Two benzimidazole resistance-associated SNPs in the isotype-1 β-tubulin gene predominate in Haemonchus contortus populations from eight regions in China

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.

Application of multiplex amplicon deep-sequencing (MAD-seq) to screen for putative drug resistance markers in the Necator americanus isotype-1 β-tubulin gene

Global control of hookworm infections relies on periodic Mass Drug Administration of benzimidazole drugs to high-risk groups, regardless of infection status. Mutations in the isotype-1 β-tubulin gene have been identified in veterinary nematodes, resulting in structural changes and reduced drug-binding. In Ghana, previous studies have demonstrated significant variability in albendazole effectiveness among people infected with the hookworm Necator americanus, although the mechanisms underlying deworming response have not been defined. Using hookworm egg samples from a cross-sectional study in Ghana, we developed a multiplex amplicon deep sequencing (MAD-seq) method to screen genomic regions encapsulating putative drug-resistance markers in N. americanus isotype-1 β-tubulin gene. Three single nucleotide polymorphisms (SNPs) corresponding to resistance-associated mutations (F167Y, E198A, F200Y) within the coding region of the isotype-1 β-tubulin gene were characterized using MAD-seq in 30 matched pre- and post-treatment samples from individuals with persistent infection following therapy. Post-sequence analysis showed that the highest mean alternative nucleotide allele at each PCR amplicon was 0.034% (167amplicon) and 0.025% (198/200amplicon), suggesting minimal allelic variation. No samples contained the F167Y SNP, while one contained low-frequency reads associated with E198A (3.15%) and F200Y (3.13%). This MAD-seq method provides a highly sensitive tool to monitor the three putative benzimidazole resistance markers at individual and community levels. Further work is required to understand the association of these polymorphisms to treatment response.

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.

Discovery of new vascular disrupting agents based on evolutionarily conserved drug action, pesticide resistance mutations, and humanized yeast

Thiabendazole (TBZ) is an FDA-approved benzimidazole widely used for its antifungal and antihelminthic properties. We showed previously that TBZ is also a potent vascular disrupting agent and inhibits angiogenesis at the tissue level by dissociating vascular endothelial cells in newly formed blood vessels. Here, we uncover TBZ's molecular target and mechanism of action. Using human cell culture, molecular modeling, and humanized yeast, we find that TBZ selectively targets only 1 of 9 human β-tubulin isotypes (TUBB8) to specifically disrupt endothelial cell microtubules. By leveraging epidemiological pesticide resistance data and mining chemical features of commercially used benzimidazoles, we discover that a broader class of benzimidazole compounds, in extensive use for 50 years, also potently disrupt immature blood vessels and inhibit angiogenesis. Thus, besides identifying the molecular mechanism of benzimidazole-mediated vascular disruption, this study presents evidence relevant to the widespread use of these compounds while offering potential new clinical applications.

Genetic diversity and population structure of Haemonchus contortus in goats from Thailand

Haemonchus contortus is one of the most economically important parasitic nematodes affecting small ruminant livestock worldwide. This study was conducted to elucidate the genetic diversity and population structure of this nematode in Thailand based on mitochondrial DNA markers, the nicotinamide dehydrogenase subunit 4 (nad4) and the cytochrome c oxidase subunit 1 (cox1) genes. One hundred and thirty-six adult worms were obtained from 86 abomasa of slaughtered goats from 13 different localities in 5 regions of Thailand. Identification to the genus Haemonchus was done using morphology. DNA sequences of the nuclear ribosomal second internal transcribed spacer (ITS2) identified each specimen to species: three fixed nucleotide (SNP) differences distinguished H. contortus from H. placei. Genetic analysis defined 118 and 122 unique haplotypes in partial sequences of nad4 (alignment length 723 bp) and cox1 (645 bp) genes, respectively. Nucleotide diversities were 0.031 and 0.043 for nad4 and cox1 genes, respectively. Low genetic differentiation was observed among H. contortus samples from various provinces in Thailand. This is the first study on the genetic diversity and population structure of H. contortus of goats in Thailand. This study has provided insights into the transmission dynamics of this parasitic nematode, information which is essential for farm management and parasite control.

The first molecular identification of benzimidazole resistance in Haemonchus contortus from goats in Thailand

Background and Aim

Haemonchus contortus is one of the major trichostrongyloid nematodes affecting small ruminant production worldwide, especially in tropical and subtropical regions. Adult H. contortus suck the blood from the host abomasum leading to anemia and often death in heavily infected animals. The mainstay of parasitic control is an anthelmintic drug, but long-term drug use may cause drug resistance. The aim of this study was to examine benzimidazole resistance in H. contortus of goats from different regions in Thailand by detecting the frequency of the F200Y polymorphism in the β-tubulin isotype 1 gene.

Materials and Methods

A total of 121 H. contortus adults were obtained from 31 naturally infected out of 37 slaughtered goats from city abattoirs in five regions of Thailand. The frequency of the F200Y polymorphism in the β-tubulin isotype 1 gene was detected following the allele-specific polymerase chain reaction protocol.

Results

The overall genotype frequencies in Thailand were homozygous resistant (RR: 24%), heterozygous (SR: 44.6%), and homozygous susceptible (SS: 31.4%). The allele frequencies were resistant allele (R: 46%) and susceptible allele (S: 54%). The R allele frequency and the RR genotype varied from 30% to 65% and 0% to 43.9%, respectively. The frequency of R alleles was significantly higher in the southern region (0.65) as compared to northern (0.30, p=0.001), western (0.38, p=0.04), and central regions (0.30, p=0.03). The RR genotype was also significantly higher in the southern region (43.9%) versus the northern (0 %, p=0.001), western (11.8%, p=0.012), and central regions (17.4%, p=0.001).

Conclusion

This is the first study of the detection of single-nucleotide polymorphisms in codon 200 of the β-tubulin isotype 1 gene of H. contortus from goats in Thailand. These findings are essential and imply that an integrated approach is needed for issues such as drug treatment, farm management, prevention, and control strategies. This is of interest to farmers, veterinarians, and the department of livestock.

In-silico comparison of inhibition of wild and drug-resistant Haemonchus contortus β-tubulin isotype-1 by glycyrrhetinic acid, thymol and albendazole interactions

Abstract

Haemonchus contortus is among the most prevalent pathogenic gastrointestinal nematodes that poses significant health issues in small ruminants. Control of Haemonchus contortus relies on benzimidazoles. However, most small ruminants have started showing benzimidazole resistance due to prolonged and intensive drug consumption It is postulated that single nucleotide polymorphism of specific amino acids, Phe200Tyr, Phe167Tyr and Glu198Ala in β-tubulin is the causal factor of this resistance. Hence, a plethora of alternative anthelmintic drug is currently being investigated. The present study intends to investigate in silico anthelmintic potential of glycyrrhetinic acid and thymol against wild and mutant β-tubulin protein of Haemonchus contortus. Based on binding energies obtained in docking studies using AutoDock 4.0, mutant β-tubulin at Phe200Tyr, Phe167Tyr and Glu198Ala illustrates insignificant changes in binding affinity of albendazole in comparison to the wild β-tubulin. However, glycyrrhetinic acid and thymol exhibited significantly greater binding affinities towards mutant β-tubulin in comparison to the albendazole-wild β-tubulin binding affinity. Hence, these phytocompounds can potentially inhibit both wild and mutant Haemonchus contortus β-tubulin polymerization. If established by in vitro and in vivo experiments, glycyrrhetinic acid could be an alternative anthelmintic compound, thus, further motivating the concept of reverse pharmacognosy.

Graphic abstract

Supplementary information

is available for this paper at 10.1007/s12639-020-01274-w.

A Whole Genome Re-Sequencing Based GWA Analysis Reveals Candidate Genes Associated with Ivermectin Resistance in Haemonchus contortus

The most important and broad-spectrum drug used to control the parasitic worms to date is ivermectin (IVM). Resistance against IVM has emerged in parasites, and preserving its efficacy is now becoming a serious issue. The parasitic nematode Haemonchus contortus (Rudolphi, 1803) is economically an important parasite of small ruminants across the globe, which has a successful track record in IVM resistance. There are growing evidences regarding the multigenic nature of IVM resistance, and although some genes have been proposed as candidates of IVM resistance using lower magnification of genome, the genetic basis of IVM resistance still remains poorly resolved. Using the full magnification of genome, we herein applied a population genomics approach to characterize genome-wide signatures of selection among pooled worms from two susceptible and six ivermectin-resistant isolates of H. contortus, and revealed candidate genes under selection in relation to IVM resistance. These candidates also included a previously known IVM-resistance-associated candidate gene HCON_00148840, glc-3. Finally, an RNA-interference-based functional validation assay revealed the HCON_00143950 as IVM-tolerance-associated gene in H. contortus. The possible role of this gene in IVM resistance could be detoxification of xenobiotic in phase I of xenobiotic metabolism. The results of this study further enhance our understanding on the IVM resistance and continue to provide further evidence in favor of multigenic nature of IVM resistance.

Haemonchus contortus: siRNA mediated knockdown of matrix metalloproteinase 12A (MMP-12) results in reduction of infectivity

BACKGROUND

RNA interference (RNAi) is an important tool to determine the role of genes. RNAi has been widely used to downregulate target molecules, resulting in the reduction of mRNA for protein expression. Matrix metalloprotease 12A (MMP-12) is known to have important roles during embryonic development, organ morphogenesis and pathological processes in animals. However, MMP-12 from Haemonchus contortus has not been characterized.

METHODS

Haemonchus contortus MMP-12 gene was cloned and recombinant protein of MMP-12 (rHc-MMP-12) was expressed. Binding activities of rHc-MMP-12 to goat peripheral blood mononuclear cells (PBMCs) were assessed by immunofluorescence assay (IFA) and the immuno-regulatory effects of rHc-MMP-12 on cell proliferation and nitric oxide production were observed by co-incubation of rHc-MMP-12 with goat PBMCs. Furthermore, a soaking method was used to knockdown the expression of Hc-MMP12 gene using three siRNA, targeting different regions of the gene and infectivity of effective siRNA on the development of H. contortus was evaluated in goat.

RESULTS

rHc-MMP-12 was successfully expressed in an expression vector as well as the tissues of the cuticle of adult H. contortus worms and a successful binding with PBMCs surface were observed. Increased cellular proliferation and nitric oxide production by goat PBMCs was observed in a dose-dependent manner. Quantitative real time PCR (qRT-PCR) results confirmed the successful silencing of Hc-MMP-12 gene in siRNA of 1, 2 and 3 treated third-stage larvae (L3) of H. contortus in vitro. The most efficient qRT-PCR-identified siRNA template was siRNA-2, with a 69% suppression rate compared to the control groups. Moreover, in an in vivo study, silencing of the Hc-MMP-12 gene by siRNA-2 reduced the number of eggs (54.02%), hatchability (16.84%) and worm burden (51.47%) as compared to snRNA-treated control group. In addition, a shorter length of worms in siRNA-2-treated group was observed as compared to control groups.

CONCLUSIONS

Our results indicate that siRNA-mediated silencing of Hc-MMP-12 gene in H. contortus significantly reduce the egg counts, larval hatchability, and adult worm counts and sizes. The findings of the present study demonstrate important roles of Hc-MMP-12 in the development of H. contortus.

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

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

Detection of Gastrointestinal Nematode Populations Resistant to Albendazole and Ivermectin in Sheep

Simple Summary

Gastrointestinal parasite infections represent a major welfare problem in small ruminants reared in extensive systems, which may be exacerbated by anthelmintic resistance. In this study, we evaluated the efficacy of two commonly used anthelmintic drugs in sheep reared in the Mexican temperate zone. We found that the genera Cooperia spp. and Trichostrongylus spp. were the nematodes predominant in all experimental animals. We also found that the sheep flock naturally infected with gastrointestinal nematodes in the temperate zone (i.e., central valley) of the State of Mexico exhibit anthelmintic resistance with marked and potentially detrimental effects on sheep welfare and production. Both albendazole and ivermectin proved to be only partly effective for the treatment of both Cooperia spp. and Trichostrongylus spp. Therefore, we suggest that nematode infections should be systematically monitored in order to implement integrated management strategies to control nematodiasis more effectively, limit anthelmintic resistance and promote sheep welfare and production.

Abstract

Gastrointestinal parasite infections represent a major welfare problem in small ruminants reared in extensive systems, which may be exacerbated by anthelmintic resistance. Therefore, we aimed to study the efficacy of albendazole and ivermectin in sheep. Eighty-six animals were selected from commercial farms in the temperate area of the State of Mexico at the age of seven months. These animals were randomly distributed into three groups: Group A, treated with albendazole, Group I, treated with ivermectin and Group C, left untreated. Faecal samples were collected before the anthelmintic was administered and 15 days post-treatment. Both Group A and Group I displayed a significant decrease of faecal egg counts when pre- and post-treatment values were compared (p = 0.003 and p = 0.049, respectively), and a significantly lower faecal egg count when compared with Group C after the treatment (p < 0.05). However, the faecal egg count reduction test showed that gastrointestinal nematodes (GIN) developed anthelmintic resistance to both albendazole and ivermectin. The results of the polymerase chain reaction (PCR) allowed the identification of Cooperia spp., and Trichostrongylus colubriformis. The allele-specific PCR results confirmed that T. colubriformis was resistant to albendazole. In conclusion, this study showed the presence of resistant GIN to albendazole and ivermectin in sheep reared in Mexican temperate zones. Therefore, nematode infections should be systematically monitored in order to implement integrated management strategies to prevent the spread of anthelmintic resistance.

Analysis of genome-wide SNPs based on 2b-RAD sequencing of pooled samples reveals signature of selection in different populations of Haemonchus contortus

The parasitic nematode Haemonchus contortus is one of the world's most important parasites of small ruminants that causes significant economic losses to the livestock sector. The population structure and selection in its various strains are poorly understood. No study so far compared its different populations using genome-wide data. Here, we focused on different geographic populations of H. contours from China (Tibet, TB; Hubei, HB; Inner Mongolia, IM; Sichuan, SC), UK and Australia (AS), using genome-wide population-genomic approaches, to explore genetic diversity, population structure and selection. We first performed next-generation high-throughput 2b RAD pool sequencing using Illumina technology, and identified single-nucleotide polymorphisms (SNPs) in all the strains. We identified 75,187 SNPs for TB, 82,271 for HB, 82,420 for IM, 79,803 for SC, 83,504 for AS and 78,747 for UK strain. The SNPs revealed low-nucleotide diversity (pi= 0.0092-0.0133) within each strain, and a significant differentiation level (average F_st = 0.34264) among them. Chinese populations TB and SC, along with the UK strain, were more divergent populations. Chinese populations IM and HB showed affinities to the Australian strain. We then analysed signature of selection and detected 44 (UK) and 03 (AS) private selective sweeps containing 49 and 05 genes, respectively. Finally, we performed the functional annotation of selective sweeps and proposed biological significance to signature of selection. Our data suggest that 2b-RAD pool sequencing can be used to assess the signature of selection in H. contortus.

Microsatellite analysis reveals extensive gene flow, and lack of population structure in the farm populations of Haemonchus contortus in northern China

The parasitic nematode Haemonchus contortus is economically an important parasite of small ruminants across the globe. China is the world's largest producer, consumer, and importer of mutton. With ubiquitous distribution across the country H. contortus is one of the potential candidates to cause huge economic losses to small ruminant farming industry in China. We herein investigated genetic diversity and population structure of six farm populations of H. contortus in northern China, and also compared them to H. contortus isolates from UK and Australia. We first prepared individual DNA samples from 240 adult worms, and generated genotyping data using eight microsatellite markers. Obtained data was then subjected to allelic frequency and population genetic analyses. The overall allelic richness (mean/locus/pop = 7.375 ± 0.844-10.125 ± 1.109), and expected heterozygosity (mean/locus/pop = 0.646 ± 0.040-0.735 ± 0.025) indicated high degree of population genetic variation across the Chinese isolates. Low level of genetic differentiation (Fst = 0.010-0.066) was observed across all the populations. AMOVA results showed high level of variation (93%) within the populations. PCA analysis revealed mixed clustering of all the populations with no visible geographical sub-structuring. Finally the population admixture analysis resulted in extensive admixing of genotypes across all the populations. With these findings we conclude that there is no obvious population genetic structure with extensive gene flow across all the farm populations of H. contortus in northern China.

A detection of benzimidazole resistance-associated SNPs in the isotype-1 β-tubulin gene in Haemonchus contortus from wild blue sheep (Pseudois nayaur) sympatric with sheep in Helan Mountains, China

Background

Benzimidazole (BZ) resistance is an increasingly serious problem due to the excessive use of this anthelmintic for controlling Haemonchus contortus, which is one of the major gastrointestinal nematodes infecting small ruminants worldwide. Three known single nucleotide polymorphisms (SNPs), F167Y (TAC), E198A (GCA) and F200Y (TAC), in the isotype-1 β-tubulin gene of H. contortus are associated with BZ resistance. Comprehending the spread and origins of BZ resistance-associated SNPs has important implications for the control of this nematode.

Results

Twenty-seven adult H. contortus were harvested from wild blue sheep (Pseudois nayaur), small wild ruminants sympatric with domestic ruminants, inhabiting the Helan Mountains, China, to monitor the status of BZ resistance. In addition, 20 adult H. contortus from domestic sheep sympatric with this wild ruminant and 36 isotype-1 β-tubulin haplotype sequences of H. contortus (two of these haplotypes, E198A3 and E198A4, possessed resistance-associated SNP E198A (GCA) from domestic ruminants in eight other geographical regions of China were used to further define the origins of BZ resistance-associated SNPs within the worms collected from blue sheep. The BZ resistance-associated SNP E198A was detected, whereas SNPs F167Y (TAC) and F200Y (TAC) were not found within the worms collected from blue sheep, and the frequency of homozygous resistant E198A (GCA) was 7.40%. The evolutionary tree and network showed consistent topologies for which there was no obvious boundary among the worms from the wild and domestic hosts, and two haplotypes (E198A1 and E198A2) possessing E198A from the wild blue sheep had two different independent origins. E198A1 had the same origin with E198A3 but E198A2 had a different origin with them. Population genetic analyses revealed a low level of Fst values (ranging from 0 to 0.19749) between all H. contortus worm groups in China.

Conclusions

Results of the current study of the three BZ resistance-associated SNPs of H. contortus from wild blue sheep suggested that only E198A (GCA) was present within the worms collected from the wild ruminants and had multiple independent origins.

Electronic supplementary material

The online version of this article (10.1186/s12917-019-1838-4) contains supplementary material, which is available to authorized users.

Molecular detection of benzimidazole resistance levels associated with F167Y and F200Y polymorphisms in Haemonchus contortus of goats from Mozambique

Benzimidazole (BZ) resistance of Haemonchus contortus has been associated with single nucleotide polymorphisms (SNPs) in codons 200 (F200Y) and 167 (F167Y) and, to a lesser extent, in codon E198A, of the β-tubulin isotype 1 gene. The present study was undertaken to survey the status of BZ resistance in naturally infected goats in smallholder farms in southern Mozambique by real-time PCR (qPCR) using TaqMan® assays. H. contortus-infective larvae (L3; n = 432) from 12 populations were individually genotyped for F200Y and F167Y SNPs to detect BZ resistance. For the F200Y SNP, the results revealed an overall mean percentages of 18.8% homozygous resistant (RR), 47.8% homozygous susceptible (SS) and 33.4% heterozygous (RS) H. contortus. For the F167Y SNP, the overall mean percentages were 1.6% RR, 94.9% SS and 3.5% RS. The percentage of resistant alleles (%R) for the F200Y and F167Y SNPs was 35.7 and 3.4%, respectively. Genotype combinations of the two mutations indicate resistant percentages ranging from 0.0 to 52.9%. From the four herds with high RR individuals, three farms dewormed the animals monthly, while the fourth farm dewormed the animals every 3 months. In farms where animals were dewormed every 6 months, low percentages of RR individuals were found, whereas no RR individuals were discovered in herds where animals were dewormed annually. These results suggest that the F200Y SNP is more significant in BZ resistance development of the surveyed population compared with the F167Y SNP.

Exploring benzimidazole resistance in Haemonchus contortus by next generation sequencing and droplet digital PCR

Anthelmintic resistance in gastrointestinal nematode (GIN) parasites of grazing ruminants is on the rise in countries across the world. Haemonchus contortus is one of most frequently encountered drug-resistant GINs in small ruminants. This blood-sucking abomasal nematode contributes to massive treatment costs and poses a serious threat to farm animal health. To prevent the establishment of resistant strains of this parasite, up-to-date molecular techniques need to be proposed which would allow for quick, cheap and accurate identification of individuals infected with resistant worms. The effort has been made in the previous decade, with the development of the pyrosequencing method to detect resistance-predicting alleles. Here we propose a novel droplet digital PCR (ddPCR) assay for rapid and precise identification of H. contortus strains as being resistant or susceptible to benzimidazole drugs based on the presence or absence of the most common resistance-conferring mutation F200Y (TAC) in the β tubulin isotype 1 gene. The newly developed ddPCR assay was first optimized and validated utilizing DNA templates from single-worm samples, which were previously sequenced using the next generation PacBio RSII Sequencing (NGS) platform. Subsequent NGS results for faecal larval cultures were then used as a reference to compare the obtained values for fractional abundances of the resistance-determining mutant allele between ddPCR and NGS techniques in each sample. Both methods managed to produce highly similar results and ddPCR proved to be a reliable tool which, when utilized at full capacity, can be used to create a powerful mutation detection and quantification assay.

PCR-RFLP screening of polymorphisms associated with benzimidazole resistance in Necator americanus and Ascaris lumbricoides from different geographical regions in Brazil

Ascaris lumbricoides and Necator americanus are soil-transmitted parasites with global geographic distribution, and they represent some of the most common and neglected infections in the world. Periodic treatment with mass drug administration (MDA) in endemic areas is the recommended action put forth by the World Health Organization. However, MDA can cause the selection of subpopulations that possess the genetic ability to overcome the mechanism of drug action. In fact, beta-tubulin gene mutations (codons 167, 198 and 200) are correlated with benzimidazole resistance in nematodes of veterinary importance. It is possible that these SNPs also have strong correlation with treatment resistance in the human geohelminths A. lumbricoides, Trichuris trichiura and hookworms. Here, we aimed to investigate the presence of some of these canonical molecular markers associated with parasite resistance to benzimidazole in N. americanus and A. lumbricoides collected from six Brazilian states. Nested-PCR and PCR-RFLP were used to detect mutations at codons 167 and 198 in 601 individual eggs of A. lumbricoides collected from 62 human stool samples; however, no mutations were found. Codons 198 and 200 were tested in 552 N. americanus eggs collected from 48 patients using the same methodology, which presented a relative frequency of 1.4% and 1.1%, respectively. The presence of these SNPs in N. americanus eggs is an important finding, indicating that with high benzimidazole drug pressure there is potential for benzimidazole resistance to be selected in this hookworm. However, at these low frequencies it does not indicate that there is at present any benzimidazole resistance problem. This is the first systematic study performed in South America, and the study yielded a landscape of the genetic variants in the beta-tubulin gene and anthelmintic resistance to soil-transmitted parasites detected by a simple, rapid and affordable genotyping assay of individual eggs.

Development of a tetra-primer ARMS-PCR for detecting the E198A SNP in the isotype-1 β-tubulin gene of Haemonchus contortus populations in China

The tetra-primer ARMS-PCR is a rapid, simple and low cost method for single nucleotide polymorphism (SNP) genotyping and has been used to detect SNPs associated with diseases and drug resistance. E198A in the isotype-1 β-tubulin gene is one of the three SNPs associated with benzimidazole resistance in parasitic nematode Haemonchus contortus. However, up to now, only PCR-RFLP method was used to test E198A in H. contortus. In the present study, we developed a tetra-primer ARMS-PCR to detect E198A in H. contortus and the accuracy of the results was compared with that of PCR-coupled sequencing. The results showed that optimization of PCR reaction system, especially the proportion of the amount of inner and outer primers, could achieve desirable amplification effect. Three different profiles displaying three distinct genotypes could be identified clearly and intuitively on the agarose gel where the samples with amplified PCR products containing two bands of 433 bp and 200 bp in size indicated susceptible homozygous (SS), those with PCR products containing two bands of 433 bp and 284 bp in length indicated resistant homozygous (RR) and the samples with amplified PCR products containing three bands of 433 bp, 284 bp and 200 bp in size indicated heterozygous (RS). The results showed that the established method can be successfully applied to the detection of E198A in H. contortus, which has high accuracy and is easy to perform.

Recent Research Progress in China on Haemonchus contortus

Haemonchus contortus is one of the most important parasites of ruminants with worldwide distribution that can bring huge economic losses to the breeding industry of cattle, sheep, and goats. In recent 20 years, studies on H. contortus in China mainly focused on the epidemiology, population genetics, anthelmintic resistance, structural and functional studies of important genes regulating the development of this parasite, interaction between parasite molecules and host cells and vaccine development against haemonchosis, and achieved good progress. However, there is no systematic review about the studies by Chinese researchers on H. contortus in China. The purpose of this review is to bring together the findings from the studies on H. contortus in China in order to obtain the knowledge gained from the recent studies in China and provide foundation for identifying future research directions to establish novel diagnostic methods, discover new drug targets and vaccine candidates for use in preventing and controlling H. contortus in China.