First Report of Resistance to Ivermectin in Parascaris univalens in Iceland

Establishment of the HPLC fluorescence detection method for plasma trace ivermectin and its pharmacokinetics in Bactrian camel

BACKGROUND AND OBJECTIVE

Ivermectin (IVM), a widely used veterinary anthelmintic, lacks recommended doses for Bactrian camels. This study aims to establish its pharmacokinetics in Bactrian camels, comparing with other livestock.

METHODS

A method for high-performance liquid chromatography fluorescence detection of IVM in plasma was developed.

RESULTS

IVM exhibited linear scaling (y = 0.6946x + 0.0088, R2 = 0.9988) within 0.025-5 ng/mL, with a lower limit of quantification of 25.00 pg/mL, high recovery (>70%) and low RSD (<7%). In Bactrian camels, IVM injection showed a low Cmax, extended Tmax and apparent secondary absorption compared to cattle and sheep.

CONCLUSIONS

Slow absorption and widespread distribution were observed, with peak concentration and area under the curve correlating positively with the dose. This study provides insights into IVM pharmacokinetics in Bactrian camels, informing dose determination and highlighting potential metabolic differences compared to other livestock.

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.

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.

Horse and donkey parasitology: differences and analogies for a correct diagnostic and management of major helminth infections

In June 2022, at the XXXII Conference of the Italian Society of Parasitology, the parallels of the main endoparasitic infections of horses and donkeys were discussed. Although these 2 species are genetically different, they can be challenged by a similar range of parasites (i.e. small and large strongyles, and Parascaris spp.). Although equids can demonstrate some level of resilience to parasites, they have quite distinct helminth biodiversity, distribution and intensity among different geographical locations and breeds. Heavily infected donkeys may show fewer clinical signs than horses. Although parasite control is primarily provided to horses, we consider that there may be a risk of drug-resistance parasitic infection through passive infection in donkeys when sharing the same pasture areas. Knowing the possible lack of drug efficacy (<90 or 80%), it is advocated the use of selective treatment for both species based on fecal egg counts. Adult horses should receive treatment when the threshold exceeds 200–500 eggs per gram (EPG) of small strongyles. Moreover, considering that there are no precise indications in donkeys, a value >300 EPG may be a safe recommendation. We have highlighted the main points of the discussion including the dynamics of helminth infections between the 2 species.

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.

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.

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.

Comparative studies on faecal egg counting techniques used for the detection of gastrointestinal parasites of equines: A systematic review

Faecal egg counting techniques (FECT) form the cornerstone for the detection of gastrointestinal parasites in equines. For this purpose, several flotation, centrifugation, image- and artificial intelligence-based techniques are used, with varying levels of performance. This review aimed to critically appraise the literature on the assessment and comparison of various coprological techniques and/or modifications of these techniques used for equines and to identify the knowledge gaps and future research directions. We searched three databases for published scientific studies on the assessment and comparison of FECT in equines and included 27 studies in the final synthesis. Overall, the performance parameters of McMaster (81.5%), Mini-FLOTAC® (33.3%) and simple flotation (25.5%) techniques were assessed in most of the studies, with 77.8% of them comparing the performance of at least two or three methods. The detection of strongyle, Parascaris spp. and cestode eggs was assessed for various FECT in 70.4%, 18.5% and 18.5% studies, respectively. A sugar-based flotation solution with a specific gravity of ≥1.2 was found to be the optimal flotation solution for parasitic eggs in the majority of FECT. No uniform or standardised protocol was followed for the comparison of various FECT, and the tested sample size (i.e. equine population and faecal samples) also varied substantially across all studies. To the best of our knowledge, this is the first systematic review to evaluate studies on the comparison of FECT in equines and it highlights important knowledge gaps in the evaluation and comparison of such techniques.

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.