Lack of efficacy of monepantel against Teladorsagia circumcincta and Trichostrongylus colubriformis

Concurrent use of two dual-combination drenches containing monepantel/abamectin and oxfendazole/levamisole in sheep: effect on marker residues 21 and 28 days after administration

AIMS

To determine the concentration, in comparison with the maximum residue limit (MRL), of anthelmintic marker residues in the target tissues (liver and fat) of sheep treated concurrently with two oral drenches, one containing monepantel and abamectin and the other oxfendazole and levamisole.

METHODS

On day 0 of the study, 12 sheep (six male and six female; 8-9-months old) were dosed according to individual body weight determined the day prior. Zolvix Plus (dual-active oral drench containing 25 g/L monepantel and 2 g/L abamectin) was administered to all animals prior to administration of Scanda (dual-active oral drench containing 80 g/L levamisole hydrochloride and 45.3 g/L oxfendazole). Six sheep (three male and three female) were slaughtered 21 and 28 days after treatment and renal fat and liver samples were collected.Using validated methods, analyses for monepantel sulfone, abamectin, levamisole and oxfendazole (expressed as total fenbendazole sulfone following conversion of the combined concentrations of oxfendazole, fenbendazole and fenbendazole sulfone) were performed on liver samples while renal fat specimens were analysed for monepantel sulfone and abamectin residues only. Detected concentrations were compared to the established MRL in sheep for each analyte determined by the Ministry for Primary Industries.

RESULTS

All residues detected in samples of liver and fat collected 21 and 28 days after treatment were below the MRL for each analyte. All liver samples collected on day 21 had detectable monepantel sulfone (mean 232 (min 110, max 388) μg/kg) and oxfendazole (mean 98.7 (min 51.3, max 165) μg/kg) residues below the MRL (5,000 and 500 μg/kg, respectively). Monepantel sulfone (mean 644 (min 242, max 1,119) μg/kg; MRL 7,000 μg/kg) residues were detected in 6/6 renal fat samples. Levamisole residues were detected in 3/6 livers (mean 40.0 (min 14.3, max 78.3) μg/kg; MRL 100 μg/kg), and abamectin residues in 1/6 livers (0.795 μg/kg; MRL 25 μg/kg) and 2/6 fat samples, (mean 0.987 (min 0.514, max 1.46) μg/kg; MRL 50 μg/kg) 21 days after treatment.

CONCLUSION AND CLINICAL RELEVANCE

These results suggest that concurrent administration of Zolvix Plus and Scanda to sheep is unlikely to result in an extended residue profile for any of the active ingredients, with all analytes measured being under the approved New Zealand MRL 21 days after treatment. This work was not completed in line with guidance for establishing official residue profiles, nor is it sufficient to propose a new withholding period.

Revisiting anthelmintic resistance in sheep flocks from São Paulo State, Brazil

Haemonchus contortus and Trichostrongylus colubriformis are the most important gastrointestinal nematodes causing serious losses in sheep production of tropical and subtropical regions. Prophylaxis of gastrointestinal nematode infections is based on anthelmintics use, but their frequent administration selects multiple-resistant parasites. To evaluate how the situation has changed over the last decades, the anthelmintic resistance status of gastrointestinal nematodes in sheep flocks was assessed in the current study and compared to previous surveys. In each one of the 15 flocks evaluated, animals (n ≥ 7) were allocated into at least five groups and treated as follows: 1) untreated control; 2) albendazole; 3) levamisole; 4) ivermectin; and 5) monepantel. If more animals were available, two additional groups were included: 6) closantel, and 7) moxidectin. The faecal egg count reduction test (FECRT) was carried out to evaluate the pre- and post-treatment using the SHINY tool. Haemonchus spp. was the most prevalent nematode from faecal cultures. The mean efficacy of albendazole was 40%. Only in two farms, levamisole presented a relatively high percentage of reduction in the FECRT about 90%, while ivermectin and moxidectin presented the worst mean efficacy of 34% and 21% among all farms, respectively. Like other anthelmintics, closantel demonstrated low efficacy (63%) across all farms evaluated. Monepantel presented an overall mean efficacy of 79%, but it was the only anthelmintic that presented efficacy ≥95%, in five farms. The results revealed that gastrointestinal nematodes with multiple anthelmintic resistance were prevalent in all 15 sheep herds. The research suggests that nematodes are becoming more and more resistant to various anthelmintic compounds, which has made the problem worse. This circumstance highlights the necessity to put into practice sustainable and long-lasting methods to prevent gastrointestinal nematode infections in sheep husbandry.

Rapid, automated quantification of Haemonchus contortus ova in sheep faecal samples

Haemonchus contortus is one of the most pathogenic nematodes affecting small ruminants globally and is responsible for large economic losses in the sheep and goat industry. Anthelmintic resistance is rampant in this parasite and thus parasite control programs must account for drug efficacy on individual farms and, sometimes, whether H. contortus is the most prevalent trichostrongylid. Historically, coproculture has been the main way to determine the prevalence of H. contortus in faecal samples due to the inability to morphologically differentiate between trichostrongylid egg types, but this process requires a skilled technician and takes multiple days to complete. Fluoresceinated peanut agglutinin (PNA) has been shown to specifically bind H. contortus and thus differentiate eggs based on whether they fluoresce, but this method has not been widely adopted. The ParasightTM System (PS) fluorescently stains helminth eggs in order to identify and quantify them, and the H. contortus PNA staining method was therefore adapted to this platform using methodology requiring only 20 min to obtain results. In this study, 74 fecal samples were collected from sheep and analyzed for PNA-stained H. contortus, using both PS and manual fluorescence microscopy. The percentage of H. contortus was determined based on standard total strongylid counts with PS or brightfield microscopy. Additionally, 15 samples were processed for coproculture with larval identification, and analyzed with both manual and automated PNA methods. All methods were compared using the coefficient of determination (R2) and the Lin's concordance correlation coefficient (ρc). ParasightTM and manual PNA percent H. contortus results were highly correlated with R2 = 0.8436 and ρc = 0.9100 for all 74 fecal samples. Coproculture versus PS percent H. contortus were also highly correlated with R2 = 0.8245 and ρc = 0.8605. Overall, this system provides a rapid and convenient method for determining the percentage of H. contortus in sheep and goat fecal samples without requiring specialized training.

Secretory IgA as Biomarker for Gastrointestinal Nematodes Natural Infection in Different Breed Sheep

Specific IgA antibody has been shown to play an important role in resistance to gastrointestinal nematode (GIN) infections in sheep, particularly in Teladorsagia circumcincta parasitosis. In some breeds, negative associations have been shown between IgA levels and worm burden in experimentally infected sheep. In the present study, we have studied the relationship between IgA levels in naturally infected sheep (582 ewes in total; 193 younger than one year old and 389 older than one year old) and fecal egg count (FEC) in the Assaf, Castellana, and Churra breeds. ELISA assays were performed to measure IgA levels against the somatic antigen of T. circumcincta third larval stage (L₃) and a 203-amino-acid fragment of the protein disulfide isomerase from the same GIN species. A multilevel random intercept model was developed to predict the infection risk according to age or breed. Spearman's correlation rank was used for statistical analysis. The prediction model showed that breed was not an influential factor in this study, although the Assaf breed could be considered slightly more susceptible than the others. In addition, age affected the infection risk, with the young ewes more susceptible to infection than the adult groups, except for the Castellana breed, whose risk of infection was similar at all ages. The most significant positive association was found between FEC and IgA measured in the nasal secretions of young ewes using both antigens (Rho = 0.5; p = 0.00); the correlation of FEC with IgA in serum was moderately significant (Rho = 0.306; p = 0.00). Comparing both antigens, the protein disulfide isomerase antigen was less reactive than the somatic antigen from L₃. In conclusion, under natural conditions, specific IgA against GIN was positively associated with FEC in sheep, with nasal secretions from young animals being the sample where this association is stronger, which, therefore, could be used as a marker of infection in further studies.

Monepantel-based anthelmintic combinations to optimize parasite control in cattle

Improvement in the use of existing anthelmintics is a high priority need for the pharmaco-parasitology research field, considering the magnitude and severity of anthelmintic resistance as an important issue in livestock production. In the work described here, monepantel (MNP) was given alone or co-administered with either macrocyclic lactone (ML) or benzimidazole (BZ) anthelmintics to calves naturally infected with ML- and BZ-resistant gastrointestinal (GI) nematodes on two different commercial cattle farms. Both pharmacokinetic (PK) and efficacy assessments were performed. On Farm A, male calves (n = 15 per group) were treated with either MNP orally (2.5 mg/kg), IVM s.c. (0.2 mg/kg), ricobendazole (RBZ) s.c. (3.75 mg/kg) or remained untreated. On Farm B, eight groups (n = 15) of male calves received treatment with either: MNP, abamectin (ABM, oral, 0.2 mg/kg), RBZ (s.c., 3.75 mg/kg), albendazole (ABZ, oral, 5 mg/kg), MNP+ABM, MNP+RBZ, MNP+ABZ (all at the above-mentioned routes and doses) or remained untreated. Seven animals from each treated group (Farm B) were randomly selected to perform the PK study. MNP and its metabolite monepantel sulphone (MNPSO2) were the main analytes recovered in plasma after HPLC analysis. The combined treatments resulted in decreased systemic exposures to MNP parent drug compared with that observed after treatment with MNP alone (P < 0.05). However, the systemic availability of the main MNP metabolite (MNPSO2) was unaffected by co-administration with either ABM, RBZ or ABZ. Efficacies of 98% (Farm A) and 99% (Farm B) demonstrated the high efficacy of MNP given alone (P < 0.05) against GI nematodes resistant to ML and BZ in cattle. While the ML (IVM, ABM) failed to control Haemonchus spp., Cooperia spp. and Ostertagia spp., MNP achieved 99% to 100% efficacy against those nematode species on both commercial farms. However, MNP alone failed to control Oesophagostomum spp. (60% efficacy) on Farm A. The co-administered treatments MNP+ABZ and MNP+RBZ reached a 100% reduction against all GI nematode genera. In conclusion, the oral treatment with MNP should be considered to deal with resistant nematode parasites in cattle. The use of MNP in combination with BZ compounds could be a valid strategy to extend its lifespan for use in cattle as well as to reverse its poor activity against Oesophagostomum spp.

[Five past twelve - the resistance situation in small ruminant gastrointestinal nematodes in Germany]

Anthelmintic resistance has reached alarming levels worldwide and already seriously threatens pasture-based small ruminant production in certain geographic regions. The situation in Europe has also dramatically deteriorated in the last decade. This review provides an overview of the occurrence of anthelmintic resistance in small ruminants with a particular focus on Germany and its neighbouring countries. It also covers mechanisms leading to the development and spread of anthelmintic resistance, and recommendations for a responsible use of anthelmintics in veterinary practice.

Nematicidal Characterization of Solanum nigrum and Mentha arvensis Leaf Extracts Using Caenorhabditis elegans as a Model Organism

Considering foremost global issues instigated by parasitic nematodes, Solanum nigrum (S. nigrum) and Mentha arvensis (M. arvensis) nematicidal potential at the gene level has been explored herein. Methanol, ethyl acetate, chloroform, n-hexane, and distilled water were used for extract preparation. Caenorhabditis elegans (C. elegans) was used as the model organism. Nematicidal and anti-egg hatching assays, fluorescence microscopy, and quantitative real-time PCR were done. S. nigrum chloroform (LD₅₀ = 1.21 mg/mL) and M. arvensis methanol (LD₅₀ = 2.47 mg/mL) extracts exhibited excellent nematicidal potential. Both plants showed potent anti-egg hatching activity (1 mg/mL). S. nigrum methanol and M. arvensis ethyl acetate extracts showed high apoptotic effect in muscles, gonads, and uterus (eggs). Stress genes, that is, gst-4, hsp-16.2, and gpdh-1 were highly expressed in affected C. elegans (treated with S. nigrum and M. arvensis leaf extracts) when compared with normal C. elegans. Phytochemicals and bioactive compounds present in plants may be the major cause of their excellent nematicidal potential, which further confirmed that both plants could be an alternative candidate(s) for novel broad-scale anthelmintic drug(s).

Carbohydrate larval antigen (CarLA IgA) responses to mixed species nematode infection in pasture grazed Angora goats

The genetics of indicator traits for resistance of Angora goats to gastrointestinal nematode parasite infections, and their relationships with productivity traits, were investigated on a commercial mixed-enterprise farm in the eastern North Island of New Zealand. Faecal egg counts (FEC), specific Immunoglobulin A (IgA) and Immunoglobulin G (IgG) antibody titres against carbohydrate larval antigen (CarLA) in saliva, live weight and fleece weights were recorded from 278 goats of 19-20 months of age, run as four separate mobs (breeding bucks, castrated males (wethers), or 2 groups of breeding does). Summary statistics showed the mobs differed significantly in liveweight, log_e (FEC+50), log_e (IgA) and log_e (IgG). Genetic parameters were estimated using an animal model with repeated records where appropriate, after adjusting for the different contemporary animal groups, using the restricted maximum likelihood (REML) package. Heritability estimates from repeated measures were 0.19 ± 0.16 for FEC, 0.28 ± 0.16 for CarLA specific IgA and 0.23 ± 0.15 for CarLA specific IgG. The CarLA specific IgA response was negatively genetically correlated with FEC (-0.99 ± 0.31) suggesting that it could be used as a selection tool for breeding resistant animals. Although the genetic and phenotypic correlations between CarLA IgA and IgG were high and significant, the analysis between log_e (FEC+50) and log_e CarLA IgG did not converge. Further, both FEC and CarLA IgA showed significant and favourable genetic correlations with live weight. In contrast, CarLA IgG showed an unfavourable phenotypic correlation with liveweight. While this is only a preliminary study, the results do suggest that the immunoassay measuring salivary CarLA IgA response may have utility as a selection tool for parasite resistance in some breeds of goats.

Antiparasitic Tannin-Rich Plants from the South of Europe for Grazing Livestock: A Review

Internal parasites are one of the main causes of health threats in livestock production, especially in extensive livestock farming. Despite the environmental toxic effects (loss of dung beetles, biodiversity, and other issues) and resistance phenomenon derived from their prolonged use, anti-parasitic chemical pharmaceuticals are frequently used, even in organic farming. Such a situation within the context of climate change requires urgent exploration of alternative compounds to solve these problems and apparent conflicts between organic farming objectives regarding the environment, public health, and animal health. This review is focused on some plants (Artemisia spp., Cichorium intybus L., Ericaceae family, Hedysarum coronarium L., Lotus spp., Onobrychis viciifolia Scop.) that are well known for their antiparasitic effect, are voluntarily grazed and ingested, and can be spontaneously found or cultivated in southern Europe and other regions with a Mediterranean climate. The differences found between effectiveness, parasite species affected, in vitro/in vivo experiments, and active compounds are explored. A total of 87 papers where antiparasitic activity of those plants have been studied are included in this review; 75% studied the effect on ruminant parasites, where gastrointestinal nematodes were the parasite group most studied (70%), and these included natural (31%) and experimental (37%) infections.

Sensitivity of Haemonchus contortus to anthelmintics using different in vitro screening assays: a comparative study

BACKGROUND

Helminthiasis and resistance to commercial anthelmintic compounds are major causes of economic losses for livestock producers, resulting in an urgent need for new drugs and reliable in vitro screening tests capable of detecting potentially active products. Considering this, a series of novel benzimidazole derivatives (5-methylbenzimidazole 1,2-disubstituted, 5-carboxybenzimidazole, 5-methylbenzimidazole 2-one) was screened on exsheathed L3 (xL3) and on the adult stage of Haemonchus contortus (Kirby anthelmintic-susceptible McMaster isolate).

METHODS

This work presents the set-up of an automated motility assay on the xL3 stage of H. contortus using an infrared tracking device (WMicrotracker One) together with a larval development test (xL3 to L4) and a motility assay on the adult stage of H. contortus. A comparative study of the sensitivity of these in vitro assays using commercial anthelmintics with different mechanisms of action was carried out, also evaluating anthelmintic activity of a series of novel benzimidazole derivatives.

RESULTS

The automated xL3 assay had the great advantage of being able to analyze many compounds simultaneously, but it showed the limitation of having lower sensitivity, requiring higher concentrations of the commercial anthelmintics tested compared to those needed for the adult motility or development assays. Although none of the novel 1,2,5-tri-substituted benzimidazole derivatives could significantly decrease the motility of xL3s, one of them (1e) significantly affected the development of xL3s to L4, and five new compounds (1b, 1d, 1e, 2a and 2c) reduced the motility of H. contortus adult stage.

CONCLUSIONS

The analysis of the results strongly suggests that the in vitro xL3 to L4 development test, particularly for the L4 stage, could be closer to the pharmacological sensitivity of the adult stage of H. contortus (target of interest) for commercial anthelmintic selected, with different mechanisms of action, and for the series of benzimidazole derivatives assayed. Therefore, an automated motility assay on L4 using the infrared tracking device is being set up. Further studies will be conducted to evaluate the in vivo anthelmintic activity of the most active novel benzimidazole derivatives.

Extensive Sheep and Goat Production: The Role of Novel Technologies towards Sustainability and Animal Welfare

Simple Summary

New technologies have been recognized as valuable in controlling, monitoring, and managing farm animal activities. It makes it possible to deepen the knowledge of animal behavior and improve animal welfare and health, which has positive implications for the sustainability of animal production. In recent years, successful technological developments have been applied in intensive farming systems; however, due to challenging conditions that extensive pasture-based systems show, technology has been more limited. Nevertheless, awareness of the available technological solutions for extensive conditions can increase the implementation of their adoption among farmers and researchers. In this context, this review addresses the role of different technologies applied to sheep and goat production in extensive systems. Examples related to precision livestock farming, omics, thermal stress, colostrum intake, passive immunity, and newborn survival are presented; biomarkers of metabolic diseases and parasite resistance breeding are discussed.

Abstract

Sheep and goat extensive production systems are very important in the context of global food security and the use of rangelands that have no alternative agricultural use. In such systems, there are enormous challenges to address. These include, for instance, classical production issues, such as nutrition or reproduction, as well as carbon-efficient systems within the climate-change context. An adequate response to these issues is determinant to economic and environmental sustainability. The answers to such problems need to combine efficiently not only the classical production aspects, but also the increasingly important health, welfare, and environmental aspects in an integrated fashion. The purpose of the study was to review the application of technological developments, in addition to remote-sensing in tandem with other state-of-the-art techniques that could be used within the framework of extensive production systems of sheep and goats and their impact on nutrition, production, and ultimately, the welfare of these species. In addition to precision livestock farming (PLF), these include other relevant technologies, namely omics and other areas of relevance in small-ruminant extensive production: heat stress, colostrum intake, passive immunity, newborn survival, biomarkers of metabolic disease diagnosis, and parasite resistance breeding. This work shows the substantial, dynamic nature of the scientific community to contribute to solutions that make extensive production systems of sheep and goats more sustainable, efficient, and aligned with current concerns with the environment and welfare.

Suppressive treatment with monepantel and the fast selection for phenotypically resistant trichostrongylids of sheep

Gastrointestinal parasite control has been a major challenge to livestock due to the failure of anthelmintic treatments. Monepantel (MNT) was introduced in 2009 as an alternative treatment option showing a new mechanism of action against nematode parasites. To study the response of MNT in a suppressive regime, 45-Suffolk and White Dorper naturally infected sheep were divided into one of three groups, G1: control – with no treatment, G2: MNT at 2.5 mg kg−1 live weight (LW) PO every 30 days, and G3: MNT at 4.0 mg kgLW−1 PO every 30 days for 6 months. Every 15 days, the animals were individually weighed (body weight, BW) and checked for Famacha (FMC) and body condition score (BCS). The efficacy of MNT was evaluated weekly by fecal egg count (FEC) every month. FEC showed >97% efficacy at the start of the experiment, revealing a significant reduction for G2 (28%) and G3 (39%) in the following months. There was no treatment, BW or BCS effect between treatments; however, there was a period (P < 0.0001) and a treatment vs period interaction (P < 0.0001) for BW. The data revealed that MNT at a therapeutic and suppressive dose had a non-linear polynomial efficacy regression (R2) of 0.988 and 0.992, respectively. This original experiment demonstrates how short-interval and suppressive MNT treatments would rapidly select Haemonchus contortus, showing a fast susceptible-resistance phenotypic population replacement. Therefore, it is suggested that MNT might be carefully used in parasite control programmes alongside other management strategies (i.e. FMC, BCS) to reduce treatment frequency and the selection process for resistance.

Most common inappropriate drug usage factors in anthelmintic treatment on sheep farms in Latvia

Background and Aim:

There is little understanding about antiparasitic drug prescription trends and implementation to reduce possible drug overuse or misuse worldwide. This study aimed to review sheep parasite control strategies and antiparasitic drug use habits in Latvia. To the best of the author’s knowledge, this is the first study in the world that describes how antiparasitic drugs are used and what are the most common drug usage errors in a sheep farm.

Materials and Methods:

A semi-structured questionnaire was designed to collect relevant information from face-to-face interviews to assess 22 sheep farmers’ knowledge and management procedures in farms. We collected information about animal feeding, herding, parasite diagnostics, and antiparasitic drug usage. The questionnaire summary included information on pasture use, parasite control management, and anthelmintic drug choice/use.

Results:

Only 36% of farms regularly managed parasite control by analyzing fecal samples for parasites, but prophylactic dewormingwas employed in all farms. Ivermectin, albendazole, levamisole, and monepantel were used on the farms and most of the farms were multidrug users; 77.3% of the farms used albendazole and 72.7% used ivermectin.

Conclusion:

The results indicated a lack of parasitological examination and parasite control of the flock, mostly empiric drug selection, incorrect dosing, inaccurate drug administration, drug storage, and use errors. A proactive approach to herd health planning, regular parasitic control, and prophylactic measures may benefit farmers and veterinarians.

Resistance of Haemonchus contortus to monepantel in sheep: first report in Espírito Santo, Brazil

The objective of this study was to provide the first report of resistance of Haemonchus contortus to monepantel in sheep in Espírito Santo. The study was conducted in a property with history of monepantel use since 2014 and register of low efficacy in studies conducted over the past few years with fecal egg count reduction test. Lambs born on the property (males and females aged approximately 100 days) were selected and after eggs per gram of feces (EPG) analysis on fecal samples, these were divided into two groups: a group treated with monepantel (2.5 mg / Kg) and a control group without anthelmintic treatment. Seven days later, the animals were euthanized to recover parasites from the gastrointestinal tract. The efficacy of the treatment was 61.35% against H. contortus, thus proving that anthelmintic resistance to monepantel was present.

A journey through 50 years of research relevant to the control of gastrointestinal nematodes in ruminant livestock and thoughts on future directions

This review article provides an historical perspective on some of the major research advances of relevance to ruminant livestock gastrointestinal nematode control over the last 50 years. Over this period, gastrointestinal nematode control has been dominated by the use of broad-spectrum anthelmintic drugs. Whilst this has provided unprecedented levels of successful control for many years, this approach has been gradually breaking down for more than two decades and is increasingly unsustainable which is due, at least in part, to the emergence of anthelmintic drug resistance and a number of other factors discussed in this article. We first cover the remarkable success story of the discovery and development of broad-spectrum anthelmintic drugs, the changing face of anthelmintic drug discovery research and the emergence of anthelmintic resistance. This is followed by a review of some of the major advances in the increasingly important area of non-pharmaceutical gastrointestinal nematode control including immunology and vaccine development, epidemiological modelling and some of the alternative control strategies such as breeding for host resistance, refugia-based methods and biological control. The last 50 years have witnessed remarkable innovation and success in research aiming to improve ruminant livestock gastrointestinal nematode control, particularly given the relatively small size of the research community and limited funding. In spite of this, the growing global demand for livestock products, together with the need to maximise production efficiencies, reduce environmental impacts and safeguard animal welfare - as well as specific challenges such as anthelmintic drug resistance and climate change- mean that gastrointestinal nematode researchers will need to be as innovative in the next 50 years as in the last.

Anthelmintic activity of a nanoformulation based on thiophenes identified in Tagetes patula L. (Asteraceae) against the small ruminant nematode Haemonchus contortus

The synthesis of thiophenic compounds, previously identified in Tagetes patula, revealed that 4-(5'-(hydroxymethyl)-[2,2'-bithiophene]-5-yl)but-3-yn-1-ol), or simply Thio1, has a pronounced in vitro anthelmintic effect against Haemonchus contortus, showing 100% efficacy in the egg hatch and larval development tests presenting EC₅₀ = 0.1731 mg.mL^-1 and EC₅₀ = 0.3243 mg.mL^-1, respectively. So, this compound was selected to preparation of a nanostructured formulation to be orally administered to Santa Inês sheep. In general, from the fecal egg count reduction test (FECRT), it was observed that the product kept the parasitic load in the digestive tract of the hosts stable, with eggs per gram of faeces (EPG) counts having a mean value < 3,000 (EPG_mean = 2167.1, efficacy = 36,45%), thus protecting the animals from health risks caused by a massive nematode infestation. To better understand the mode of action of this thiophene derivative, in silico molecular modeling studies were carried out with the glutamate-activated chloride channel (GluCl), a well-known molecular target of anthelmintic compounds. Based on the affinity score (GlideScore = -5.7 kcal.mol^-1) and the proposed binding mode, Thio1 could be classified as a potential GluCl ligand, justifying the promising results observed in the anthelmintic assays.

Current Status for Controlling the Overlooked Caprine Fasciolosis

Simple Summary

Retaining sustainable agricultural systems is essential to feed the expanding population. Helminth parasite infections impact livestock production values and yields, including infections in goats, which are often overlooked. There is a requirement to collate caprine-specific knowledge surrounding fasciolosis, caused by Fasciola hepatica and Fasciola gigantica (liver flukes). Current liver fluke control methods include drug application and pasture management. This review aims to outline goat-specific fasciolosis vaccine development and the potential for alternative control methods.

Abstract

The disease fasciolosis is caused by the liver flukes Fasciola hepatica and F. gigantica, which infect a wide range of mammals and production livestock, including goats. These flatworm parasites are globally distributed and predicted to cost the livestock industry a now conservative USD 3 billion per year in treatment and lowered on-farm productivity. Infection poses a risk to animal welfare and results in lowered fertility rates and reduced production yields of meat, milk and wool. This zoonotic disease is estimated to infect over 600 million animals and up to 2.4 million humans. Current and future control is threatened with the global emergence of flukes resistant to anthelmintics. Drug resistance calls for immediate on-farm parasite management to ensure treatments are effective and re-infection rates are kept low, while a sustainable long-term control method, such as a vaccine, is being developed. Despite the recent expansion of the goat industry, particularly in developing countries, there are limited studies on goat-focused vaccine control studies and the effectiveness of drug treatments. There is a requirement to collate caprine-specific fasciolosis knowledge. This review will present the current status of liver fluke caprine infections and potential control methods for application in goat farming.

Anthelmintic activity of aminoalcohol and diamine derivatives against the gastrointestinal nematode Teladorsagia circumcincta

Gastrointestinal nematodes (GIN) infections are a serious problem in livestock production due to the great economic losses they cause. Their control is increasingly difficult because of the rapid development of drug resistance and the limited number of available drugs. Therefore, this study evaluated 18 aminoalcohol and 16 diamine derivatives against eggs, first and third stage larvae from a susceptible and a resistant isolate of Teladorsagia circumcincta collected from sheep. The effectiveness of the in vitro anthelmintic activity of the compounds was evaluated using three different procedures: Egg Hatch Test (EHT), Larval Mortality Test (LMT) and Larval Migration Inhibition Test (LMIT). Those compounds with activities higher than 90 % in the initial screening at 50 μM were selected to determine their half maximal effective concentration (EC₅₀). In parallel, cytotoxicity assays were conducted on Caco2 and HepG2 cell lines to calculate Selectivity Indexes (SI) for each compound. The diamine 30 presented the best results in preventing egg hatching, displaying the lowest EC₅₀ value (1.01 ± 0.04 μM) of all compounds tested and the highest SI (21.21 vs. Caco-2 cells). For the LMIT, the diamine 34 showed the highest efficacy, with EC₅₀ values of 2.67 ± 0.08 and 3.02 ± 0.09 μM on the susceptible and resistant isolate of the parasite, respectively.

Monepantel pharmaco-therapeutic evaluation in cattle: Pattern of efficacy against multidrug resistant nematodes

The goal of the current work was to perform an integrated evaluation of monepantel (MNP) pharmacokinetics (PK) and pharmacodynamics, measured as anthelmintic efficacy, after its oral administration to calves naturally infected with GI nematodes resistant to ivermectin (IVM) and ricobendazole (RBZ) on three commercial farms. On each farm, forty-five calves were randomly allocated into three groups (n = 15): MNP oral administration (2.5 mg/kg); IVM subcutaneous (SC) administration (0.2 mg/kg); and RBZ SC administration (3.75 mg/kg). Eight animals from the MNP treated group (Farm 1) were selected to perform the PK study. Drug concentrations were measured by HPLC. The efficacy was determined by the faecal egg count reduction test (FECRT). MNP and MNP-sulphone (MNPSO₂) were the main analytes recovered in plasma. MNPSO₂ systemic exposure was markedly higher compared to that obtained for MNP. Higher Cmax and AUC values were obtained for the active MNPSO₂ metabolite (96.8 ± 29.7 ng/mL and 9220 ± 1720 ng h/mL) compared to MNP (21.5 ± 4.62 ng/mL and 1709 ± 651 ng h/mL). The MNPSO₂ AUC value was 6-fold higher compared to the parent drug. Efficacies of 99% (Farm 1), 96% (Farm 2) and 98% (Farm 3) demonstrated the high activity of MNP (P < 0.05) against GI nematodes resistant to IVM (reductions between 27 and 68%) and RBZ (overall efficacy of 75% on Farm 3). While IVM failed to control Haemonchus spp. and Cooperia spp., and RBZ failed to control Coooperia spp. and Ostertagia spp., MNP achieved 100% efficacy against Haemonchus spp., Cooperia spp. and Ostertagia spp. However, a low efficacy of MNP against Oesophagostomum spp. (efficacies ranging from 22 to 74%) was observed. In conclusion, oral treatment with MNP should be considered for dealing with IVM and benzimidazole resistant nematode parasites in cattle. The work described here reports for the first time an integrated assessment of MNP pharmaco-therapeutic features and highlights the need to be considered as a highly valuable tool to manage nematode resistant to other chemical families.

Nanotechnological Improvement of Veterinary Anthelmintics

Helminths infections are among the most important problems in animal health and husbandry. Moreover, zoonotic helminths endanger rural communities, particularly in developing countries. Helminthiasis are not only important in relation to the harmful effects of parasites; additional issues like anthelmintic resistance spread became more important over time. As new anthelmintic development takes many years and millions of dollars of investment, some strategies are currently focused on the modification of already available drugs, in order to improve their efficacy and overcome their limitations. In this field, nanotechnology has brought a novel approach, showing advantages like the regulation of the drug's delivery and kinetics, reaching of specific targets, and possibilities to avoid the systemic spread and side effects. Taking this into account, the present review aims to introduce some of the current knowledge in anthelmintic improvement based on nanotechnology, and how researchers could benefit from this technology in order to overcome the drugs limitations. Finally, some insights into potential field applications are discussed, based on the most important concerns of current anthelmintic therapy.

Anthelmintic resistance in commercial sheep farms in Costa Rica

Forty-eight commercial sheep farms were sampled between the years 2017 and 2019 to evaluate the percentage of reduction of the three families of broad-spectrum anthelmintic drugs available in Costa Rica - benzimidazoles (albendazole), macrocyclic lactones (ivermectin) and imidazothiazoles (levamisole) - in grazing animals by using the fecal egg count reduction test. Animals were selected based on their egg per gram counts after their fecal samples were processed by a modified McMaster technique. The remaining fecal samples were taken to the laboratory for fecal culture and larval identification. The prevalence of farms with albendazole resistance was 100%, ivermectin 96% and levamisole 17%. Seven (n = 47) farms resulted with triple resistance, 39 with double and 1 farm was resistant to 1 AH tested. Haemonchus spp. was the most commonly isolated parasite in pre- and post-treatment larval culture. This is the first report of Oesophagostomum spp. and Teladorsagia sp. resistant to albendazole, Oesophagostomum spp., Teladorsagia sp., Chabertia sp. and Cooperia sp. resistant to ivermectin, and the presence of strains of Haemonchus spp. and Trichostrongylus sp. resistant to the 3 anthelmintics tested. The results of this study demonstrate that anthelmintic resistance is widespread, particularly in Haemonchus spp., and that the major drugs available in the country have lost much of their effectiveness against sheep nematodes.

Advances in the discovery and development of anthelmintics by harnessing natural product scaffolds

Widespread resistance to currently-used anthelmintics represents a major obstacle to controlling parasitic nematodes of livestock animals. Given the reliance on anthelmintics in many control regimens, there is a need for the continued discovery and development of new nematocides. Enabling such a focus are: (i) the major chemical diversity of natural products; (ii) the availability of curated, drug-like extract-, fraction- and/or compound-libraries from natural sources; (iii) the utility and practicality of well-established whole-worm bioassays for Haemonchus contortus-an important parasitic nematodes of livestock-to screen natural product libraries; and (iv) the availability of advanced chromatographic (HPLC), spectroscopic (NMR) and spectrometric (MS) techniques for bioassay-guided fractionation and structural elucidation. This context provides a sound basis for the identification and characterisation of anthelmintic candidates from natural sources. This chapter provides a background on the importance and impact of helminth infections/diseases, parasite control and aspects of drug discovery, and reviews recent work focused on (i) screening well-defined compound libraries to establish the methods needed for large-scale screening of natural extract libraries; (ii) discovering plant and marine extracts with nematocidal or nematostatic activity, and purifying bioactive compounds and assessing their potential for further development; and (iii) synthesising analogues of selected purified natural compounds for the identification of possible 'lead' candidates. The chapter describes some lessons learned from this work and proposes future areas of focus for drug discovery. Collectively, the findings from this recent work show potential for selected natural product scaffolds as candidates for future development. Developing such candidates via future chemical optimisation, efficacy and safety evaluations, broad spectrum activity assessments, and target identification represents an exciting prospect and, if successful, could pave the way to subsequent pre-clinical and clinical evaluations.

Nemabiome metabarcoding reveals differences between gastrointestinal nematode species infecting co-grazed sheep and goats

Our current understanding of differences in the epidemiology of gastrointestinal nematode (GIN) species in co-grazed sheep and goats is inadequate with reference to the development of sustainable control strategies. The next-generation metabarcoding sequencing method referred to as the 'nemabiome' allows some of these differences to be explored to describe the intensity of co-infecting GIN species. We applied this platform to study sheep and goats that were co-grazed on Guinea grass pasture in northeastern Brazil. Co-grazed goats and sheep were treated with a monepantel anthelmintic, then exposed to the same gastrointestinal nematode species. Overall, there were differences in the prevalence of GIN species identified in the sheep and goats; Trichostrongylus colubriformis and Teladorsagia circumcincta predominated in goat kids, while Haemonchus contortus predominated in adult does, ewes and lambs once burdens became re-established after anthelmintic treatment. Description of the pattern of re-infection following anthelmintic treatment was prevented by the unpredicted poor efficacy of 2.5 mg/kg and 5 mg/kg, respectively, of monepantel against O. columbianum and T. circumcincta in lambs, and T. circumcincta adult does. Differences in drug efficacy between host age and species groups may be important when considering sustainable GIN control strategies for co-grazed animals. The aggregated FECs of the adult does and goat kids representing re-established GIN burdens, were higher than those of the co-grazed adult ewes and lambs. This implies that there are inherent differences in GIN species adaptation to the two naïve small ruminant host species, and shows the need for better understanding of the factors giving rise to this situation associated with exposure to infective larvae and host responses. At the start of the study, the adult does were co-infected with several GIN species, with the highest intensity of T. circumcincta, contrasting with the situation in the adult ewes, in which H. contortus predominated. However, once burdens became re-established after treatment, H. contortus predominated in both adult does and ewes. This demonstrates the potential for host burdens of H. contortus to establish and predominate after anthelmintic treatment when burdens of co-infecting GIN species are low.

Combating Parasitic Nematode Infections, Newly Discovered Antinematode Compounds from Marine Epiphytic Bacteria

Parasitic nematode infections cause debilitating diseases and impede economic productivity. Antinematode chemotherapies are fundamental to modern medicine and are also important for industries including agriculture, aquaculture and animal health. However, the lack of suitable treatments for some diseases and the rise of nematode resistance to many available therapies necessitates the discovery and development of new drugs. Here, marine epiphytic bacteria represent a promising repository of newly discovered antinematode compounds. Epiphytic bacteria are ubiquitous on marine surfaces where they are under constant pressure of grazing by bacterivorous predators (e.g., protozoans and nematodes). Studies have shown that these bacteria have developed defense strategies to prevent grazers by producing toxic bioactive compounds. Although several active metabolites against nematodes have been identified from marine bacteria, drug discovery from marine microorganisms remains underexplored. In this review, we aim to provide further insight into the need and potential for marine epiphytic bacteria to become a new source of antinematode drugs. We discuss current and emerging strategies, including culture-independent high throughput screening and the utilization of Caenorhabditis elegans as a model target organism, which will be required to advance antinematode drug discovery and development from marine microbial sources.

Antiparasitics in Animal Health: Quo Vadis?

Antiparasitics acting on endo- or ectoparasites represent the second largest segment of the global animal health market, accounting for 23% of market share. However, relatively few novel antiparasitic agents have been introduced into the market during recent decades. One exception, and a groundbreaking 21st century success story, are the isoxazolines, whose full potential has not yet been entirely explored. Unfortunately, resistance issues are present across most parasitic diseases, which generates a clear market need for novel resistance-breaking antiparasitics with new modes/mechanisms of action. Recent advances in science and technologies strongly suggest that the time is right to invest in new modalities such as parasitic vaccines or in environmentally friendly interventions.

First case of monepantel resistant nematodes of sheep in Sweden

In this study, we describe for the first time monepantel (MOP) resistance in gastrointestinal nematodes (GIN) in a Swedish sheep flock. On the farm, which had recurrent problems with Haemonchus contortus infection, the efficacy of most available anthelmintics (AH) in Sweden (i.e. ivermectin, albendazole, levamisole and monepantel), was monitored. This was done with the faecal egg count reduction test (FECRT) on three different occasions between August 2017 and April 2020. Although, MOP was used in ewes for the first time in this herd in October 2018 and then demonstrated to be highly efficacious (100% reduction), MOP-resistant worms (52% reduction) appeared in lambs already in April 2020. Resistance was detected only after two further rounds of treatment of the lambs after weaning. It is assumed that a contributing factor to this extremely rapid development was related to the fact that ewes and lambs treated during the housing period were let out on clean pasture after treatment. The ewes were treated during the housing period 2018 and grazed a clean pasture the following spring. The same ewes were treated a second time after housing 2018. The lambs were grazed with these ewes in summer 2018 and after weaning they were treated and moved to another clean pasture during the fall 2018. Anthelmintic resistance was also confirmed on two occasions to different compounds of ivermectin and once to albendazole, but not to levamisole which was tested twice. In conclusion, this is the first description of triple resistance to AH drugs in GIN of sheep in Sweden.

Small Ruminant Production Based on Rangelands to Optimize Animal Nutrition and Health: Building an Interdisciplinary Approach to Evaluate Nutraceutical Plants

The plant kingdom can influence the productivity and health of herbivores at different levels. However, demonstrating this process in a scientific manner entails substantial endeavors from different disciplines. In the present review, we will describe the features of a native vegetation system traditionally used by small ruminants and use its particularities to build an interdisciplinary approach to evaluate the nutraceutical properties of plants. Initially, we will establish the context of the low deciduous forest (LDF), considering some botanical and nutritional aspects, as well as the presence of plant secondary compounds (PSC) and gastrointestinal nematodes (GIN). Furthermore, we will focus on coevolutionary aspects that undoubtedly shaped the plants-nutrients-PSC-GIN-herbivore relationship. In addition, the concept of nutraceutical will be discussed to provide clarity and aspects to be considered for their evaluation. Then, ethological, agronomical, nutritional, PSC, parasitological and animal species issues are deepened placing emphasis on methodological approaches. Special focus is given to condensed tannins, as they are the fourth largest group of PSCs and the most studied in livestock sciences. Validation of the nutraceutical properties of plants from native vegetation systems should be seen as a process derived from many scientific disciplines that feed into each other in a cyclic manner.

Sustainable Approaches to Parasite Control in Ruminant Livestock

It is increasingly difficult to manage and control gastrointestinal nematode parasites in pasture-based ruminant livestock operations because of the high prevalence of anthelmintic resistance. Anthelmintics should be combined with alternative forms of control. Sustainable tools include copper oxide wire particles and condensed tannin-rich plants, which target primarily Haemonchus contortus in small ruminants. Nematophagous fungi reduce larvae on pasture and target nematode larvae in feces of most livestock species. In addition, and perhaps most importantly, genetic selection focuses on parasite resistance. Producers should use as many tools as possible to minimize the need for pharmaceutical interventions and optimize animal production.

Plant-Based Natural Products for the Discovery and Development of Novel Anthelmintics against Nematodes

Intestinal parasitic nematodes infect approximately two billion people worldwide. In the absence of vaccines for human intestinal nematodes, control of infections currently relies mainly on chemotherapy, but resistance is an increasing problem. Thus, there is an urgent need for the discovery and development of new anthelmintic drugs, especially ones with novel mechanisms of action. Medicinal plants hold great promise as a source of effective treatments, including anthelmintic therapy. They have been used traditionally for centuries and are mostly safe (if not, their toxicity is well-known). However, in most medicinal plants the compounds active against nematodes have not been identified thus far. The free-living nematode C. elegans was demonstrated to be an excellent model system for the discovery of new anthelmintics and for characterizing their mechanism of action or resistance. The compounds discussed in this review are of botanical origin and were published since 2002. Most of them need further studies of their toxicity, mechanisms and structure-activity relationship to assess more fully their potential as drugs.

A perspective on the discovery of selected compounds with anthelmintic activity against the barber's pole worm-Where to from here?

Parasitic roundworms (nematodes) cause substantial morbidity and mortality in animals worldwide. Anthelmintic treatment is central to controlling these worms, but widespread resistance to most of the commercially available anthelmintics for veterinary and agricultural use is compromising control, such that there is an urgency to discover new and effective drugs. The purpose of this article is to review information on parasitic nematodes, the treatment and control of parasitic nematode infections and aspects of discovering new anthelmintics in the context of anthelmintic resistance problems, and then to discuss some progress that our group has made in identifying selected compounds with activity against nematodes. The focus of our recent work has been on discovering new chemical entities and known drugs with anthelmintic activities against Haemonchus contortus as well as other socioeconomically important parasitic nematodes for subsequent development. Using whole worm-based phenotypic assays, we have been screening compound collections obtained via product-development-partnerships and/or collaborators, and active compounds have been assessed for their potential as anthelmintic candidates. Following the screening of 15,333 chemicals from five distinct compound collections against H. contortus, we have discovered one new chemical entity (designated SN00797439), two human kinase inhibitors (SNS-032 and AG-1295), 14 tetrahydroquinoxaline analogues, one insecticide (tolfenpyrad) and two tolfenpyrad (pyrazole-5-carboxamide) derivatives (a-15 and a-17) with anthelmintic activity in vitro. Some of these 20 'hit' compounds have selectivity against H. contortus in vitro when compared to particular human cell lines. In our opinion, some of these compounds could represent starting points for 'lead' development. Accordingly, the next research steps to be pursued include: (i) chemical optimisation of representative chemicals via structure-activity relationship (SAR) evaluations; (ii) assessment of the breadth of spectrum of anthelmintic activity on a range of other parasitic nematodes, such as strongyloids, ascaridoids, enoplids and filarioids; (iii) detailed investigations of the absorption, distribution, metabolism, excretion and toxicity (ADMET) of optimised chemicals with broad nematocidal or nematostatic activity; and (iv) establishment of the modes of action of lead candidates.

Anthelmintic resistance and common worm control practices in sheep farms in Flanders, Belgium

In contrast to many other European countries, no data were available on the presence of anthelmintic resistance in gastrointestinal nematodes in sheep in Belgium. A faecal egg count reduction test was performed in 26 sheep flocks in Flanders, Northern Belgium. Results indicated widespread resistance against benzimidazoles (albendazole, fenbendazole and mebendazole), with treatment failure on all 8 farms investigated. Haemonchus contortus and Teladorsagia circumcincta were the predominant species after treatment failure. Amino acid substitutions associated with benzimidazole resistance were detected at the codon positions 167 (8%) and 200 (92%) of the isotype-1 beta tubulin gene in H. contortus, codon positions 198 (47%) and 200 (43%) in T. circumcincta and position 200 (100%) in T. colubriformis. Resistance against macrocyclic lactones (ivermectin, doramectin and moxidectin) was recorded on 7 out of 20 flocks, mainly in H. contortus and T. circumcincta. Treatment failure was also observed for closantel (in combination with mebendazole) and for monepantel, on one farm each. Trichostrongylus spp. were implicated with resistance against monepantel. A questionnaire survey on farm management and worm control measures indicated that worm control was often not sustainable. Ewes and lambs were treated frequently (on average 2.6 and 3.2 times per year), mostly without weighing. Only few sheep farmers (9%) regularly used faecal egg counts to monitor worm infections. Despite the FECRT showing otherwise, most of the farmers perceived the efficacy of anthelmintics as very good (30%) or good (54%).

Genotypic characterisation of monepantel resistance in historical and newly derived field strains of Teladorsagia circumcincta

Recent reports of monepantel (MPTL) resistance in UK field isolates of Teladorsagia circumcincta has highlighted the need for a better understanding of the mechanism of MPTL-resistance in order to preserve its anthelmintic efficacy in this economically important species. Nine discrete populations of T. circumcincta were genotypically characterised; three MPTL-susceptible isolates, three experimentally selected MPTL-resistant strains and three field derived populations. Full-length Tci-mptl-1 gene sequences were generated and comparisons between the MPTL-susceptible isolates, MPTL-resistant strains and one field isolate, showed that different putative MPTL-resistance conferring mutations were present in different resistant isolates. Truncated forms of the Tci-mptl-1 gene were also observed. The genetic variability of individual larvae, within and between populations, was examined using microsatellite analyses at 10 'neutral' loci (presumed to be unaffected by MPTL). Results confirmed that there was little background genetic variation between the populations, global FST <0.038. Polymorphisms present in exons 7 and 8 of Tci-mptl-1 enabled genotyping of individual larvae. A reduction in the number of genotypes was observed in all MPTL-resistant strains compared to the MPTL-susceptible strains that they were derived from, suggesting there was purifying selection at Tci-mptl-1 as a result of MPTL-treatment. The potential link between benzimidazole (BZ)-resistance and MPTL-resistance was examined by screening individual larvae for the presence of three SNPs associated with BZ-resistance in the β-tubulin isotype-1 gene. The majority of larvae were BZ-susceptible homozygotes at positions 167 and 198. Increased heterozygosity at position 200 was observed in the MPTL-resistant strains compared to their respective MPTL-susceptible population. There was no decrease in the occurrence of BZ-resistant genotypes in larvae from each population. These differences, in light of the purifying selection at this locus in all MPTL-resistant isolates, suggests that Tci-mptl-1 confers MPTL-resistance in T. circumcincta, as in Haemonchus contortus, but that different mutations in Tci-mptl-1 can confer resistance in different populations.

The uptake, effects and biotransformation of monepantel in meadow plants used as a livestock feed

Drugs are potentially dangerous environmental contaminants, as they are designed to have biological effects at low concentrations. Monepantel (MOP), an amino-acetonitrile derivative, is frequently used veterinary anthelmintics, but information about MOP environmental circulation and impact is almost non-existent. We studied the phytotoxicity, uptake and biotransformation of MOP in two fodder plants, Plantago lanceolata and Medicago sativa. The seeds and whole plant regenerants were cultivated with MOP. The plant roots and the leaves were collected after 1, 2, 3, 4, 5 and 6 weeks of cultivation. The lengths of roots and proline concentrations in the roots and leaves were measured to evaluate MOP phytotoxicity. The UHPLC-MS/MS technique with a Q-TOF mass analyser was used for the identification and semi-quantification of MOP and its metabolites. Our results showed no phytotoxicity of MOP. However, both plants were able to uptake, transport and metabolize MOP. Comparing both plants, the uptake of MOP was much more extensive in Medicago sativa (almost 10-times) than in Plantago lanceolate. Moreover, 9 various metabolites of MOP were detected in Medicago sativa, while only 7 MOP metabolites were found in Plantago lanceolata. Based on metabolites structures, scheme of the metabolic pathways of MOP in both plants was proposed. MOP and its main metabolite (MOP sulfone), both anthelmintically active, were present not only in roots but also in leaves that can be consumed by animals. This indicates the potential for undesirable circulation of MOP in the environment, which could lead to many pharmacological and toxicological consequences.

Implication of the fecal egg count reduction test (FECRT) in sheep for better use of available drugs

Abstract The aim here is to present data on the efficacy of anthelmintics in sheep flocks in Rio de Janeiro, Brazil, and to discuss the interpretation of the fecal egg count reduction test (FECRT) for each nematode genus. Fecal eggs counts and pre- and post-treatment coprocultures were performed, the former to evaluate the efficacy of and the latter to determine the overall parasite prevalence. An additional efficacy test was performed at Farm # 1 a year after the initial test. Severe anthelmintic resistance was found for the flocks, with no FECRT sensitivity at any of the 22 farms evaluated. However, an analysis of the infective larvae showed that some drugs were effective against certain parasitic genera; i.e., levamisole was more effective against Haemonchus spp. and moxidectin against Trichostrongylus spp. In the additional FECRT performed at Farm # 1, moxidectin and nitroxynil were ineffective separately, but when applied in combination they were highly effective due to their efficacy against Haemonchus (nitroxynil) and Trichostrongylus (moxidectin), respectively. The use of the FECRT targeting the parasitic nematode species prevalent on farms may make it possible to choose more effective anthelmintics.

Review of the Eprinomectin effective doses required for dairy goats: Where do we go from here?

Eprinomectin (EPM) has been recently granted a marketing authorisation in the European Union for use in goats, with a zero-day milk withdrawal period. Considering the high prevalence of benzimidazole resistance worldwide and the economic implications of managing milk residues, EPM may today be considered the main (or even the only) affordable treatment option, at least in dairy goats in the EU. However, the chosen dose (1 mg/kg) seems to be suboptimal, especially for lactating goats, and the chosen route of administration (Pour-on) highly subject to inter-individual variability. Considering the scarcity of anthelmintic resources, such a dosage regimen might threat the sustainability of this crucial drug in goat milk production and needs to be urgently discussed and reassessed.

Preventive chemotherapy and anthelmintic resistance of soil-transmitted helminths - Can we learn nothing from veterinary medicine?

Current parasite control programs in veterinary species have moved away from mass anthelmintic treatment approaches due to the emergence of significant anthelmintic resistance (AR), and the availability of few classes of anthelmintics. A number of parallels between livestock and human helminths exist that warn of the risk of AR in human soil-transmitted helminthiases, yet current public health interventions continue to prioritize mass treatment strategies, a known risk factor for AR. This review discusses the existing parallels between human and animal helminth biology and management, along with current public health recommendations and strategies for helminth control in humans. The effectiveness of current recommendations and alternative management strategies are considered.

Extreme-QTL mapping of monepantel resistance in Haemonchus contortus

Background

Haemonchus contortus, a gastrointestinal nematode parasite of sheep, is mainly controlled by anthelmintics; the occurrence of anthelmintic resistance leads to treatment failures and increases economic burden. Because molecular mechanisms involved in drug resistance can be elucidated by genomic studies, an extreme quantitative trait locus (X-QTL) mapping approach was used to identify co-segregation of the resistance phenotype with genetic markers to detect the genome-wide variants associated with monepantel resistance in H. contortus.

Methods

A cross between H. contortus isolates using parental susceptible (Par-S) males and monepantel resistant (Par-R) females resulted in SR progeny, while reciprocal cross resulted in RS progeny. Pools (n = 30,000) of infective larvae (L3) recovered from Par-R, and from SR and RS populations in the F3 generation, collected both before (unselected group) and 7 days after (selected group) selection with monepantel treatment in sheep hosts, were subjected to genome sequencing (Pool-Seq). Pairwise comparisons of allele frequencies between unselected and selected groups were performed for each population by Fisher’s exact test (FET) and for both populations combined by a Cochran-Mantel-Haenszel (CMH) test.

Results

Mapping rates varied from 80.29 to 81.77% at a 90.4X mean coverage of aligned reads. After correction for multiple testing, significant (P < 0.05) changes in allele frequencies were detected by FET for 6 and 57 single nucleotide polymorphisms (SNPs) in the SR and RS populations, respectively, and by the CMH test for 124 SNPs in both populations. The significant variants located on chromosome 2 generated a selection signal in a genomic region harboring the mptl-1, deg-3 and des-2 genes, previously reported as candidates for monepantel resistance. In addition, three new variants were identified in the mptl-1 gene.

Conclusions

This study expands knowledge on genome-wide molecular events underlying H. contortus resistance to monepantel. The identification of a genome region harboring major genes previously associated with monepantel resistance supports the results of the employed X-QTL approach. In addition, a deletion in exon 11 of the mptl-1 gene should be further investigated as the putative causal mutation leading to monepantel resistance.

Electronic supplementary material

The online version of this article (10.1186/s13071-019-3663-9) contains supplementary material, which is available to authorized users.

A producer survey of knowledge and practises on gastrointestinal nematode control within the Australian goat industry

Gastrointestinal nematodes (GINs) have been identified in Australia as a major problem in goat production, with few anthelmintics registered for use in goats. Therefore, anecdotally many producers use anthelmintics that have not been registered for goats. Using unregistered products could increase selection pressure for anthelmintic resistance as well as safety and/or meat or milk chemical residues of products from treated goats. This producer survey was conducted in 2014 to establish Australian goat producer knowledge, perception and practises of GIN treatment and control. Eighty-eight producers responded to the survey. Of these respondents, 90% thought that GINs were a problem for the Australian goat industry, and 73% considered GINs had caused production losses or health impacts for their goats during the 5 years prior to the survey. With regard to anthelmintic resistance, 7% believed that anthelmintic resistance was not a problem at all, 93% acknowledged anthelmintic resistance was a problem in Australian goats herds, with 25% of these reporting their properties as being affected. The majority (81%) of respondents believed the number of anthelmintics registered for goats was inadequate for effective GIN control. Of the 85% of producers who used an anthelmintic during the survey period, 69% had used a treatment not registered for use in goats. Fifty respondents listed the anthelmintic dosage used, and 50% of those had used a dose rate greater than the recommended label dose. The average frequency of administration of anthelmintic was 2.5 times per annum. Of the 51% of respondents who listed the frequency of their treatments given during the survey period, 16% administered four or more treatments annually to the majority of their goats and 8% administered treatments on an "as needed" basis. Faecal egg count (FEC) had been performed on 72% of properties in at least one of the six years covered by the survey. These results indicated that the majority of surveyed producers use anthelmintics that are not registered for use in goats and at different dose rates to label. These practises have the potential for increasing the spread of anthelmintic resistance in the GIN populations of goats and sheep. Further, giving dose rates in excess of label recommendations could impact goat safety and/or product residues. Further research is needed to investigate these risks and evaluate more sustainable GIN control options for goat herds. In addition more effective dissemination of information is necessary for the improvement of the Australian goat industry.

Lupin (Lupinus spp.) seeds exert anthelmintic activity associated with their alkaloid content

The growing range of drug resistant parasitic nematode populations threatens the sustainability of ruminant farming worldwide. In this context, nutraceuticals, animal feed that provides necessary dietary requirements while ensuring parasite control, could contribute to increase farming sustainability in developed and low resource settings. In this study, we evaluated the anthelmintic potential of lupin seed extracts against the major ruminant trichostrongylids, Haemonchus contortus and Teladorsagia circumcincta. In vitro observations showed that seed extracts from commercially available lupin varieties could significantly but moderately inhibit larval migration. This anthelmintic effect was mediated by the seed alkaloid content and was potent against both fully susceptible and multidrug resistant H. contortus isolates as well as a susceptible T. circumcincta isolate. Analytical chemistry revealed a set of four lupanine and sparteine-derivatives with anthelmintic activity, and electrophysiology assays on recombinant nematode acetylcholine receptors suggested an antagonistic mode of action for lupin alkaloids. An in vivo trial in H. contortus infected lupin-fed ewes and goats failed to demonstrate any direct anthelmintic effect of crude lupin seeds but infected lupin-fed goats suffered significantly less parasite-mediated blood losses. Altogether, our findings suggest that the anthelmintic potential of lupin remains limited. However, the potent alkaloids identified could lead to the development of novel drugs or may be used in combination with current anthelmintics to improve their efficacy.

The current status of anthelmintic resistance in a temperate region of Australia; implications for small ruminant farm management

Widespread anthelmintic resistance in small ruminants is a constraint on the profitability of the meat/wool industry. Limited published data is available on the prevalence and efficacy of anthelmintics, particularly in Australia where parasites affecting ruminant systems vary greatly between geographic regions. This paper reports on the anthelmintic resistance status in a temperate region of Victoria, Australia, a major sheep producing state largely affected by Trichostrongylus species and Teladorsagia circumcincta. The prevalence of anthelmintic resistance to any product was high (71%), with farms reporting varying levels of drug efficacies (21-100%). Resistance to older chemical groups (i.e. fenbendazole and levamisole) and single active macrocyclic lactone treatments was higher than newer chemical groups and combination treatments. This report provides clarity on anthelmintic resistance in the temperate region of Victoria and more importantly suggests that more comprehensive, regional specific anthelmintic resistance studies are required to understand the real level of chemical resistance threatening the effective control of worms.

In vivo selection for Haemonchus contortus resistance to monepantel

Gastrointestinal nematodes significantly affect the ovine industry, and Haemonchus contortus is considered the most pathogenic parasite in tropical regions. This situation is aggravated when the main strategy to control worms fails because of the genetic resistance that parasites acquire against anthelmintics. Aiming to anticipate the events involved in anthelmintic resistance, we induced monepantel resistance in H. contortus by in vivo subdosing of sheep hosts. Four successive passages of a monepantel-susceptible H. contortus isolate in Santa Ines or Ile de France sheep hosts resulted in three monepantel-resistant (efficacy varying from 0 to 58.5%) H. contortus isolates. Sheep hosts were treated from 0.075 mg/kg to the therapeutic dose of 2.5 mg/kg of monepantel in 19-26 rounds of selection for 112-133 weeks. Success in inducing H. contortus resistance to monepantel may have been affected by worm burden and by host-parasite interactions, including a possible effect of the breed of sheep hosts. We conclude that subdosing of sheep, although time-consuming, is an efficient in vivo strategy for the induction of monepantel resistance in H. contortus. The resistant parasites can be used in further studies to elucidate the genetic and biochemical events involved in the acquisition of anthelmintic resistance.

Multigeneric resistance to monepantel on a UK sheep farm

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Multigeneric monepantel resistance detected in UK sheep flock.

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Teladorsagia, Trichostrongylus and Oesophagostomum genera implicated post treatment.

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Monepantel efficacy based on worm burden reduction ranged from 22 to 78%.

The amino acetonitrile derivative, monepantel, represented the first new broad spectrum anthelmintic to be brought to market for use in sheep for over 25 years when it was introduced in 2009. This study characterised monepantel efficacy, using faecal egg count reduction and controlled efficacy tests, against gastrointestinal nematodes following a report of treatment failure in a UK lowland sheep flock. Twelve lambs were each artificially administered 15,000 infective larvae that had been propagated from lamb faeces collected from the farm of interest. The controlled efficacy test showed that a recommended dose rate of monepantel (2.5 mg/kg body weight) administered at day 28 post infection was ineffective at removing the infection in the treated lambs. The result demonstrated simultaneous resistance to monepantel in Teladorsagia circumcincta, Trichostrongylus vitrinus and Oesophagostomum venulosum with efficacies based on adult worm burden reductions, compared to untreated controls, of 78%, 27% and 22% respectively. Monepantel efficacy based on undifferentiated egg count in treated animals, seven day post administration, compared to untreated controls was 85%. The results raise questions about the origins of, and predisposing factors for, resistance development in the three different species, and reinforces the value of differentiating post treatment faecal egg counts to genus or species level.

Selected α-pyrones from the plants Cryptocarya novoguineensis (Lauraceae) and Piper methysticum (Piperaceae) with activity against Haemonchus contortus in vitro

Due to the widespread occurrence and spread of anthelmintic resistance, there is a need to develop new drugs against resistant parasitic nematodes of livestock animals. The Nobel Prize-winning discovery and development of the anti-parasitic drugs avermectin and artemisinin has renewed the interest in exploring natural products as anthelmintics. In the present study, we screened 7500 plant extracts for in vitro-activity against the barber's pole worm, Haemonchus contortus, a highly significant pathogen of ruminants. The anthelmintic extracts from two plants, Cryptocarya novoguineensis and Piper methysticum, were fractionated by high-performance liquid chromatography (HPLC). Subsequently, compounds were purified from fractions with significant biological activity. Four α-pyrones, namely goniothalamin (GNT), dihydrokavain (DHK), desmethoxyyangonin (DMY) and yangonin (YGN), were purified from fractions from the two plants, GNT from C. novoguineensis, and DHK, DMY and YGN (= kavalactones) from P. methysticum. The three kavalactones induced a lethal, eviscerated (Evi) phenotype in treated exsheathed third-stage larvae (xL3s), and DMY and YGN had moderate potencies (IC₅₀ values of 31.7 ± 0.23 μM and 23.7 ± 2.05 μM, respectively) at inhibiting the development of xL3s to fourth-stage larvae (L4s). Although GNT had limited potency (IC₅₀ of 200–300 μM) at inhibiting L4 development, it was the only compound that reduced L4 motility (IC₅₀ of 6.25–12.50 μM). The compounds purified from each plant affected H. contortus in an irreversible manner. These findings suggest that structure-activity relationship studies of α-pyrones should be pursued to assess their potential as anthelmintics.

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7500 plant extracts were screened against Haemonchus for anthelmintic activity.

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Three of these extracts were potent inhibitors of larval motility and/or development.

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Pure α-pyrones isolated from active fractions exhibited significant nematocidal activity.

Nematode resistance to five anthelmintic classes in naturally infected sheep herds in Northeastern Brazil

Abstract This study aimed to evaluate the occurrence of nematode resistance to anthelmintics on sheep herds from the semi-arid region of Paraíba, Northeastern Brazil. Fecal Egg Count Reduction Test (FECRT) was carried out on 20 properties. In each herd, 30 animals were divided into five groups containing six animals each: group I, treated with albendazole 10%, 4 mg/kg; group II, ivermectin 0.08%, 0.2 mg/kg; group III, closantel 10%, 10 mg/kg; group IV, levamisole hydrochloride 5%, 5 mg/kg; and group V, monepantel 2.5%, 2.5 mg/kg. All treatments were administered orally as a single dose. Fecal samples were collected on days zero and 10 after treatment, to perform FECRT and coprocultures. Multiresistance was observed in all the properties; 95% had high resistance to albendazole, 85% to ivermectin, 80% to closantel, 40% to levamisole, and 45% to monepantel. On property 15, where monepantel was ineffective, a second FECRT for this anthelmintic was carried out 4 months after the first, resulting in 75% efficacy. Immediately after the FECRT result, two ewes were euthanized and necropsied, and Haemonchus contortus, Trichostrongylus axei, Trichostrongylus colubriformis, Oesophagostomum columbianum, and Trichuris ovis were recovered. It was concluded that the resistance of sheep gastrointestinal nematodes to antthelmintic, including monepantel, is high.

2,4-Diaminothieno[3,2-d]pyrimidines, a new class of anthelmintic with activity against adult and egg stages of whipworm

The human whipworm Trichuris trichiura is a parasite that infects around 500 million people globally, with consequences including damage to physical growth and educational performance. Current drugs such as mebendazole have a notable lack of efficacy against whipworm, compared to other soil-transmitted helminths. Mass drug administration programs are therefore unlikely to achieve eradication and new treatments for trichuriasis are desperately needed. All current drug control strategies focus on post-infection eradication, targeting the parasite in vivo. Here we propose developing novel anthelmintics which target the egg stage of the parasite in the soil as an adjunct environmental strategy. As evidence in support of such an approach we describe the actions of a new class of anthelmintic compounds, the 2,4-diaminothieno[3,2-d]pyrimidines (DATPs). This compound class has found broad utility in medicinal chemistry, but has not previously been described as having anthelmintic activity. Importantly, these compounds show efficacy against not only the adult parasite, but also both the embryonated and unembryonated egg stages and thereby may enable a break in the parasite lifecycle.

The human whipworm, Trichuris trichiura, infects around 500 million people globally, impacting on their physical growth and educational performance. There are currently huge mass drug administration (MDA) programs aiming to control whipworm, along with the other major soil transmitted helminths, Ascaris and hookworm. However single doses of albendazole and mebendazole, which are used in MDA, have particularly poor effectiveness against whipworm, with cure rates less than 40%. This means that MDA may not be able to control and eliminate whipworm infection, and risks the spread of resistance to albendazole and mebendazole in the parasite population. We are attempting to develop new treatments for parasitic worm infection, particularly focused on whipworm. We report the identification of a class of compounds, diaminothienopyrimidines (DATPs), which have not previously been described as anthelmintics. These compounds are effective against adult stages of whipworm, and also block the development of the model nematode C. elegans. Our DATP compounds reduce the ability of treated eggs to successfully establish infection in a mouse model of human whipworm. These results support a potential environmental spray to control whipworm by targeting the infectious egg stage in environmental hotspots.