Phenotypic and genotypic characterisation of benzimidazole susceptible and resistant isolates of Haemonchus contortus

First Report of Benzimidazole Resistance in Field Population of Haemonchus contortus from Sheep, Goats and Cattle in Bosnia and Herzegovina

Haemonchus contortus is a globally significant parasitic nematode in ruminants, with widespread resistance to benzimidazole due to its excessive and prolonged use. Given the extensive use of benzimidazole anthelmintics in Bosnia and Herzegovina, we hypothesized that resistance is prevalent. The aim of this study was to identify the presence of anthelmintic resistance to benzimidazole in H. contortus from naturally infected sheep, goats and cattle in Bosnia and Herzegovina through the detection of the Phe/Tyr polymorphism in the amino acid at position 200 of the β-tubulin protein. From 19 locations in Bosnia and Herzegovina, a total of 83 adult H. contortus were collected from the abomasum of ruminants. Among these, 45 H. contortus specimens were isolated from sheep, 19 from goats and 19 from cattle. Results showed that 77.8% of H. contortus in sheep exhibited homozygous resistant genotypes at position 200 of the β-tubulin gene, with 15.5% being heterozygous. In goats, all tested H. contortus (100%) were homozygous resistant, and no heterozygous resistant or homozygous sensitive genotypes were found. Cattle had 94.7% homozygous resistant H. contortus, with no heterozygous resistant genotypes detected. In H. contortus from sheep and cattle, 6.7% and 5.3%, respectively, displayed homozygous sensitive genotypes. This study, for the first time, highlights the presence of a resistant population of H. contortus in sheep, goats and cattle in Bosnia and Herzegovina, using the rt-qPCR method. The resistance likely spread from sheep or goats to cattle, facilitated by shared pastures and the practice of transhumance, indicating a widespread and growing issue of anthelmintic resistance.

Assessment of gastrointestinal nematode anthelmintic resistance and acaricidal efficacy of fluazuron-flumethrin on sheep and goat ticks in the North West province of South Africa

Background and Aim

Anthelmintic resistance (AR) and acaricide resistance (ACR) pose great economic threat to communal livestock raised by rural communities, limiting sustainable production. This study was conducted to assess the occurrence of AR and ACR against nematodes and ticks that infest small ruminants (sheep and goats) from small-scale farming communities in the North West Province of South Africa, as well as document the associated risk factors.

Materials and Methods

The study was conducted on small-scale farming locations in two districts of the North West Province, namely, Dr. Ruth Segomotsi Mompati district and Dr. Kenneth Kaunda district, from November 2019 to March 2020. A questionnaire survey based specifically on antiparasitic treatment and related management practices was administered to 86 small-scale farmers. A fecal egg count reduction test (FECRT) was used to determine in vivo AR in small ruminants against benzimidazole (BZD), levamisole, and macrocyclic lactone on nine ruminant farms. Then, deoxyribonucleic acid was extracted from L3 larvae and resistant nematodes were identified using a polymerase chain reaction, targeting the internal transcribed spacer 2 gene. An egg hatch assay (EHA) and a larval mortality assay (LMA) were used to determine in vitro AR against thiabendazole (TBZ and BZD) in the same farms. Acaricide resistance against fluazuron-flumethrin (Drastic Deadline eXtreme) pour-on was assessed using an adult immersion test (AIT) on Rhipicephalus evertsi.

Results

Questionnaire results indicated that most farmers (89%) relied solely on anthelmintics. Farmers used visual appraisal to estimate the dosage, which is the primary cause of resistance. The FECRT revealed AR in all the farms. Egg hatch assay results revealed AR development against TBZ in all districts, with >95% of the eggs hatching at variable doses. Larval mortality assay results revealed the development of resistance against BZD, with 50% of L3 larvae surviving at different doses in all farms. Adult immersion test results indicated that fluazuron-flumethrin (>99%) exhibited high acaricidal efficacy against R. evertsi by inhibiting tick oviposition.

Conclusion

This investigation found that sheep and goats in the studied areas are developing AR to gastrointestinal parasites. The findings of in vivo tests showed resistance with fecal egg count reduction percentage of <95% or lower confidence limit of <90%. The results of EHA and LMA revealed no evidence of inhibition of egg development and larval mortality, indicating the development of resistance. Acaricide resistance was not detected against fluazuron-flumethrin, which is commonly used in the study areas. Thus, developing management methods for these economically significant livestock nematodes, including teaching small-scale farmers how to properly administer anthelmintics and acaricides to their livestock, is urgently needed.

Variation in allele frequencies in benzimidazole resistant and susceptible isolates of Haemonchus contortus during patent infection in lambs

We evaluated the variation in the frequency of benzimidazole (BZ) resistance-associated alleles at codons 200, 167 and 368 (F200Y, F167Y, V368L) of the β-tubulin isotype 1 gene during the patent period in isolates of Haemonchus contortus susceptible and resistant to BZ using pyrosequencing. Four lambs 5-6 months old were infected with 5000-6000 infective third-stage larvae (L3) of the susceptible MHco1 and the multi-resistant MHco4 isolates, respectively. Faecal samples were collected 28-times during 20-90 days post-infection (dpi). Coprocultures were subsequently prepared to produce L3 for genotyping. The frequency of the resistant allele (TAC) at codon 200 in MHco1 was lowest at 43 and 76 dpi with at each time point 0% and highest at 36 dpi with 10.85%, with a mean of 6.47% ± 2.39 and a coefficient of variation of 37.01%. The frequency of the TAC at codon 200 in MHco4 was lowest at 76 dpi with 25.6% and highest at 90 dpi with 49.25%, with a mean of 35.7% ± 4.42 and a coefficient of variation of 12.39%. No resistance alleles were detected in MHco1 at either codon 167 or 368. For MHco4 isolate, resistance alleles were detected only on codon 167 with a mean of 8.00% ± 4.83 and a mean coefficient of variation of 60.40%. Our results demonstrate the considerable variation in the frequency of resistant alleles in the susceptible and resistant isolates during the patent period. This variation should be considered when testing for the presence of BZ resistance in populations of gastrointestinal parasites, especially those with a low frequency of TAC.

First Report of Anthelmintic Resistance in Gastrointestinal Nematodes in Goats in Romania

Currently, there are three classes of anthelmintics most commonly used in small ruminants: the benzimidazoles (BZs), macrocyclic lactones (MLs) and cholinergic agonists (especially levamisole; LEV). The widespread use of those products has led to the emergence of drug-resistant parasite strains which represents a serious threat to the livestock industry. In the present study, we describe for the first time a case of resistance to anthelmintics in goats in Romania. The study was carried out in 2021 in a dairy goat herd from the Transylvania region. Two types of diagnostic methods were used to confirm anthelmintic resistance (AR). First, the faecal egg count reduction test (FECRT), an in vivo AR diagnostic method, was used to evaluate the efficacy of eprinomectin (EPM). The results of this test were analysed applying two different calculative methods that are used only in treated animals (without the control group). Furthermore, two in vitro methods were used: the egg hatch test (EHT) for the detection of resistance to BZs, and the larval development test (LDT) for detection of resistance to all three classes of anthelmintics. The results of FECRT indicate the resistance of gastrointestinal nematodes (GINs) to EPM in both calculative methods (FECR₁ = -88% and FECR₂ = -202%). In addition, the results obtained for ivermectin aglycone (IVM-AG) in LDT also indicate resistance to drugs from MLs group, especially avermectins. Similarly, the results of in vitro methods (EHT and LDT) indicate resistance to BZs in this herd. LEV was the only drug that stopped the development of L3 larvae 100% (LDT). H. contortus was the only nematode species found in coproculture after EPM treatment. Furthermore, H. contotus L3 larvae was the only species found in the wells with the highest concentrations of thiabendazole (TBZ) and IVM-AG in LDT. This suggests that resistance to both BZs and MLs was present for that species.

Does the in vitro egg hatch test predict the failure of benzimidazole treatment in Haemonchus contortus?

Considerable research has been directed towards optimising in vitro tests that can diagnose resistance in pre-parasitic stages of parasites. The objective of this study was to compare the in vivo faecal egg count reduction test (FECRT), the in vitro egg hatch test (EHT), and the molecular determination of the frequency of a codon 200 allele of β-tubulin isotype 1 associated with benzimidazole resistance in larval stages of Haemonchus contortus obtained from infected goats. Animals were infected with composite infective doses representing 10, 20, 30, 40, 60, and 80% resistant alleles. Faecal samples for the EHT were collected on 28, 33, and 35 days post-infection. The results of the in vivo FECRT indicated that albendazole treatment reduced infections consisting of composite doses of 10, 20, 30, 40, 60, and 80% larvae of the resistant isolate by 91.3, 78.0, 63.3, 48.4, 36.5, and 41.4%, respectively. The drug concentration at which 50% of the eggs were prevented from developing hatching larvae (ED₅₀) in the in vitro EHT varied from 0.09 ± 0.01 to 15.63 ± 12.10 μg/mL thiabendazole. The results of the in vitro EHT indicated that the test could estimate in vivo resistance well. The EHT could thus accurately estimate the in vivo efficacy of the drug and percentage of the resistance allele in the population using hatching parameters in delineation doses. This finding was also supported by comparing the FECRT data to the hatching percentages in the EHT on 30 goat farms in Slovakia with natural mixed infections of gastrointestinal parasites.

Prevalence of anthelmintic resistance of gastrointestinal nematodes in Polish goat herds assessed by the larval development test

Background

Helminthic infections, in particular those caused by gastrointestinal nematodes (GIN), are found worldwide and are among the most economically important diseases of goats. Anthelmintic resistance (AR) in GIN of goats is currently present worldwide, and single- or multidrug resistant species are widespread. The aim of this study was to determine the prevalence of AR to benzimidazoles (BZ), macrocyclic lactones (ML) and imidazothiazoles represented by levamisole (LEV) in the Polish goat herds by using an in vitro larval development test, which is useful especially in large-scale epidemiological surveys.

Results

This cross-sectional study was conducted from September 2018 to June 2019 and enrolled 42 dairy goat herds scattered over the entire country. The most commonly used anthelmintic class in goat herds in Poland were BZ (92%), followed by ML (85%) and LEV (13%). BZ-resistant GIN populations were found in 37 herds (88%, CI 95%: 75 to 95%), ML-resistant GIN populations in 40 herds (95%, CI 95, 84 to 99%), and LEV-resistant GIN populations in 5 herds (12%, CI 95%: 5 to 25%). Multidrug resistance involving all three anthelmintic classes was found in 5 herds (12%, CI 95, 5 to 25%). Based on the morphological features of stage 3 larvae the main resistant GIN turned out to be Haemonchus contortus and Trichostrongylus spp. The use of BZ and frequency of anthelmintic treatments were significantly related to the presence of AR to BZ in Polish goat herds.

Conclusions

This cross-sectional study demonstrates the existence of AR to BZ, ML and LEV on Polish goat farms. Resistance to BZ and ML is widespread, while AR to LEV is currently at a low level. A considerable proportion of herds harbours multidrug resistant GIN, which requires further consideration. An effective anthelmintic treatment strategy, reasonable preventive measures and better understanding of the resistance-related management practices by farmers and veterinarians may delay further development of AR.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12917-020-02721-9.

Molecular evidence on the emergence of benzimidazole resistance SNPs in field isolates of Marshallagia marshalli (Nematoda: Trichostrongylidae) in sheep

The infection with members of the Trichostrongylid nematodes has been frequently reported from sheep and goats. Because of the widespread use of Benzimidazoles (BZs), the resistance suspected to occur in some worms populations. In this study, we focused on the prevalent nematode, Marshallagia marshalli, from the abomasa of sheep. Samples were obtained from at least 10 infected farms and diagnosed with morphological and molecular methods. For resistance analysis, genomic DNA from pooled adult samples of all farms were analysed for the beta tubulin gene to detect any polymorphisms at codon positions of F167Y, E198A and F200Y. According to the results, seven farms (70%) revealed resistance (R) allele at F200Y with relatively high frequency. No other mutations were identified at the other two positions. Also, except for one homozygous (RR) occasion, the isolates with R allele had heterozygous (RS) genotype. This finding indicates that the worm populations are still affected by drugs of the BZ class. However, the genetic data also notes on developing resistance mechanisms in M. marshalli populations in sheep.

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.

Application of target repositioning and in silico screening to exploit fatty acid binding proteins (FABPs) from Echinococcus multilocularis as possible drug targets

Fatty acid binding proteins (FABPs) are small intracellular proteins that reversibly bind fatty acids and other hydrophobic ligands. In cestodes, due to their inability to synthesise fatty acids and cholesterol de novo, FABPs, together with other lipid binding proteins, have been proposed as essential, involved in the trafficking and delivery of such lipophilic metabolites. Pharmacological agents that modify specific parasite FABP function may provide control of lipid signalling pathways, inflammatory responses and metabolic regulation that could be of crucial importance for the parasite development and survival. Echinococcus multilocularis and Echinococcus granulosus are, respectively, the causative agents of alveolar and cystic echinococcosis (or hydatidosis). These diseases are included in the World Health Organization's list of priority neglected tropical diseases. Here, we explore the potential of FABPs from cestodes as drug targets. To this end, we have applied a target repurposing approach to identify novel inhibitors of Echinococcus spp. FABPs. An ensemble of computational models was developed and applied in a virtual screening campaign of DrugBank library. 21 hits belonging to the applicability domain of the ensemble models were identified, and 3 of the hits were assayed against purified E. multilocularis FABP, experimentally confirming the model's predictions. Noteworthy, this is to our best knowledge the first report on isolation and purification of such four FABP, for which initial structural and functional characterization is reported here.

The first report of multidrug resistance in gastrointestinal nematodes in goat population in Poland

Background

Prophylactic anthelmintic treatment with one of three basic classes of anthelmintics (benzimidazoles, macrocyclic lactones and imidazothiazoles) is still the mainstay of control of gastrointestinal nematode infections in small ruminants worldwide. As a consequence, anthelmintic resistance is a serious threat to small ruminant health and production. While the resistance to one class of anthelmintics has already been reported in most of countries, the newly-emerging problem is the resistance to two or even all of classes referred to as multidrug resistance. This study aimed to evidence the presence of multidrug resistance of gastrointestinal nematodes in goats in Poland.

Results

The combination of one in vivo method (fecal egg count reduction test) and two in vitro methods (egg hatch test and larval development test) performed in two goat herds in the southern Poland showed the presence of gastrointestinal nematodes resistant to fenbendazole and ivermectin in both herds. Moreover, in one herd it revealed the development of resistance to the last effective anthelmintic, levamisole, in response to one-year intensive use. Haemonchus contortus was the most prevalent gastrointestinal nematode in samples in which resistance to benzimidazoles and ivermectin was found, whereas Trichostrongylus colubriformis predominated when resistance to levamisole was observed.

Conclusion

This study shows for the first time that multidrug resistance of gastrointestinal nematodes to three basic classes of anthelmintics is already present in goat population in Poland. Moreover, it may indicate that different species or genera of gastrointestinal nematodes are responsible for the resistance to specific anthelmintics.

Assessment of the F200Y mutation frequency in the β tubulin gene of Haemonchus contortus following the exposure to a discriminating concentration of thiabendazole in the egg hatch test

The ruminant livestock production sector is under threat due to the infections with gastrointestinal nematode parasites and the subsequent development of anthelmintic resistance. One of most common and pathogenic species in small ruminants is Haemonchus contortus. The ability to control the infections with this and other gastrointestinal nematodes relies heavily on the use of anthelmintic drugs. Although resistance to all major classes of anthelmintics has been shown in H. contortus, the precise mechanism of resistance acquisition is only known for benzimidazoles. F200Y (TAC) is a common point mutation in the isotype 1 β tubulin gene which is associated with an effective increase in the resistance towards benzimidazole drugs. Here, we show the utility of using this mutation as a marker in a droplet digital PCR assay to track how two H. contortus laboratory strains, characterized by different resistance levels, change with respect to this mutation, when subjected to increasing concentrations of thiabendazole. Additionally, we wanted to investigate whether exposure to a discriminating dose of thiabendazole in the egg hatch test resulted in the death of all H. contortus eggs with a susceptible genotype. We found the MHco5 strain to maintain an overall higher frequency of the F200Y mutation (80-100%) over all drug concentrations, whilst a steady, gradual increase from around 30%-60% was observed in the case of the MHco4 strain. This is further supported by the dose-response curves, displaying a much higher tolerance of the MHco5 strain (LD₅₀ = 0.38 μg/ml) in comparison to the MHco4 strain (LD₅₀ = 0.07 μg/ml) to the effects of thiabendazole. All things considered, we show that the F200Y mutation is still a viable and reliable marker for the detection and surveillance of benzimidazole drug resistance in H. contortus in Europe.

Frequency of Resistance to Benzimidazoles of Haemonchus contortus Helminths from Dairy Sheep, Goats, Cattle and Buffaloes in Greece

The study investigated the presence of resistance to benzimidazoles in Haemonchus contortus helminths from ruminant species in Greece through the detection of the Phe/Tyr polymorphism in the amino acid at position 200 of the β-tubulin protein. In total, 288 adult female H. contortus helminths collected from the abomasum of various ruminant animals in Greece were tested. Of these, 96 were collected from sheep, 96 from goats, 48 from cattle, and 48 from buffaloes. The frequencies of the homozygous and heterozygous resistant genotypes at the position 200 of the β-tubulin gene of helminths recovered from sheep were 96.9% and 3.1%, respectively. The frequencies of the homozygous and heterozygous resistant genotypes, respectively, were 100.0% and 0.0% in helminths from goats, 25.0% and 75.0% in helminths from cattle and 8.3% and 91.7% in helminths from buffaloes. In all parasitic populations, no homozygous susceptible genotypes were detected. The present study highlighted, for the first time, the emergence of benzimidazole-resistant H. contortus in goats, cattle, and buffaloes in Greece, using an allele-specific PCR. It is postulated that benzimidazole-resistant alleles were transferred from sheep or goats to cattle and buffaloes at the commonly grazing pastures in Greece.

Large scale screening for benzimidazole resistance mutations in Nematodirus battus, using both pyrosequence genotyping and deep amplicon sequencing, indicates the early emergence of resistance on UK sheep farms

Benzimidazoles (BZ) have been the anthelmintic of choice for controlling Nematodirus battus infections since their release in the 1950s. Despite heavy reliance on this single anthelmintic drug class, resistance was not identified in this nematode until 2010 (Mitchell et al., 2011). The study aimed to explore the prevalence of BZ-resistance mutations in N. battus from UK sheep flocks using deep amplicon sequencing and pyrosequencing platforms. Based on evidence from other gastrointestinal nematodes, resistance in N. battus is likely to be conferred by single nucleotide polymorphisms (SNP) within the β-tubulin isotype 1 locus at codons 167, 198 and 200. Pyrosequencing and deep amplicon sequencing assays were designed to identify the F167Y (TTC to TAC), E198A (GAA to GCA) and F200Y (TTC to TAC) SNPs. Nematodirus battus populations from 253 independent farms were analysed by pyrosequencing; 174 farm populations were included in deep amplicon sequencing and 170 were analysed using both technologies. F200Y was the most prevalent SNP identified throughout the UK, in 12-27% of the populations tested depending on assay, at a low overall individual frequency of 2.2 ± 0.6% (mean ± SEM, based on pyrosequencing results). Four out of the five populations with high frequencies (>20%) of the F200Y mutation were located in NW England. The F167Y SNP was identified, for the first time in this species, in four of the populations tested at a low frequency (1.2% ± 0.01), indicating the early emergence of the mutation. E198A or E198L were not identified in any of the isolates. Results obtained were comparable between both techniques for F200Y (Lins' CCC, r_c = 0.96) with discrepancies being limited to populations with low frequencies. The recent emergence of resistance in this species will provide a unique opportunity to study the early stages of anthelmintic resistance within a natural setting and track its progress in the future.

Anthelmintic resistance in goat herds-In vivo versus in vitro detection methods

Anthelmintic resistance (AR) is a serious threat to animal health and has a major economic impact worldwide due to production and financial losses. The aim of this study was to determine the occurrence of AR on 30 goat farms in Slovakia during the pasturing seasons and to compare three widely used in vitro and in vivo methods for detecting AR in field conditions. A three-year survey was conducted during the pasturing seasons of 2014-2016. Goats on each farm were split into treated and control groups and were treated by recommended (5 mg/kg body weight) and double doses (10 mg/kg b.w.) of albendazole. Comparisons between percent reduction in a faecal egg count reduction test (FECRT) and an egg hatch test (EHT) and the presence of L₃ larvae in a larval development test (LDT) using resistant concentrations of benzimidazole (BZ) were monitored after treatment. The FECRT indicated percent reductions of 69.2-86.2% for the single dose and of 36.3-45.4% for the double dose. The EHT indicated that all farms had BZ-resistant nematodes. Low (<15% hatching) and high (>15% hatching) levels of resistance were detected on 13 and 17 farms, respectively. The LDT failed to detect resistant larvae on seven farms but detected low and high levels of resistance on seven and 14 farms, respectively. The data indicate a moderate correlation between in vitro and in vivo tests for detecting BZ resistance among the 30 goat farms. The hatching detected by the EHT and the presence of L₃ larvae by the LDT at resistant BZ concentrations provided reasonable identification of low levels of resistance in the parasite populations, but the use of a double dose for a treatment may underestimate the real occurrence of low levels of resistant parasites on goat farms.

Unique pharmacological properties of serotoninergic G-protein coupled receptors from cestodes

Background

Cestodes are a diverse group of parasites, some of them being agents of neglected diseases. In cestodes, little is known about the functional properties of G protein coupled receptors (GPCRs) which have proved to be highly druggable targets in other organisms. Notably, serotoninergic G-protein coupled receptors (5-HT GPCRs) play major roles in key functions like movement, development and reproduction in parasites.

Methodology/Principal findings

Three 5-HT GPCRs from Echinococcus granulosus and Mesocestoides corti were cloned, sequenced, bioinformatically analyzed and functionally characterized. Multiple sequence alignment with other GPCRs showed the presence of seven transmembrane segments and conserved motifs but interesting differences were also observed. Phylogenetic analysis grouped these new sequences within the 5-HT7 clade of GPCRs. Molecular modeling showed a striking resemblance in the spatial localization of key residues with their mammalian counterparts. Expression analysis using available RNAseq data showed that both E. granulosus sequences are expressed in larval and adult stages. Localization studies performed in E. granulosus larvae with a fluorescent probe produced a punctiform pattern concentrated in suckers. E. granulosus and M. corti larvae showed an increase in motility in response to serotonin. Heterologous expression revealed elevated levels of cAMP production in response to 5-HT and two of the GPCRs showed extremely high sensitivity to 5-HT (picomolar range). While each of these GPCRs was activated by 5-HT, they exhibit distinct pharmacological properties (5-HT sensitivity, differential responsiveness to ligands).

Conclusions/Significance

These data provide the first functional report of GPCRs in parasitic cestodes. The serotoninergic GPCRs characterized here may represent novel druggable targets for antiparasitic intervention.

Cestode parasites are flatworms with the ability to parasitize almost every vertebrate species. Several of these parasites are etiological agents of neglected diseases prioritized by WHO, such as hydatid disease, or hydatidosis, a zoonosis caused by species of the genus Echinococcus that affects millions of people worldwide. Due to the scarcity of anthelmintic drugs available and the emergence of resistant parasites, the discovery of new anthelmintic drugs is mandatory. Neuromuscular function has been the target of commonly used drugs against parasitic diseases to impact movement, parasite development and reproduction. Here we describe three new proteins, some of them highly expressed in cestodes which could be relevant for motility. Using different approaches, the three proteins were identified as G protein coupled receptors for serotonin, an important neurotransmitter and a known modulator of cestode motility. These new receptors exhibit unique characteristics including a particular sensitivity to serotonin as well as a distinctive pharmacology, which will assist their targeting for chemotherapeutic intervention.

First report of multiple anthelmintic resistance in nematodes of sheep in Colombia

This study aimed to report the presence of parasites resistant to the most used anthelmintic drugs in sheep in Colombia. Four farms (denominated farm 1, 2, 3 and 4) were selected where the animals were not treated with anthelmintics for two months before the trial. Animals with faecal egg count (FEC) above 150 and of different ages were allocated into six groups, each consisting of at least 5 animals. The drugs and dosages used were: ivermectin 1% (0.2 mg/kg), albendazole 25% (5 mg/kg), fenbendazole 10% (5 mg/kg), levamisole 10% (5 mg/kg), and moxidectin 1% (0.2 mg/kg). Anthelmintic efficacy was determined by the FEC reduction test (FECRT) with a second sampling 14 days post-treatment. The efficacy of albendazole and fenbendazole at farm 1 was above 95%, which was different from the others farms. The FECRT indicated the presence of multidrug resistance in the other farms where no tested drugs showed activity higher than 79% (albendazole: 0 to 55%, fenbendazole: 51.4 to 76.6%, ivermectin: 67.3 to 93.1%, levamisole: 0 to 78.1%, and moxidectin: 49.2 to 64.1%).Haemonchus contortus was the predominant (96%) species, followed by a small presence of Trichostrongylus sp. (3%) andCooperia sp. (1%). Therefore, we report for the first time the existence of multiple anthelmintic resistance in gastrointestinal nematodes of sheep in Colombia.

Prevalence of anthelmintic resistance on Lithuanian sheep farms assessed by in vitro methods

Background

This study examines the prevalence of drug resistance in gastrointestinal nematodes to macrocyclic lactones (ML) and benzimidazoles (BZ) in Lithuanian sheep using sensitive and precise in vitro methods. The survey was conducted from August 2013 to November 2014. Thirty-three farms with sheep previously treated with BZ and ivermectin (IVM) were included in the study. On 12 farms where only BZ were used, egg hatch discrimination dose testing (EHDDT) was conducted to detect anthelmintic resistance (AR) to BZ. On eight farms where only ML were used, micro agar larval development testing (MALDT) was conducted to detect AR to ivermectin (IVM). On the remaining 13 farms, where both classes of drugs were used, EHDDT and MALDT were both applied to detect multidrug resistance to BZ and IVM.

Results

BZ-resistant gastrointestinal nematodes were found on all 25 farms with a previous history of BZ use. High levels of resistance (>40 % of hatching) were recorded on 36 % of these farms, and low levels (<20 % of hatching) on 40 % of farms. IVM-resistant populations were found on 13 out of 21 sheep farms using this drug. Of these 13 farms with AR to IVM, low levels of resistance (<30 % development) were recorded on 84.6 % of farms and high levels (>30 % development) on 15.4 % of farms. No resistance to IVM was recorded on 38.1 % of farms. Multi-drug resistance was detected on five farms out of 13 (38.5 %) using both classes of drugs.

Conclusions

The present study demonstrates the existence of AR to BZ and ML on Lithuanian sheep farms thus confirming results in a previous in vivo study. Cases of multi-drug resistance were recorded in the present study and require further consideration. An appropriate strategy for anthelmintic treatment, measures to prevent gastrointestinal nematode infection and a better understanding of the management practices associated with resistance may slow down further development of AR.

Phenotypic and genotypic analysis of benzimidazole resistance in the ovine parasite Nematodirus battus

Benzimidazole resistance is common amongst many ovine trichostrongylid nematodes species globally. Although anthelmintics have been used for over half a century in some areas of the world for the control of Nematodirus battus, resistance has never been detected. Veterinary investigations conducted in 2010 demonstrated reduced efficacy in a flock that had been treated previously with fenbendazole (FBZ), suggesting probable resistance in N. battus. Infective larvae (L₃; designated MNba2) were generated from the original material to conduct a controlled efficacy test (CET). Faecal egg counts showed an average of 37% reduction in the FBZ treated group 7 days post treatment compared to the untreated lambs. Average worm burden results showed no reduction after FBZ treatment compared to the untreated group (3850 and 3850 worms respectively). A molecular assay to assess the frequency of the commonly associated single nucleotide polymorphisms (SNP) in the β-tubulin isotype 1 gene, F200Y and E198A, was developed. Larval genotypes were predominantly homozygous resistant at codon 200 SNP, ranging from 56%-83% and remained stable at 70% for adult worm populations taken from treated and control lambs in the CET. Only susceptible genotypes were found at codon 198. The allele frequency for F200Y ranged between 80-83% in adult worms taken from the CET from treated and control lambs. The results confirmed initial findings and demonstrated the first report of FBZ resistance in N. battus whilst providing evidence that the P200 point mutation in the β-tubulin isotype 1 gene is a potential mechanism of resistance in the species.

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.

Variability of the egg hatch assay to survey benzimidazole resistance in nematodes of small ruminants under field conditions

The egg hatch assay (EHA) is one of the main in vitro methods for detection of benzimidazole resistance in nematode parasites of small ruminants. However, although the EHA has been standardised at the laboratory level, the diagnostic performance of this method has not been fully characterised for field screenings. In the present work, monthly variation of benzimidazole resistance estimated by EHA was surveyed over two years in three sheep flocks and in one goat and an additional sheep flock sharing the same pastures. Resistance was measured by calculating both the effective dose of thiabendazole (TBZ) that inhibited hatching of ≥50% of parasite eggs (ED₅₀) and the proportion (Pdd) of eggs hatching at a discriminating dose of 0.1 μg/ml TBZ. Pdd exhibited higher variability than ED₅₀, in agreement with the higher sensitivity of Pdd to changes in resistance levels. Both resistance parameters, however, were highly correlated, and their variation was similarly related to the same factors. Resistance levels differed among sheep flocks, and the resistance level of the goat flock was higher than that measured for the sheep flock sharing the same pasture. Moreover, monthly variation of resistance in goats did not mirror that recorded in sheep. Resistance levels varied seasonally, with the highest values recorded in the spring, and they were inversely related to the number of days that samples were stored under anaerobic conditions. In addition, they were directly associated with the relative abundance of Teladorsagia spp. but inversely related to the relative abundance of Haemonchus spp. After controlling for the effects of these identified factors for variation, inter-monthly sampling variation due to unknown factors was the main source of variability, accounting for more than 60-70% of variance for both resistance parameters and yielding absolute estimation errors higher than 0.06 for ED₅₀ or 0.2 for Pdd when resistance was estimated from a single sampling. Optimum sample size, estimated from variance components, suggested that at least 4-5 samplings would be needed to halve this absolute error, whereas additional samplings would slightly increase precision but at the cost of substantially increasing sampling effort. More research is needed to identify the main factors involved in this inter-sampling variation to standardise the implementation of EHA under field conditions.

Wild deer as potential vectors of anthelmintic-resistant abomasal nematodes between cattle and sheep farms

Gastrointestinal (GI) nematodes are among the most important causes of production loss in farmed ruminants, and anthelmintic resistance is emerging globally. We hypothesized that wild deer could potentially act as reservoirs of anthelmintic-resistant GI nematodes between livestock farms. Adult abomasal nematodes and faecal samples were collected from fallow (n = 24), red (n = 14) and roe deer (n = 10) from venison farms and areas of extensive or intensive livestock farming. Principal components analysis of abomasal nematode species composition revealed differences between wild roe deer grazing in the areas of intensive livestock farming, and fallow and red deer in all environments. Alleles for benzimidazole (BZ) resistance were identified in β-tubulin of Haemonchus contortus of roe deer and phenotypic resistance confirmed in vitro by an egg hatch test (EC₅₀ = 0.149 µg ml⁻¹ ± 0.13 µg ml⁻¹) on H. contortus eggs from experimentally infected sheep. This BZ-resistant H. contortus isolate also infected a calf experimentally. We present the first account of in vitro BZ resistance in wild roe deer, but further experiments should firmly establish the presence of phenotypic BZ resistance in vivo. Comprehensive in-field studies should assess whether nematode cross-transmission between deer and livestock occurs and contributes, in any way, to the development of resistance on livestock farms.

Transcriptome analysis of a parasitic clade V nematode: comparative analysis of potential molecular anthelmintic targets in Cylicostephanus goldi

Clade V nematodes comprise several parasitic species that include the cyathostomins, primary helminth pathogens of horses. Next generation transcriptome datasets are available for eight parasitic clade V nematodes, although no equine parasites are included in this group. Here, we report next generation transcriptome sequencing analysis for the common cyathostomin species, Cylicostephanus goldi. A cDNA library was generated from RNA extracted from 17 C. goldi male and female adult parasites. Following sequencing using a 454 GS FLX pyrosequencer, a total of 475,215 sequencing reads were generated, which were assembled into 26,910 contigs. Using Gene Ontology and Kyoto Encyclopedia of Genes and Genomes databases, 27% of the transcriptome was annotated. Further in-depth analysis was carried out by comparing the C. goldi dataset with the next generation transcriptomes and genomes of other clade V nematodes, with the Oesophagostomum dentatum transcriptome and the Haemonchus contortus genome showing the highest levels of sequence identity with the cyathostomin dataset (45%). The C. goldi transcriptome was mined for genes associated with anthelmintic mode of action and/or resistance. Sequences encoding proteins previously associated with the three major anthelmintic classes used in horses were identified, with the exception of the P-glycoprotein group. Targeted resequencing of the glutamate gated chloride channel α4 subunit (glc-3), one of the primary targets of the macrocyclic lactone anthelmintics, was performed for several cyathostomin species. We believe this study reports the first transcriptome dataset for an equine helminth parasite, providing the opportunity for in-depth analysis of these important parasites at the molecular level. Sequences encoding enzymes involved in key processes and genes associated with levamisole/pyrantel and macrocyclic lactone resistance, in particular the glutamate gated chloride channels, were identified. This novel data will inform cyathostomin biology and anthelmintic resistance studies in future.

Anthelmintic resistance in sheep in Europe: a selected review

Intensive use of anthelmintics to control gastrointestinal nematodes selects for anthelmintic resistance, which has become an important issue in many European countries. Presence of nematode strains resistant to benzimidazoles, imidazothiazoles and/or macrocyclic lactones has been repeatedly reported, particularly for the three most important genera, Haemonchus, Teladorsagia and Trichostrongylus. Additionally, multiple drug-resistant populations of these parasites have also been detected. Examples are given for the situation in European countries with differing climatic conditions and management systems of small ruminants. The widespread emergence of multi-resistant nematodes proves that the past intensive suppressive chemical control strategies may not be a successful approach any longer. Experience from the up to now development of anthelmintic resistance suggests that modern control schemes should not rely on sole use of anthelmintics, but employ other, more complex and sustainable recipes, combing chemical, environmental and immunological control.