Development and evaluation of a loop-mediated isothermal amplification (LAMP) assay for the detection of the E198A SNP in the isotype-1 β-tubulin gene of Haemonchus contortus populations in China

Real-time single-base specific detection of the Haemonchus contortus S168T variant associated with levamisole resistance using loop-primer endonuclease cleavage loop-mediated isothermal amplification

Haemonchus contortus is a parasitic haematophagous nematode that primarily affects small ruminants and causes significant economic loss to the global livestock industry. Treatment of haemonchosis typically relies on broad-spectrum anthelmintics, resistance to which is an important cause of treatment failure. Resistance to levamisole remains less widespread than to other major anthelmintic classes, prompting the need for more effective and accurate surveillance to maintain its efficacy. Loop-primer endonuclease cleavage loop-mediated isothermal amplification (LEC-LAMP) is a recently developed diagnostic method that facilitates multiplex target detection with single nucleotide polymorphism (SNP) specificity and portable onsite testing. In this study, we designed a new LEC-LAMP assay and applied it to detect the levamisole resistance marker S168T in H. contortus. We explored multiplexing probes for both the resistant S168T and the susceptible S168 alleles in a single-tube assay. We then included a generic probe to detect the acr-8 gene in the multiplex assay, which could facilitate the quantification of both resistance markers and overall genetic material from H. contortus in a single step. Our results showed promising application of these technologies, demonstrating a proof-of-concept assay which is amenable to detection of resistance alleles within the parasite population, with the potential for multiplex detection, and point-of-care application enabled by lateral flow end-point detection. However, further optimisation and validation is necessary.

Development of a three-colour digital PCR for early and quantitative detection of benzimidazole resistance-associated single nucleotide polymorphisms in Haemonchus contortus

Haemonchus contortus is the most pathogenic nematode in small ruminants and anthelmintic resistance (AR) hampers its efficient control. Early detection of AR status is required to reduce selection for AR and cannot be achieved using phenotypic tests. For benzimidazoles (BZs), the detection of AR-associated alleles characterised by single nucleotide polymorphisms (SNPs) in the isotype 1 β-tubulin gene allows early AR detection in strongyles. The F200Y, F167Y, E198A and E198L polymorphisms have been described in BZ-resistant populations with a clear variation in frequencies between regions. A novel digital PCR (dPCR) enables the detection of all of the above-described polymorphisms in H. contortus. Assays were validated using synthetic DNA fragments containing these SNPs. Then, larvae obtained and pooled at farm level from 26 Austrian and 10 Italian sheep farms were analysed. For all assays a detection limit of 15 copies/μl of resistance alleles and a high level of accuracy were demonstrated, allowing to detect allele frequencies of 1% in most samples. In Austrian samples, elevated frequencies of F200Y resistance alleles were detected on all farms. Polymorphisms in codon 167 and codon 198 were identified in H. contortus from Austria for the first time. In Italian samples, the frequency of resistance alleles was still comparatively low, but F200Y resistance alleles were traceable. In conclusion we developed for the first time dPCR assays that target all SNPs of relevance associated with BZ-resistance in H. contortus. Future research on AR development could benefit from an early onset of SNP-based surveillance that would include the developed assays for all SNPs of relevance. Improved surveillance in the long term will include other important, though less pathogenic, nematode genera in the analyses.

In vitro anthelmintic activity of an R-carvone nanoemulsions towards multiresistant Haemonchus contortus

This work aimed to evaluate the in vitro anthelmintic effect of carvone nanoemulsions on Haemonchus contortus. Three R-carvone nanoemulsions were prepared: uncoated R-carvone nanoemulsions homogenized in a sonicator (UNAlg-son) and homogenized in an ultrahomogenizer (UNAlg-ultra) and sodium alginate-coated R-carvone (CNAlg-ultra). The physicochemical characterizations of the nanoemulsions were carried out. The anthelmintic activity was evaluated using egg hatch test (EHT), larval development test (LDT) and adult worm motility test (AWMT). Changes in cuticle induced in adult H. contortus were evaluated by scanning electron microscopy (SEM). The results were subjected to analysis of variance and compared using the Tukey test (P < 0.05). The effective concentration to inhibit 50% (EC50) of egg hatching and larval development was calculated. The particle sizes were 281.1 nm (UNAlg-son), 152.7 nm (UNAlg-ultra) and 557.8 nm (CNAlg-ultra), and the zeta potentials were −15 mV (UNAlg-son), −10.8 mV (UNAlg-ultra) and −24.2 mV (CNAlg-ultra). The encapsulation efficiency was 99.84 ± 0.01%. SEM of the nanoemulsions showed an increase in size. In EHT, the EC50 values of UNAlg-son, UNAlg-ultra and CNAlg-ultra were 0.19, 0.02 and 0.17 mg mL−1, respectively. In LDT, they were 0.29, 0.31 and 0.95 mg mL−1 for UNAlg-son, UNAlg-ultra and CNAlg-ultra, respectively. The adult motility inhibition was 100% after 12 h of exposure to UNAlg-ultra and CNAlg-ultra, while for UNAlg-son, it was 79.16%. SEM showed changes in the buccal capsule and cuticular damage. It was concluded that R-carvone nanoemulsions showed antiparasitic action demonstrating promise for the control of infections caused by gastrointestinal nematodes in small ruminants.

Advances in diagnosis and control of anthelmintic resistant gastrointestinal helminths infecting ruminants

Infection with gastrointestinal helminths is widely spread among ruminant causing severe losses and adversely affects the livestock husbandry. Synthetic chemotherapeutics have been utilized throughout years, as a means of combating helminthiasis. Anthelmintic resistance (AR) has a serious concern on livestock industry which, mainly arises as outcome of misuse, improper dosing and frequent utilization of the synthetic drugs.Various gastrointestinal helminths have the capability to survive the therapeutic dose of anthelmintics and become resistant to the major anthelmintic classes. Early diagnosis might delay or reduce the risk of AR. Conventional phenotyping methods were commonly used for detection of anthelmintic resistant helminths, but appeared to lack of sensitivity, especially when the frequency of resistant allele is very low. Several molecular assays were carried out to detect the AR with greater accuracy. Sustainable effective preventive and control measures for gastrointestinal helminths infection remain the corner stone to overcome AR. Rational use of anthelmintics with keeping unexposed proportion of worm populations, could have the potentiality to maintain and prolong the efficacy of anthelmintics. Several alternative anthelmintic treatments might offer valuable solutions either alone or adjunct to synthetic drugs to dilute the spread of resistance alleles among the helminths population. This article reviews current status of various diagnostic methods and control measures for anthelmintic resistant gastrointestinal helminths infecting ruminants and tries to present a practical protocol to avoid or delay the development of AR.

Validation of a colorimetric LAMP to detect Loxosceles experimental envenomation

Diagnostic tests for brown spider accidents are unavailable and impact treatment decisions, increasing costs and patient risks. In this work, we used for the first time a fast, simple, and visual method based on the loop-mediated isothermal amplification assay (LAMP) to detect Loxosceles envenomation. Using the DNA from L. similis legs, we observed a high sensitivity using this test since as low as 0.32 pg of DNA could be detected. This pH-dependent colorimetric assay was 64 times more sensitive than PCR to detect spider DNA. The test was specific for Loxosceles once no cross-reaction was observed when testing DNA from different agents that cause similar dermonecrotic injuries. The test allowed the detection of Loxosceles intermedia DNA from hair, serum, and exudate samples obtained from experimentally-envenomed rabbit within 72 h. The method sensitivity varied according to the sample and the collection time, reaching 100% sensitivity in serum and hair, respectively, 1 h and 24 h after the experimental envenomation. Due to its ease of execution, speed, sensitivity, and specificity, LAMP presents an excellent potential for identifying Loxosceles spp. Envenomation. This can reduce the burden on the Health System and the morbidity for the patient by implementing the appropriate therapy immediately.In addition, this work opens up the perspective to other venomous animal accident identification using LAMP.

Anthelmintic resistance in ruminants: challenges and solutions

Anthelmintic resistance (AR) is a growing concern for effective parasite control in farmed ruminants globally. Combatting AR will require intensified and integrated research efforts in the development of innovative diagnostic tests to detect helminth infections and AR, sustainable anthelmintic treatment strategies and the development of complementary control approaches such as vaccination and plant-based control. It will also require a better understanding of socio-economic drivers of anthelmintic treatment decisions, in order to support a behavioural shift and develop targeted communication strategies that promote the uptake of evidence-based sustainable solutions. Here, we review the state-of-the-art in these different fields of research activity related to AR in helminths of livestock ruminants in Europe and beyond. We conclude that in the advent of new challenges and solutions emerging from continuing spread of AR and intensified research efforts, respectively, there is a strong need for transnational multi-actor initiatives. These should involve all key stakeholders to develop indicators of infection and sustainable control, set targets and promote good practices to achieve them.

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

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

Discrimination of a single nucleotide polymorphism in the haptoglobin promoter region, rs5472, using a competitive fluorophore-labeled probe hybridization assay following loop-mediated isothermal amplification

Personalized peptide vaccination, which involves activation of the host immune system against cancer cells using personalized peptide vaccines (PPVs), can improve overall survival in multiple cancer types. However, the clinical efficacies of PPVs vary for unknown reasons. Recently, a single nucleotide polymorphism (NG_012651.1:g.4461_5460[4960A>G]) in the haptoglobin promoter region, rs5472, was significantly associated with clinical response of PPV. Therefore, rs5472 is expected to be a predictive biomarker for PPV therapy. Here, we described a single nucleotide discrimination method for rs5472 analysis by combining the loop-mediated isothermal amplification and quenching probe methods. In evaluation of saliva samples, this method showed high concordance with the results of Sanger sequencing (100%, n = 36). Importantly, this method did not require calculation of melting temperature for single nucleotide discrimination and could therefore be carried out on a simple instrument. Accordingly, this method may be more robust and applicable to near-patient testing.