Haemonchus contortus β-tubulin isotype 1 gene F200Y and F167Y SNPs are both selected by ivermectin and oxfendazole treatments with differing impacts on anthelmintic resistance

A systematic review of the molecular mechanisms related to anthelmintic resistance in Haemonchus contortus: A contemporary narrative

Haemonchus contortus is a gastrointestinal parasite that affects ruminants (cattle, sheep, etc.), having a significant welfare impact worldwide. The rise of anthelmintic resistance poses a growing challenge to adequate control, compromising the success of treatments. This study presents a systematic review of the molecular mechanisms involved in the resistance of H. contortus to anthelmintic drugs. Following an extensive literature search (9075 total articles/excluding duplications), 61 articles were examined. From these, benzimidazoles (BZD) and macrocyclic lactone (ML) were the most reported drug classes (17 and 29, respectively). The mutations in the β-tubulin gene were the primary mechanism of BZD resistance. Important comparisons from early reports of resistance mechanisms to ML (published before 2020) mainly based on parasite-population gene expression (e.g., ligand-gated chloride channels, LGCC, and P-glycoproteins, PGP) with more recent genomic and transcriptomic data (e.g., transcription factor, cky-1 gene) are highlighted. Additionally, resistance mechanisms to levamisole (LEV) and monepantel are discussed, showing evidence of polymorphisms in genes related to the nicotinic acetylcholine receptors (nAChR). Considering the available data, it is possible to divide the reports into two technological periods, evidencing that the availability of a chromosome-level genome for H. contortus in association with experiments based on controlled genetic crosses and transcriptome-wide data allowed for the visualization of genes and polymorphisms that were previously indistinguishable from unrelated genetic variation (i.e., genetic noise). Therefore, the study of anthelmintic resistance mechanisms is facing new possibilities, reflecting the large data banks and the speed at which this information is being processed. We suggest that new publications on drug resistance should adopt the approaches and refer to this new era of scientific discoveries. Consistent data interpretation, including artificial intelligence (AI) support, will help us to suggest novel biological mechanisms involved in drug resistance and predict its evolution, allowing a more comprehensible approach toward sustainable parasite control strategies.

Expression of transporter genes in anthelmintic resistant isolates of Haemonchus contortus

ATP-binding cassette (ABC) transporters, including P-glycoproteins (PGP), have been implicated in drug resistance in different organisms including Haemonchus contortus. This study confirmed the resistance status of H. contortus isolates selected for ivermectin (IVM) and oxfendazole (OXF) resistances using the fecal egg count reduction test and evaluated the gene expression of seven ABC transporters using RT-qPCR for two biological scenarios: the effect of selection for anthelmintic resistance and the effect of drug exposure on gene expression. Gene expression results showed that selection for IVM resistance led to the significant upregulation of Hco-pgp-9a (1.5-fold), Hco-pgp-11 (3-fold) and Hco-haf-9 (1.5-fold) (p < 0.05). Similarly, selection for OXF resistance led to the significant upregulation of Hco-pgp-9a (3-fold), Hco-pgp-11 (4-fold) and Hco-haf-9 (2-fold) when comparing with the unselected ISE isolate (p < 0.05). Exposure of selected isolates to anthelmintics lead to no significant upregulation of the studied transporter genes. We also observed instances where there was strong intragroup variation regarding samples originating from parasites obtained from different individual hosts pointing that the interactions of the animal host with the tested anthelmintics may also play a role in the expression of the studied nematode genes.

Comparison of P-glycoprotein gene expression of two Haemonchus contortus isolates from Yucatan, Mexico, with resistant or susceptible phenotype to ivermectin in relation to a susceptible reference strain

The variability in the expression of different P-glycoprotein (P-gp) genes in parasitic nematodes of ruminants such as Haemonchus contortus (Hco-pgp) may be caused by different factors including nematode biology, geographical region and anthelmintic pressure. This study analysed the relative expression level of 10 P-gp genes in two H. contortus (Hco-pgp) field isolates from Yucatan, Mexico: 1) PARAISO (IVM-resistant) and 2) FMVZ-UADY (IVM-susceptible). These isolates were compared with a susceptible reference isolate from Puebla, Mexico, namely "CENID-SAI". In all cases H. contortus adult males were used. The Hco-pgp genes (1, 2, 3, 4, 9, 10, 11, 12, 14 and 16) were analysed for each isolate using the RT-qPCR technique. The Hco-pgp expressions were pairwise compared using the 2-ΔΔCt method and a t-test. The PARAISO isolate showed upregulation compared to the CENID-SAI isolate for Hco-pgp 1, 3, 9, 10 and 16 (P < 0.05), and the PARAISO isolate showed upregulation vs. FMVZ-UADY isolate for Hco-pgp 2 and 9 (P < 0.05), displaying 6.58- and 5.93-fold differences (P < 0.05), respectively. In contrast, similar Hco-pgp gene expression levels were recorded for FMVZ-UADY and CENID-SAI isolates except for Hco-pgp1 (P <0.1), which presented a significant upregulation (6.08-fold). The relative expression of Hco-pgp allowed confirming the IVM-resistant status of the PARAISO isolate and the IVM-susceptible status of the FMVZ-UADY isolate when compared to the CENID-SAI reference isolate. Therefore, understanding the association between the Hco-pgp genes expression of H. contortus and its IVM resistance status could help identifying the genes that could be used as molecular markers in the diagnosis of IVM resistance. However, it is important to consider the geographic origin of the nematode isolate and the deworming history at the farm of origin.

Genomic landscape of drug response reveals mediators of anthelmintic resistance

Like other pathogens, parasitic helminths can rapidly evolve resistance to drug treatment. Understanding the genetic basis of anthelmintic drug resistance in parasitic nematodes is key to tracking its spread and improving the efficacy and sustainability of parasite control. Here, we use an in vivo genetic cross between drug-susceptible and multi-drug-resistant strains of Haemonchus contortus in a natural host-parasite system to simultaneously map resistance loci for the three major classes of anthelmintics. This approach identifies new alleles for resistance to benzimidazoles and levamisole and implicates the transcription factor cky-1 in ivermectin resistance. This gene is within a locus under selection in ivermectin-resistant populations worldwide; expression analyses and functional validation using knockdown experiments support that cky-1 is associated with ivermectin survival. Our work demonstrates the feasibility of high-resolution forward genetics in a parasitic nematode and identifies variants for the development of molecular diagnostics to combat drug resistance in the field.

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.

Anthelmintic activity of nanoencapsulated carvacryl acetate against gastrointestinal nematodes of sheep and its toxicity in rodents

The objective of this study was to evaluate the efficacy of carvacryl acetate (CVA) and nanoencapsulated CVA (nCVA) on gastrointestinal nematodes of sheep. The CVA was nanoencapsulated with chitosan/gum arabic and the efficacy of nanoencapsulation (EE), yield, zeta potential, nanoparticle morphology and release kinetics at pH 3 and 8 were analyzed. Acute and subchronic toxicity were evaluated in rodents and reduction of egg counts in the faeces (FECRT) of sheep. The sheep were divided into four groups (n = 10): G1, 250 mg/kg CVA; G2, 250 mg/kg nCVA; G3, polymer matrix and G4: 2.5 mg/kg monepantel. EE and nCVA yield were 65% and 57%, respectively. The morphology of the nanoparticles was spherical, size (810.6±286.7 nm), zeta potential in pH 3.2 (+18.3 mV) and the 50% release of CVA at pHs 3 and 8 occurred at 200 and 10 h, respectively. nCVA showed LD50 of 2,609 mg/kg. CVA, nCVA and monepantel reduced the number of eggs per gram of faeces (epg) by 57.7%, 51.1% and 97.7%, respectively. The epg of sheep treated with CVA and nCVA did not differ from the negative control (P>0.05). Nanoencapsulation reduced the toxicity of CVA; however, nCVA and CVA presented similar results in the FECRT.

Chemical constituents of Calotropis procera latex and ultrastructural effects on Haemonchus contortus

Abstract This study aimed to evaluate the anthelmintic and ultrastructural effects of Calotropis procera latex on Haemonchus contortus. C. procera latex was twice centrifuged at 10,000×g and dialyzed to obtain a fraction rich in proteins, named LP (latex protein), and at 3,000 rpm to obtain a fraction rich in secondary metabolites, named LNP (latex non-protein). Specimens of H. contortus exposed to LNP, LP and PBS in the Adult Worm Motility Test (AWMT) were submitted to scanning (SEM) and transmission (TEM) electron microscopy to verify changes in their ultrastructure. Phytochemical tests in the LNP indicated the presence of phenols, steroids, alkaloids and cardenolides. High-Performance Liquid Chromatography (HPLC) characterized the presence of the compounds gallic acid and quercetin in the LNP. The protein content in the LP was 43.1 ± 1.1 mg/mL and 7.7 ± 0.3 mg/mL in LNP. In AWMT, LNP and LP inhibited the motility of 100% of the nematodes, with LNP being more effective than LP and ivermectin more effective than both (p <0.05). Cuticle changes were observed by SEM and TEM in nematodes treated with LP and LNP. Calotropis procera latex has anthelmintic effects against H. contortus, causing damage to its cuticle and other alterations in its ultrastructure.