.6% utilise faecal egg counts to inform treatment decisions. Conclusions Prevalence data confirmed the endemic nature of cyathostomin and P. equorum infections, as well as low levels of tapeworm and S. vulgaris infections on Australian horse farms. Worm-management practices were reminiscent of traditional interval-style treatment regimens that rely heavily on macrocyclic lactone anthelmintics. Implications These results suggest a need for more strategic approaches to internal-parasite control in horses to slow the development of anthelmintic resistance. Such programs need to consider the risk of re-establishment of the pathogenic S. vulgaris in significant numbers.

Risk factors for equine intestinal parasite infections and reduced efficacy of pyrantel embonate against Parascaris sp

Gastrointestinal parasites, Parascaris sp. and strongyles, are common in young horses worldwide and control of these parasites is challenged by increasing anthelmintic resistance. Our aim was to identify risk factors for these infections as well as to assess the efficacy of fenbendazole (dose 7.5 mg/kg) and pyrantel embonate (dose 19 mg/kg) against Parascaris sp. We also evaluated association between owner observed symptoms and patent infections with these parasites. Fecal samples were collected from 367 young horses in Finland and a questionnaire study was conducted. Fecal egg counts were performed by Mini-FLOTAC® method. Univariable logistic regression models using patent infection status (Yes/No), separately for Parascaris sp. and strongyle infections as an outcome were run initially to screen potential risk factors collected by the questionnaire. After the initial screening, multiple logistic regression models were constructed and run to account for correlated data structure, risk factors and potential confounders simultaneously. Two significant risk factors for a patent Parascaris sp. infection were found: breeding farm size (p = 0.028) and frequency of horse movements (p = 0.010). Horses originating from large breeding farms were more likely (OR = 2.47, 95% confidence interval (CI) 1.10-5.51) to shed Parascaris sp. eggs upon relocation to training stables compared to horses originating from small breeding farms. Horses living in farms with frequent horse movements to other premises had higher odds (OR = 3.56, 95% CI: 1.35-9.39) of a patent Parascaris sp. infection compared to farms with less frequent horse movements. Risk factors for patent strongyle infection included age (p < 0.001) and season (p = 0.017). Horses were less likely (OR = 0.27, 95% CI: 0.10 - 0.66) to shed strongylid eggs during the spring compared to the winter. Horses excreting over 200 ascarid eggs per gram were included in the anthelmintic efficacy trial. A mean FECR less than 90% was interpreted as presence of anthelmintic resistance. The mean FECR was 98.5% (95% CI: 95.8-100) and 68.0% (95% CI: 52.7-83.3) in the fenbendazole (n = 31) and pyrantel (n = 26) treatment groups, respectively. In conclusion, we identified two new risk factors for patent Parascaris sp. infection; breeding farm size and frequency of horse movements. Reduced efficacy of pyrantel against Parascaris sp. was observed for the second time in Europe. A relatively high Parascaris sp. prevalence in yearlings (34%) and two-year-olds (20%) was observed, which has not been reported earlier. An association between symptoms and a patent Parascaris sp. infection was observed in foals.

The application of faecal egg count results and statistical inference for clinical decision making in foals

This study investigated the impact of variability in Parascaris spp. and strongyle faecal egg counts (FEC) from foals on treatment decision-making and detection of a patent infection. A single faecal sample was collected once daily for three days from 53 foals and a FEC was performed on three separate portions of each sample (total of nine egg counts per foal). Differences in the decision to administer an anthelmintic using the results of a single count (C₁), the mean of three (X¯_1-3) or nine counts (X¯_1-9) and the upper 5% confidence limit of the gamma confidence interval (CI) of the estimate of the distribution mean (μ) from three (UCL_1-3) and nine counts (UCL_1-9) were determined for a range of egg count thresholds. The UCL_1-9 was used as the best estimate of μ, hypothesis testing for treatment and the comparison of treatment decision-making using C₁, X¯_1-3, X¯_1-9 and UCL_1-3. The results of this study demonstrated that a point estimate (C₁ or X¯_1-3) was of limited value for estimating the distribution mean of egg counts in faeces and there was overall poor agreement in treatment decision-making for individual foals using C₁ compared with UCL_1-9. Of the foals with C₁ of zero eggs per gram, 54% and 47% had Parascaris and strongyle eggs in subsequent counts, respectively. The egg density in faeces is inhomogeneous, resulting in considerable variability in egg count results for an individual foal: between faecal piles, different portions of a faecal pile and days. The use of the negative binomial distribution CI for μ takes this variability into account and is recommended for use when interpreting FEC data from horses.

Systematic review of gastrointestinal nematodes of horses from Australia

Background

Equine gastrointestinal nematodes (GINs) have been the subject of intermittent studies in Australia over the past few decades. However, comprehensive information on the epidemiology of equine GINs, the efficacy of available anthelmintic drugs and the prevalence of anthelmintic resistance (AR) in Australasia is lacking. Herein, we have systematically reviewed existing knowledge on the horse GINs recorded in Australia, and main aspects of their pathogeneses, epidemiology, diagnoses, treatment and control.

Methods

Six electronic databases were searched for publications on GINs of Australian horses that met our inclusion criteria for the systematic review. Subsets of publications were subjected to review epidemiology, diagnoses, pathogeneses, treatment and control of GINs of horses from Australia.

Results

A total of 51 articles published between 1950 to 2018 were included. The main GINs reported in Australian horses were cyathostomins (at least 28 species), Draschia megastoma, Habronema muscae, H. majus, Oxyuris equi, Parascaris equorum, Strongyloides westeri and Trichostrongylus axei across different climatic regions of Queensland, New South Wales, Victoria, and Western Australia. Nematodes are diagnosed based on the traditional McMaster egg counting technique, though molecular markers to characterise common GINs of equines were characterised in 1990s. The use of anthelmintic drugs remains the most widely-used strategy for controlling equine GIN parasites in Australia; however, the threshold of faecal egg count that should trigger treatment in horses, remains controversial. Furthermore, anthelmintic resistance within GIN population of horses is becoming a common problem in Australia.

Conclusions

Although GINs infecting Australian horses have been the subject of occasional studies over the past few decades, the effective control of GIN infections is hampered by a generalised lack of knowledge in various disciplines of equine parasitology. Therefore, coordinated and focused research is required to fill our knowledge gaps in these areas to maximise equine health and minimise economic losses associated with the parasitic infections in Australia.

Electronic supplementary material

The online version of this article (10.1186/s13071-019-3445-4) contains supplementary material, which is available to authorized users.

Anthelmintic efficacy of single active and combination products against commonly occurring parasites in foals

Parasite control in foals is complicated by the concurrent presence of biologically diverse parasites with differing levels of anthelmintic resistance. Several combination anthelmintic products are available for use in horses, but information on their efficacies against important equine parasites is scarce. Two trials were performed in New Zealand during 2008 and 2011 on four different farms with substantially different anthelmintic treatment histories. The first trial evaluated the efficacy of an ivermectin/praziquantel/oxibendazole combination, a single active oxibendazole, and a single-active macrocyclic lactone (ML) in 49 foals located on three farms. The second trial evaluated two combination anthelmintic products and three single-active ML products and enrolled a total of 110 foals on three farms. Foals in the second trial were allocated to one of six anthelmintic treatment groups; oxfendazole/pyrantel embonate, pyrantel embonate/ivermectin/praziquantel, ivermectin/praziquantel, abamectin/praziquantel, moxidectin/praziquantel, and a placebo-treated control. In both trials, foals were monitored monthly prior to treatment, and fecal egg counts (FECs) of Parascaris spp., strongylid, and Strongyloides westeri were determined. A "rolling enrolment" process was implemented whereby foals were systematically allocated to a treatment group and treated with the corresponding anthelmintic following the first appearance of Parascaris spp. eggs in the faeces. A generalised linear model was used to evaluate the effect of farm and treatment on Day14 FEC (ln) for each parasite. Three different FECR calculation methods were employed as follows; i) FECR(T) pre and post treatment ii) FECR (C) in the treated group compared with control, and iii) FECR (P) pre- and post- treatment in the treated and control groups. Across both trials, treatment with ML single active products failed to achieve >95% reduction in Parascaris spp. FEC on two of three farms. The pyrantel embonate/oxfendazole and ivermectin/ praziquantel/oxibendazole combinations demonstrated full efficacy against Parascaris spp. This is in contrast to the anti-strongylid efficacies determined, where the pyrantel embonate/oxfendazole combination and single active oxibendazole had reduced efficacy on one farm, while the macrocyclic lactones generally had good efficacy. Strongyloides egg counts were sporadic in both trials, and allowed limited insight into anthelmintic efficacy. The study illustrated the importance of keeping an untreated or placebo-treated control group in studies evaluating anti-Parascaris efficacy and it demonstrated the utility of a rolling enrolment procedure, where foals are enrolled over the course of a defined period of time. Furthermore, the study demonstrated the value of a farm specific FECR monitoring programme and the complexity of parasite control in foals, where combination anthelmintic products can be employed to target multiple species of parasites.

Efficacy of moxidectin and an ivermectin-praziquantel combination against ascarids, strongyles, and tapeworms in Thoroughbred yearlings in field tests on a farm in Central Kentucky in 2016

Field tests were performed on Thoroughbred yearlings (n=143), evaluating efficacy of moxidectin (MOX) against ascarids and strongyles and the efficacy of an ivermectin (IVM)-praziquantel (PRAZ) combination against those nematodes and tapeworms on a farm in Central Kentucky. The study was started on March 1, 2016 and completed on August 23, 2016. Fecal samples were collected from yearlings every two weeks for counts of ascarid and strongyle eggs per gram of feces (EPGs) and for determining the presence of tapeworm eggs. MOX was given to 88 yearlings on March 1; 55 yearlings were nontreated controls on this date but were treated two weeks later with MOX. On June 15, 2016, all yearlings (n=87) remaining on the farm were treated with IVM-PRAZ combination. Ascarids were present in low numbers for MOX-treated horses, and the drug had virtually no effect. The low number of ascarid infected horses before any treatment during the study was most likely due to age related immunity. Efficacy against strongyles was alike for both MOX and the IVM- PRAZ combination. At two weeks post-treatment, strongyle EPG values were reduced over 90%, started increasing at four weeks post-treatment, and returned to near pre-treatment values at six weeks post-treatment. Tapeworm efficacy of the IVM-PRAZ treatment was 96% at two weeks and was maintained for the entire ten-week post-treatment examination period.