Anthelmintic resistance detection methods

Predicting the risk and speed of drug resistance emerging in soil-transmitted helminths during preventive chemotherapy

Control of soil-transmitted helminths relies heavily on regular large-scale deworming of high-risk groups (e.g., children) with benzimidazole derivatives. Although drug resistance has not yet been documented in human soil-transmitted helminths, regular deworming of cattle and sheep has led to widespread benzimidazole resistance in veterinary helminths. Here we predict the population dynamics of human soil-transmitted helminth infections and drug resistance during 20 years of regular preventive chemotherapy, using an individual-based model. With the current preventive chemotherapy strategy of mainly targeting children in schools, drug resistance may evolve in soil-transmitted helminths within a decade. More intense preventive chemotherapy strategies increase the prospects of soil-transmitted helminths elimination, but also increase the speed at which drug efficacy declines, especially when implementing community-based preventive chemotherapy (population-wide deworming). If during the last decade, preventive chemotherapy against soil-transmitted helminths has led to resistance, we may not have detected it as drug efficacy has not been structurally monitored, or incorrectly so. These findings highlight the need to develop and implement strategies to monitor and mitigate the evolution of benzimidazole resistance.

Seasonal Prevalence and Status of Anthelmintic Resistance of Goats' Gastrointestinal Nematodes, Mirab Abaya, Southern Ethiopia

Goats are an important source of livelihood especially for smallholder communities. But gastrointestinal nematodosis is the greatest threats of goat production. A repeated cross-sectional and field experimental study design was conducted from December 2020 to August 2021 in Mirab Abaya district, with the aim of seasonal prevalence gastrointestinal nematode infection and assessment of anthelmintic resistance. A systematic random sampling strategy was used to select the study goats. The overall prevalence of gastrointestinal nematode infections of goats in the study area was 57.9% (95% CI: 54.4-61.4), of which 48.7% (95% CI: 43.7-53.7) and 67.2% (95% CI: 62.3-71.7) accounted to dry and wet seasons, respectively. The multivariable logistic regression analysis showed that season, age, sex, and flock size were significantly (p < 0.05) influenced the prevalence of gastrointestinal nematode infection of goats. The number of eggs per gram of faeces (EPG) was ranged from 100 to 2500. The overall mean egg per gram of faeces (EPG) was 461.1 ± 20.9. The mean EPG of wet season (532.7 ± 28.6) was higher than the dry season (362.3 ± 29.1). From faecal culture, 552 nematode larvae were recovered, and the most commonly identified nematode genera were Haemonchus (36.4%) that followed by Trichostrongylus (28.1%), Oesophagostomum (15.4%), Bunostomum (11.4), Teladorsagia (5.4%), and Strongyloides (3.0%) species. From the anthelmintic resistance test in the field, the percentage reduction and 95% confidence limit of albendazole were 96% (84.2-99.0) and 97.0% (84.6-99.4) in dry and wet seasons, respectively. Here, the lower limit of 95% CI was less than 90% both in dry and wet seasons; and hence, albendazole was suspected for resistance development by gastrointestinal nematode. From a pooled faecal culture that collected from albendazole-treated goats, Haemonchus species was recovered. Therefore, due attention shall be by animal health professionals in the area in the use of albendazole. Animal health extension work to create awareness of how anthelmintic is used is helpful in reducing the risk. Changing the type of anthelmintic drug after using for some period will minimize the risk of anthelmintic resistance development.

Ex-vivo efficacy of commercially available anthelmintics against blood feeding stomach worm Haemonchus contortus of ruminants

Haemonchus contortus is the most prevalent and pathogenic gastrointestinal nematodes (GINs) in ruminants causing extensive economic losses. It is essential to estimate the efficacy of common commercially available anthelmintics against Haemonchus contortus parasite. Here, we standardized an ex-vivo culture platform for H. contortus and evaluated the efficacy of commonly used anthelmintics namely, albendazole (ABZ), levamisole (LVM), ivermectin (IVM), closantel (CLS) and rafoxanide (RFX). Adult worms were collected from abomasa of slaughtered animals, cultured in MEM, DMEM, M199 or RPMI with or without 20% FBS for up to 72 h. Cultured worms were incubated with ABZ, LVM, IVM, RFX or CLS in DMEM supplemented with 20% FBS at different concentrations (0.5-50 µg/ml) in triplicates and examined at 0, 3, 6, 12, 24, 36 and 48 h post treatment. Of the culture conditions, DMEM supplemented with 20% FBS supported the survival of H. contortus for (P < 0.001) longer period of time which was used in the evaluation of anthelmintics. The efficacy of CLS and RFX were significantly (P < 0.001) higher than other drugs and 100% mortality was observed at 2 µg/ml of CLS and RFX within 12 h post treatment. However, ABZ, LVM, and IVM showed significant effect at the concentration of 50 µg/ml with 48, 36, and 24 h, respectively. Morphological changes included severe cuticle disruption around the buccal cavity, posterior region and vulva as well as loss of cuticle structure integrity coupled with expulsion and fragmentation of digestive components of parasites when treated with 50 µg/ml of ABZ, LVM, and IVM and 2 µg/ml of RFX and CLS. Collectively, DMEM supplemented with 20% FBS can be used as ex-vivo culture platform for maintenance of H. contortus, and RFX and CLS can be used as the promising drugs for the prevention, control and treatment of H. contortus infections.

World Association for the Advancement of Veterinary Parasitology (W.A.A.V.P.) guideline for diagnosing anthelmintic resistance using the faecal egg count reduction test in ruminants, horses and swine

The faecal egg count reduction test (FECRT) remains the method of choice for establishing the efficacy of anthelmintic compounds in the field, including the diagnosis of anthelmintic resistance. We present a guideline for improving the standardization and performance of the FECRT that has four sections. In the first section, we address the major issues relevant to experimental design, choice of faecal egg count (FEC) method, statistical analysis, and interpretation of the FECRT results. In the second section, we make a series of general recommendations that are applicable across all animals addressed in this guideline. In the third section, we provide separate guidance details for cattle, small ruminants (sheep and goats), horses and pigs to address the issues that are specific to the different animal types. Finally, we provide overviews of the specific details required to conduct an FECRT for each of the different host species. To address the issues of statistical power vs. practicality, we also provide two separate options for each animal species; (i) a version designed to detect small changes in efficacy that is intended for use in scientific studies, and (ii) a less resource-intensive version intended for routine use by veterinarians and livestock owners to detect larger changes in efficacy. Compared to the previous FECRT recommendations, four important differences are noted. First, it is now generally recommended to perform the FECRT based on pre- and post-treatment FEC of the same animals (paired study design), rather than on post-treatment FEC of both treated and untreated (control) animals (unpaired study design). Second, instead of requiring a minimum mean FEC (expressed in eggs per gram (EPG)) of the group to be tested, the new requirement is for a minimum total number of eggs to be counted under the microscope (cumulative number of eggs counted before the application of a conversion factor). Third, we provide flexibility in the required size of the treatment group by presenting three separate options that depend on the (expected) number of eggs counted. Finally, these guidelines address all major livestock species, and the thresholds for defining reduced efficacy are adapted and aligned to host species, anthelmintic drug and parasite species. In conclusion, these new guidelines provide improved methodology and standardization of the FECRT for all major livestock species.

The Brown Alga Bifurcaria bifurcata Presents an Anthelmintic Activity on All Developmental Stages of the Parasitic Nematode Heligmosomoides polygyrus bakeri

The current control of gastrointestinal (GI) parasitic nematodes mainly relies on the widespread use of anthelmintics, which has inevitably led to resistance. Therefore, there is an urgent need to find new sources of antiparasitic compounds. Macroalgae represent a rich source of active molecules and are widely described as having medicinal properties. In the present study, we investigated the potential anthelmintic activity of aqueous extracts from three species of algae (Bifurcaria bifurcata, Grateloupia turuturu and Osmundea pinnatifida) on the murine parasite Heligmosomoides polygyrus bakeri. Using a set of complementary in vitro tests, including larval development assays, egg hatching tests and nematicidal activity assays on larvae and adults, we report the nematicidal activity of aqueous extracts of B. bifurcata. In addition, aqueous extract fractionation using liquid/liquid partitioning with a solvent of increasing polarity was performed in order to identify the groups of active molecules underlying the anthelmintic activity. Non-polar extracts (heptane, ethyl acetate) demonstrated high anthelmintic potential, highlighting the role of non-polar metabolites such as terpenes. Here, we highlight the strong anthelmintic potential of the brown alga B. bifurcata on a mouse model of GI parasites, thus confirming the strong interest in algae as natural alternatives for the control of parasitic nematodes.

Population replacement of benzimidazole-resistant Haemonchus contortus with susceptible strains: evidence of changes in the resistance status

The spread of anthelmintic resistance (AR) in nematode populations threatens the viability of sheep production systems worldwide, and warrants the adoption of sensitive, practical, and standardized tests to detect AR. The aim of this study was to characterize the replacement of an Haemonchus contortus population resistant to benzimidazoles (BZDs) by a susceptible one, by means of both phenotypic and genotypic techniques. Phenotypic methods to assess BZD resistance included in vivo tests, such as the fecal egg count reduction test (FECRT), and in vitro tests, such as the egg hatch assay (EHA). Additionally, genotypification of polymorphisms associated with BZD resistance by sequencing a fragment of the isotype 1 β-tubulin gene was carried out. The initial, BZD-resistant population (initial Balcarce population) exhibited an egg count reduction (ECR) of 59.3%. Following refugium replacement, the final population (final Balcarce population) exhibited an ECR of 95.2%. For the initial Balcarce population, the median effective dose (ED₅₀) for the EHA was 0.607 μg thiabendazole (TBZ)/mL, with a rate of eclosion at a discriminating dose (E_DD) of 0.1 μg TBZ/mL of 76.73%. For the final Balcarce population, ED₅₀ was 0.02 μg TBZ/mL, and E_DD was 1.97%. In the initial population, 93% of the analyzed individuals exhibited genotypic combinations associated with BZD resistance (53% Phe/Phe₁₆₇-Tyr/Tyr₂₀₀, 37% Phe/Tyr₁₆₇-Phe/Tyr₂₀₀, and 3% Phe/Tyr₁₆₇-Glu/Leu₁₉₈). Conversely, no combination associated with resistance was found in individuals from the final population. All of the tests were useful for detecting AR to BZDs. The results from the genetic and phenotypical studies were consistent, and the resulting information greatly aided in interpreting the outcomes of the population replacement and the potential impact of this strategy on management of AR.

Evaluation of in vitro methods of anthelmintic efficacy testing against Ascaridia galli

To investigate methods for in vitro assessment of anthelmintic efficacy against the chicken nematode Ascaridia galli this study firstly evaluated sample preparation methods including recovery of eggs from excreta using different flotation fluids and induced larval hatching by the deshelling-centrifugation method and the glass-bead method with or without bile. It then evaluated two in vitro assays, the in-ovo larval development assay (LDA) and larval migration inhibition assay (LMIA), for anthelmintic efficacy testing against A. galli using fresh eggs and artificially hatched larvae, respectively. Four anthelmintics, thiabendazole (TBZ), fenbendazole (FBZ), levamisole (LEV) and piperazine (PIP) were employed using an A. galli isolate of known susceptibility. The results suggested that the LDA and LMIA could successfully be used to generate concentration response curves for the tested drugs. The LDA provided EC50 values for inhibition of egg embryonation of 0.084 and 0.071 μg/ml for TBZ and FBZ, respectively. In the LMIA, the values of effective concentration (EC50) of TBZ, FBZ, LEV and PIP were 105.9, 6.32, 349.9 and 6.78 × 107 nM, respectively. For such in vitro studies, a saturated sugar solution showed high egg recovery efficiency (67.8%) and yielded eggs of the highest morphological quality (98.1%) and subsequent developmental ability (93.3%). The larval hatching assays evaluated did not differ in hatching efficiency but the deshelling-centrifugation method yielded larvae that had slightly better survival rates. For final standardization of these tests and establishment of EC50 reference values, tests using isolates of A. galli of defined resistance status need to be performed.

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.

First Report of Multiple Drug-resistant Gastrointestinal Nematodes of Sheep in Arbat District, Sulaymaniyah, Iraq Detected By in Vivo and in Vitro Methods

Introduction

The control of gastrointestinal nematodes (GINs) in small ruminants is principally dependent on anthelmintic therapy, which encounters the rising problem of anthelmintic resistance (AR) development. Veterinarians reported anthelmintic failure in several sheep farms in Arbat District, Sulaymaniyah, northern Iraq, which called for a systematic study about the efficacy of three commonly used drugs: albendazole, ivermectin, and levamisole.

Material and Methods

A faecal egg count reduction test (FECRT) was conducted to elucidate the anthelmintics’ efficacies, with coprocultures to determine the GINs parasitising sheep in the study area. Larval development assays (LDAs) were conducted to determine the drugs’ median inhibitory concentrations (IC₅₀).

Results

The FECRT revealed that AR was widespread to all three drugs, and ivermectin was the least effective, reducing the faecal egg counts (FECs) by 50.5% to 57.1%. The coprocultures revealed that the GIN genera of sheep in Arbat District were Trichostrongylus, Nematodirus, and Trichuris, and the resistance was mainly due to Trichostrongylus species. The mean IC₅₀ of albendazole, ivermectin, and levamisole were 0.073 ng/mL, 7.97 ng/mL, and 1.43 ng/mL, respectively.

Conclusion

This study is the first Iraqi report of AR confirmed by both in vivo FECRT and in vitro LDA methods.

Comparative Evaluation of Two In Vitro Tests for Detection of Ivermectin Resistance in Haemonchus contortus of Small Ruminants in Uttar Pradesh, India

PURPOSE

Resistance against ivermectin in India has been detected solely implementing in vivo tests and there is no published report of resistance employing in vitro methods. The present study was carried out to study ivermectin resistance in H. contortus of small ruminants by two in vitro tests and to determine their efficacy in effectively detecting ivermectin resistance in the field isolates.

METHODS

The present study was carried out in the small ruminant farms of the western region of Uttar Pradesh, India. Faecal samples with high egg per gram of faeces for H. contortus were selected. Two in vitro tests namely Micro agar larval development test and larval development assay were performed for assessing ivermectin resistance in field isolates of H. contortus by subjecting the eggs to different concentrations of ivermectin aglycone.

RESULTS

The results of the two in vitro tests implicated towards the susceptibility of H. contortus isolates in the area under study. The standard deviations of the two tests was compared and was found to be statistically non-significant.

CONCLUSION

It can be said that both in vitro tests are reliable for detecting resistance against different anthelmintics including ivermectin.

A loop-mediated isothermal amplification (LAMP) assay to identify isotype 1 β-tubulin locus SNPs in synthetic double-stranded Haemonchus contortus DNA

Development of sustainable gastrointestinal nematode (GIN) control strategies depends on the ability to identify the frequencies of drug-susceptible and resistant genotypes in GIN populations arising from management practices undertaken on individual farms. Resistance to BZ drugs in GINs has been shown to be conferred by the presence of defined SNPs in the isotype 1 β-tubulin locus. Loop-mediated isothermal amplification (LAMP) assays are amenable to use on a range of DNA templates and are potentially adaptable to use in practical, cost-effective, pen-side diagnostic platforms that are needed to detect anthelmintic resistance in the field. In this study, we designed primers and examined LAMP assays to detect each of the three major isotype 1 β-tubulin SNPs conferring genetic susceptibility to BZ drugs. We used artificial pools of synthetic DNA, containing different proportions of susceptible and resistant SNPs to determine reproducibility of the assays. We demonstrated the detection of each of the isotype 1 β-tubulin SNPs conferring susceptibility to BZ drugs using the optimal LAMP assay. Isotype 1 β-tubulin SNP typing was effective in detecting BZ susceptibility, but the accuracy was reduced in samples with less than 60 % susceptible DNA. Our results show the potential for LAMP SNP typing to detect genetic susceptibility or resistance to anthelmintic drugs in livestock GINs, and some of the limitations in our approach that will need to be overcome in order to evaluate this assay using field samples.

Anthelmintic resistance of Haemonchus contortus from sheep flocks in Brazil: concordance of in vivo and in vitro (RESISTA-Test©) methods

This study evaluated the resistance status of Haemonchus contortus from sheep flocks in the state of São Paulo, Brazil, through comparison between the fecal egg count reduction test (FECRT) and the larval development test (LDT). For the FECRT, 35 sheep were selected in each of five flocks and divided into groups treated with: benzimidazole, levamisole, ivermectin, monepantel and control. Feces were collected for EPG and fecal cultures. The LDT was performed using thiabendazole (TBZ), levamisole (LEV), ivermectin aglycone (IVM-A) and Zolvix (ZLV). Resistance to all drugs was detected using FECRT in 100% of the flocks, except in relation to ZLV (40% resistant and 20% suspected of resistance). LDT indicated resistance to TBZ and IVM-A in all flocks, to LEV in 80% of flocks and to ZLV in 10%. Total agreement was obtained between the two tests for TBZ and IVM (k = 1.0), while for LEV (k = 0.8) and ZLV (k = 0.9), substantial and almost perfect agreement were obtained, respectively. The concordance between the tests was significant, thus showing that it is possible to use the outcome of the LDT to predict the FECRT, and hence validating the former as a fast diagnostic test for use by sheep farmers in Brazil.

A 4 year observation of gastrointestinal nematode egg counts, nemabiomes and the benzimidazole resistance genotypes of Teladorsagia circumcincta on a Scottish sheep farm

Anthelmintic resistance threatens the sustainability of sheep production globally. Advice regarding strategies to reduce the development of anthelmintic resistance incorporates the outcomes of modelling exercises. Further understanding of gastrointestinal nematode species diversity, and population dynamics and genetics (which may vary between species) is required to refine these models; and field studies combining faecal egg outputs, species composition and resistance genetics are needed to calibrate them. In this study, faecal samples were taken from ewes and lambs on a commercial farm in south-eastern Scotland at approximately 3 t-4 week intervals between spring and autumn over a period of 4 years. Faecal egg counts were performed on these samples, and L₃ were collected from pooled coprocultures. Deep amplicon sequencing was used to determine both the species composition of these L₃ and the proportions of benzimidazole-resistant single nucleotide polymorphisms in the isotype-1 β-tubulin locus of the predominant species, Teladorsagia circumcincta L₃. Despite consistent management throughout the study, the results show variation in gastrointestinal nematode species composition with time and between age groups, that was potentially associated with weather conditions. The F200Y benzimidazole resistance mutation is close to genetic fixation in the T. circumcincta population on this farm. There was no evidence of variation in isotype-1 β-tubulin single nucleotide polymorphisms frequency between age groups, and no genetic evidence of reversion to benzimidazole susceptibility, despite targeted benzimidazole usage. This study highlights the need to include speciation when investigating gastrointestinal nematode epidemiology and anthelmintic resistance, and serves as an example of how genetic data may be analysed alongside species diversity and faecal egg counts, when markers for other anthelmintic classes are identified.

Preliminary Report on the Effect of Savanna Plants Leucaena leucocephala, Parkia platycephala and Senna alata against Eggs and Immature Stages of Trichostrongylid Nematodes In Vitro

The current study evaluated the anthelmintic effect of different extracts of Leucaena leucocephala, Parkia platycephala, and Senna alata on trichostrongylid eggs and infective larvae and determined the potential active components of each plant. Dried and macerated plant material was concentrated using rotaevaporation to obtain the crude extract (CE), followed by solvent partitioning to obtain hexanic (HexE), acetatic (AcE), and butanolic (BuE) extracts used for phytochemical analysis and anthelmintic efficacy testing in vitro. All the crude and partitioned extracts tested showed inhibition activity in the hatching of trichostrongylid eggs. Larvicidal efficacy was observed at CE concentrations of 2.5, 5.0, and 7.5 mg/mL for P. platycephala and S. alata. However, L. leucocephala CE did not significantly reduce the number of living larvae in the tested concentrations. Chromatographic analysis revealed several active metabolites; gallic acid, ellagic acid, naringin, morin, and kaempferol on AcE of P. platycephala; gallic acid, rutin, and ellagic acid on BuE of P. platycephala; and gallic acid and naringin on BuE of L. leucocephala. The extracts of P. platycephala, L. leucocephala, and S. alata leaves showed egg hatching inhibition and larvicidal activity, probably produced by tannins and flavonoids, which may act alone or by synergism.

Experimental evidence for the lack of sensitivity of in vivo faecal egg count reduction testing for the detection of early development of benzimidazole resistance

The objective of this study was to compare the results of an in vitro egg hatch test (EHT), micro-agar larval development test (MALDT) and in vivo faecal egg count reduction test (FECRT) between worm strains obtained from goats and sheep identically infected with the gastrointestinal parasitic nematode Haemonchus contortus. Results from the in vivo and in vitro tests were compared with benzimidazole (BZ)-resistance-associated β-tubulin allele frequencies determined using Pyrosequencing™. BZ resistance was not detected by the in vivo FECRT, where reductions of > 99% for both the resistant and the susceptible H. contortus strains were detected in both species. Discriminating doses in EHT and MALDT for the resistant strain indicated a low level (approx. 25%) of resistant individuals. Genotyping indicated that the susceptible strain had 10% BZ-resistant β-tubulin codon 200 alleles and the resistant strain had 26% respective resistant alleles. The in vitro tests and allele-frequency distribution suggested low levels of resistance in both strains; however, the FECRT did not support the evidence of resistant individuals of either strain in either species, suggesting a potential underestimation of low-level resistance in sheep and goats when employing this test.

Cuminaldehyde induces oxidative stress-mediated physical damage and death of Haemonchus contortus

Cuminaldehyde (CA), a monoterpenoid, preset in many plant sources including cumin, induces reactive oxygen-related damage and death in Haemonchus contortus, a parasitic worm with an LD50, values of 127.3 ± 7.5, 184.5 ± 12.1 and 104.1 ± 7.9 μg/mL for an adult female, adult male worms (12 h) and L3 larvae, respectively (24 h). Fifty percent of inhibition of egg hatching (IC50) was obtained at 142.4 ± 11.4 μg/mL after 48 h of exposure. Scanning electron microscopy revealed physical damage to the anterior and posterior ends, intestinal, ovarian, and esophageal regions of the warms on exposure to ca. The exposure of worms to CA also led to a systemic increase in reactive oxygen species (ROS) within 3 h. The better activity was seen with CA compared to standard antihelminthic drug albendazole (Alb). 74 μg/mL CA showed 2.3 fold more increase of catalase (CAT), 0.61 fold increase of superoxide dismutase (SOD), 3.3 fold increase of glutathione peroxidase (GPx) activity and 17.5 fold increase of glutathione (GSH) activity in comparison with Alb (500 μg/mL) for the same time of exposure (3 h). A firm increase of (2.9 fold) was also observed in nitric oxide synthase (NOS) activity within 12 h of exposure with CA (74 μg/mL) in comparison with Alb. Therefore the preclinical potential of CA is much higher than widely used antihelminthic drug Alb. The results open new opportunities to explore CA as a new active antihelminthic molecule.

A field study on the occurrence of gastrointestinal nematodes in sheep over the wet and dry seasons in two West Indian Islands

Gastrointestinal nematode (GIN) infestations are a major constraint to sheep production in the West Indies (WI). Intensive and semi-intensive management systems are most commonly employed. These islands display tropical weather patterns with wet and dry seasons. Semi-intensive farming combined with increased rainfall during the wet season has been reported to be most favourable for development and survival of GIN. This study was conducted to determine whether there was a relationship between GIN burdens in sheep with seasonality and management practices of farmers in Trinidad and Tobago (T&T). Farms were visited on a monthly basis from January to December 2017. A maximum of ten sheep, three to nine months of age, were selected from each farm. A total of 3,053 faecal samples were collected and analysed using the Modified McMaster technique. Environmental data on daily precipitation and temperature were collected from the Trinidad and Tobago Meteorological Office during the period of sampling. A mixed effects negative binomial regression model was constructed to analyse the relationship between gastrointestinal nematode faecal egg counts (GINFEC) with season, management system and use of dewormers as fixed effects and farm as a random effect. Average diurnal temperatures of T&T fluctuated between 23.2°C to 32.6°C and 23.9°C to 32.3°C in the dry and wet seasons, respectively. Average daily precipitation ranged between 1.6-1.8 mm and 6.1-8.5 mm during the dry and wet seasons, respectively. A decreased risk of 0.34 (95% CI 0.25-0.47, p < .0001) for GINFEC was observed in dewormed animals versus not dewormed. Semi-intensive management systems experienced an increased risk of GINFEC by 1.39 (95% CI 1.05-1.84, p = .021) compared with intensive and the risk of GINFEC was reduced by 0.40 (95% CI 0.33-0.49, p < .0001) in the wet season versus the dry. A higher prevalence of GIN was observed during the drier months of the year. Climatic conditions observed in T&T remained favourable for GIN survival, development and distribution year-round. Proper management is therefore required for reducing the occurrence of GIN in sheep of T&T throughout the year. This is the first reported study in the WI on the influence of seasonality and management on GIN infestations in sheep during the dry and wet seasons. Further investigation is needed to elucidate why GIN burdens appear to be higher in the dry season than the wet season. This study can be used as a baseline for public education in T&T as well as other developing countries.

Multiple anthelmintic resistance in gastrointestinal nematodes of small ruminants in Bangladesh

Anthelmintic resistance (AR) against gastrointestinal nematodes (GINs) of sheep and goats is a global concern. To address the problem, this study assessed the status of AR in different government and private sheep and goat farms in Bangladesh. We conducted fecal egg count reduction test (FECRT) and Egg hatch assay (EHA) experiments. For the detection of resistant larvae, pooled fecal samples from treated and non-treated groups were subjected to coproculture. Furthermore, 195 adult Haemonchus parasites were genotyped to ascertain benzimidazole (BZ) resistance allele from seven topographic zones of Bangladesh using allele specific PCR (AS-PCR). In FECRT, the percentage reduction along with 95% confidence intervals indicated that GINs were resistant to albendazole (ABZ), levamisole (LEV) and ivermectin (IVM). Coproculture revealed that Haemonchus spp., Oesophagostomum spp. and Trichostrongylus spp. were resistant to anthelmintics. ABZ resistance was also confirmed by in vitro EHA in all the farms except the private goat farm in Mymensingh. The genotype frequencies were 6% for homozygous resistant (rr), 59% for heterozygous (rS) and 35% for homozygous susceptible (SS) among different topographic zones. The allelic frequency of the mutation conferring resistance (r) ranged from 25% to 47% signifying resistance to BZ in nematodes of sheep/goats. The genotype frequencies (rr, rS and SS) and allelic frequencies (r and S) varied significantly (p˂0.05) in different zones in Bangladesh. Overall, the data suggest an alarming condition created by multiple AR in Bangladesh.

Caenorhabditis elegans muscle Cys-loop receptors as novel targets of terpenoids with potential anthelmintic activity

The anthelmintic treatment of nematode infections remains the pillar of worm control in both human and veterinary medicine. Since control is threatened by the appearance of drug resistant nematodes, there is a need to develop novel compounds, among which phytochemicals constitute potential anthelmintic agents. Caenorhabditis elegans has been pivotal in anthelmintic drug discovery and in revealing mechanisms of drug action and resistance. By using C. elegans, we here revealed the anthelmintic actions of three plant terpenoids -thymol, carvacrol and eugenol- at the behavioral level. Terpenoids produce a rapid paralysis of worms with a potency rank order carvacrol > thymol > eugenol. In addition to their paralyzing activity, they also inhibit egg hatching, which would, in turn, lead to a broader anthelmintic spectrum of activity. To identify drug targets, we performed an in vivo screening of selected strains carrying mutations in receptors involved in worm locomotion for determining resistance to the paralyzing effect of terpenoids. The assays revealed that two Cys-loop receptors with key roles in worm locomotion -Levamisole sensitive nicotinic receptor (L-AChR) and GABA(A) (UNC-49) receptor- are involved in the paralyzing effects of terpenoids. To decipher the mechanism by which terpenoids affect these receptors, we performed electrophysiological studies using a primary culture of C. elegans L1 muscle cells. Whole cell recordings from L1 cells demonstrated that terpenoids decrease macroscopic responses of L-AChR and UNC-49 receptor to their endogenous agonists, thus acting as inhibitors. Single-channel recordings from L-AChR revealed that terpenoids decrease the frequency of opening events, probably by acting as negative allosteric modulators. The fact that terpenoids act at different receptors may have important advantages regarding efficacy and development of resistance. Thus, our findings give support to the use of terpenoids as either an alternative or a complementary anthelmintic strategy to overcome the ever-increasing resistance of parasites to classical anthelmintic drugs.

Parasitic nematodes (roundworms) are of major significance as human pathogens and have important economic impact worldwide due to considerable losses in livestock and food crops. Drug treatment of nematode infections (anthelmintic drugs) are the pillar of worm control in human and veterinary medicine. Due to the appearance of drug resistant nematodes, there is a need of developing novel drugs, among which phytochemicals, that have environmental sustainability advantages, may constitute potential anthelmintic compounds. As parasitic nematodes are not ideal laboratory animals, the free-living nematode Caenorhabditis elegans, which shares many physiological characteristics with parasites and is sensitive to anthelmintic drugs, has emerged as a model organism for anthelmintic drug discovery. We found that three terpenoid compounds present in essential oil of plants–thymol, carvacrol and eugenol–produce rapid paralysis of C. elegans and inhibit egg hatching, thus mediating both rapid and long-term anthelmintic effects. By testing mutant worms that lack receptor proteins essential for locomotion we identified two different muscle receptors, nicotinic and GABA receptors, as terpenoid targets of the paralyzing effects. Electrophysiological studies from C. elegans cultured muscle cells demonstrated that terpenoids inhibit the function of these receptors. Thus, by modulating two receptors with key roles in worm motility, these terpenoids emerge as novel anthelmintic compounds.

Development of amplicon sequencing for the analysis of benzimidazole resistance allele frequencies in field populations of gastrointestinal nematodes

Anthelmintic resistant gastrointestinal helminths have become a major cause of poor health in sheep and goats. Sensitive and specific molecular markers are needed to monitor the genotypic frequency of resistance in field parasite populations. Gastrointestinal nematode resistance to benzimidazole is caused by a mutation in one of three positions within the isotype 1 β-tubulin gene. In the absence of markers for resistance to the other broad spectrum anthelmintic classes, these provide a relevant study example. Determination of the prevalence of these single nucleotide polymorphisms in field nematode populations can be impractical using conventional molecular methods to examine individual parasites; which can be laborious and lack sensitivity in determining low levels of resistance in parasite populations. Here, we report the development of a novel method based on an Illumina MiSeq deep amplicon sequencing platform to sequence the isotype 1 β-tubulin locus of the small ruminant gastrointestinal nematode, Teladorsagia circumcincta, and determine the frequency of the benzimidazole resistance mutations. We validated the method by assessing sequence representation bias, comparing the results of Illumina MiSeq and pyrosequencing, and applying the method to populations containing known proportions of resistant and susceptible larvae. We applied the method to field samples collected from ewes and lambs on over a period of one year on three farms, each highlighting different aspects of sheep management and approaches to parasite control. The results show opportunities to build hypotheses with reference to selection pressures leading to differences in resistance allele frequencies between sampling dates, farms and ewes or lambs, and to consider the impact of their genetic fixation or otherwise. This study provides proof of concept of a practical, accurate, sensitive and scalable method to determine frequency of anthelmintic resistance mutations in gastrointestinal nematodes in field studies and as a management tool for livestock farmers.

Anthelmintic activity of plants against gastrointestinal nematodes of goats: a review

The gastrointestinal nematodes (GIN) stand out as an important cause of disease in small ruminant, especially on goat farm. Widespread resistance to synthetic anthelminthics has stimulated the research for alternative strategies of parasite control, including the use of medicinal plants. The present work summarizes the in vitro and in vivo studies of plants with activity against GIN of goats, focusing on the description of chemical constituents related to this effect. This review retrieved 56 scientific articles from 2008 to 2018 describing more than 100 different plant species. The most frequently investigated family was Fabaceae (30.7%). Most in vitro studies on the activity of plant extracts and fractions were carried out with of free-living stages nematodes. In vivo studies were conducted mainly with the use of plants in animal feed and generally showed lower effectiveness compared to in vitro assays. The main plant secondary metabolites associated with anthelmintic effect are condensed tannins, saponin and flavonoids. However, the studies with compounds isolated from plants and elucidation of their mechanisms of action are scarce. Herbal medicines are thought to be promising sources for the development of effective anthelmintic agents.

Preliminary studies on in vitro methods for the evaluation of anticoccidial efficacy/resistance in ruminants

Ovine Eimeria spp. infections cause increased mortality, reduced welfare and substantial economic losses, and anticocccidials are important for their control. Recent reports of anticoccidial resistance against ovine Eimeria spp. necessitate the development of in vitro methods for the detection of reduced anticoccidial efficacy, especially since the in vivo methods are both expensive, time consuming and requires the use of otherwise healthy animals. The aim of the present study was therefore to approach a preliminary standardization of in vitro assays for evaluation of the efficacy of the most commonly used anticoccidials in ruminants. For this purpose, apart from the evaluation of inhibition of oocyst sporulation, most effort was concentrated on assessment of the capacity of the different anticoccidials to inhibit both the invasion and further development (up to the first schizogony) of E. ninakohlyakimovae sporozoites in bovine colonic epithelial cells (BCEC). For this purpose, infected cultures were monitored 1, 8 and 15 days post infection to determine the infection rate, number of immature schizonts and number, size and appearance of mature schizonts, respectively. No clear inhibitory effect was found with any of the anticoccidial formulations tested, and we could not identify why there were no measurable effects from the different anticoccidials. Despite the lack of positive results, further investigations should be encouraged, as this could decrease the need for animal experiments and could be used in the initial assessment of anticoccidial efficacy of new drugs.

Chamomile Methanolic Extract Mitigates Small Bowel Inflammation and ROS Overload Related to the Intestinal Nematodes Infection in Mice

BACKGROUND

Chamomile (Matricaria recutita L.) is a plant which has been reported to be effective in treating several parasitic and digestive diseases. The present study was conducted to evaluate the anthelmintic activity of chamomile methanolic extract (CME).

METHODS

In vitro, the anthelmintic activities of CME were investigated on the L3 larvae of Heligmosomoides polygyrus in comparison to albendazole. In vivo, Swiss albino mice were infected with infective third (L3) larval stage of H. polygyrus by intragastric administration. Moreover, the effect of CME and albendazole on worm eggs, adult worms, serum cytokine production, and oxidative stress was studied.

RESULTS

All used doses of CME showed a potent anthelmintic activity both in vitro and in vivo and the effect being similar to treatment with albendazole. Moreover, H. polygyrus infestation was accompanied by an intestinal oxidative stress status characterized by an increased lipoperoxidation, a depletion of antioxidant enzyme activity, as well as an overload of hydrogen peroxide. We have also recorded an increase of pro-inflammatory mediator (TNF-α, IL-6, and IL-1β) levels after treatment with CME (14 ± 0.8; 41 ± 2; 58 ± 4 pg/mg protein, respectively, with the concentration 800 mg/kg, body weight) when compared with infected control mice (20 ± 1; 59 ± 2, and 83 ± 4 pg/mg protein, respectively). However, extract treatment alleviated all the deleterious effects associated with H. polygyrus infection.

CONCLUSION

These findings suggest that CME can be used in the control of gastrointestinal helminthiasis and associated oxidative stress.

Effects of extended-release eprinomectin on productivity measures in cow-calf systems and subsequent feedlot performance and carcass characteristics of calves

The objective of this study was to estimate the impact of a single injection of extended-release eprinomectin on economically relevant production variables in beef cows and calves as well as subsequent feedlot health, performance, and carcass traits of calves compared with a traditional, short duration anthelmintic. Animals from 13 cooperator herds across seven states were stratified within herd and assigned to one of two treatments; injectable doramectin (DOR; Dectomax; n = 828) or injectable eprinomection (EPR; Longrange; n = 832). Fecal samples were randomly collected from a subset of cows at both treatment and the end of grazing to evaluate fecal egg count (FEC). Continuous and categorical data were analyzed using the MIXED and GLIMMIX procedures of SAS, respectively. Cow treatment body weight (BW) and final BW were not different (P ≥ 0.40) between treatments. There were no differences (P ≥ 0.12) between treatments in cow ADG, change in BW, or body condition scores during the grazing season. While FEC at treatment did not differ (P = 0.18), cows treated with EPR had lower final FEC at the end of the grazing season (P = 0.02) and a greater reduction of FEC over the grazing season (P = 0.01). Calf treatment BW, weaning BW, and ADG did not differ between treatments (P ≥ 0.34). Incidence of pinkeye tended to be less (P = 0.06) for cows treated with EPR but was not different for calves (P = 0.43). Conception to AI, overall pregnancy rates, and calving interval were not different between treatments (P ≥ 0.45). A subset of calves from each herd was sent to Tri-County Steer Carcass Futurity (TCSCF) feedlot for the finishing phase. Calf BW did not differ at initiation of feeding (P = 0.20). While EPR calves tended to be heavier at reimplantation (P = 0.07), final BW and overall ADG were not different between treatments (P ≥ 0.13). Health records indicated lower morbidity for EPR calves (P = 0.05). Carcass performance including HCW, dressing percent, backfat, KPH, REA, YG, were not different between treatment groups (P ≥ 0.12). However, EPR calves had a greater marbling score, greater average quality grade (P < 0.01), and higher proportion of calves that graded average choice or greater (P = 0.03). Results of this study indicate no difference in cow or preweaning calf performance, however, carcass quality in the feedlot phase was improved. Thus, economic analysis indicates opportunities for return on investment if animals treated with EPR have improved health status and/or carcass quality during the feeding phase.

Anthelmintic resistance and novel control options in equine gastrointestinal nematodes

Control of equine nematodes has relied on benzimidazoles (BZs), tetrahydropyrimidines and macrocyclic lactones. The intensive use of anthelmintics has led to the development of anthelmintic resistance (AR) in equine cyathostomins and Parascaris equorum. Field studies indicate that BZ and pyrantel resistance is widespread in cyathostomins and there are also increasing reports of resistance to macrocyclic lactones in cyathostomins and P. equorum. The unavailability of reliable laboratory-based techniques for detecting resistance further augments the problem of nematode control in horses. The only reliable test used in horses is the fecal egg count reduction test; therefore, more focus should be given to develop and validate improved methodologies for diagnosing AR at an early stage, as well as determining the mechanisms involved in resistance development. Therefore, equine industry and researchers should devise and implement new strategies for equine worm control, such as the use of bioactive pastures or novel feed additives, and control should increasingly incorporate alternative and evidence-based parasite control strategies to limit the development of AR. This review describes the history and prevalence of AR in equine nematodes, along with recent advances in developing resistance diagnostic tests and worm control strategies in horses, as well as giving some perspective on recent research into novel control strategies.

Comparative efficacy of ivermectin and Nigella sativa against helminths in Aseel chickens (Gallus gallus domesticus)

In this study, we evaluated the in vivo comparative efficacy of ivermectin and Nigella sativa extract against helminths in Aseel chickens, and the effects of helminths on blood parameters before and after treatment in Aseel chickens. Forty naturally infected adult Aseel chickens were randomly divided into four groups (n = 10 each): group A (ivermectin at 300 μg/kg); group B (N. sativa extract at 200 mg/kg); group C (ivermectin at 300 μg/kg + N. sativa extract at 200 mg/kg); group D was kept as a positive control to monitor time-related changes. On day 28 post treatment, the mean percentages of faecal egg-count reduction (FECR %) in groups A, B and C were recorded as 93.58, 88.09 and 100.00%, respectively. Further data analysis showed significantly higher efficacy in group C (100 ± 0.00%) than in groups A and B (P &lt; 0.001). Highly significant (P &lt; 0.001) improvements in mean percentage values of packed cell volume (PCV %) were recorded in groups A and C on days 14 and 28 post treatment. Meanwhile, the improvements in mean values of haemoglobin (Hb) concentration in groups A, B and C were highly significant (P &lt; 0.001) when compared to that of group D on day 28 post treatment. The synergistic combination of ivermectin and N. sativa extract possessed greater efficacy than either ivermectin or N. sativa extract used alone. Furthermore, both PCV % and Hb concentration values gradually increased in the treated groups compared to the control group, in which PCV % and Hb concentration gradually decreased throughout the trial.

The use of the larval development assay for predicting the in vivo efficacy of levamisole against Haemonchus contortus and Trichostrongylus colubriformis

The larval development assay has been used for many years to measure the sensitivity of the free-living life stages of trichostrongylid nematodes to anthelmintics. The assay has applications in both drug discovery and the diagnosis of drug resistance. We revisited the usefulness of the larval development assay for diagnosis of resistance to levamisole using field-derived isolates of Haemonchus contortus and Trichostrongylus colubriformis showing varying levels of resistance to this drug in vivo. Each of the resistant isolates showed a plateau in their larval development assay dose-response at the highest drug concentrations tested, representing a highly-resistant fraction, amounting to between 6.9 and 55.1% of the populations. The remaining population fractions for the resistant isolates showed IC₅₀ values from 1.4- to 17.8-fold higher than their corresponding susceptible isolate of the same species. We used a data set from the DrenchRite^® test user manual to derive equations describing the relationship between the IC₅₀ values for these low / moderate resistance components of each population and in vivo drug efficacy, and then used these equations to estimate the expected in vivo efficacy of levamisole against this population component of each isolate. A combination of this expected efficacy, with the known zero efficacy of the drug in vivo against the highly-resistant population fractions in each isolate, allowed us to calculate a predicted drug efficacy for the whole population for each isolate. The predicted levamisole efficacies for the three resistant H. contortus isolates were 88.8, 84.1 and 43.7%. These compared favourably with the actual efficacy of the drug against these isolates as determined in faecal egg count reduction tests or total worm count studies: 79, 66.3 and 40.6%, respectively. Similarly, for T. colubriformis, predicted efficacies of 82.0 and 1.8% compared favourably with the actual efficacies of 65-92 % and 0%, respectively. This study illustrates the usefulness of the larval development assay as a diagnostic tool for predicting in vivo efficacy of levamisole against H. contortus and T. colubriformis.

Motility in the L3 stage is a poor phenotype for detecting and measuring resistance to avermectin/milbemycin drugs in gastrointestinal nematodes of livestock

Motility is a commonly used in vitro phenotype for assessing anthelmintic activity of candidate compounds, and for detecting anthelmintic resistance in nematodes. Third-stage larvae (L3) of parasitic nematodes are commonly used in motility-based assays because L3 are simple to obtain and can remain viable in storage for extended periods. To improve the measurement of motility of microscopic stages of nematodes, our laboratory developed the Worminator, which quantitatively measures motility of parasites. Using the Worminator, we compared the dose-response characteristics of several avermectin/milbemycin (AM) compounds using L3 from both AM-susceptible and AM-resistant Cooperia spp. (abamectin, doramectin, eprinomectin, ivermectin, moxidectin) and Haemonchus contortus (eprinomectin, ivermectin, moxidectin). Concentrations tested with the Worminator ranged from 0.156 to 40 μM. Differences in EC₅₀ between AM-susceptible and AM-resistant isolates of Cooperia spp. and Haemonchus contortus were small, with resistance ratios ranging from 1.00 to 1.34 for Cooperia spp., 0.99 to 1.65 for Haemonchus contortus. Larval migration inhibition assays were conducted using the same isolates and were equally ineffective for detection of resistance with resistance ratios less than 2.0. These results contrast with those of the Larval Development Assay where we obtained a resistance ratio of 16.48 using the same isolates of Haemonchus contortus. Moreover, even at the highest concentration tested (40 μM), 100% inhibition of motility was never achieved and EC₅₀ for Worminator assays were more than 100× higher than peak plasma levels achieved in vivo following treatment. These data demonstrate that dose-response characteristics for inhibition of motility in L3 of gastrointestinal nematodes of livestock do not significantly differ for AM-susceptible and AM-resistant isolates. These data challenge the suitability of motility as a phenotype for detecting and measuring resistance to AM drugs in gastrointestinal nematodes of livestock.

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Motility of L3 is a poor phenotype for detection of avermectin resistance.

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Resistance ratios were less than 2.0 between susceptible and resistant isolates.

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Confidence intervals overlapped between susceptible and resistant isolates.

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Concentration to inhibit L3 motility is 100× peak plasma concentration in vivo.

The use of <i>Lespedeza cuneata</i> for natural control of gastrointestinal nematodes in Merino sheep

Lespedeza cuneata (poorman’s lucerne; sericea lespedeza), a tannin-rich perennial legume, was offered as hay to dry Merino ewes in a confined feeding experiment to evaluate the effect on the level of gastrointestinal parasite infection in sheep. Medicago sativa (a low tannin containing perennial legume) was used as the control treatment. Parameters faecal egg count (FEC), FAMACHA^© scores and rectal temperatures were used. FECs were substantially lower (p = 0.05) in the Lespedeza group after 35 days, together with a trend of higher rectal temperatures, compared with the Medicago group. Although non-significant (p > 0.05), the higher rectal temperatures suggested a lower level of anaemia in the sheep on the Lespedeza ration and, therefore, a lower parasite-worm burden. However, FAMACHA^© scores showed no significant (p > 0.05) differences between treatments despite the differences in FEC that were recorded, indicating that host homeostasis was possibly mediated by improved nutrition as a result of the high protein content of both experimental diets.

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.

Assessment of flukicide efficacy against Fasciola hepatica in sheep in Sweden in the absence of a standardised test

Anthelmintic resistance (AR) to Fasciola hepatica is emerging worldwide. Recently, AR to the adulticide compound albendazole (ABZ) was shown in Argentina and Spain. In Sweden, ABZ treatment failure against F. hepatica was first reported in sheep in 2012. The present study tested the efficacy of ABZ and triclabendazole (TCBZ) in sheep naturally infected with F. hepatica using a combination of three different diagnostic methods: faecal egg counts (FEC), coproantigen ELISA (cELISA) and Fasciola egg hatch test (FEHT). Two deworming trials, in November 2014 and January 2015, were performed on two sheep farms (farms A and B) in south-western Sweden. Except ABZ in November, treatment with ABZ or TCBZ achieved sufficient efficacy (97-100%) against adult F. hepatica on farm A. In contrast, ABZ treatment failed in the sheep flock on farm B, despite low initial faecal egg output. On farm B, ABZ efficacy based on FEC was 67% (95% CI: 35-84) and four of eight ewes tested were coproantigen-positive 21 days post-treatment. Ovicidal activity of ABZ against Fasciola eggs in isolates from both farms and one additional bovine isolate were tested by FEHT to exclude the presence of juvenile flukes and other factors such as dosing failure and poor quality of drug product. Irrespective of drug trial, data from FEHT showed significantly lower ovicidal activity of ABZ for the ovine farm B isolate than for the isolate from farm A. This confirms that the low efficacy of ABZ in sheep flock B was associated with ABZ resistance. Overall, the usefulness of three complementary methods for detection of ABZ resistance in the field was demonstrated.

Comparison of two in vitro methods for the detection of ivermectin resistance in Haemonchus contortus in sheep

Gastrointestinal parasitic nematodes in sheep cause severe economic losses. Anthelmintics are the most commonly used drugs for prophylaxis and therapy against parasitic helminths. The problem of drug resistance has developed for all commercially available anthelmintics in several genera and classes of helminths. In vitro and in vivo tests are used to detect anthelmintic resistance. Two in vitro methods (larval migration inhibition test and micromotility test) for the detection of ivermectin (IVM) resistance were compared using IVM-resistant and IVM-susceptible isolates of Haemonchus contortus. The degree of resistance for each test was expressed as a resistance factor (RF). The micromotility test was more sensitive for quantitatively measuring the degree of resistance between susceptible and resistant isolates. The RFs for this test for IVM and eprinomectin ranged from 1.00 to 108.05 and from 3.87 to 32.32, respectively.

Phenotypic assessment of the ovicidal activity of monepantel and monepantel sulfone on gastro-intestinal nematode eggs

The in vitro ovicidal activity of the amino acetonitrile derivative, monepantel (MPTL) and its active metabolite monepantel sulfone (MPTL-SO2) were assessed against a number of commercially important nematode species of ruminants, namely Teladorsagia circumcincta, Haemonchus contortus and Trichostrongylus axei. An egg hatch test (EHT) was used to make the assessment of both drug sensitive and drug resistant isolates. Both MPTL and MPTL-SO2 showed moderate ovicidal activity in vitro against all of the species examined, although species specific differences as measured by inhibitory concentration were observed. Analysis of the drug sensitive isolates showed H. contortus to be the most sensitive to both MPTL and MPTL-SO2 (ED50 1.7 and 2.7 μg/ml respectively) followed by T. circumcincta (ED50 2.1 and 2.7 μg/ml respectively) followed by T. axei (ED50 68.7 and 60.1 μg/ml respectively). Overall the EHT results would suggest no "global" in vitro discriminatory dose for detection of MPTL resistance is likely to be achievable, using the egg hatch test, due to large inherent variability observed between species. The test identified a dose dependent increase in MPTL and MPTL-SO2 sensitivity in two MPTL resistant T. circumcincta isolates and therefore offers to be a promising tool for the phenotypic characterisation of MPTL sensitivity, allowing exploration into the mechanisms involved in selection and development of MPTL resistance.

Overview of anthelmintic resistance of gastrointestinal nematodes of small ruminants in Brazil

Abstract Frequent and inappropriate use of all classes of antiparasitic drugs in small ruminants has led to failures in their effectiveness, culminating in a global problem of anthelmintic resistance. Brazil stands out as one of the world’s leaders in publications about anthelmintic resistance, and for having the most numerous reports of this resistance in small ruminants in the Americas. These studies have involved mainly the fecal egg count reduction test (FECRT) and its correlation with field management practices. In vivoeffectiveness testing is conducted in areas where livestock is of greater economic significance, e.g., in the South (sheep) and Northeast (goats), or is important for research and economic centers, such as the Southeast (sheep). The most widely studied species is sheep, for which the widest range of drugs is also evaluated. Despite significant advances achieved in molecular research, laboratory analyses should include knowledge about the reality in the field so that they can become feasible for the producer. Moreover, molecular studies can be underpinned by the analysis of field studies, such as the maintenance of antiparasitic effectiveness over time and the mechanisms involved in this process.

Anthelmintic Resistance in Haemonchus contortus: History, Mechanisms and Diagnosis

Haemonchus contortus has shown a great ability to develop resistance to anthelmintic drugs. In many instances, resistance has appeared less than 10years after the introduction of a new drug class. Field populations of this species now show resistance to all major anthelmintic drug classes, including benzimidazoles (BZs), imidazothiazoles and macrocyclic lactones. In addition, resistance to the recently introduced amino-acetonitrile derivative class (monepantel) has already been reported. The existence of field populations showing resistance to all three major drug classes, and the early appearance of resistance to monepantel, threatens the sustainability of sheep and goat production systems worldwide. This chapter reviews the history of the development of resistance to the various anthelmintics in H. contortus and examines the mechanisms utilized by this species to resist the effects of these drugs. Some of these mechanisms are well understood, particularly for BZ drugs, while our knowledge and understanding of others are increasing. Finally, we summarize methods available for the diagnosis of resistance. While such diagnosis currently relies largely on the faecal egg count reduction test, which suffers from issues of expense and sensitivity, we describe past and current efforts to utilize cheaper and less laborious phenotypic assays with free-living life stages, and then describe progress on the development of molecular assays to provide sensitive resistance-detection tests.

Assessment of in vitro and in vivo anthelminthic potential of extracts of Allium sativum bulb against naturally occurring ovine gastrointestinal nematodiosis

BACKGROUND

The rapid development of anthelminthic resistance has limited the success of traditional control programmes, thereby forcing researchers to search for ethno-veterinary alternatives.

OBJECTIVE

The objective is to assess the anthelminthic potential of various extracts of the bulb of Allium sativum in naturally infected sheep.

ANIMALS AND METHODS

In vitro anthelminthic activities of crude aqueous and methanolic extracts of the bulb of A. sativum were investigated against the egg (500 eggs/ml) and larvae of naturally infected sheep. The aqueous extract of A. sativum was also investigated for in vivo anthelminthic activity in three groups (n = 15 each) of naturally infected Chokla sheep with a negative control group receiving no treatment, a positive control group was given a single oral dose of albendazole at 7.5 mg/kg bodyweight, and a group administered a single oral dose of an aqueous extract at 5 g/animal. Data were analysed using the general linear model.

RESULTS

Aqueous extract showed better efficacy in egg hatch assay and larval development test. However, in larval paralysis test, reverse trend was seen as methanolic extract was more potent than the aqueous counterpart. A significant amount of 57% faecal egg count reduction was observed in in vivo trail using the aqueous extract on day 21 post-treatment, although in initial stages it showed 30% and 83% effectiveness on days 7 and 14 post-treatment, respectively. No deleterious ill effect was found in any of the haematological and biochemical parameters.

CONCLUSIONS

Bulb of A. sativum possesses good anthelminthic efficacy and further research is thereby warranted before recommending it for nematode control programme in ovines.

Inhibition of Haemonchus contortus larval development by fungal lectins

Background

Lectins are carbohydrate-binding proteins that are involved in fundamental intra- and extracellular biological processes. They occur ubiquitously in nature and are especially abundant in plants and fungi. It has been well established that certain higher fungi produce lectins in their fruiting bodies and/or sclerotia as a part of their natural resistance against free-living fungivorous nematodes and other pests. Despite relatively high diversity of the glycan structures in nature, many of the glycans targeted by fungal lectins are conserved among organisms of the same taxon and sometimes even among different taxa. Such conservation of glycans between free-living and parasitic nematodes is providing us with a useful tool for discovery of novel chemotherapeutic and vaccine targets. In our study, a subset of fungal lectins emanating from toxicity screens on Caenorhabditis elegans was tested for their potential to inhibit larval development of Haemonchus contortus.

Methods

The effect of Coprinopsis cinerea lectins - CCL2, CGL2, CGL3; Aleuria aurantia lectin – AAL; Marasmius oreades agglutinin - MOA; and Laccaria bicolor lectin – Lb-Tec2, on cultivated Haemonchus contortus larval stages was investigated using a larval development test (LDT). To validate the results of the toxicity assay and determine lectin binding capacity to the nematode digestive tract, biotinylated versions of lectins were fed to pre-infective larval stages of H. contortus and visualized by fluorescent microscopy. Lectin histochemistry on fixed adult worms was performed to investigate the presence and localisation of lectin binding sites in the disease-relevant developmental stage.

Results

Using an improved larval development test we found that four of the six tested lectins: AAL, CCL2, MOA and CGL2, exhibited a dose-dependent toxicity in LDT, as measured by the number of larvae developing to the L3 stage. In the case of AAL, CGL2 and MOA lectin, doses as low as 5 μg/ml caused >95 % inhibition of larval development while 40 μg/ml were needed to achieve the same inhibition by CCL2 lectin. MOA was the only lectin tested that caused larval death while other toxic lectins had larvistatic effect manifesting as L1 growth arrest. Using lectin histochemistry we demonstrate that of all lectins tested, only the four toxic ones displayed binding to the larvae’s gut and likewise were found to interact with glycans localized to the gastrodermal tissue of adults.

Conclusion

The results of our study suggest a correlation between the presence of target glycans of lectins in the digestive tract and the lectin-mediated toxicity in Haemonchus contortus. We demonstrate that binding to the structurally conserved glycan structures found in H. contortus gastrodermal tissue by the set of fungal lectins has detrimental effect on larval development. Some of these glycan structures might represent antigens which are not exposed to the host immune system (hidden antigens) and thus have a potential for vaccine or drug development. Nematotoxic fungal lectins prove to be a useful tool to identify such targets in parasitic nematodes.

Electronic supplementary material

The online version of this article (doi:10.1186/s13071-015-1032-x) contains supplementary material, which is available to authorized users.

Parasite control in pasture-grazed dairy cattle: are we at the edge of a precipice?

Gastrointestinal nematode (GIN) parasites are one of the most production-limiting infections of pasture-based dairy cattle in Australasia. Intensification of dairy production systems in both countries has meant that farmers have come to rely heavily on anthelmintic drenches to control GIN parasitism. However, anthelmintic resistance is now widespread in New Zealand, particularly to the market-leading macrocyclic-lactones. Less work has been conducted on anthelmintic resistance in Australia but preliminary results of a study currently underway suggests that there are high levels of resistance on Victorian dairy farms. The identification and mitigation of risk factors for the development of resistance is crucial for long-term sustainability of control. These include the use of drenches with variable efficacy – particularly pour-on and injectable formulations. New Zealand studies suggest that this may be as a result of active not reaching parasites within the gut lumen as effectively as oral formulations. Also, the raising of young stock as monocultures is a risk factor for the development of resistance as it significantly reduces the numbers of unselected (and presumably susceptible) parasites on pasture. These risks can be mitigated: using effective drenches removes more resistant parasites. This often means the use of combination products containing more than one anthelmintic class. Combination products are more effective in the face of existing resistance, and can slow the development of resistance. Also, ensuring an adequate level of unselected parasites on pasture for ingestion by young stock will delay the development of resistance. While there are differences between dairying systems, both countries are likely to benefit from more active and collaborative research efforts to improving parasite control practices on dairy farms in their respective countries.

Anthelmintic resistance in sheep gastrointestinal nematodes in Slovakia detected by in-vitro methods

Background

The intensive use of anthelmintics for the control of helminthic infections has resulted in the development of anthelmintic resistance, which has become a major practical problem in many countries. A variety of tests are available to monitor anthelmintic resistance but most of them are expensive, laborious and time consuming and therefore unpractical for large field surveys. The main aim of this survey was thus to detect the occurrence of benzimidazole (BZ) and macrocyclic lactone resistance on sheep farms in Slovakia by using novel and modified in vitro methods that are inexpensive, easy to use and quick and therefore practical for large surveys.

Results

BZ-resistant gastrointestinal nematodes were found on all 27 farms. Two farms (7.4%) had high levels of resistance (>40% of hatching), and 22 farms had low levels (<20% of hatching) of resistant nematodes. IVM-resistant populations were found on 14 of 49 sheep farms. The prevalence of BZ and IVM resistance has slightly increased on Slovak sheep farms during the last two decades.

Conclusions

Both the BZ and IVM surveys indicated that resistance against anthelmintics was present on Slovak sheep farms. Resistance against the BZ class of anthelmintics had been stable for two decades, but a slight increase on IVM resistance was confirmed. Farmers must thus observe the preventive measures to avoid a faster onset of IVM resistance, otherwise the presence of resistant parasites and ineffective treatment may harm the economy of their farms.

Monepantel: the most studied new anthelmintic drug of recent years

Monepantel (MOP), a new anthelmintic drug from a group of amino-acetonitrile derivatives, has been intensively studied during last years. Many authors examined this new drug from different perspectives, e.g. efficacy against different species and stages of parasites, mode of action, metabolism, pharmacokinetics, toxicity, resistance, ecotoxicity, etc. MOP is an anthelmintic for livestock (currently only sheep and goats), with molecular mode of action which is different to all other anthelmintics. MOP has a broad-spectrum of activity against gastrointestinal nematodes of sheep, including adults and L4 larvae of the most important species. The key feature of MOP is its full effectiveness against strains of nematodes resistant to benzimidazoles, levamisole, macrocyclic lactones and closantel. After oral administration, MOP is quickly absorbed into the bloodstream and quickly metabolized to MOP sulfone that has a similar efficacy as the parent molecule. Several other MOP metabolites formed in ovine hepatocytes were described. MOP and its metabolites are considered to be non-toxic to environment and its components, such as soil microflora, aquatic organisms, dung organisms, vegetation, etc. The aim of the presented review was not to collect all reported data but to bring an overview of various approaches in the study of MOP and to evaluate their principal results.

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.