Anthelmintic resistance: past, present and future

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

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

Towards precision parasite management for livestock gastrointestinal nematodes in 2030

The management of parasitic nematodes calls for a shift from conventional, indiscriminate, anthelmintic use to a more precise approach, directed by diagnostics. We should accept those parasite infection intensities that have minimal impact on production and welfare rather than attempt to eliminate them. The diagnostic toolbox for gastrointestinal nematodes (GINs) faces challenges due to anthelmintic resistance (AR), which is species-specific, drug-class-specific, and varies by region. We discuss which traditional tools may become obsolete and which tools need development to gain widespread use. Social science research highlights the need for dialogue between farmers and veterinarians that emphasises effective parasite management and upskilling the veterinary workforce for more sustainable practices centred on diagnostics to be adopted in practice by 2030.

Anthelmintic resistance in ruminants: challenges and solutions

Anthelmintic resistance (AR) is a growing concern for effective parasite control in farmed ruminants globally. Combatting AR will require intensified and integrated research efforts in the development of innovative diagnostic tests to detect helminth infections and AR, sustainable anthelmintic treatment strategies and the development of complementary control approaches such as vaccination and plant-based control. It will also require a better understanding of socio-economic drivers of anthelmintic treatment decisions, in order to support a behavioural shift and develop targeted communication strategies that promote the uptake of evidence-based sustainable solutions. Here, we review the state-of-the-art in these different fields of research activity related to AR in helminths of livestock ruminants in Europe and beyond. We conclude that in the advent of new challenges and solutions emerging from continuing spread of AR and intensified research efforts, respectively, there is a strong need for transnational multi-actor initiatives. These should involve all key stakeholders to develop indicators of infection and sustainable control, set targets and promote good practices to achieve them.

Natural Products Are a Promising Source for Anthelmintic Drug Discovery

Parasitic nematodes infect almost all forms of life. In the human context, parasites are one of the major causative factors for physical and intellectual growth retardation in the developing world. In the agricultural setting, parasites have a great economic impact through a reduction in livestock performance or control cost. The main method of controlling these devastating conditions is the use of anthelmintic drugs. Unfortunately, there are only a few anthelmintic drug classes available in the market and significant resistance has developed in most of the parasitic species of livestock. Therefore, development of new anthelmintics with different modes of action is critical for sustainable parasitic control in the future. The drug development pipeline is broadly limited to two types of molecules, namely synthetic compounds and natural plant products. Compared to synthetic compounds, natural products are highly diverse, and many have historically proven valuable in folk medicine to treat various gastrointestinal ailments. This review focus on the use of traditional knowledge-based plant extracts in the development of new therapeutic leads, the approaches used as screening techniques, and common bottlenecks and opportunities in plant-based anthelmintic drug discovery.

The threat of reduced efficacy of anthelmintics against gastrointestinal nematodes in sheep from an area considered anthelmintic resistance-free

BACKGROUND

The worldwide increased difficulty to combat gastrointestinal nematode (GIN) infection in sheep, due to progressing anthelmintic resistance (AR), calls for an enhanced and standardized implementation of early detection of AR. This study provides a snapshot of the current AR status against benzimidazoles and macrocyclic lactones in southern Italy, generated with standardized techniques.

METHODS

On 10 sheep farms, the efficacy of albendazole (ALB) and either eprinomectin (EPR) or ivermectin (IVM) was evaluated based on the faecal egg count reduction test (FECRT) performed with the Mini-FLOTAC. For each tested drug, 40 sheep were rectally sampled at D0 and sampled again 14 days after the treatment (D14). The FECRT was calculated from individual samples and pooled samples which consist of 5 individual samples. Efficacy was classified as 'reduced, 'suspected' and 'normal'. Coprocultures were set for D0 and D14 faecal samples of each group. From farms with FECR < 95%, an in vitro egg hatch test (EHT) and a follow-up FECRT using fenbendazole (FBZ) were conducted.

RESULTS

Based on the FECR, high efficacy (from 95.7% to 100%) was observed for ALB and IVM in eight farms (Farms 3-10). On Farm 1 and Farm 2, the efficacy for the macrocyclic lactones was classified as 'normal', but 'reduced' efficacy was observed for ALB on Farm 1 (FECR = 75%) and 'suspected' efficacy on Farm 2 (FECR = 93.3%) with the predominant GIN genus Trichostrongylus followed by Haemonchus at D14. The FEC results of pooled samples strongly correlated with those of individual samples, for FEC at D0 (r_s = 0.984; P < 0.0001) and at D14 (rs = 0.913; P < 0.0001). The classifications of efficacy in Farm 1 (FECR = 86.0%) and Farm 2 (FECR = 93.0%) in the follow-up FECRT with FBZ coincide with the main FECRT trial. The in vitro EHT confirmed AR in both farms (Farm 1: 89%; Farm 2: 74%).

CONCLUSIONS

In regions like southern Italy, where the negative impacts from AR have played a minor role, efficient monitoring of AR is important in order to evaluate potential risks and being able to promptly respond with countermeasures.

Are Trichostrongylus tenuis control and resistance avoidance simultaneously manageable by reducing anthelmintic intake by grouse?

Benzimidazole-based anthelmintics bound to grit (medicated grit) are annually prescribed on request by veterinary practices to grouse managers to control Trichostrongylus tenuis an intestinal parasite of red grouse Lagopus lagopus scotica Those prescribing medication typically do without knowledge of parasite loads and hence often prescribe when loads are low and unlikely to impact the host. Inappropriate use of anthelmintics in livestock has led to development of parasite resistance to anthelmintics. To encourage grouse managers to reduce anthelmintic use, the authors experimentally withdrew medication from parts of eight moors. The authors monitored parasite and grouse responses by counting eggs and adult worms and grouse mortality and breeding success. Rapid increases in parasite egg counts in early spring culminated in resuming medication at three wet, blanket-peat sites; one in the first spring and two in the second. Medication was restored, despite low parasite counts, at a fourth moor. On the remaining four moors, drier heaths in the east, parasite levels remained low, were not associated with grouse mortality, but breeding success was 16 per cent lower in years without medication. Better parasite monitoring by grouse managers and vets alike may reduce anthelmintic use, helping prevent drug resistance, but this may be off-set by reduced grouse productivity.

In vitro ovicidal effect of a Senecio brasiliensis extract and its fractions on Haemonchus contortus

BACKGROUND

Haemonchosis affects sheep husbandry and its treatment is often compromised due to the development of anthelminthic resistance. Plant-derived bioactive compounds have been studied as alternative to control Haemonchus contortus. The objective of this study was to evaluate the effect of Senecio brasiliensis extracts on H. contortus egg hatching and infective larvae migration.

RESULTS

The aqueous extract from dried and fresh plant and alkaloid-enriched fraction of the previously dried leaves of S. brasiliensis inhibited H. contortus egg hatching. The main plant compound in alkaloid fraction was integerrimine, a pyrrolizidine alkaloid (PA). However, the aqueous extract from dried plant displayed higher efficacy when compared to their alkaloid enriched or non-polar fractions, meaning that, although PAs contributed to the ovicidal effect, other compounds in the plant can also contribute to their effect. Furthermore, the aqueous extract from dried plant also had higher efficacy than aqueous extract from fresh plant in larvae migration inhibition. Finally, extract from dried plant presented low in vitro cytotoxic effect.

CONCLUSION

Taken together our results suggest a good anthelmintic effect of S. brasiliensis, especially when aqueous extract is prepared from dried plant. Further in vivo studies should be performed focused on forms of administration of this extract in rearing sheep.

Of dogs and hookworms: man's best friend and his parasites as a model for translational biomedical research

We present evidence that the dog hookworm (Ancylostoma caninum) is underutilised in the study of host-parasite interactions, particularly as a proxy for the human-hookworm relationship. The inability to passage hookworms through all life stages in vitro means that adult stage hookworms have to be harvested from the gut of their definitive hosts for ex vivo research. This makes study of the human-hookworm interface difficult for technical and ethical reasons. The historical association of humans, dogs and hookworms presents a unique triad of positive evolutionary pressure to drive the A. caninum-canine interaction to reflect that of the human-hookworm relationship. Here we discuss A. caninum as a proxy for human hookworm infection and situate this hookworm model within the current research agenda, including the various 'omics' applications and the search for next generation biologics to treat a plethora of human diseases. Historically, the dog hookworm has been well described on a physiological and biochemical level, with an increasing understanding of its role as a human zoonosis. With its similarity to human hookworm, the recent publications of hookworm genomes and other omics databases, as well as the ready availability of these parasites for ex vivo culture, the dog hookworm presents itself as a valuable tool for discovery and translational research.

A BRIEF REVIEW ON THE MODE OF ACTION OF ANTINEMATODAL DRUGS

Anthelmintics are some of the most widely used drugs in veterinary medicine. Here we review the mechanism of action of these compounds on nematode parasites. Included are the older classes of compounds; the benzimidazoles, cholinergic agonists and macrocyclic lactones. We also consider newer anthelmintics, including emodepside, derquantel and tribendimidine. In the absence of vaccines for most parasite species, control of nematode parasites will continue to rely on anthelmintic drugs. As a consequence, vigilance in detecting drug resistance in parasite populations is required. Since resistance development appears almost inevitable, there is a continued and pressing need to fully understand the mode of action of these compounds. It is also necessary to identify new drug targets and drugs for the continued effective control of nematode parasites.

Investigating anthelmintic efficacy against gastrointestinal nematodes in cattle by considering appropriate probability distributions for faecal egg count data

The Faecal Egg Count Reduction Test (FECRT) is the most widely used field-based method for estimating anthelmintic efficacy and as an indicator of the presence of anthelmintic resistant nematodes in cattle, despite never having been validated against the gold standard of controlled slaughter studies. The objectives of this study were to assess the normality of cattle faecal egg count (FEC) data and their transformed versions, since confidence intervals used to aid the interpretation of the FECRT, are derived from data assumed to be normally distributed, and violation of this assumption could potentially lead to the misclassification of anthelmintic efficacy. Further, probability distributions and associated parameters were evaluated to determine those most appropriate for representing cattle FEC data, which could be used to estimate percentage reductions and confidence limits. FEC data were analysed from 2175 cattle on 52 farms using a McMaster method at two different diagnostic sensitivities (30 and 15 eggs per gram (epg)) and a sensitive centrifugal flotation technique (SCFT) with a sensitivity of 1 epg. FEC data obtained from all egg count methods were found to be non-normal even upon transformation; therefore, it would be recommended that confidence or credible intervals be generated using either a Bootstrapping or Bayesian approach, respectively, since analyses using these frameworks do not necessarily require the assumption of normality. FEC data obtained using the SCFT method were best represented by distributions associated with the negative binomial and hence arithmetic means could be used in FECRT calculations.

Where FEC data were obtained with less sensitive counting techniques (i.e. McMaster 30 or 15 epg), zero-inflated distributions and their associated central tendency were the most appropriate and would be recommended to use, i.e. the arithmetic group mean divided by the proportion of non-zero counts present; otherwise apparent anthelmintic efficacy could be misrepresented.

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Efficacy can be misrepresented if inappropriate central tendencies are used in calculations.

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Sensitivity of counting technique used influences the distributions of best representation.

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Confidence intervals assuming normality of data would not be recommended to use with FEC data.

Evaluation of Anthelmintic Activity and Composition of Pumpkin (Cucurbita pepo L.) Seed Extracts-In Vitro and in Vivo Studies

A significant number of studies report growing resistance in nematodes thriving in both humans and livestock. This study was conducted to evaluate the in vitro and in vivo anthelmintic efficiency of Curcubita pepo (C. pepo) L. hot water extract (HWE), cold water extract (CWE) or ethanol extract (ETE) on two model nematodes: Caenorhabditis elegans (C. elegans) and Heligmosoides bakeri (H. bakeri).

METHODS

Raman, IR and LC-MS spectroscopy analyses were performed on the studied plant material to deliver qualitative and quantitative data on the composition of the obtained extracts: ETE, HWE and CWE. The in vitro activity evaluation showed an impact of C. pepo extracts on C. elegans and different developmental stages of H. bakeri. The following in vivo experiments on mice infected with H. bakeri confirmed inhibitory properties of the most active pumpkin extract selected by the in vitro study. All of the extracts were found to contain cucurbitine, aminoacids, fatty acids, and-for the first time-berberine and palmatine were identified. All C. pepo seed extracts exhibited a nematidicidal potential in vitro, affecting the survival of L1 and L2 H. bakeri larvae. The ETE was the strongest and demonstrated a positive effect on H. bakeri eggs hatching and marked inhibitory properties against worm motility, compared to a PBS control. No significant effects of pumpkin seed extracts on C. elegans integrity or motility were found. The EtOH extract in the in vivo studies showed anthelmintic properties against both H. bakeri fecal egg counts and adult worm burdens. The highest egg counts reduction was observed for the 8 g/kg dose (IC50 against H. bakeri = 2.43; 95% Cl = 2.01-2.94). A decrease in faecal egg counts (FEC) was accompanied by a significant reduction in worm burden of the treated mice compared to the control group.

CONCLUSIONS

Pumpkin seed extracts may be used to control of Gastrointestinal (G.I.) nematode infections. This relatively inexpensive alternative to the currently available chemotherapeutic should be considered as a novel drug candidate in the nearest future.

In vitro ovicidal activity of Peganum harmala seeds extract on the eggs of Fasciola hepatica

Peganum harmala seeds extract has been previously reported to have antimicrobial and other medicinal properties. The aim of this study was to evaluate the ovicidal activity of the methanolic extract of P. harmala seeds against the eggs of F. hepatica. The phenolic compounds of the methanolic extract of P. harmala seeds were identified by HPLC analysis. Catechin, rutin, p-Coumaric acid, chloregenic acid and hesperetin were found to be the major phenolic compounds. F. hepatica eggs were collected from the gall bladder of naturally infected sheep. The eggs were exposed to two concentrations of P. harmala seeds extract (1 and 3 mg/mL) for 24 and 48 h. To investigate the effect of the P. harmala seeds extract on the miracidial formation, the treated eggs were incubated at 28 °C for 14 days. The results indicated that F. hepatica eggs were susceptible to the methanolic extract of P. harmala seeds. Following 24 h exposure of the eggs to P. harmala seeds extract with concentrations of 1 and 3 mg/mL, the miracidial formation reduced to 5 and 2.2 % respectively (compared with 60 % for the control group). Following 48 h of exposure of the eggs to P. harmala seeds extract with 1 mg/mL concentration, the miracidial formation reduced to 0.5 %. In this exposure time, no miracidial formation was observed in the eggs exposed to P. harmala seeds extract with concentration of 3 mg/mL. Therefore, the results of this study indicated that P. harmala seeds extract has high ovicidal activity against the eggs of F. hepatica. Accordingly, this extract may have the potential flukicidal activity against the immature and mature F. hepatica.

The 'Toolbox' of strategies for managing Haemonchus contortus in goats: What's in and what's out

A dynamic and innovative approach to managing the blood-consuming nematode Haemonchus contortus in goats is critical to crack dependence on veterinary anthelmintics. H. contortus management strategies have been the subject of intense research for decades, and must be selected to create a tailored, individualized program for goat farms. Through the selection and combination of strategies from the Toolbox, an effective management program for H. contortus can be designed according to the unique conditions of each particular farm. This Toolbox investigates strategies including vaccines, bioactive forages, pasture/grazing management, behavioural management, natural immunity, FAMACHA, Refugia and strategic drenching, mineral/vitamin supplementation, copper Oxide Wire Particles (COWPs), breeding and selection/selecting resistant and resilient individuals, biological control and anthelmintic drugs. Barbervax(®), the ground-breaking Haemonchus vaccine developed and currently commercially available on a pilot scale for sheep, is prime for trialling in goats and would be an invaluable inclusion to this Toolbox. The specialised behaviours of goats, specifically their preferences to browse a variety of plants and accompanying physiological adaptations to the consumption of secondary compounds contained in browse, have long been unappreciated and thus overlooked as a valuable, sustainable strategy for Haemonchus management. These strategies are discussed in this review as to their value for inclusion into the 'Toolbox' currently, and the future implications of ongoing research for goat producers. Combining and manipulating strategies such as browsing behaviour, pasture management, bioactive forages and identifying and treating individual animals for haemonchosis, in addition to continuous evaluation of strategy effectiveness, is conducted using a model farm scenario. Selecting strategies from the Toolbox, with regard to their current availability, feasibility, economical cost and potential ease of implementation depending on the systems of production and their complementary nature, is the future of managing H. contortus in farmed goats internationally and maintaining the remaining efficacy of veterinary anthelmintics.

Substituted Carbazoles – A New Class of Anthelmintic Agent

A series of novel carbazoles were synthesized based on structural modifications to lead carbazole 1 (EC100 = 2.5 μM against Haemonchus contortus in vitro), which was revealed in a small molecule screening program as a potentially promising platform for the development of new anthelmintic drugs. Subsequently, analogues 19, 21, 41, 42 (EC100 = 1.25 μM, all), and 39 (EC100 = 0.625 μM) were demonstrated to exhibit enhanced in vitro anthelmintic activity over the lead structure, with compound 39 also being shown to be active in vivo against Heligmosomoides polygyrus.

Protein profiling of Haemonchus contortus found in sheep of Kashmir valley

Economic losses due to helminth parasites in sheep throughout the world are considerable. Haemonchus contortus is a blood sucking intestinal helminth that lives in the abomasum of small ruminants worldwide. This parasite can be devastating to producers as it causes decreased production levels due to clinical signs such as anaemia, edema and death. For isolation of the proteins of the parasite, a well defined methodology was adopted. The abomasae of sheep in which this parasite resides were collected from abattoirs of various districts and were then carried to laboratory for screening. In case of collection sites falling in far areas, the organs were screened on spot. The parasites were collected in normal saline, washed and stored in 0.05 M PBS with pH of 7.4 at 0 °C. After refrigeration, frozen nematodes were thawed, homogenized and centrifuged at 1,000-15,000 rpm for 15 min. The supernatant was thus collected as a protein mixture and stored at -20 °C. Protein concentration of the samples was estimated by Lowry method. The samples were then analyzed through PAGE and then through SDS-PAGE. Protein estimation of the samples was estimated to be 4.2 mg/ml. The processed parasite samples were then subjected to PAGE and SDS-PAGE to determine the presence of the proteins. It showed high concentration of proteins in its whole protein profile. The proteins were seen as continuous bands intermixing with each other in PAGE analysis. The present study revealed two bands of molecular weights-55 and 33 kDa in PAGE analysis. The proteins when analyzed through SDS-PAGE were mostly found in the range of 25-70 kDa. The SDS-PAGE analysis showed four prominent bands. These bands were of the molecular weights of 66, 40, 33 and 26 kDa. The present work was a challenging one since only a single study was conducted in this region on this aspect and thus obviously was a big task to peep into the field where scanty input was available.

A review on the effect of macrocyclic lactones on dung-dwelling insects: Toxicity of macrocyclic lactones to dung beetles

Avermectins and milbemycins are commonly used in agro-ecosystems for the control of parasites in domestic livestock. As integral members of agro-ecosystems with importance in maintaining pasture health through dung burial behaviour, dung beetles are an excellent nontarget bio-indicator taxon for examining potential detrimental effects of pesticide application. The current review focuses on the relative toxicity of four different anthelmintics (ivermectin, eprinomectin, doramectin and moxidectin) in dung residues using dung beetles as a bioindicator species. One of the implications of this review is that there could be an effect that extends to the entire natural assemblage of insects inhabiting and feeding on the dung of cattle treated with avermectin or milbemycin products. Over time, reduced reproductive rate would result in decreased dung beetle populations and ultimately, a decrease in the rate of dung degradation and dung burial.

Immune gene expression in the spleen of chickens experimentally infected with Ascaridia galli

Ascaridia galli is a gastrointestinal nematode infecting chickens. Chickens kept in alternative rearing systems or at free-range experience increased risk for infection with resulting high prevalences. A. galli infection causes reduced weight gain, decreased egg production and in severe cases increased mortality. More importantly, the parasitised chickens are more susceptible to secondary infections and their ability to develop vaccine-induced protective immunity against other diseases may be compromised. Detailed information about the immune response to the natural infection may be exploited to enable future vaccine development. In the present study, expression of immune genes in the chicken spleen during an experimental infection with A. galli was investigated using the Fluidigm(®) BioMark™ microfluidic qPCR platform which combines automatic high-throughput with attractive low sample and reagent consumption. Spleenic transcription of immunological genes was compared between infected chickens and non-infected controls at week 2, 6, and 9 p.i. corresponding to different stages of parasite development/maturation. At week 2 p.i. increased expression of IL-13 was observed in infected chickens. Increased expression of MBL, CRP, IFN-α, IL-1β, IL-8, IL-12β and IL-18 followed at week 6 p.i. and at both week 6 and 9 p.i. expression of DEFβ1 was highly increased in infected chickens. In summary, apart from also earlier reported increased expression of the Th2 signature cytokine IL-13 we observed only few differentially expressed genes at week 2 p.i. which corresponds to the larvae histotrophic phase. In contrast, we observed increased expression of pro-inflammatory cytokines and acute phase proteins in infected chickens, by week 6 p.i. where the larvae re-enter the intestinal lumen. Increased expression of DEFβ1 was observed in infected chickens at week 6 p.i. but also at week 9 p.i. which corresponds to a matured stage where adult worms are present in the intestinal lumen.

MHC-DQB1 Variation and Its Association with Resistance or Susceptibility to Cystic Echinococcosis in Chinese Merino Sheep

Cystic echinococcosis (CE), one of the world’s most geographically widespread diseases, still represents a considerable economic and public health significance, although a variety of methods has been used to control the disease. It has been demonstrated that genetic factors, especially variations in MHC loci, can influence the outcome of CE infection in the human population. The study described here was designed to determine whether variation in MHC-DQB1 was associated with susceptibility or resistance to CE in sheep. If so, it would lay a theoretical foundation for breeding disease resistance sheep in future. This study was carried out on 204 Chinese Merino sheep, including 101 CE sheep and 103 healthy controls. The polymorphism of MHC-DQB1 exon 2 was detected by polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) method, and x² test was used to compare genotype frequencies between CE sheep and healthy controls. A total of 22 alleles and 42 genotypes were identified in DQB1 exon 2 in Chinese Merino sheep. In addition, x² test showed that frequencies of DQB1-TaqIaa and DQB1-HaeIIInn genotypes were significantly higher in the healthy group (82.5% and 57.3%, respectively) than that in the CE group (57.4% and 28.9%, respectively) (both p values = 0, OR = 0.286, 0.303, respectively), suggesting that these genotypes appeared to be associated with resistance to CE. Whereas, frequencies of DQB1-TaqIab and DQB1-HaeIIImn genotypes were significantly higher in the CE group (36.9% and 32.0%, respectively), as compared with the healthy group (16.5% and 11.15%, respectively) (p = 0.001, 0.001 and OR = 2.963, 3.629, respectively), indicating that these genotypes might be associated with susceptibility to CE. It is concluded that the genetic polymorphism within MHC-DQB1 might influence immune responses to pathogens, thus leading to the development of CE or protection against CE in Chinese Merino sheep, which would pave the way for breeding disease resistance sheep in future.

The effect of vitamin E supplementation on an experimental Haemonchus contortus infection in lambs

The objective of this study was to investigate the effect of vitamin E supplementation on an experimental Haemonchus contortus infection in lambs. Twenty lambs were stratified into two treatment groups based on fecal egg count. Worm-free lambs, 28-32 weeks of age, were supplemented with vitamin E (d-α-tocopherol) for 12 weeks following the recommendations of the National Research Council for the minimum daily requirement (control; 5.3 IU/kg body weight (BW)/day (d), n=10) or the requirement for optimal immune function (VE10; 10 IU/kg BW/d, n=10). Five weeks following initiation of vitamin E supplementation, lambs were infected with 10,000 H. contortus third stage larvae. Samples were taken weekly to quantify serum α-tocopherol, serum total non-specific immunoglobulin (Ig)G, whole worm antigen specific IgG, packed cell volume (PCV), and fecal egg count (FEC). Expression of cytokine genes IFN-λ and IL-4 were measured in peripheral blood collected prior to slaughter. Lambs were necropsied six weeks after infection and the α-tocopherol concentration of liver, muscle and lymph node were measured as well as abomasal worm burden and histologic evaluation of the abomasum for inflammation and enumeration of eosinophils and globule leukocytes. The livers of VE10 lambs contained slightly more α-tocopherol than control lambs. No differences were observed in serum, muscle or lymph node α-tocopherol concentration, serum IgG or peripheral mRNA expression of IL-4 or IFN-λ between control and VE10 lambs. However, lambs supplemented at 10IU/kg BW/d had a lower PCV reduction, FEC and worm burden 49% less than control lambs. Worm burden was negatively correlated with eosinophil (-0.720, P<0.05) and globule leukocyte count (-0.867, P<0.05). Strong positive correlations were observed within the inflammatory cell response in VE10 lambs that was absent in control lambs. These data indicate that additional vitamin E supplementation resulted in lower worm burden and greater recruitment of innate effector cells to the site of infection. Further studies are necessary to elucidate the mechanism by which vitamin E affects greater recruitment of innate effector cells to the abomasum during gastrointestinal nematode infection of lambs.

A systematic review and meta-analysis of factors associated with anthelmintic resistance in sheep

BACKGROUND

Anthelmintic drugs have been widely used in sheep as a cost-effective means for gastro-intestinal nematode (GIN) control. However, growing anthelmintic resistance (AHR) has created a compelling need to identify evidence-based management recommendations that reduce the risk of further development and impact of AHR.

OBJECTIVE

To identify, critically assess, and synthesize available data from primary research on factors associated with AHR in sheep.

METHODS

Publications reporting original observational or experimental research on selected factors associated with AHR in sheep GINs and published after 1974, were identified through two processes. Three electronic databases (PubMed, Agricola, CAB) and Web of Science (a collection of databases) were searched for potentially relevant publications. Additional publications were identified through consultation with experts, manual search of references of included publications and conference proceedings, and information solicited from small ruminant practitioner list-serves. Two independent investigators screened abstracts for relevance. Relevant publications were assessed for risk of systematic bias. Where sufficient data were available, random-effects Meta-Analyses (MAs) were performed to estimate the pooled Odds Ratio (OR) and 95% Confidence Intervals (CIs) of AHR for factors reported in ≥2 publications.

RESULTS

Of the 1712 abstracts screened for eligibility, 131 were deemed relevant for full publication review. Thirty publications describing 25 individual studies (15 observational studies, 7 challenge trials, and 3 controlled trials) were included in the qualitative synthesis and assessed for systematic bias. Unclear (i.e. not reported, or unable to assess) or high risk of selection bias and confounding bias was found in 93% (14/15) and 60% (9/15) of the observational studies, respectively, while unclear risk of selection bias was identified in all of the trials. Ten independent studies were included in the quantitative synthesis, and MAs were performed for five factors. Only high frequency of treatment was a significant risk factor (OR=4.39; 95% CI=1.59, 12.14), while the remaining 4 variables were marginally significant: mixed-species grazing (OR=1.63; 95% CI=0.66, 4.07); flock size (OR=1.02; 95% CI=0.97, 1.07); use of long-acting drug formulations (OR=2.85; 95% CI=0.79, 10.24); and drench-and-shift pasture management (OR=4.08; 95% CI=0.75, 22.16).

CONCLUSIONS

While there is abundant literature on the topic of AHR in sheep GINs, few studies have explicitly investigated the association between putative risk or protective factors and AHR. Consequently, several of the current recommendations on parasite management are not evidence-based. Moreover, many of the studies included in this review had a high or unclear risk of systematic bias, highlighting the need to improve study design and/or reporting of future research carried out in this field.

Antibodies trap tissue migrating helminth larvae and prevent tissue damage by driving IL-4Rα-independent alternative differentiation of macrophages

Approximately one-third of the world's population suffers from chronic helminth infections with no effective vaccines currently available. Antibodies and alternatively activated macrophages (AAM) form crucial components of protective immunity against challenge infections with intestinal helminths. However, the mechanisms by which antibodies target these large multi-cellular parasites remain obscure. Alternative activation of macrophages during helminth infection has been linked to signaling through the IL-4 receptor alpha chain (IL-4Rα), but the potential effects of antibodies on macrophage differentiation have not been explored. We demonstrate that helminth-specific antibodies induce the rapid trapping of tissue migrating helminth larvae and prevent tissue necrosis following challenge infection with the natural murine parasite Heligmosomoides polygyrus bakeri (Hp). Mice lacking antibodies (J_H^−/−) or activating Fc receptors (FcRγ^−/−) harbored highly motile larvae, developed extensive tissue damage and accumulated less Arginase-1 expressing macrophages around the larvae. Moreover, Hp-specific antibodies induced FcRγ- and complement-dependent adherence of macrophages to larvae in vitro, resulting in complete larval immobilization. Antibodies together with helminth larvae reprogrammed macrophages to express wound-healing associated genes, including Arginase-1, and the Arginase-1 product L-ornithine directly impaired larval motility. Antibody-induced expression of Arginase-1 in vitro and in vivo occurred independently of IL-4Rα signaling. In summary, we present a novel IL-4Rα-independent mechanism of alternative macrophage activation that is antibody-dependent and which both mediates anti-helminth immunity and prevents tissue disruption caused by migrating larvae.

Intestinal helminths present a pressing problem in developing countries with approximately 2 billion people suffering from chronic infection. To date no successful vaccines are available and a detailed mechanistic understanding of anti-helminth immunity is urgently needed to improve strategies for prevention and therapy. Antibodies form a crucial component of protective immunity against challenge infections with intestinal helminths. However, the exact mechanisms by which antibodies target these large multi-cellular parasites have remained obscure. We now demonstrate that helminth-specific antibodies induce the rapid trapping of tissue migrating helminth larvae by activating phagocytes. In the absence of antibodies or their receptors, helminth-infected mice developed extensive tissue damage, revealing a novel role for antibodies in limiting parasite-caused tissue disruption. Furthermore, helminth-specific antibodies reprogrammed macrophages to express wound-healing factors such as the arginine-metabolizing enzyme Arginase-1. Interestingly, the Arginase-1 product L-ornithine directly impaired the motility of helminth larvae. In summary, our study provides detailed mechanistic insights into how antibodies can modulate phagocyte function to provide protection against a large multi-cellular parasite. Our findings suggest that novel anti-helminth vaccines should target the larval surface and activate wound-healing macrophages to provide rapid protection against tissue-disruptive larvae.

Seasonal variations of EPG Levels in gastro-intestinal parasitic infection in a southeast asian controlled locale: a statistical analysis

We present a data based statistical study on the effects of seasonal variations in the growth rates of the gastro-intestinal (GI) parasitic infection in livestock. The alluded growth rate is estimated through the variation in the number of eggs per gram (EPG) of faeces in animals. In accordance with earlier studies, our analysis too shows that rainfall is the dominant variable in determining EPG infection rates compared to other macro-parameters like temperature and humidity. Our statistical analysis clearly indicates an oscillatory dependence of EPG levels on rainfall fluctuations. Monsoon recorded the highest infection with a comparative increase of at least 2.5 times compared to the next most infected period (summer). A least square fit of the EPG versus rainfall data indicates an approach towards a super diffusive (i. e. root mean square displacement growing faster than the square root of the elapsed time as obtained for simple diffusion) infection growth pattern regime for low rainfall regimes (technically defined as zeroth level dependence) that gets remarkably augmented for large rainfall zones. Our analysis further indicates that for low fluctuations in temperature (true on the bulk data), EPG level saturates beyond a critical value of the rainfall, a threshold that is expected to indicate the onset of the nonlinear regime. The probability density functions (PDFs) of the EPG data show oscillatory behavior in the large rainfall regime (greater than 500 mm), the frequency of oscillation, once again, being determined by the ambient wetness (rainfall, and humidity). Data recorded over three pilot projects spanning three measures of rainfall and humidity bear testimony to the universality of this statistical argument.

Combinação de drogas antiparasitárias como uma alternativa para o controle de nematódeos gastrintestinais multirresistentes em ovinos

Este estudo foi realizado com o objetivo de encontrarem-se tratamentos anti-helmínticos eficazes sobre uma população de nematódeos gastrintestinais de ovinos, a qual desenvolveu resistência a todas as classes de drogas com ação nematicida disponíveis para ruminantes no mercado brasileiro. Valendo-se da eficácia calculada de tratamentos convencionais a partir de um estudo prévio e, assim, conhecendo-se sua ação sobre diferentes gêneros de nematódeos presentes no rebanho, selecionaram-se drogas as quais, utilizadas em combinações ou em altas doses, pudessem aumentar significativamente a eficácia dos tratamentos. Utilizou-se o percentual de redução da contagem de ovos nas fezes e as culturas de larvas para avaliar a ação anti-helmíntica dos tratamentos testados. A combinação de moxidectina 1% + disofenol 20% apresentou 99% de eficácia, e as combinações de moxidectina 1% + triclorfon 10% e de moxidectina 1% + fosfato de levamisol 22,3% superaram os 90% de eficácia. A utilização de combinações de princípios ativos, com diferentes mecanismos de ação, pode promover a recuperação da eficácia dos tratamentos anti-helmínticos sobre populações multirresistentes de nematódeos gastrintestinais de ovinos.

Effect of vitamin E supplementation on naturally acquired parasitic infection in lambs

Gastrointestinal nematode infections cause substantial economic losses in pasture-based sheep farming worldwide. Host nutritional status has been identified as a key component of immune function. While vitamin E supplementation is known to have broad-spectrum effects on immune function in livestock, to our knowledge, there are no reports on the effect of vitamin E supplementation on trichostrongylid parasite infections in lambs. This study evaluated the effect of parenteral vitamin E supplementation on naturally acquired parasite infection in lambs. Twenty-seven spring lambs were sequentially assigned to receive injections of vitamin E (15 or 30 IU D-α-tocopherol/kg body weight (BW) or placebo, every two weeks, from birth to 28 weeks of age. Blood was collected at weeks 0, 2, 4, 8, 12, 16, 20, 24, and 28 to determine serum α-tocopherol concentration. Once the youngest animal reached 15 weeks of age all lambs were dewormed and grazed together on a pasture known to be contaminated with trichostrongylid larvae. Fecal egg count and blood packed cell volume (%) were determined on each lamb immediately prior to deworming and for the first seven weeks of pasture infection. Lambs were euthanized when they reached 28 weeks of age for determination of parasite worm burdens. Vitamin E supplementation at 30 IU/kg BW increased serum α-tocopherol over that of placebo (P<0.001) however, there was no effect of vitamin E supplementation on liver (P=0.804) or muscle (P=0.16) α-tocopherol content. There was no effect of vitamin E supplementation on fecal egg counts, packed cell volume, worm burden or nematode species distribution. Nematode genera identified were Haemonchus (30%), Trichostrongylus (42%), Nematodirus (27%), Strongyloides sp. (<1%), and Aonchotheca sp. (<1%). These results indicate that biweekly injections of vitamin E at 15 and 30 IU d-α-tocopherol/kg BW, had no effect on parasitological parameters used in the study to assess gastrointestinal nematode infection.

A suite of genes expressed during transition to parasitic lifestyle in the trichostrongylid nematode Haemonchus contortus encode potentially secreted proteins conserved in Teladorsagia circumcincta

The control of gastro-intestinal nematodes remains largely based on anthelminthic treatments, however spreading of anthelmintic resistance has reduced their efficacy. The genes involved in the transition to parasitic lifestyle could constitute targets of interest to develop alternative control strategies. In the trichostrongylid nematode Haemonchus contortus, we have used a SSH (Suppressive Subtractive Hybridization) based approach to generate two distinct subtracted cDNA libraries specifically enriched in cDNA expressed during the early parasitic fourth stage larvae L4 (5 days post-infection). A total of 200 clones were subjected to dot-blot experiments and 46 clones were selected for further characterization. The 46 corresponding expressed sequence tags (EST) were found to cluster into nine contigs. The corresponding full-length cDNA was obtained for all candidates. The genes encoding potentially secreted proteins were investigated in more detail. RT-PCR experiments confirmed their specific expression or over expression from the early L4 larvae to the adult stages and search for homologs in the trichostrongylid species T. circumcincta was performed in order to investigate whether they may be novel cross-specific targets.

The effects of condensed tannins extracted from different plant species on egg hatching and larval development of Teladorsagia circumcincta (Nematoda: Trichostrongylidae)

The effects of condensed tannins (CTs) extracted from five species of plants on egg hatching and larval development of Teladorsagia circumcincta (Stadelmann, 1894) (syn. Ostertagia circumcincta) were evaluated using in vitro bioassays. The extracts of CTs were obtained from Lotus pedunculatus (LP), Lotus corniculatus (LC), Dorycnium pentaphyllum (DP), Dorycnium rectum (DR) and Rumex obtusifolius (RO). The results of egg hatching assay showed that about 53%, 68%, 51%, 60% and 46% of the eggs hatched when in vitro incubations contained 900 microg/ml of CTs from LP, LC, DP, DR and RO, respectively (P < 0.001 relative to control incubation), while in control incubations (no CT added) 87% of the eggs hatched. In the larval development assay, development was allowed to proceed for 7 days, by which time 89% of the hatched larvae in control wells (no CTs) had reached the infective third stage (L3). In incubations containing 200 microg CT from LP, LC, DP, DR and RO/ml, about 8%, 15%, 14%, 8% and 4% of the eggs attained full development to L3 larvae, respectively (P < 0.001 relative to control incubation). Only 1% of the eggs were able to develop to L3 larvae in incubations containing 400 microg CT extracted from LC/ml, whilst in the incubations containing the same concentration of other CTs the eggs were not able to develop to L3 larvae. It seems that CTs are not only slowing down the larval development but also kill the undeveloped larvae. At 400 microg/ml, for example, CT from LP, LC, DP, DR and RO killed 67%, 48%, 68%, 93% and 91% of first-stage (L1) and second-stage (L2) larvae, respectively. This study shows that CTs are able to disrupt the life cycle of nematodes.

Discovery of veterinary antiparasitic agents in the 21st century: a view from industry

Discovery of antiparasitic agents is a challenging process, requiring discovery of molecules with the ability to kill parasites but not their hosts. Customer preference is for fewer doses and ease of application, but this is not always compatible with reduced withdrawal times, human food safety and/or user safety. This article describes some of the difficulties faced by researchers in the search for new antiparasitic agents, while highlighting advances that may improve the discovery process and the chance of success in discovering novel drugs.

In vitro nematicidal activity of extracts of Canthium mannii (Rubiaceae), on different life-cycle stages of Heligmosomoides polygyrus (Nematoda, Heligmosomatidae)

The increasing prevalence of anthelmintic-resistant strains of helminths, drug residues in animal products and high cost of conventional anthelmintics has created an interest in studying medicinal plants as an alternative source of anthelmintic. The potential nematicidal activities of four extracts from the bark of Canthium mannii (Rubiaceae) stem were investigated in vitro. Extracts were diluted in distilled water (DW) to obtain five different concentrations (1.5, 2.0, 2.5, 3.0 and 3.5 mg/ml) and put in contact with eggs and larvae of Heligmosomoides polygyrus. The different stages of the life cycle were also put in contact with the same concentration of mebendazole (MBZ, positive control). One millilitre of each extract at different concentrations and control were added to 1 ml solution containing 30–40 eggs or 10–15 larvae (L1, L2 and L3) and distributed in different Petri dishes. The eggs and larvae were incubated at 24°C and exposure times were: 48 h for un-embryonated eggs, 6 h for embryonated eggs; 2, 4, 6 and 24 h for L1 and L2 larvae, 24–48 h for infective larvae (L3), and 5 days for the larval development test (from L1 to L3). DW and 1% dimethyl sulphoxide (DMSO) were used as placebo and DMSO control, respectively. Significant effects were obtained with three of the four extracts, and differences were observed depending on the parasite stage. Cold water extract (CWE), hot water extract (HWE) and ethanol extract (ETE) inhibited embryonic development (40, 45 and 10%) and hatching of embryonated eggs (40, 85 and 80%), respectively, at 3.5 mg/ml. Only ETE killed L1 (97.18%) and L2 (92.68%) larvae of H. polygyrus after 24 h at 3.5 mg/ml and drastically reduced the production rate (6% at 3.0 and 3.5 mg/ml) of infective larvae (L3) after 5 days of incubation compared to other extracts (P < 0.05). However, the infective larvae of H. polygyrus were resistant to the effect of each of the tested products (extracts and mebendazole). These in vitro results suggested that extracts of C. mannii, used by traditional healers in Dschang, Western Region of Cameroon (Central Africa) to cure intestinal helminthiasis and abdominal pains of their patients, possess nematicidal properties. The active principles responsible for the activity could be secondary metabolites such as alkaloids and saponins present in the extracts. It is suggested that further experiments incorporating in vivo purification of extracts and toxicological investigations should be carried out.

Evaluation of the efficacy of anthelmintics sold on Ethiopian markets against Haemonchus contortus in experimentally infected Sheep

A total of 54 lambs, aged between 6-8 months were experimentally infected with Haemonchus contortus to evaluate the efficacy of different anthelmintic brands sold on Ethiopian markets using the faecal egg count reduction test (FECRT) and controlled anthelmintic efficacy trial. Accordingly four different albendazole (Alzole, Analgon-300, Albenjung_s and Ahshialben-300), two tetramisole (Tetsole and Ashitetra 600) and two tetramisole-oxyclozanide (Tetraclozan sheep and Tetraclozash 900) brands were evaluated at the dosage rates recommended by the manufacturers. Animals were allocated into nine groups of six animals each, and balanced for faecal egg counts (FEC), based on their pre-treatment FEC and treatments were randomized among the groups. One group was kept untreated as a control. Faecal egg count was conducted on day 30 post-infection (day of treatment) and on the 10th day post-treatment. Evaluation of anthelmintics based on FECRT revealed high efficacy (99.55-100% reduction in FEC) for all anthelmintic brands tested against H. contortus. The worm count reduction test using controlled anthelmintic efficacy trial also supported the above finding with 99-100% efficacy of the tested anthelmintics. Therefore, the suspicion on the anthelmintic products as being substandard in quality is not credible, at least, for the brands investigated in this study and it might rather be attributed to under dosing. The need for a good extension system for livestock producers with regard to good anthelmintic usage practices, in light of the inevitable development of anthelminitic resistance, is emphasized. Regular surveillance and laboratory quality evaluation of the anthelmintic products in Ethiopia is indicated.

Pyrantel in small animal medicine: 30 years on

Pyrantel, a tetrahydropyrimidine nicotinic agonist anthelmintic, has been used in companion animal medicine since the 1970s to control two important nematode groups, the hookworms and the roundworms. Given the zoonotic potential of these parasites, pyrantel has served a dual role in helping to protect the health of both companion animals and the public for more than 30 years. This review describes the history and mechanism of action of this drug, and collates evidence that resistance to pyrantel has developed in at least one canine nematode, the hookworm Ancylostoma caninum. The role of in vitro diagnosis tests in managing anthelmintic resistance in companion animal parasites is discussed, as are management practices that may reduce the rate at which resistance develops.

Heme transport and detoxification in nematodes: subproteomics evidence of differential role of glutathione transferases

In contrast to their mammalian hosts, parasitic nematodes are heme auxotrophs and require pathways for the uptake and transport of exogenous heme for incorporation into hemoproteins. Phase II detoxification Nu-class glutathione transferase (GST) proteins have a proposed role as heme-binding ligandins in parasitic nematodes. The genome-verified free-living nematode Caenorhabditis elegans also cannot synthesize heme and is an ideal functional genomics model to delineate the role of individual nematode GSTs in heme trafficking and heme detoxification. In this study, C. elegans was exposed to externally controlled heme concentrations ranging from 20-fold suboptimal growth levels to 10-fold supra-optimal growth levels to mimic fluctuations in blood- and tissue-feeding parasitic cousins from the same nematode group. A new heme-responsive GST (GST-19) was identified by subproteomics approaches. Functional characterization of this and two other C. elegans GSTs revealed that they all have high affinity for heme compounds similar to mammalian soluble heme carrier proteins such as HBP23 ( K d approximately 10 (-8) M). In the genomics-predicted absence of orthologous mammalian soluble heme-binding proteins in nematodes, we propose that Nu-class GSTs are candidates in the cellular processing of heme compounds. Toxic heme binding may be coupled to enzymatic protection from its breakdown as several GSTs possess glutathione peroxidase activity.

The effects of feeding sericea lespedeza hay on growth rate of goats naturally infected with gastrointestinal nematodes

Goat production is increasing in the United States due to high ethnic demand, but infection with gastrointestinal nematode (GIN) parasites is a major constraint to the industry. Increasing GIN resistance to chemical anthelmintics worldwide has led to the development of alternative control strategies, including use of forages containing condensed tannins (CT). An experiment was designed using infected and dewormed male kids (Kiko x Spanish, 6 mo old, 18.9 +/- 3.25 kg) fed diets containing 25% concentrate and either 75% sericea lespedeza [SL; Lespedeza cuneata (Dum-Cours.) G. Don], a high CT forage (87 to 181 g of CT/kg), or 75% bermudagrass [BG; Cynodon dactylon (L.) Pers.] hay (n = 10/treatment). The kids were weighed every 14 d, and fecal and blood samples were taken weekly for fecal egg counts and packed cell volume determination, respectively. Fecal cultures were processed every 14 d to determine CT effect on larval development. At slaughter, adult GIN were collected from the abomasum and small intestines for counting and speciation. Blood samples were also analyzed for plasma urea-N, and ruminal VFA and pH were determined. The infected SL-fed kids had consistently lower (P < 0.05) fecal egg counts than the infected BG goats throughout the trial and greater (P < 0.05) packed cell volume beginning by d 77. Average daily gain was greater (P < 0.001) in kids fed SL- than BG-based diets, regardless of infection status (104.3 +/- 5.0 and 75.5 +/- 4.8 g/d, respectively). Total VFA and acetate concentrations were greater (P < 0.001) in the BG- than in SL-fed goats, whereas propionate levels were unaffected by diet. Acetate:propionate ratio (P = 0.01) and plasma urea-N (P = 0.03) levels were greater in BG-fed goats, whereas rumen pH was greater (P < 0.001) in the SL-fed goats. Feeding SL hay can reduce GIN infection levels and increase performance of goats compared with BG hay.

Evolution of pathogens in a man-made world

Human activities have resulted in substantial, large-scale environmental modifications, especially in the past century. Ecologists and evolutionary biologists are increasingly coming to realize that parasites and pathogens, like free-living organisms, evolve as the consequence of these anthropogenic changes. Although this area now commands the attention of a variety of researchers, a broad predictive framework is lacking, mainly because the links between human activities, the environment and parasite evolution are complex. From empirical and theoretical examples chosen in the literature, we give an overview of the ways in which humans can directly or indirectly influence the evolution of different traits in parasites (e.g. specificity, virulence, polymorphism). We discuss the role of direct and indirect factors as diverse as habitat fragmentation, pollution, biodiversity loss, climate change, introduction of species, use of vaccines and antibiotics, ageing of the population, etc. We also present challenging questions for further research. Understanding the links between anthropogenic changes and parasite evolution needs to become a cornerstone of public health planning, economic development and conservation biology.