Are new anthelmintics needed to eliminate human helminthiases?

Anthelmintics in the environment: Their occurrence, fate, and toxicity to non-target organisms

Anthelmintics are drugs used for the treatment and prevention of diseases caused by parasitic worms (helminths). While the importance of anthelmintics in human as well as in veterinary medicine is evident, they represent emerging contaminants of the environment. Human anthelmintics are mainly used in tropical and sub-tropical regions, while veterinary anthelmintics have become frequently-occurring environmental pollutants worldwide due to intensive agri- and aquaculture production. In the environment, anthelmintics are distributed in water and soil in relation to their structure and physicochemical properties. Consequently, they enter various organisms directly (e.g. plants, soil invertebrates, water animals) or indirectly through food-chain. Several anthelmintics elicit toxic effects in non-target species. Although new information has been made available, anthelmintics in ecosystems should be more thoroughly investigated to obtain complex knowledge on their impact in various environments. This review summarizes available information about the occurrence, behavior, and toxic effect of anthelmintics in environment. Several reasons why anthelmintics are dangerous contaminants are highlighted along with options to reduce contamination. Negative effects are also outlined.

The Proteome and Lipidome of Extracellular Vesicles from Haemonchus contortus to Underpin Explorations of Host-Parasite Cross-Talk

Many parasitic worms have a major adverse impact on human and animal populations worldwide due to the chronicity of their infections. There is a growing body of evidence indicating that extracellular vesicles (EVs) are intimately involved in modulating (suppressing) inflammatory/immune host responses and parasitism. As one of the most pathogenic nematodes of livestock animals, Haemonchus contortus is an ideal model system for EV exploration. Here, employing a multi-step enrichment process (in vitro culture, followed by ultracentrifugation, size exclusion and filtration), we enriched EVs from H. contortus and undertook the first comprehensive (qualitative and quantitative) multi-omic investigation of EV proteins and lipids using advanced liquid chromatography-mass spectrometry and informatics methods. We identified and quantified 561 proteins and 446 lipids in EVs and compared these molecules with those of adult worms. We identified unique molecules in EVs, such as proteins linked to lipid transportation and lipid species (i.e., sphingolipids) associated with signalling, indicating the involvement of these molecules in parasite-host cross-talk. This work provides a solid starting point to explore the functional roles of EV-specific proteins and lipids in modulating parasite-host cross-talk, and the prospect of finding ways of disrupting or interrupting this relationship to suppress or eliminate parasite infection.

An overview of human helminthioses in Vietnam: Their prevention, control and lessons learnt

In Vietnam, helminthioses remain a major threat to public health and contribute to the maintenance of poverty in highly endemic regions. Through increased awareness of the damaging effects caused by helminthioses, the Vietnamese government has implemented many national programs over the past 30 years for the prevention and control of the most important helminthioses, such as, lymphatic filariasis, soil transmitted helminths, food borne zoonotic helminths, and others. Various control strategies have been applied to reduce or eliminate these worms, e.g. mass drug administration, economic development, control of vectors or intermediate hosts, public health interventions through education, proper composting procedures for excreta potentially containing helminth eggs, and the expansion of food supply chains and improved technologies for the production and inspection of food products. These control measures have resulted in a significant reduction in the distribution and transmission of helminth infections and have improved the overall living conditions and health outcomes of the Vietnamese citizens. However, the persistence of several helminth diseases continues in some endemic areas, especially where poverty is widespread and local traditions include the consumption of raw foods, especially fish and meats. This manuscript provides an overview of the helminth infection prevention and control programs conducted in Vietnam, their achieved results, learned lessons, and future works.

Pharmacological Profiling of a Brugia malayi Muscarinic Acetylcholine Receptor as a Putative Antiparasitic Target

The diversification of anthelmintic targets and mechanisms of action will help ensure the sustainable control of nematode infections in response to the growing threat of drug resistance. G protein-coupled receptors (GPCRs) are established drug targets in human medicine but remain unexploited as anthelmintic substrates despite their important roles in nematode neuromuscular and physiological processes. Bottlenecks in exploring the druggability of parasitic nematode GPCRs include a limited helminth genetic toolkit and difficulties establishing functional heterologous expression. In an effort to address some of these challenges, we profile the function and pharmacology of muscarinic acetylcholine receptors in the human parasite Brugia malayi, an etiological agent of human lymphatic filariasis. While acetylcholine-gated ion channels are intensely studied as targets of existing anthelmintics, comparatively little is known about metabotropic receptor contributions to parasite cholinergic signaling. Using multivariate phenotypic assays in microfilariae and adults, we show that nicotinic and muscarinic compounds disparately affect parasite fitness traits. We identify a putative G protein-linked acetylcholine receptor of B. malayi (Bma-GAR-3) that is highly expressed across intramammalian life stages and adapt spatial RNA in situ hybridization to map receptor transcripts to critical parasite tissues. Tissue-specific expression of Bma-gar-3 in Caenorhabditis elegans (body wall muscle, sensory neurons, and pharynx) enabled receptor deorphanization and pharmacological profiling in a nematode physiological context. Finally, we developed an image-based feeding assay as a reporter of pharyngeal activity to facilitate GPCR screening in parasitized strains. We expect that these receptor characterization approaches and improved knowledge of GARs as putative drug targets will further advance the study of GPCR biology across medically important nematodes.

Anthelmintic Agents from African Medicinal Plants: Review and Prospects

Soil-transmitted helminthiasis affects more than 1.5 billion people globally and largely remains a sanitary problem in Africa. These infections place a huge economic burden on poor countries and affect livestock production, causing substantial economic losses and poor animal health. The emergence of anthelmintic resistance, especially in livestock, and the potential for its widespread in humans create a need for the development of alternative therapies. Medicinal plants play a significant role in the management of parasitic diseases in humans and livestock, especially in Africa. This report reviews anthelmintic studies that have been conducted on medicinal plants growing in Africa and published within the past two decades. A search was made in various electronic databases, and only full articles in English were included in the review. Reports show that aqueous and hydroalcoholic extracts and polar fractions obtained from these crude extracts form the predominant (80%) form of the extracts studied. Medicinal plants, extracts, and compounds with different chemical groups have been studied for their anthelmintic potential. Polyphenols and terpenoids are the most reported groups. More than 64% of the studies employed in vitro assays against parasitic and nonparasitic nematode models. Egg hatch inhibition, larval migration inhibition, and paralysis are the common parameters assessed in vitro. About 72% of in vivo models involved small ruminants, 15% rodents, and 5% chicken. Egg and worm burden are the main factors assessed in vivo. There were no reports on interventions in humans cited within the period under consideration. Also, few reports have investigated the potential of combining plant extracts with common anthelmintic drugs. This review reveals the huge potential of African medicinal plants as sources of anthelmintic agents and the dire need for in-depth clinical studies of extracts, fractions, and compounds from African plants as anthelmintic agents in livestock, companion animals, and humans.

Loa loa in the Vitreous Cavity of the Eye: A Case Report and State of Art

Loa loa is a filarial nematode responsible for loiasis, endemic to West-Central Africa south of the Sahara and transmitted by flies. This study reports a case of L. loa in the vitreous cavity of the eye of a young patient, along with an in-depth literature review. A 22-year-old woman from Cameroon who migrated from Cameroon to Italy was referred to the Emergency Ophthalmology Department at Policlinico di Bari in July 2021 with the presence of a moving parasite in the subconjunctiva of the left eye. A recent onset of a papular lesion on the dorsal surface of the right wrist and a nodular lesion in the scapular region were detected. L. loa filariasis was diagnosed based on anamnestic data, clinical and paraclinical signs, and a parasitological test confirming the presence of microfilariae in two blood samples collected in the morning of two different days. Because of the unavailability of diethylcarbamazine (DEC), albendazole (ALB) 200 mg twice daily was administered for 21 days. A mild exacerbation of pruritus occurred during treatment, but resolved with the use of an antihistamine. A single dose of 12 mg ivermectin was prescribed at the end of the treatment with albendazole. Unlike other endemic parasite infections, L. loa is not included in the Global Program to Eliminate Lymphatic Filariasis, because it is not mentioned in the WHO and CDC list of neglected tropical diseases. This can result in an overall risk of lack of attention and studies on loiasis, with lack of data on global burden of the disease.

Environmental circulation of the anthelmintic drug albendazole affects expression and activity of resistance-related genes in the parasitic nematode Haemonchus contortus

Veterinary anthelmintics excreted from treated animals pass to soil, subsequently to plants and then to their consumers. This circulation might have various consequences, including drug-resistance promotion in helminths. The present study was designed to follow the effect of the environmental circulation of the common anthelmintic drug albendazole (ABZ) in real farm conditions on the parasitic nematode Haemonchus contortus in vivo. Two fields with fodder plants (clover and alfalfa) were fertilized, the first with dung from ABZ-treated sheep (at the recommended dosage), the second with dung from non-treated sheep (controls). After a 10-week growth period, the fresh fodder from both fields was used to feed two groups of sheep, which were infected with H. contortus. Eggs and adult nematodes from the animals of both groups were isolated, and various parameters were compared. No significant changes in the eggs' sensitivity to ABZ and thiabendazole were observed. However, significantly increased expression of several cytochromes P450 and UDP-glycosyl transferases as well as increased oxidation and glycosylation of ABZ and ABZ-sulfoxide (ABZ-SO) was found in the exposed nematodes. These results show that ABZ environmental circulation improves the ability of the helminths to deactivate ABZ.

Mucosal Vaccination With Recombinant Tm-WAP49 Protein Induces Protective Humoral and Cellular Immunity Against Experimental Trichuriasis in AKR Mice

Trichuriasis is one of the most common neglected tropical diseases of the world's poorest people. A recombinant vaccine composed of Tm-WAP49, an immunodominant antigen secreted by adult Trichuris stichocytes into the mucosa of the cecum to which the parasite attaches, is under development. The prototype is being evaluated in a mouse model of Trichuris muris infection, with the ultimate goal of producing a mucosal vaccine through intranasal delivery. Intranasal immunization of mice with Tm-WAP49 formulated with the adjuvant OCH, a truncated analog of alpha-GalCer with adjuvanticity to stimulate natural killer T cells (NKT) and mucosal immunity, induced significantly high levels of IgG and its subclasses (IgG1 and IgG2a) in immunized mice. This also resulted in a significant reduction of worm burden after challenge with T. muris-infective eggs. The addition of QS-21 adjuvant to this vaccine formulation further reduced worm counts. The improved protection from the dual-adjuvanted vaccine correlated with higher serum antibody responses (IgG, IgG1, IgG2a, IgA) as well as with the induction of antigen-specific IgA in the nasal mucosa. It was also associated with the robust cellular responses including functional subsets of CD4 T cells producing IL-4, and cytotoxic CD8 T cells expressing granzyme B. The worm reduction achieved by mucosal immunization was higher than that induced by subcutaneous immunization. Intranasal immunization also induced a significantly higher nasal mucosa-secreted antigen-specific IgA response, as well as higher functional cellular responses including CD4⁺IL4⁺ (Th1) and CD8⁺GnzB⁺ (Th2) T cells, and antigen-specific INFγ-producing T cells in both spleen and MLNs and antibody-producing B cells (CD19⁺B220⁺/B220⁺GL7⁺). Mucosal immunization further induced long-term T lymphocyte memory with increased central (CD62L⁺CD44⁺) and effector (CD62L^-CD44⁺) memory subsets of both CD4 and CD8 T cells at 60 days after the last immunization. In summary, intranasal immunization with recombinant Tm-WAP49 protein induced strong protection versus murine trichuriasis. It represents a promising vaccination approach against intestinal nematodes.

Sertraline as a new potential anthelmintic against Haemonchus contortus: toxicity, efficacy, and biotransformation

Haemonchus contortus is a parasitic nematode of ruminants which causes significant losses to many farmers worldwide. Since the drugs currently in use for the treatment of haemonchosis are losing their effectiveness due to the drug-resistance of this nematode, a new or repurposed drug is highly needed. As the antipsychotic drug sertraline (SRT) has been shown to be effective against the parasitic nematodes Trichuris muris, Ancylostoma caninum and Schistosoma mansoni, the aim of the present study was to evaluate the possible effect of SRT on H. contortus. The potential hepatotoxicity of SRT was tested in sheep, a common H. contortus host. In addition, the main metabolic pathways of SRT in H. contortus and the ovine liver were identified. While no effect of SRT on H. contortus egg hatching was observed, SRT was found to significantly decrease the viability of H. contortus adults in drug-sensitive and resistant strains, with its effect comparable to the commonly used anthelmintics levamisole and monepantel. Moreover, SRT in anthelmintically active concentrations showed no toxicity to the ovine liver. Biotransformation of SRT in H. contortus was weak, with most of the drug remaining unmetabolized. Production of the main metabolite hydroxy-SRT did not differ significantly between strains. Other minor metabolites such as SRT-O-glucoside, dihydroxy-SRT, and SRT-ketone were also identified in H. contorts adults. Compared to H. contortus, the ovine liver metabolized SRT more extensively, mainly via desmethylation and glucuronidation. In conclusion, the potency of SRT against H. contortus was proven, and it should be tested further toward possible repurposing.

Proof of the environmental circulation of veterinary drug albendazole in real farm conditions

Anthelmintics, drugs against parasitic worms, are frequently used in livestock and might act as danger environmental microcontaminants. The present study was designed to monitor the possible circulation of common anthelmintic drug albendazole (ABZ) and its metabolites in the real agriculture conditions. The sheep were treated with the recommended dose of ABZ. Collected faeces were used for the fertilization of a field with fodder plants (alfalfa and clover) which served as feed for sheep from a different farm. The selective ultrasensitive mass spectrometry revealed surprisingly high concentrations of active ABZ metabolite (ABZ-sulphoxide) in all samples (dung, plants, ovine plasma, rumen content and faeces). Our results prove for the first time an undesirable permeation of ABZ metabolites from sheep excrement into plants (used as fodder) and subsequently to other sheep in real agricultural conditions. This circulation causes the permanent exposition of the ecosystems and food-chain to the drug and can promote the development of drug resistance in helminths.

Efficacy and safety of albendazole and high-dose ivermectin co-administration in school-aged children infected with Trichuris trichiura in Honduras: A Randomized Controlled Trial

BACKGROUND

The efficacy of currently available anthelminthics against Trichuris trichiura infections is significatively lower than for other soil-transmitted helminths (STH). The combination of ivermectin (IVM) and albendazole (ALB) has shown significant improvements in efficacy.

METHODS

Safety and efficacy randomized controlled clinical trial comparing 3 experimental regimens against ALB monotherapy for the treatment of T. trichiura infections in northern Honduras. Infected children were randomized to one of the following treatments: (Arm 1) single-dose ALB 400 mg; (Arm 2) single-dose ALB 400 mg/IVM 600 μg/kg; (Arm 3) ALB 400 mg for 3 consecutive days; or (Arm 4) ALB 400 mg/IVM 600 μg/kg for 3 consecutive days. Efficacy was measured through egg reduction rate (ERR) and cure rate (CR), both assessed 14-21 days after treatment using the Kato-Katz method. Safety was evaluated by analyzing the frequency and severity of adverse events.

RESULTS

A total of 176 children were randomized to one of the 4 treatment arms, 117 completed treatment and follow-up. The ERR for Arms 1 to 4 were: 47.7%, 96.7%, 72.1% and 100%, respectively; with p-values <0.001 between IVM groups and ALB only arms. The CRs were 4.2%, 88.6%, 33.3% and 100%, respectively. A total of 48 (85.4% mild) AEs were reported in 36 children.

CONCLUSIONS

The combined use of ALB and high-dose IVM is a highly effective and well tolerated treatment for the treatment of T. trichiura infections offering a significantly improved treatment for the control of this infection.

Advances in vaccine development for human trichuriasis

Trichuriasis known as whipworm infection caused by Trichuris trichiura, is a highly prevalent soil-transmitted helminthiasis in low- and middle-income countries located in tropical and subtropical areas and affecting approximately 360 million people. Children typically harbour the largest burden of T. trichiura and they are usually co-infected with other soil-transmitted helminth (STH), including Ascaris lumbricoides and hookworm. The consequences of trichuriasis, such as malnutrition and physical and cognitive growth restriction, lead to a massive health burden in endemic regions. Despite the implementation of mass drug administration of anthelminthic treatment to school-age children, T. trichiura infection remains challenging to control due to the low efficacy of current drugs as well as high rates of post-treatment re-infection. Thus, the development of a vaccine that would induce protective immunity and reduce infection rate or community faecal egg output is essential. Hurdles for human whipworm vaccine development include the lack of suitable vaccine antigen targets and animal models for human T. trichiura infection. Instead, rodent whipworm T. muris infected mouse models serve as a major surrogate for testing immunogenicity and efficacy of vaccine candidates. In this review, we summarize recent advances in animal models for T. trichiura antigen discovery and testing of vaccine candidates, while providing an overall view of the current status of T. trichiura vaccine development.

Barcode sequence could be a good target for developing a species-specific anti-parasite agent based on CRISPR-Cas9

Parasitic infections are a severe issue in many regions of the world. We assume that if a chemical can destroy a DNA barcode sequence, then this chemical could be developed as a species-specific parasiticidal agent. To test this hypothesis, we designed sgRNAs that target the sequences of both a DNA barcode (ITS-2) and a control (5.8S rDNA) in Cryptocaryon irritans. In in vivo tests, we found that exposure to Cas9 mRNA mixed with sgRNAs was able to significantly reduce the hatching rate of tomont and the survival rate of theront. Quantitative Real-time PCR demonstrated that the DNAs of tomont and theront exposed to sgRNAs and Cas9 mRNA were significantly disrupted, no matter whether they were exposed to a single sgRNA or a mixture of two sgRNAs. DNA sequencing also suggested the test group that was exposed to a single sgRNA mixed with Cas9-induced mutation at sgRNA targeted fragments and the test group exposed to two sgRNAs combined with Cas9-induced deletion of large pieces. The findings and principles provided by this study contribute to the development of novel nucleic acid therapeutic drugs for cryptocaryoniasis and other parasitic diseases and provide insight into the development of species-specific parasiticidal agents.

Fifteen Years of Sm-p80-Based Vaccine Trials in Nonhuman Primates: Antibodies From Vaccinated Baboons Confer Protection in vivo and in vitro From Schistosoma mansoni and Identification of Putative Correlative Markers of Protection

Recent advances in systems biology have shifted vaccine development from a largely trial-and-error approach to an approach that promote rational design through the search for immune signatures and predictive correlates of protection. These advances will doubtlessly accelerate the development of a vaccine for schistosomiasis, a neglected tropical disease that currently affects over 250 million people. For over 15 years and with contributions of over 120 people, we have endeavored to test and optimize Sm-p80-based vaccines in the non-human primate model of schistosomiasis. Using RNA-sequencing on eight different Sm-p80-based vaccine strategies, we sought to elucidate immune signatures correlated with experimental protective efficacy. Furthermore, we aimed to explore the role of antibodies through in vivo passive transfer of IgG obtained from immunized baboons and in vitro killing of schistosomula using Sm-p80-specific antibodies. We report that passive transfer of IgG from Sm-p80-immunized baboons led to significant worm burden reduction, egg reduction in liver, and reduced egg hatching percentages from tissues in mice compared to controls. In addition, we observed that sera from Sm-p80-immunized baboons were able to kill a significant percent of schistosomula and that this effect was complement-dependent. While we did not find a universal signature of immunity, the large datasets generated by this study will serve as a substantial resource for further efforts to develop vaccine or therapeutics for schistosomiasis.

Characterisation of cuticular inflation development and ultrastructure in Trichuris muris using correlative X-ray computed tomography and electron microscopy

The parasitic nematode Trichuris trichiura is a significant burden on public health in developing countries, and currently available drugs exhibit a poor cure rate. Worms live within a specialised tunnel of host intestinal epithelial cells and have anterior-ventral projections of the cuticle termed “cuticular inflations”, which are thought to be involved in host-parasite interactions. This work aimed to characterise structure and suggest a function of cuticular inflations in the most tractable and widely-used model of trichuriasis, Trichuris muris. Using scanning electron microscopy, we show for the first time that most cuticular inflations develop between the second and third larval moults. Correlative X-ray computed tomography (CT)-steered Serial Block Face Scanning Electron Microscopy (SBF-SEM) and transmission electron microscopy enabled ultrastructural imaging of cuticular inflations, and showed the presence of an additional, web-like layer of cuticle between the median and cortical layers of the inflation. Additionally, we characterised variation in inflation morphology, resolving debate as to the inflations’ true shape in situ. Cells underlying the inflations had many mitochondria, and we highlight their potential capacity for active transport as an area for future investigation. Overall, insights from the powerful imaging techniques used provide an excellent basis for future study of cuticular inflation function.

Drug discovery technologies: Caenorhabditis elegans as a model for anthelmintic therapeutics

Helminthiasis is one of the gravest problems worldwide. There is a growing concern on less available anthelmintics and the emergence of resistance creating a major threat to human and livestock health resources. Novel and broad-spectrum anthelmintics are urgently needed. The free-living nematode Caenorhabditis elegans could address this issue through automated high-throughput technologies for the screening of large chemical libraries. This review discusses the strong advantages and limitations for using C elegans as a screening method for anthelmintic drug discovery. C elegans is the best model available for the validation of novel effective drugs in treating most, if not all, helminth infections, and for the elucidation the mode of action of anthelmintic candidates. This review also focuses on available technologies in the discovery of anthelmintics published over the last 15 years with particular attention to high-throughput technologies over conventional screens. On the other hand, this review highlights how combinatorial and nanomedicine strategies could prolong the use of anthelmintics and control resistance problems.

Elucidation of Cellular Responses in Non-human Primates With Chronic Schistosomiasis Followed by Praziquantel Treatment

For decades, mass drug treatment with praziquantel (PZQ) has been utilized to treat schistosomiasis, yet reinfection and the risk of drug resistance are among the various factors precluding successful elimination of schistosomiasis. Tractable models that replicate "real world" field conditions are crucial to effectively evaluate putative schistosomiasis vaccines. Herein, we describe the cellular immune responses and cytokine expression profiles under field conditions that include prior infection with schistosomes followed by treatment with PZQ. Baboons were exposed to Schistosoma mansoni cercariae through trickle infection over 5 weeks, allowed for chronic disease to develop, and then treated with PZQ. Peripheral blood mononuclear cells (PBMCs) were monitored for cellular immune response(s) at each disease stage and PZQ therapy. After initial infection and during chronic disease, there was an increase in non-classical monocytes, NK and NKT cells while the CD4:CD8 T cell ratio inverted from a 2:1 to 1:2.5. The cytokine expressions of PBMCs after trickle infections were polarized more toward a Th2 response with a gradual increase in Th1 cytokine expression at chronic disease stage. Following PZQ treatment, with the exception of an increase in B cells, immune cell populations reverted back toward naïve levels; however, expression of almost all Th1, Th2, and Th17 cytokines was significantly increased. This preliminary study is the first to follow the cellular immune response and cytokine expression profiles in a non-human primate model simulating field conditions of schistosomiasis and PZQ therapy, providing a promising reference in predicting the immune response to future vaccines for schistosomiasis.

Protective immunity elicited by the nematode-conserved As37 recombinant protein against Ascaris suum infection

Background

Ascaris lumbricoides is one of the three major soil-transmitted gastrointestinal helminths (STHs) that infect more than 440 million people in the world, ranking this neglected tropical disease among the most common afflictions of people living in poverty. Children infected with this roundworm suffer from malnutrition, growth stunting as well as cognitive and intellectual deficits. An effective vaccine is urgently needed to complement anthelmintic deworming as a better approach to control helminth infections. As37 is an immunodominant antigen of Ascaris suum, a pig roundworm closely related to the human A. lumbricoides parasite, recognized by protective immune sera from A. suum infected mice. In this study, the immunogenicity and vaccine efficacy of recombinant As37 were evaluated in a mouse model.

Methodology/Principal findings

As37 was cloned and expressed as a soluble recombinant protein (rAs37) in Escherichia coli. The expressed rAs37 was highly recognized by protective immune sera from A. suum egg-infected mice. Balb/c mice immunized with 25 μg rAs37 formulated with AddaVax^™ adjuvant showed significant larval worm reduction after challenge with A. suum infective eggs when compared with a PBS (49.7%) or adjuvant control (48.7%). Protection was associated with mixed Th1/2-type immune responses characterized by high titers of serological IgG1 and IgG2a and stimulation of the production of cytokines IL-4, IL-5, IL-10 and IL-13. In this experiment, the AddaVax^™ adjuvant induced better protection than the Th1-type adjuvant MPLA (38.9%) and the Th2-type adjuvant Alhydrogel (40.7%). Sequence analysis revealed that As37 is a member of the immunoglobulin superfamily (IgSF) and highly conserved in other human STHs. Anti-As37 antibodies strongly recognized homologs in hookworms (Necator americanus, Ancylostoma ceylanicum, A. caninum) and in the whipworm Trichuris muris, but there was no cross-reaction with human spleen tissue extracts. These results suggest that the nematode-conserved As37 could serve as a pan-helminth vaccine antigen to prevent all STH infections without cross-reaction with human IgSF molecules.

Conclusions/Significance

As37 is an A. suum expressed immunodominant antigen that elicited significant protective immunity in mice when formulated with AddaVax^™. As37 is highly conserved in other STHs, but not in humans, suggesting it could be further developed as a pan-helminth vaccine against STH co-infections.

Ascaris infection is the most common infection of humans living in poverty worldwide and can result in malnutrition and stunted physical and mental development in children. A preventive vaccine is urgently needed as a complementary approach to anthelmintic deworming to increase the efficiency of STH infection control. To develop a vaccine against Ascaris infection, an immunodominant antigen, As37 of A. suum, was cloned and expressed as a soluble recombinant protein in E. coli. The recombinant As37 protein (rAs37) was highly recognized by protective immune sera from A. suum infected mice. Balb/c mice immunized with 25 μg rAs37 formulated with the adjuvant AddaVax^™ showed significant larval worm reduction against challenge with A. suum infective eggs when compared to a PBS (49.7%) or adjuvant control (48.7%). Protection was associated with a mixed Th1/2-type immune response characterized by high titers of serological IgG1 and IgG2a and stimulation of the production of cytokines IL-4, IL-5, IL-10 and IL-13. The AddaVax^™ adjuvant induced better protection than the Th1-type adjuvant MPLA (38.9%) and the Th2-type adjuvant Alhydrogel (40.7%). Sequence analysis revealed that As37 was a member of the immunoglobulin superfamily (IgSF) and highly conserved in other human STHs. Anti-As37 antibodies strongly recognized homologs in hookworms (Necator americanus, A. ceylanicum, A. caninum) and in the whipworm T. muris, but there was no cross-reaction with human spleen tissue extracts. These results indicate that the nematode-conserved As37 protein could be developed as a pan-helminth vaccine antigen to prevent all STH infections without reacting with human IgSF molecules.

Efficacy of Anthelminthic Drugs and Drug Combinations Against Soil-transmitted Helminths: A Systematic Review and Network Meta-analysis

Background

Periodic mass distribution of benzimidazole anthelminthic drugs is the key strategy to control soil-transmitted helminths (STHs) globally. However, benzimidazoles have low efficacy against Trichuris trichiura, and there are concerns about benzimidazole resistance potentially emerging in humans. Therefore, identifying alternative drug regimens is a pressing priority. We present a systematic review and network meta-analysis comparing the efficacy of 21 different anthelminthic drug regimens, including standard, novel, and combination treatments.

Methods

We searched PubMed, Medline, Embase, Web of Science, and Cochrane databases and identified studies comparing anthelminthic treatments to each other or placebo. The outcomes calculated were relative risk (RR) of cure and difference in egg reduction rates (dERR). We used an automated generalized pairwise modeling framework to generate mixed treatment effects against a common comparator, the current standard treatment (single-dose albendazole).

Results

Our search identified 4876 studies, of which 114 were included in the meta-analysis. Results identified several drug combinations with higher efficacy than single-dose albendazole for T. trichiura, including albendazole-ivermectin (RR of cure, 3.22 [95% confidence interval {CI}, 1.84-5.63]; dERR, 0.97 [95% CI, .21-1.74]), albendazole-oxantel pamoate (RR, 5.07 [95% CI, 1.65-15.59]; dERR, 0.51 [95% CI, .50-.52]), mebendazole-ivermectin (RR, 3.37 [95% CI, 2.20-5.16]), and tribendimidine-oxantel pamoate (RR, 4.06 [95% CI, 1.30-12.64]).

Conclusions

There are several promising drug combinations that may enhance the impact of STH control programs on T. trichiura, without compromising efficacy against Ascaris lumbricoides and hookworm. We suggest further, large-scale trials of these drug combinations and consideration of their use in STH control programs where T. trichiura is present.

International Prospective Register of Systematic Reviews Registration

CRD42016050739.

Anthelmintics in the future: current trends in the discovery and development of new drugs against gastrointestinal nematodes

The control of gastrointestinal nematodes (GINs), the most abundant and serious parasites of livestock, has become difficult because of the limited number of available drugs and fast development of drug resistance. Thus, considerable efforts have been devoted to developing new anthelmintics that are efficient against nematodes, especially resistant species. Here, we summarize the most recent results using various approaches: target-based or high-throughput screening (HTS) of compound libraries; the synthesis of new derivatives or new combinations of current anthelmintics; the repurposing of drugs currently approved for other indications; and lastly, the identification of active plant products. We also evaluate the advantages and disadvantages of each of these approaches.

Antitumor and anti-nematode activities of α-mangostin

α-Mangostin, one of the major xanthones isolated from pericarp of mangosteen (Garcinia mangostana Linn), exhibits a wide range of pharmacological activities, including antioxidant, anti-inflammatory, antimicrobial as well as anticancer, both in in vitro and in vivo studies. In the present study, α-mangostin' anti-cancer and anti-parasitic properties were tested in vitro against three human cell lines, including squamous carcinoma (SCC-15) and glioblastoma multiforme (U-118 MG), compared to normal skin fibroblasts (BJ), and in vivo against Caenorhabditis elegans. The drug showed cytotoxic activity, manifested by decrease of cell viability, inhibition of proliferation, induction of apoptosis and reduction of adhesion at concentrations lower than 10 μM (the IC₅₀ values were 6.43, 9.59 and 8.97 μM for SCC-15, U-118 MG and BJ, respectively). The toxicity, causing cell membrane disruption and mitochondria impairment, was selective against squamous carcinoma with regard to normal cells. Moreover, for the first time anti-nematode activity of α-mangostin toward C. elegans was described (the LC₅₀ = 3.8 ± 0.5 μM), with similar effect exerted by mebendazole, a well-known anthelmintic drug.

Kankanet: An artificial neural network-based object detection smartphone application and mobile microscope as a point-of-care diagnostic aid for soil-transmitted helminthiases

Background

Endemic areas for soil-transmitted helminthiases often lack the tools and trained personnel necessary for point-of-care diagnosis. This study pilots the use of smartphone microscopy and an artificial neural network-based (ANN) object detection application named Kankanet to address those two needs.

Methodology/Principal findings

A smartphone was equipped with a USB Video Class (UVC) microscope attachment and Kankanet, which was trained to recognize eggs of Ascaris lumbricoides, Trichuris trichiura, and hookworm using a dataset of 2,078 images. It was evaluated for interpretive accuracy based on 185 new images. Fecal samples were processed using Kato-Katz (KK), spontaneous sedimentation technique in tube (SSTT), and Merthiolate-Iodine-Formaldehyde (MIF) techniques. UVC imaging and ANN interpretation of these slides was compared to parasitologist interpretation of standard microscopy.Relative to a gold standard defined as any positive result from parasitologist reading of KK, SSTT, and MIF preparations through standard microscopy, parasitologists reading UVC imaging of SSTT achieved a comparable sensitivity (82.9%) and specificity (97.1%) in A. lumbricoides to standard KK interpretation (97.0% sensitivity, 96.0% specificity). The UVC could not accurately image T. trichiura or hookworm. Though Kankanet interpretation was not quite as sensitive as parasitologist interpretation, it still achieved high sensitivity for A. lumbricoides and hookworm (69.6% and 71.4%, respectively). Kankanet showed high sensitivity for T. trichiura in microscope images (100.0%), but low in UVC images (50.0%).

Conclusions/Significance

The UVC achieved comparable sensitivity to standard microscopy with only A. lumbricoides. With further improvement of image resolution and magnification, UVC shows promise as a point-of-care imaging tool. In addition to smartphone microscopy, ANN-based object detection can be developed as a diagnostic aid. Though trained with a limited dataset, Kankanet accurately interprets both standard microscope and low-quality UVC images. Kankanet may achieve sensitivity comparable to parasitologists with continued expansion of the image database and improvement of machine learning technology.

For rainforest-enshrouded rural villages of Madagascar, soil-transmitted helminthiases are more the rule than the exception. However, the microscopy equipment and lab technicians needed for diagnosis are a distance of several days’ hike away. We piloted a solution for these communities by leveraging resources the villages already had: a traveling team of local health care workers, and their personal Android smartphones. We demonstrated that an inexpensive, commercially available microscope attachment for smartphones could rival the sensitivity and specificity of a regular microscope using standard field fecal sample processing techniques. We also developed an artificial neural network-based object detection Android application, called Kankanet, based on open-source programming libraries. Kankanet was used to detect eggs of the three most common soil-transmitted helminths: Ascaris lumbricoides, Trichuris trichiura, and hookworm. We found Kankanet to be moderately sensitive and highly specific for both standard microscope images and low-quality smartphone microscope images. This proof-of-concept study demonstrates the diagnostic capabilities of artificial neural network-based object detection systems. Since the programming frameworks used were all open-source and user-friendly even for computer science laymen, artificial neural network-based object detection shows strong potential for development of low-cost, high-impact diagnostic aids essential to health care and field research in resource-limited communities.

Effect of nanoparticles on the therapeutic efficacy of praziquantel against Schistosoma mansoni infection in murine models

Praziquantel (PZQ) is the main treatment of Schistosomiasis mansoni. However, resistance to it was described. So, there is a necessity to develop novel drugs or to enhance the present drugs. This work aimed to assess the efficacy of PZQ alone and when loaded on liposomes in treatment of S. mansoni infection by parasitological and histopathological studies in experimental murine models. 112 male laboratories bred Swiss Albino mice were used in this work. They were divided into four groups: Group 1: control group; Group 2: infected then treated by PZQ (500 mg/kg) at 7, 30 and 45 days post infection; Group 3: infected then treated by liposome encapsulated PZQ (lip.PZQ) (500 mg/kg) at 7, 30 and 45 days post infection; Group 4: infected then treated by free liposomes at 7, 30 and 45 days post infection. The results showed that G3 caused the highest significant reduction of the total worm count, eggs/gram liver tissue and intestine (97.2%, 99.3%, 99.5%) respectively. Followed by G2 (85.1%, 97.6%, 89.8%) respectively. Regarding the histopathological studies, G3 showed the highest significant reduction in number and diameter of hepatic granuloma (97.6% and 98.1%), followed by G2 (77.2% and 75%) when compared to other groups. In conclusion, lip.PZQ is more effective than free PZQ from all aspects especially when administered 45 days PI.

Isolation and characterization of a naturally occurring multidrug-resistant strain of the canine hookworm, Ancylostoma caninum

Soil-transmitted nematodes infect over a billion people and place several billion more at risk of infection. Hookworm disease is the most significant of these soil-transmitted nematodes, with over 500 million people infected. Hookworm infection can result in debilitating and sometimes fatal iron-deficiency anemia, which is particularly devastating in children and pregnant women. Currently, hookworms and other soil-transmitted nematodes are controlled by administration of a single dose of a benzimidazole to targeted populations in endemic areas. While effective, people are quickly re-infected, necessitating frequent treatment. Widespread exposure to anthelmintic drugs can place significant selective pressure on parasitic nematodes to generate resistance, which has severely compromised benzimidazole anthelmintics for control of livestock nematodes in many areas of the world. Here we report, to our knowledge, the first naturally occurring multidrug-resistant strain of the canine hookworm Ancylostoma caninum. We reveal that this isolate is resistant to fenbendazole at the clinical dosage of 50 mg/kg for 3 days. Our data shows that this strain harbors a fixed, single base pair mutation at amino acid 167 of the β-tubulin isotype 1 gene, and by using CRISPR/Cas9 we demonstrate that introduction of this mutation into the corresponding amino acid in the orthologous β-tubulin gene of Caenorhabditis elegans confers a similar level of resistance to thiabendazole. We also show that the isolate is resistant to the macrocyclic lactone anthelmintic ivermectin. Understanding the mechanism of anthelmintic resistance is important for rational design of control strategies to maintain the usefulness of current drugs, and to monitor the emergence of resistance. The isolate we describe represents the first multidrug-resistant strain of A. caninum reported, and our data reveal a resistance marker that can emerge naturally in response to heavy anthelminthic treatment.

Can CRISPR help in the fight against parasitic worms?

The first reports of CRISPR/Cas9 genome editing in flatworms could usher in a new era of research on these dangerous human parasites.

Flubendazole as a macrofilaricide: History and background

Benzimidazole anthelmintics have long been employed for the control of soil-transmitted helminth infections. Flubendazole (FBZ) was approved in 1980 for the treatment of gastrointestinal nematode infections in both veterinary and human medicine. It has also long been known that parenteral administration of FBZ can lead to high macrofilaricidal efficacy in a variety of preclinical models and in humans. As part of an effort to stimulate the discovery and development of new macrofilaricides, particularly for onchocerciasis, research has recently been devoted to the development of new formulations that would afford high oral bioavailability of FBZ, paving the way for potential clinical development of this repurposed drug for the treatment of human filariases. This review summarizes the background information that led to this program and summarizes some of the lessons learned from it.

DEMONSTRATION OF THE ANTHELMINTIC POTENCY OF MARIMASTAT IN THE HELIGMOSOMOIDES POLYGYRUS RODENT MODEL

In the course of a structure based drug discovery program the known anticancer candidate marimastat was uncovered as a potent inhibitor of an enzyme in nematode cuticle biogenesis. It was shown to kill Caenorhabditis elegans, and the sheep parasites Haemonchus contortus and Teladorsagia circumcinta via an entirely novel nematode-specific pathway, specifically by inhibiting cuticle-remodelling enzymes that the parasites require for the developmentally essential moulting process. This discovery prompted an investigation of the compound's effect on Heligmosomoides polygyrus parasites in a mouse model of helminth infection. Mice were administered the drug via oral gavage daily from day of infection for a period of 2 wk. A second group received the drug via intra-peritoneal implantation of an osmotic minipump for 4 wk. Control groups were administered identical volumes of water by oral gavage in both cases. Counts of H. polygyrus faecal egg and larval load showed that marimastat effected a consistent and significant reduction in egg laying, and a consistent but minor reduction in adult worm load when administered every day, starting on the first day of infection. However, the drug failed to have any significant effect on egg counts or worm burdens when administered to mice with established infections. Therefore, marimastat does not appear to show promise as an anthelmintic in gastrointestinal nematode infections, although other metalloproteases such as batimastat may prove more effective.

Chronic schistosomiasis suppresses HIV-specific responses to DNA-MVA and MVA-gp140 Env vaccine regimens despite antihelminthic treatment and increases helminth-associated pathology in a mouse model

Future HIV vaccines are expected to induce effective Th1 cell-mediated and Env-specific antibody responses that are necessary to offer protective immunity to HIV infection. However, HIV infections are highly prevalent in helminth endemic areas. Helminth infections induce polarised Th2 responses that may impair HIV vaccine-generated Th1 responses. In this study, we tested if Schistosoma mansoni (Sm) infection altered immune responses to SAAVI candidate HIV vaccines (DNA and MVA) and an HIV-1 gp140 Env protein vaccine (gp140) and whether parasite elimination by chemotherapy or the presence of Sm eggs (SmE) in the absence of active infection influenced the immunogenicity of these vaccines. In addition, we evaluated helminth-associated pathology in DNA and MVA vaccination groups. Mice were chronically infected with Sm and vaccinated with DNA+MVA in a prime+boost combination or MVA+gp140 in concurrent combination regimens. Some Sm-infected mice were treated with praziquantel (PZQ) prior to vaccinations. Other mice were inoculated with SmE before receiving vaccinations. Unvaccinated mice without Sm infection or SmE inoculation served as controls. HIV responses were evaluated in the blood and spleen while Sm-associated pathology was evaluated in the livers. Sm-infected mice had significantly lower magnitudes of HIV-specific cellular responses after vaccination with DNA+MVA or MVA+gp140 compared to uninfected control mice. Similarly, gp140 Env-specific antibody responses were significantly lower in vaccinated Sm-infected mice compared to controls. Treatment with PZQ partially restored cellular but not humoral immune responses in vaccinated Sm-infected mice. Gp140 Env-specific antibody responses were attenuated in mice that were inoculated with SmE compared to controls. Lastly, Sm-infected mice that were vaccinated with DNA+MVA displayed exacerbated liver pathology as indicated by larger granulomas and increased hepatosplenomegaly when compared with unvaccinated Sm-infected mice. This study shows that chronic schistosomiasis attenuates both HIV-specific T-cell and antibody responses and parasite elimination by chemotherapy may partially restore cellular but not antibody immunity, with additional data suggesting that the presence of SmE retained in the tissues after antihelminthic therapy contributes to lack of full immune restoration. Our data further suggest that helminthiasis may compromise HIV vaccine safety. Overall, these findings suggested a potential negative impact on future HIV vaccinations by helminthiasis in endemic areas.

Chronic parasitic worm infections are thought to reduce the efficacy of vaccines. Given that HIV and worm infections are common in sub-Saharan Africa (SSA) and their geographical distribution vastly overlaps, it is likely that future HIV vaccines in SSA will be administered to a large proportion of people with chronic worm infections. This study examined the impact of S. mansoni worm infections on the immunogenicity of candidate HIV vaccines in a mouse model. S. mansoni worm-infected animals had lower magnitudes of HIV vaccine responses compared with uninfected animals and elimination of worms by praziquantel treatment prior to vaccination conferred only partial restoration of normal immune responses to vaccination. The presence of S. mansoni eggs trapped in the tissues in the absence of live infection was associated with poor vaccine responses. In addition, this study found that effective immunization with some HIV vaccine regimens could potentially worsen worm-associated pathology when given to infected individuals. These novel findings suggest further research in HIV vaccines and future vaccination policies regarding the current clinical vaccines and future HIV vaccination with respect to parasitic worm infections especially in SSA.

Discovery of genomic intervals that underlie nematode responses to benzimidazoles

Parasitic nematodes impose a debilitating health and economic burden across much of the world. Nematode resistance to anthelmintic drugs threatens parasite control efforts in both human and veterinary medicine. Despite this threat, the genetic landscape of potential resistance mechanisms to these critical drugs remains largely unexplored. Here, we exploit natural variation in the model nematodes Caenorhabditis elegans and Caenorhabditis briggsae to discover quantitative trait loci (QTL) that control sensitivity to benzimidazoles widely used in human and animal medicine. High-throughput phenotyping of albendazole, fenbendazole, mebendazole, and thiabendazole responses in panels of recombinant lines led to the discovery of over 15 QTL in C. elegans and four QTL in C. briggsae associated with divergent responses to these anthelmintics. Many of these QTL are conserved across benzimidazole derivatives, but others show drug and dose specificity. We used near-isogenic lines to recapitulate and narrow the C. elegans albendazole QTL of largest effect and identified candidate variants correlated with the resistance phenotype. These QTL do not overlap with known benzimidazole target resistance genes from parasitic nematodes and present specific new leads for the discovery of novel mechanisms of nematode benzimidazole resistance. Analyses of orthologous genes reveal conservation of candidate benzimidazole resistance genes in medically important parasitic nematodes. These data provide a basis for extending these approaches to other anthelmintic drug classes and a pathway towards validating new markers for anthelmintic resistance that can be deployed to improve parasite disease control.

The treatment of roundworm (nematode) infections in both humans and animals relies on a small number of anti-parasitic drugs. Resistance to these drugs has appeared in veterinary parasite populations and is a growing concern in human medicine. A better understanding of the genetic basis for parasite drug resistance can be used to help maintain the effectiveness of anti-parasitic drugs and to slow or to prevent the spread of drug resistance in parasite populations. This goal is hampered by the experimental intractability of nematode parasites. Here, we use non-parasitic model nematodes to systematically explore responses to the critical benzimidazole class of anti-parasitic compounds. Using a quantitative genetics approach, we discovered unique genomic intervals that control drug effects, and we identified differences in the effects of these intervals across compounds and doses. We were able to narrow a major-effect genomic region associated with albendazole resistance and to establish that candidate genes discovered in our genetic mappings are largely conserved in important human and animal parasites. This work provides new leads for understanding parasite drug resistance and contributes a powerful template that can be extended to other anti-parasitic drug classes.

Differential human gut microbiome assemblages during soil-transmitted helminth infections in Indonesia and Liberia

BACKGROUND

The human intestine and its microbiota is the most common infection site for soil-transmitted helminths (STHs), which affect the well-being of ~ 1.5 billion people worldwide. The complex cross-kingdom interactions are not well understood.

RESULTS

A cross-sectional analysis identified conserved microbial signatures positively or negatively associated with STH infections across Liberia and Indonesia, and longitudinal samples analysis from a double-blind randomized trial showed that the gut microbiota responds to deworming but does not transition closer to the uninfected state. The microbiomes of individuals able to self-clear the infection had more alike microbiome assemblages compared to individuals who remained infected. One bacterial taxon (Lachnospiracae) was negatively associated with infection in both countries, and 12 bacterial taxa were significantly associated with STH infection in both countries, including Olsenella (associated with reduced gut inflammation), which also significantly reduced in abundance following clearance of infection. Microbial community gene abundances were also affected by deworming. Functional categories identified as associated with STH infection included arachidonic acid metabolism; arachidonic acid is the precursor for pro-inflammatory leukotrienes that threaten helminth survival, and our findings suggest that some modulation of arachidonic acid activity in the STH-infected gut may occur through the increase of arachidonic acid metabolizing bacteria.

CONCLUSIONS

For the first time, we identify specific members of the gut microbiome that discriminate between moderately/heavily STH-infected and non-infected states across very diverse geographical regions using two different statistical methods. We also identify microbiome-encoded biological functions associated with the STH infections, which are associated potentially with STH survival strategies, and changes in the host environment. These results provide a novel insight of the cross-kingdom interactions in the human gut ecosystem by unlocking the microbiome assemblages at taxonomic, genetic, and functional levels so that advances towards key mechanistic studies can be made.

Metabolism of albendazole, ricobendazole and flubendazole in Haemonchus contortus adults: Sex differences, resistance-related differences and the identification of new metabolites

Haemonchus contortus (family Trichostrongylidae, Nematoda), a hematophagous gastrointestinal parasite found in small ruminants, has a great ability to develop resistance to anthelmintic drugs. We studied the biotransformation of the three benzimidazole anthelmintics: albendazole (ABZ), ricobendazole (albendazole S-oxide; RCB) and flubendazole (FLU) in females and males of H. contortus in both a susceptible ISE strain and resistant IRE strain. The ex vivo cultivation of living nematodes in culture medium with or without the anthelmintics was used. Ultrasensitive UHPLC/MS/MS analysis revealed 9, 7 and 12 metabolites of ABZ, RCB and FLU, respectively, with most of these metabolites now described in the present study for the first time in H. contortus. The structure of certain metabolites shows the presence of biotransformation reactions not previously reported in nematodes. There were significant qualitative and semi-quantitative differences in the metabolites formed by male and female worms. In most cases, females metabolized drugs more extensively than males. Adults of the IRE strain were able to form many more metabolites of all the drugs than adults of the ISE strain. Some metabolites were even found only in adults of the IRE strain. These findings suggest that increased drug metabolism may play a role in resistance to benzimidazole drugs in H. contortus.

Soil-transmitted helminth infections

More than a quarter of the world's population is at risk of infection with the soil-transmitted helminths Ascaris lumbricoides, hookworm (Ancylostoma duodenale and Necator americanus), Trichuris trichiura, and Strongyloides stercoralis. Infected children and adults present with a range of medical and surgical conditions, and clinicians should consider the possibility of infection in individuals living in, or returning from, endemic regions. Although safe and effective drugs are donated free to endemic countries, only half of at-risk children received treatment in 2016. This Seminar describes the epidemiology, lifecycles, pathophysiology, clinical diagnosis, management, and public health control of soil-transmitted helminths. Previous work has questioned the effect of population-level deworming; however, it remains beyond doubt that treatment reduces the severe consequences of soil-transmitted helminthiasis. We highlight the need for refined diagnostic tools and effective control options to scale up public health interventions and improve clinical detection and management of these infections.

The self-curing phenomenon of schistosome infection in rhesus macaques: insight from in vitro studies

A reduction in the burden of schistosomiasis is potentially achievable by integrating a schistosomiasis vaccine with current control measures. Here, we determine parasite-specific in vitro responses of B, T, and NK cells from naive uninfected rhesus macaques to Schistosoma mansoni (Sm) egg (SmEA) and worm antigen (SmWA) preparations isolated from infected baboons. Pronounced B cell responses to SmEA and NK cell responses to both SmEA and SmWA were observed. High levels of IL-2 and IL-21 responses against Sm antigens were observed in T and non-T cells of lymph nodes (LNs) and gut lamina propria-derived lymphocytes (LPLs). Data analysis showed multifunctionality of LN-derived CD4⁺ , CD8⁺ , and CD4⁺ CD8⁺ double positive T cells against either SmWA or SmWA+SmEA antigen preparations. Distinct SmEA-specific multifunctional responses were observed in gut LPLs, suggesting simultaneous responses against egg antigens. These data provide insight into the immune effectors involved in schistosome responses by rhesus macaques.

Mining Filarial Genomes for Diagnostic and Therapeutic Targets

Filarial infections of humans cause some of the most important neglected tropical diseases. The global efforts for eliminating filarial infections by mass drug administration programs may require additional tools (safe macrofilaricidal drugs, vaccines, and diagnostic biomarkers). The accurate and sensitive detection of viable parasites is essential for diagnosis and for surveillance programs. Current community-wide treatment modalities do not kill the adult filarial worms effectively; hence, there is a need to identify and develop safe macrofilaricidal drugs. High-throughput sequencing, mass spectroscopy methods and advances in computational biology have greatly accelerated the discovery process. Here, we describe post-genomic developments toward the identification of diagnostic biomarkers and drug targets for the filarial infection of humans.

In vitro and in vivo activity of R- and S- praziquantel enantiomers and the main human metabolite trans-4-hydroxy-praziquantel against Schistosoma haematobium

Background

Praziquantel (PZQ) is the mainstay of schistosomiasis control and has been successfully used for decades. However, its mechanism of action is not fully understood. While the majority of studies have been conducted on Schistosoma mansoni, it is not known which enantiomer, R- or S-praziquantel (R-/S-PZQ), is responsible for the activity on Schistosoma haematobium.

Methods

In vitro and in vivo studies were conducted to evaluate the activity of R- and S-PZQ, racemic PZQ and the main human metabolite, namely trans-4-OH-PZQ, on S. haematobium. IC₅₀ values on adult S. haematobium were determined in vitro. Dose-response relationship studies were performed in golden Syrian hamsters, harbouring a chronic S. haematobium infection.

Results

R-PZQ displayed the highest activity against adult worms in vitro, revealing an IC₅₀ of 0.007 μg/ml at 4 h and 0.01 μg/ml at 72 h. In contrast, S-PZQ was 501× less active (eudysmic ratio at 4 h), with an IC₅₀ of 3.51 and 3.40 μg/ml (4 and 72 h, respectively). Racemic PZQ and trans-4-OH-PZQ resulted in an IC₅₀ of 0.03 μg/ml and 1.47 μg/ml both at 4 and 72 h, respectively. In vivo, R-PZQ was the most potent drug with worm burden reductions (WBRs) of 98.5, 75.6 and 73.3% at 125.0, 62.5 and 31.0 mg/kg, respectively. A single oral dose of 250.0 mg/kg PZQ resulted in a WBR of 99.3%. S-PZQ was highly active in vivo at 250.0 and 500.0 mg/kg with WBRs of 83.0 and 94.1%, respectively. The lowest tested dose of S-PZQ, 125.0 mg/kg, showed moderate activity (WBR of 46.7%). The calculated ED₅₀ for R- and S-PZQ were 24.7 and 127.6 mg/kg, respectively, with a corresponding eudysmic ratio of 5.17.

Conclusion

Our data support the theory of R-PZQ driving the antischistosomal activity. Interestingly, also S-PZQ proved to possess a significant activity towards S. haematobium, particularly in vivo.

A mysterious family of calcium-binding proteins from parasitic worms

There is a family of proteins from parasitic worms which combine N-terminal EF-hand domains with C-terminal dynein light chain-like domains. Data are accumulating on the biochemistry and cell biology of these proteins. However, little is known about their functions in vivo Schistosoma mansoni expresses 13 family members (SmTAL1-SmTAL13). Three of these (SmTAL1, SmTAL2 and SmTAL3) have been subjected to biochemical analysis which demonstrated that they have different molecular properties. Although their overall folds are predicted to be similar, small changes in the EF-hand domains result in differences in their ion binding properties. Whereas SmTAL1 and SmTAL2 are able to bind calcium (and some other) ions, SmTAL3 appears to be unable to bind any divalent cations. Similar biochemical diversity has been seen in the CaBP proteins from Fasciola hepatica Four family members are known (FhCaBP1-4). All of these bind to calcium ions. However, FhCaBP4 dimerizes in the presence of calcium ions, FhCaBP3 dimerizes in the absence of calcium ions and FhCaBP2 dimerizes regardless of the prevailing calcium ion concentration. In both the SmTAL and FhCaBP families, the proteins also differ in their ability to bind calmodulin antagonists and related drugs. Interestingly, SmTAL1 interacts with praziquantel (the drug of choice for treating schistosomiasis). The pharmacological significance (if any) of this finding is unknown.

Genomic introgression mapping of field-derived multiple-anthelmintic resistance in Teladorsagia circumcincta

Preventive chemotherapy has long been practiced against nematode parasites of livestock, leading to widespread drug resistance, and is increasingly being adopted for eradication of human parasitic nematodes even though it is similarly likely to lead to drug resistance. Given that the genetic architecture of resistance is poorly understood for any nematode, we have analyzed multidrug resistant Teladorsagia circumcincta, a major parasite of sheep, as a model for analysis of resistance selection. We introgressed a field-derived multiresistant genotype into a partially inbred susceptible genetic background (through repeated backcrossing and drug selection) and performed genome-wide scans in the backcross progeny and drug-selected F2 populations to identify the major genes responsible for the multidrug resistance. We identified variation linking candidate resistance genes to each drug class. Putative mechanisms included target site polymorphism, changes in likely regulatory regions and copy number variation in efflux transporters. This work elucidates the genetic architecture of multiple anthelmintic resistance in a parasitic nematode for the first time and establishes a framework for future studies of anthelmintic resistance in nematode parasites of humans.

Teladorsagia circumcincta is an economically significant nematode (roundworm) pathogen affecting sheep and goats in temperate regions of the world. The widespread use of prophylactic treatment has resulted in rapid selection for anthelmintic (anti-worm drug) resistance in this and other species of livestock parasites. The mechanism of resistance is not well understood because most studies have focused on the role of candidate genes using simplistic models of single gene selection, despite evidence that the evolution of resistance is more complex. Here, we report on a comprehensive whole-genome analysis that elucidated resistance-associated genes, which was facilitated by developing a pair of T. circumcincta strains sharing a largely common genetic background but differing markedly in their susceptibility to anthelmintic drugs. The results show that multiple genetic factors contribute to anthelmintic resistance in a variety of ways, including possible reduction/modulation in target site sensitivity, reduced target site expression, and increased drug efflux, to name a few. This suggests that drug resistance in these parasites is a multifactorial quantitative trait rather than a simple discrete Mendelian character. With this study, we established a genomics-based experimental paradigm for investigating anthelmintic resistance, at a time when its medical importance is rapidly increasing.

Isothermal Diagnostic Assays for Monitoring Single Nucleotide Polymorphisms in Necator americanus Associated with Benzimidazole Drug Resistance

BACKGROUND

Soil-transmitted helminths (STHs) are the most prevalent intestinal helminths of humans, and a major cause of morbidity in tropical and subtropical countries. The benzimidazole (BZ) drugs albendazole (ABZ) and mebendazole (MBZ) are used for treatment of human STH infections and this use is increasing dramatically with massive drug donations. Frequent and prolonged use of these drugs could lead to the emergence of anthelmintic resistance as has occurred in nematodes of livestock. Previous molecular assays for putative resistance mutations have been based mainly on PCR amplification and sequencing. However, these techniques are complicated and time consuming and not suitable for resource-constrained situations. A simple, rapid and sensitive genotyping method is required to monitor for possible developing resistance to BZ drugs.

METHODS

To address this problem, single nucleotide polymorphism (SNP) detection assays were developed based on the Smart amplification method (SmartAmp2) to target codons 167, 198, and 200 in the β-tubulin isotype 1 gene for the hookworm Necator americanus.

FINDINGS

Diagnostic assays were developed and applied to analyze hookworm samples by both SmartAmp2 and conventional sequencing methods and the results showed high concordance. Additionally, fecal samples spiked with N. americanus larvae were assessed and the results showed that the Aac polymerase used has high tolerance to inhibitors in fecal samples.

CONCLUSION

The N. americanus SmartAmp2 SNP detection assay is a new genotyping tool that is rapid, sensitive, highly specific and efficient with the potential to be used as a field tool for monitoring SNPs associated with BZ resistance. However, further validation on large numbers of field samples is required.

Sm-p80-Based Schistosomiasis Vaccine: Preparation for Human Clinical Trials

Mass antiparasitic drug administration programs and other control strategies have made important contributions in reducing the global prevalence of helminths. Schistosomiasis, however, continues to spread to new geographic areas. The advent of a viable vaccine and its deployment, coupled with existing control efforts, is expected to make significant headway towards sustained schistosomiasis control. In 2016, Science ranked the schistosomiasis vaccine as one of the top 10 vaccines that needs to be urgently developed. A vaccine that is effective against geographically distinct forms of intestinal/hepatic and urinary disease is essential to make a meaningful impact in global reduction of the disease burden. In this opinion article, we focus on salient features of schistosomiasis vaccines in different phases of the clinical development pipeline and highlight the Sm-p80-based vaccine which is now being prepared for human clinical trials.

Comprehensive Transcriptome Meta-analysis to Characterize Host Immune Responses in Helminth Infections

Helminth infections affect more than a third of the world’s population. Despite very broad phylogenetic differences among helminth parasite species, a systemic Th2 host immune response is typically associated with long-term helminth infections, also known as the “helminth effect”. Many investigations have been carried out to study host gene expression profiles during helminth infections. The objective of this study is to determine if there is a common transcriptomic signature characteristic of the helminth effect across multiple helminth species and tissue types. To this end, we performed a comprehensive meta-analysis of publicly available gene expression datasets. After data processing and adjusting for study-specific effects, we identified ~700 differentially expressed genes that are changed consistently during helminth infections. Functional enrichment analyses indicate that upregulated genes are predominantly involved in various immune functions, including immunomodulation, immune signaling, inflammation, pathogen recognition and antigen presentation. Down-regulated genes are mainly involved in metabolic process, with only a few of them are involved in immune regulation. This common immune gene signature confirms previous observations and indicates that the helminth effect is robust across different parasite species as well as host tissue types. To the best of our knowledge, this study is the first comprehensive meta-analysis of host transcriptome profiles during helminth infections.

Many studies have been conducted to understand the immune modulatory effects in helminth infections. To determine whether there is a common transcriptomic signature characteristic of the helminth effect, we performed a comprehensive meta-analysis of publicly available gene expression datasets. The results revealed a distinct pattern of gene expression that is consistent across multiple helminth species and host tissue types, with upregulated genes dominated by those involved in immune regulation, Th2 immunity and inflammatory responses.

Alternative energy production pathways in Taenia crassiceps cysticerci in vitro exposed to a benzimidazole derivative (RCB20)

Biochemical studies of benzimidazole derivatives are important to determine their mode of action and activity against parasites. The lack of antihelminthic alternatives to treat parasitic infections and albendazole resistance cases make the search for new antiparasitary drugs of utmost importance. The 6-chloro-5-(1-naphthyloxy)-2-(trifluoromethyl)-1H-benzimidazole (RCB20) is a benzimidazole derivative with promising effect. This study evaluated the effect of different concentrations of RCB20 in the alternative energetic pathway of in vitro Taenia crassiceps cysticerci. The parasites were in vitro exposed to 6·5 and 13 µm of RCB20 and albendazole sulfoxide (ABZSO). The quantification of acetate, acetoacetate, β-hydroxybutyrate, fumarate and propionate was performed by high-performance liquid chromatography. The quantification of urea, creatinine and total proteins was performed by spectrophotometry. The increase in β-hydroxybutyrate reflects the enhancement of the fatty acid oxidation in the treated groups. Volatile fatty acids secretion, acetate and propionate, was increased in the treated groups. The secretion mechanisms of the treated parasites were impaired due to organic acids increased concentrations in the cysticerci. It is possible to conclude that the metabolic effect on alternative energetic pathways is slightly increased in the parasites treated with RCB20 than the ones treated with ABZSO.

Identification and activity of inhibitors of the essential nematode-specific metalloprotease DPY-31

Infection by parasitic nematodes is widespread in the developing world causing extensive morbidity and mortality. Furthermore, infection of animals is a global problem, with a substantial impact on food production. Here we identify small molecule inhibitors of a nematode-specific metalloprotease, DPY-31, using both known metalloprotease inhibitors and virtual screening. This strategy successfully identified several μM inhibitors of DPY-31 from both the human filarial nematode Brugia malayi, and the parasitic gastrointestinal nematode of sheep Teladorsagia circumcincta. Further studies using both free living and parasitic nematodes show that these inhibitors elicit the severe body morphology defect 'Dumpy' (Dpy; shorter and fatter), a predominantly non-viable phenotype consistent with mutants lacking the DPY-31 gene. Taken together, these results represent a start point in developing DPY-31 inhibition as a totally novel mechanism for treating infection by parasitic nematodes in humans and animals.