F200Y polymorphism of the β-tubulin isotype 1 gene in Haemonchus contortus and sheep flock management practices related to anthelmintic resistance in eastern Amazon

High frequency of benzimidazole resistance polymorphisms and age-class differences in trichostrongyle nematodes of ranched bison from the south-central United States

Bison production is a growing sector of the United States agriculture, with more consumers choosing bison products. Commercial bison are kept on smaller pastures and treated with anthelmintics for gastrointestinal nematodes (GIN) to maintain production. However, there is a lack of information regarding the GIN parasite communities in ranched bison or the extent of their resistance to anthelmintics. Our objectives were: i) to determine the GIN species present and the extent of resistance to the benzimidazole drug class in commercial bison herds in the southern US and ii) to assess age class differences in GIN species composition and BZ resistance. Composite coprocultures from bison in Texas (n = 14) and Oklahoma (n = 2), and individual bison of different age classes from a single ranch in central Texas (n = 43) were analyzed using ITS2 rDNA nemabiome metabarcoding to determine the trichostrongylid species composition. For both the composite and individual samples, the most common trichostrongylid species found were Haemonchus contortus, Haemonchus placei, and Ostertagia ostertagi. Among the known canonical isotype-1 β-tubulin BZ resistance polymorphisms (at codons 200, 198, 167), the 200Y (TTC > TAC) substitution was the most widespread across the two southern states, with a prevalence of 81.3 %. Other polymorphisms, such as 167Y (TTC > TAC) and 198L (GAA > TTA), were also detected, and both had prevalences of 62.5 %. Ostertagia ostertagi was found to have very high frequencies (overall mean frequency = 62.6 %; range = 28.3-100 %) of the 200Y (TTC > TAC) polymorphism in all age classes sampled. Overall, benzimidazole resistance polymorphisms were found at moderate to high frequency in the three major economically important GIN species in ranched bison in Texas and Oklahoma, suggesting a potential widespread distribution of benzimidazole resistance polymorphisms in the southern United States. This work has important implications for all other grazing livestock and illustrates the importance of early detection of anthelmintic resistance and the need for mitigation strategies.

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.

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.

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.

Assessing anthelmintic resistance risk in the post-genomic era: a proof-of-concept study assessing the potential for widespread benzimidazole-resistant gastrointestinal nematodes in North American cattle and bison

As genomic research continues to improve our understanding of the genetics of anthelmintic drug resistance, the revolution in DNA sequencing technologies will provide increasing opportunities for large-scale surveillance for the emergence of drug resistance. In most countries, parasite control in cattle and bison has mainly depended on pour-on macrocyclic lactone formulations resulting in widespread ivermectin resistance. Consequently, there is an increased interest in using benzimidazole drugs which have been used comparatively little in cattle and bison in recent years. This situation, together with our understanding of benzimidazole resistance genetics, provides a practical opportunity to use deep-amplicon sequencing to assess the risk of drug resistance emergence. In this paper, we use deep-amplicon sequencing to scan for those mutations in the isotype-1 β-tubulin gene previously associated with benzimidazole resistance in many trichostrongylid nematode species. We found that several of these mutations occur at low frequency in many cattle and bison parasite populations in North America, suggesting increased use of benzimidazole drugs in cattle has the potential to result in widespread emergence of resistance in multiple parasite species. This work illustrates a post-genomic approach to large-scale surveillance of early emergence of anthelmintic resistance in the field.

Molecular characterization and functional analysis of Eimeria tenella malate dehydrogenase

Eimeria tenella is a serious intracellular parasite that actively invades cecal epithelial cells of chickens. The widespread use of drugs causes severe resistance to Eimeria tenella. We detected that malate dehydrogenase (MDH), one of the differentially expressed genes, was upregulated in diclazuril-resistant and maduramicin-resistant strains through transcriptome sequencing. In this study, we cloned and expressed MDH of E. tenella (EtMDH). Quantitative real-time polymerase chain reactions (qPCR) and Western blots were used to analyze the expression of EtMDH in resistant and sensitive strains, indicating EtMDH was upregulated in two resistant strains at the messenger RNA and protein levels. Enzyme activity was tested through absorbance measurement and the EtMDH activity increased in two resistant strains. Expression levels of EtMDH in four developmental stages of E. tenella were tested through qPCR and Western blot. Invasion inhibition assays explored if EtMDH was involved in invasion of DF-1 cells by E. tenella sporozoites. Indirect immunofluorescence assays investigated EtMDH distribution during parasite development in DF-1 cells invaded by E. tenella sporozoites. Experimental results showed that EtMDH may be related to drug resistance of E. tenella during its development and invasion. EtMDH may be an effective molecular marker for detection of E. tenella drug resistance.

Genotypic and phenotypic evaluation for benzimidazole resistance or susceptibility in Haemonchus contortus isolates

Haemonchus contortus isolates were evaluated for benzimidazole (BZ) resistance or susceptibility by allele-specific PCR based on β-tubulin isotype 1 gene polymorphisms at the F167Y, E198A, and F200Y sites. Two isolates, one presumed susceptible from wild pronghorn antelope (PH) and one known to be resistant from goats (VM), were also assayed phenotypically for BZ resistance or susceptibility in the larval development assay (Drenchrite®). The BZ EC50 was 0.198 μM (intermediate between susceptible and weak resistant) for PH with critical well 5 (intermediate between susceptible and weak resistant) and 1.456 μM (intermediate weak resistant and resistant) for VM with critical well 8.5 (resistant). Genotypically, DNA extracted from pooled VM L3 larvae in the Drenchrite® wells with the highest BZ concentration was homozygous susceptible (SS) at the F167Y and E198A sites and homozygous resistant (RR) at the F200Y site by PCR, and sequence analysis bore this out. PH L3 larvae DNA from a control well (no BZ) was SS at all three sites by PCR, confirmed by sequence analysis. All single adult worm samples (N = 21) from PH, VM, Egypt goat (EG), and a Texas llama were SS at F167Y and E198A by PCR; however, only 3 PH worms and 1 EG worm were SS at F200Y. Three additional PH worms were RS and upon cloning two clones were identified as resistant by sequencing and two as susceptible. Clones from single adult worms VM, llama, and EG samples that were RR by PCR at F200Y were sequence verified as resistant. In this study, F200Y was the most frequently found genotypic marker for BZ resistance or susceptibility in the different Haemonchus isolates.