Population dynamics of Wolbachia bacterial endosymbionts in Brugia malayi

Wolbachia and Lymphatic Filarial Nematodes and Their Implications in the Pathogenesis of the Disease

Lymphatic filariasis (LF) is an infection of three closely related filarial worms such as Wuchereria bancrofti, Brugia malayi, and Brugia timori. These worms can cause a devastating disease that involves acute and chronic lymphoedema of the extremities, which can cause elephantiasis in both sexes and hydroceles in males. These important public health nematodes were found to have a mutualistic relationship with intracellular bacteria of the genus Wolbachia, which is essential for the development and survival of the nematode. The host's inflammatory response to parasites and possibly also to the Wolbachia endosymbiont is the cause of lymphatic damage and disease pathogenesis. This review tried to describe and highlight the mutualistic associations between Wolbachia and lymphatic filarial nematodes and the role of bacteria in the pathogenesis of lymphatic filariasis. Articles for this review were searched from PubMed, Google Scholar, and other databases. Article searching was not restricted by publication year; however, only English version full-text articles were included.

Unveiling the intricacies of allosteric regulation in aspartate kinase from the Wolbachia endosymbiont of Brugia Malayi: Mechanistic and therapeutic insights

Aspartate kinase (AK), an enzyme from the Wolbachia endosymbiont of Brugia malayi (WBm), plays a pivotal role in the bacterial cell wall and amino acid biosynthesis, rendering it an attractive candidate for therapeutic intervention. Allosteric inhibition of aspartate kinase is a prevalent mode of regulation across microorganisms and plants, often modulated by end products such as lysine, threonine, methionine, or meso-diaminopimelate. The intricate and diverse nature of microbial allosteric regulation underscores the need for rigorous investigation. This study employs a combined experimental and computational approach to decipher the allosteric regulation of WBmAK. Molecular Dynamics (MD) simulations elucidate that ATP (cofactor) and ASP (substrate) binding induce a closed conformation, promoting enzymatic activity. In contrast, the binding of lysine (allosteric inhibitor) leads to enzyme inactivation and an open conformation. The enzymatic assay demonstrates the optimal activity of WBmAK at 28 °C and a pH of 8.0. Notably, the allosteric inhibition study highlights lysine as a more potent inhibitor compared to threonine. Importantly, this investigation sheds light on the allosteric mechanism governing WBmAK and imparts novel insights into structure-based drug discovery, paving the way for the development of effective inhibitors against filarial pathogens.

Cross-validation of chemical and genetic disruption approaches to inform host cellular effects on Wolbachia abundance in Drosophila

Introduction

Endosymbiotic Wolbachia bacteria are widespread in nature, present in half of all insect species. The success of Wolbachia is supported by a commensal lifestyle. Unlike bacterial pathogens that overreplicate and harm host cells, Wolbachia infections have a relatively innocuous intracellular lifestyle. This raises important questions about how Wolbachia infection is regulated. Little is known about how Wolbachia abundance is controlled at an organismal scale.

Methods

This study demonstrates methodology for rigorous identification of cellular processes that affect whole-body Wolbachia abundance, as indicated by absolute counts of the Wolbachia surface protein (wsp) gene.

Results

Candidate pathways, associated with well-described infection scenarios, were identified. Wolbachia-infected fruit flies were exposed to small molecule inhibitors known for targeting those same pathways. Sequential tests in D. melanogaster and D. simulans yielded a subset of chemical inhibitors that significantly affected whole-body Wolbachia abundance, including the Wnt pathway disruptor, IWR-1 and the mTOR pathway inhibitor, Rapamycin. The implicated pathways were genetically retested for effects in D. melanogaster, using inducible RNAi expression driven by constitutive as well as chemically-induced somatic GAL4 expression. Genetic disruptions of armadillo, tor, and ATG6 significantly affected whole-body Wolbachia abundance.

Discussion

As such, the data corroborate reagent targeting and pathway relevance to whole-body Wolbachia infection. The results also implicate Wnt and mTOR regulation of autophagy as important for regulation of Wolbachia titer.

Improved metagenome assemblies through selective enrichment of bacterial genomic DNA from eukaryotic host genomic DNA using ATAC-seq

Genomics can be used to study the complex relationships between hosts and their microbiota. Many bacteria cannot be cultured in the laboratory, making it difficult to obtain adequate amounts of bacterial DNA and to limit host DNA contamination for the construction of metagenome-assembled genomes (MAGs). For example, Wolbachia is a genus of exclusively obligate intracellular bacteria that live in a wide range of arthropods and some nematodes. While Wolbachia endosymbionts are frequently described as facultative reproductive parasites in arthropods, the bacteria are obligate mutualistic endosymbionts of filarial worms. Here, we achieve 50-fold enrichment of bacterial sequences using ATAC-seq (Assay for Transposase-Accessible Chromatin using sequencing) with Brugia malayi nematodes, containing Wolbachia (wBm). ATAC-seq uses the Tn5 transposase to cut and attach Illumina sequencing adapters to accessible DNA lacking histones, typically thought to be open chromatin. Bacterial and mitochondrial DNA in the lysates are also cut preferentially since they lack histones, leading to the enrichment of these sequences. The benefits of this include minimal tissue input (<1 mg of tissue), a quick protocol (<4 h), low sequencing costs, less bias, correct assembly of lateral gene transfers and no prior sequence knowledge required. We assembled the wBm genome with as few as 1 million Illumina short paired-end reads with >97% coverage of the published genome, compared to only 12% coverage with the standard gDNA libraries. We found significant bacterial sequence enrichment that facilitated genome assembly in previously published ATAC-seq data sets from human cells infected with Mycobacterium tuberculosis and C. elegans contaminated with their food source, the OP50 strain of E. coli. These results demonstrate the feasibility and benefits of using ATAC-seq to easily obtain bacterial genomes to aid in symbiosis, infectious disease, and microbiome research.

Repurposed Drugs That Activate Autophagy in Filarial Worms Act as Effective Macrofilaricides

Onchocerciasis and lymphatic filariasis are two neglected tropical diseases caused by filarial nematodes that utilize insect vectors for transmission to their human hosts. Current control strategies are based on annual or biannual mass drug administration (MDA) of the drugs Ivermectin or Ivermectin plus Albendazole, respectively. These drug regimens kill the first-stage larvae of filarial worms (i.e., microfilariae) and interrupt the transmission of infections. MDA programs for these microfilaricidal drugs must be given over the lifetime of the filarial adult worms, which can reach 15 years in the case of Onchocerca volvulus. This is problematic because of suboptimal responses to ivermectin in various endemic regions and inefficient reduction of transmission even after decades of MDA. There is an urgent need for the development of novel alternative treatments to support the 2030 elimination goals of onchocerciasis and lymphatic filariasis. One successful approach has been to target Wolbachia, obligatory endosymbiotic bacteria on which filarial worms are dependent for their survival and reproduction within the human host. A 4-6-week antibiotic therapy with doxycycline, for example, resulted in the loss of Wolbachia that subsequently led to extensive apoptosis of somatic cells, germline, embryos, and microfilariae, as well as inhibition of fourth-stage larval development. However, this long-course regimen has limited use in MDA programs. As an alternative approach to the use of bacteriostatic antibiotics, in this study, we focused on autophagy-inducing compounds, which we hypothesized could disturb various pathways involved in the interdependency between Wolbachia and filarial worms. We demonstrated that several such compounds, including Niclosamide, an FDA-approved drug, Niclosamide ethanolamine (NEN), and Rottlerin, a natural product derived from Kamala trees, significantly reduced the levels of Wolbachia in vitro. Moreover, when these compounds were used in vivo to treat Brugia pahangi-infected gerbils, Niclosamide and NEN significantly decreased adult worm survival, reduced the release of microfilariae, and decreased embryonic development depending on the regimen and dose used. All three drugs given orally significantly reduced Wolbachia loads and induced an increase in levels of lysosome-associated membrane protein in worms from treated animals, suggesting that Niclosamide, NEN, and Rottlerin were effective in causing drug-induced autophagy in these filarial worms. These repurposed drugs provide a new avenue for the clearance of adult worms in filarial infections.

Dirofilariasis mouse models for heartworm preclinical research

Introduction

Dirofilariasis, including heartworm disease, is a major emergent veterinary parasitic infection and a human zoonosis. Currently, experimental infections of cats and dogs are used in veterinary heartworm preclinical drug research.

Methods

As a refined alternative in vivo heartworm preventative drug screen, we assessed lymphopenic mouse strains with ablation of the interleukin-2/7 common gamma chain (γc) as susceptible to the larval development phase of Dirofilaria immitis.

Results

Non-obese diabetic (NOD) severe combined immunodeficiency (SCID)γc^-/- (NSG and NXG) and recombination-activating gene (RAG)2^-/-γc^-/- mouse strains yielded viable D. immitis larvae at 2-4 weeks post-infection, including the use of different batches of D. immitis infectious larvae, different D. immitis isolates, and at different laboratories. Mice did not display any clinical signs associated with infection for up to 4 weeks. Developing larvae were found in subcutaneous and muscle fascia tissues, which is the natural site of this stage of heartworm in dogs. Compared with in vitro-propagated larvae at day 14, in vivo-derived larvae had completed the L4 molt, were significantly larger, and contained expanded Wolbachia endobacteria titres. We established an ex vivo L4 paralytic screening system whereby assays with moxidectin or levamisole highlighted discrepancies in relative drug sensitivities in comparison with in vitro-reared L4 D. immitis. We demonstrated effective depletion of Wolbachia by 70%-90% in D. immitis L4 following 2- to 7-day oral in vivo exposures of NSG- or NXG-infected mice with doxycycline or the rapid-acting investigational drug, AWZ1066S. We validated NSG and NXG D. immitis mouse models as a filaricide screen by in vivo treatments with single injections of moxidectin, which mediated a 60%-88% reduction in L4 larvae at 14-28 days.

Discussion

Future adoption of these mouse models will benefit end-user laboratories conducting research and development of novel heartworm preventatives via increased access, rapid turnaround, and reduced costs and may simultaneously decrease the need for experimental cat or dog use.

Inability of Dirofilaria immitis infective larvae from mosquitoes fed on blood from microfilaremic dogs during low-dose and short-treatment regimens of doxycycline and ivermectin to complete normal development in heartworm naïve dogs

BACKGROUND

This study was conducted to determine whether heartworm infective larvae (L₃) collected from mosquitoes fed on dogs during low-dose, short-treatment-regimen doxycycline and ivermectin could develop normally in dogs.

METHODS

Twelve Beagles in a separate study were infected with 10 pairs of adult male and female Dirofilaria immitis by IV transplantation and randomly allocated to three groups of four dogs. Starting on Day 0, Group 1 received doxycycline orally at 10 mg/kg sid for 30 days plus ivermectin (min., 6 mcg/kg) on Days 0 and 30; Group 2 received doxycycline orally at 10 mg/kg sid until individual dogs became microfilaria negative (72-98 doses) and ivermectin every other week for six to seven doses. These dogs served as microfilaremic blood donors for the current mosquito studies. Aedes aegypti were allowed to feed on group-pooled blood samples from treated Groups 1-M and 2-M and untreated control Group 3-M on Days 22 (Study M-A) and 42 (Study M-C) and from Groups 1-M and 2-M on Day 29 (Study M-B) after treatment was started. From the Day 22 mosquito feeding, two dogs in Groups 1-M and 2-M and one dog in Group 3-M were given 50 L₃ by SC inoculation. From the Day 29 feeding, two dogs in Groups 1-M and 2-M were given 50 L₃. From the Day 42 feeding, two dogs in Group 1-M received 30 L₃, while two dogs in Group 2-M and one dog in Group 3-M received 40 L₃. All 14 dogs were necropsied for recovery and enumeration of adult heartworms 163-183 days PI.

RESULTS

None of the 12 dogs that received L₃ from mosquitoes fed on blood from treated dogs 22, 29 or 42 days after treatment started had any adult heartworms at necropsy, while the two control dogs had a total of 26 and 43 heartworms, respectively.

CONCLUSIONS

Treatment of microfilaremic dogs with doxycycline plus an ML, which later renders the L₃ incapable of normal development in the animal host, widens the scope of the multimodal approach to heartworm prevention in reducing the spread of heartworm disease.

Long-term evaluation of viability of microfilariae and intravenously transplanted adult Dirofilaria immitis in microfilaremic dogs treated with low-dose, short- and long-treatment regimens of doxycycline and ivermectin

BACKGROUND

Microfilarial (mf) counts were monitored over 21.3 months for any rebound that might occur in counts, and adulticidal efficacy was assessed following administration of low dosage with short- and long-treatment regimens of doxycycline and ivermectin to heartworm-microfilaremic dogs.

METHODS

Twelve heartworm-naïve beagles infected with 10 pairs of adult Dirofilaria immitis by intravenous transplantation were randomly allocated to three groups of four dogs. All treatments started on day 0. On day 0, Group 1 (short-treatment regimen) received doxycycline orally at 10 mg/kg once daily for 30 days plus ivermectin orally (minimum, 6 mcg/kg) on days 0 and 30. Group 2 (long-treatment regimen) received doxycycline orally at 10 mg/kg once daily until individual dogs became mf-negative (72-98 days) and ivermectin every other week until individual dogs became mf-negative (6-7 doses). Group 3 was the untreated control. Mf counts and antigen (Ag) tests were conducted. Dogs were necropsied for recovery and enumeration of heartworms on day 647.

RESULTS

Day -1 mean mf counts were 15,613, 23,950, and 15,513 mf/ml for groups 1, 2, and 3, respectively. Mean counts for Groups 1 and 2 declined until days 239 and 97, respectively, when all were negative. Group 3 had high mf counts throughout the study. There was not a rebound in mf counts in any of the treated dogs after they became amicrofilaremic. All dogs in group 1 and group 3 were Ag-positive throughout the study and had at least one live female worm at necropsy. All dogs in treated Group 2 were positive for Ag through day 154, but were antigen-negative on days 644 and 647, as all had only male worms. Mean live adult worm recoveries for Groups 1, 2, and 3 were 6.8 (range, 5-8), 3.3 (range, 1-6), and 16.0 (range, 14-17), respectively, with a percent reduction in adult worm counts of 57.5% for Group 1 and 79.3% for Group 2.

CONCLUSIONS

These data lend support to the use of the American Heartworm Society Canine Guidelines for adulticide therapy recommending the initiation of doxycycline plus a macrocyclic lactone (ML) at the time of the heartworm-positive diagnosis.

Toward novel treatment against filariasis: Insight into genome-wide co-evolutionary analysis of filarial nematodes and Wolbachia

Infectious diseases caused by filarial nematodes are major health problems for humans and animals globally. Current treatment using anti-helminthic drugs requires a long treatment period and is only effective against the microfilarial stage. Most species of filarial nematodes harbor a specific strain of Wolbachia bacteria, which are essential for the survival, development, and reproduction of the nematodes. This parasite-bacteria obligate symbiosis offers a new angle for the cure of filariasis. In this study, we utilized publicly available genome data and putative protein sequences from seven filarial nematode species and their symbiotic Wolbachia to screen for protein-protein interactions that could be a novel target against multiple filarial nematode species. Genome-wide in silico screening was performed to predict molecular interactions based on co-evolutionary signals. We identified over 8,000 pairs of gene families that show evidence of co-evolution based on high correlation score and low false discovery rate (FDR) between gene families and obtained a candidate list that may be keys in filarial nematode-Wolbachia interactions. Functional analysis was conducted on these top-scoring pairs, revealing biological processes related to various signaling processes, adult lifespan, developmental control, lipid and nucleotide metabolism, and RNA modification. Furthermore, network analysis of the top-scoring genes with multiple co-evolving pairs suggests candidate genes in both Wolbachia and the nematode that may play crucial roles at the center of multi-gene networks. A number of the top-scoring genes matched well to known drug targets, suggesting a promising drug-repurposing strategy that could be applicable against multiple filarial nematode species.

The filarial and the antibiotics: Single or combination therapy using antibiotics for filariasis

Filarial infections caused by nematodes are one of the major neglected tropical diseases with public health concern. Although there is significant decrease in microfilariae (mf) prevalence following mass drug administration (IVM/DEC/ALB administration), this is transient, in that there is reported microfilaria repopulation 6-12 months after treatment. Wolbachia bacteria have been recommended as a novel target presenting antibiotic-based treatment for filarial disease. Potency of antibiotics against filarial diseases is undoubtful, however, the duration for treatment remains a hurdle yet to be overcome in filarial disease treatment.

Aspartyl Protease Inhibitors as Anti-Filarial Drugs

The current treatments for lymphatic filariasis and onchocerciasis do not effectively kill the adult parasitic nematodes, allowing these chronic and debilitating diseases to persist in millions of people. Thus, the discovery of new drugs with macrofilaricidal potential to treat these filarial diseases is critical. To facilitate this need, we first investigated the effects of three aspartyl protease inhibitors (APIs) that are FDA-approved as HIV antiretroviral drugs on the adult filarial nematode, Brugia malayi and the endosymbiotic bacteria, Wolbachia. From the three hits, nelfinavir had the best potency with an IC₅₀ value of 7.78 µM, followed by ritonavir and lopinavir with IC₅₀ values of 14.3 µM and 16.9 µM, respectively. The three APIs have a direct effect on killing adult B. malayi after 6 days of exposure in vitro and did not affect the Wolbachia titers. Sequence conservation and stage-specific gene expression analysis identified Bm8660 as the most likely primary aspartic protease target for these drug(s). Immunolocalization using antibodies raised against the Bm8660 ortholog of Onchocerca volvulus showed it is strongly expressed in female B. malayi, especially in metabolically active tissues such as lateral and dorsal/ventral chords, hypodermis, and uterus tissue. Global transcriptional response analysis using adult female B. pahangi treated with APIs identified four additional aspartic proteases differentially regulated by the three effective drugs, as well as significant enrichment of various pathways including ubiquitin mediated proteolysis, protein kinases, and MAPK/AMPK/FoxO signaling. In vitro testing against the adult gastro-intestinal nematode Trichuris muris suggested broad-spectrum potential for these APIs. This study suggests that APIs may serve as new leads to be further explored for drug discovery to treat parasitic nematode infections.

Wolbachia depletion blocks transmission of lymphatic filariasis by preventing chitinase-dependent parasite exsheathment

Lymphatic filariasis is a vector-borne neglected tropical disease prioritized for global elimination. The filarial nematodes that cause the disease host a symbiotic bacterium, Wolbachia, which has been targeted using antibiotics, leading to cessation of parasite embryogenesis, waning of circulating larvae (microfilariae [mf]), and gradual cure of adult infection. One of the benefits of the anti-Wolbachia mode of action is that it avoids the rapid killing of mf, which can drive inflammatory adverse events. However, mf depleted of Wolbachia persist for several months in circulation, and thus patients treated with antibiotics are assumed to remain at risk for transmitting infections. Here, we show that Wolbachia-depleted mf rapidly lose the capacity to develop in the mosquito vector through a defect in exsheathment and inability to migrate through the gut wall. Transcriptomic and Western blotting analyses demonstrate that chitinase, an enzyme essential for mf exsheathment, is down-regulated in Wolbachia-depleted mf and correlates with their inability to exsheath and escape the mosquito midgut. Supplementation of in vitro cultures of Wolbachia-depleted mf with chitinase enzymes restores their ability to exsheath to a similar level to that observed in untreated mf. Our findings elucidate a mechanism of rapid transmission-blocking activity of filariasis after depletion of Wolbachia and adds to the broad range of biological processes of filarial nematodes that are dependent on Wolbachia symbiosis.

Transporter gene expression and Wolbachia quantification in adults of Dirofilaria immitis treated in vitro with ivermectin or moxidectin alone or in combination with doxycycline for 12 hours

Due to their marked larvicidal activity, macrocyclic lactones (MLs) are used for the prevention of heartworm disease ( Dirofilaria immitis) in dogs. They have also been shown to eliminate adult parasites after long-term administration, with a so-called "slow-kill" effect. In addition, recent studies have established that a combination of doxycycline, which eliminates the endosymbiont Wolbachia, and MLs has superior adulticide effects when compared to MLs alone. It has been hypothesized that the apparent synergism between doxycycline/MLs may be due to interaction with drug efflux transport proteins. The aim of the present study was to evaluate gene expression of several transport proteins in D. immitis adults treated in vitro either with doxycycline alone, ivermectin alone, moxidectin alone, or a combination of ivermectin or moxidectin with doxycycline for 12h. Quantitative PCR analysis showed a sex-dependent response to treatments. In female worms, Dim-pgp-10, Dim-haf-1 and Dim-haf-5 were upregulated compared to controls with doxycycline alone and when combined with ivermectin. Moxidectin did not induce any changes in gene expression. In males, moxidectin administered alone induced a slight increase in Dim-pgp-10, Dim-pgp-11and Di-avr-14, while ivermectin in combination with doxycycline produced significant upregulation of the ML receptor Di-avr-14. These results suggest possible synergism between the two drug classes and different susceptibility of males vs. females to adulticide effects.

Human Pulmonary Dirofilariasis: A Review for the Clinicians

Human pulmonary dirofilariasis (HPD) is a rare zoonotic disease caused by Dirofilaria immitis, the nematode responsible for canine cardiopulmonary dirofilariasis (dog heartworm). The incidence of HPD is on the rise throughout the world due to increased awareness and factors affecting the vector (mosquito). Humans are accidental hosts for D. immitis. Most patients are asymptomatic and present with an incidental pulmonary nodule that mimics primary or metastatic pulmonary malignancy. Some patients suffer from pulmonary and systemic symptoms in the acute phase of pneumonitis caused by pulmonary arterial occlusion by the preadult worms resulting in pulmonary infarction and intense inflammation. These patients may have ill-defined pulmonary infiltrate on chest radiology. Pulmonary nodules represent the end result of initial pneumonitis. There are no specific clinical, laboratory, or radiologic findings that differentiate HPD from other causes of a pulmonary nodule. Although serologic tests exist, they are usually not commercially available. The majority of patients are diagnosed by histopathologic identification of the decomposing worm following surgical resection of the lesion.

Biochemical characterization of Recombinase A from Wolbachia endosymbiont of filarial nematode Brugia malayi (wBmRecA)

Lymphatic filariasis is a debilitating disease that affects over 890 million people in 49 countries. A lack of vaccines, non-availability of adulticidal drugs, the threat of emerging drug resistance against available chemotherapeutics and an incomplete understanding of the immunobiology of the disease have sustained the problem. Characterization of Wolbachia proteins, the bacterial endosymbiont which helps in the growth and development of filarial worms, regulates fecundity in female worms and mediates immunopathogenesis of Lymphatic Filariasis, is an important approach to gain insights into the immunopathogenesis of the disease. In this study, we carried out extensive biochemical characterization of Recombinase A from Wolbachia of the filarial nematode Brugia malayi (wBmRecA) using an Electrophoretic Mobility Shift Assay, an ATP binding and hydrolysis assay, DNA strand exchange reactions, DAPI displacement assay and confocal microscopy, and evaluated anti-filarial activity of RecA inhibitors. Confocal studies showed that wBmRecA was expressed and localised within B. malayi microfilariae (Mf) and uteri and lateral chord of adult females. Recombinant wBmRecA was biochemically active and showed intrinsic binding capacity towards both single-stranded DNA and double-stranded DNA that were enhanced by ATP, suggesting ATP-induced cooperativity. wBmRecA promoted ATP hydrolysis and DNA strand exchange reactions in a concentration-dependent manner, and its binding to DNA was sensitive to temperature, pH and salt concentration. Importantly, the anti-parasitic drug Suramin, and Phthalocyanine tetrasulfonate (PcTs)-based inhibitors Fe-PcTs and 3,4-Cu-PcTs, inhibited wBmRecA activity and affected the motility and viability of Mf. The addition of Doxycycline further enhanced microfilaricidal activity of wBmRecA, suggesting potential synergism. Taken together, the omnipresence of wBmRecA in B. malayi life stages and the potent microfilaricidal activity of RecA inhibitors suggest an important role of wBmRecA in filarial pathogenesis.

Forward genetics in Wolbachia: Regulation of Wolbachia proliferation by the amplification and deletion of an addictive genomic island

Wolbachia is one of the most prevalent bacterial endosymbionts, infecting approximately 40% of terrestrial arthropod species. Wolbachia is often a reproductive parasite but can also provide fitness benefits to its host, as, for example, protection against viral pathogens. This protective effect is currently being applied to fight arboviruses transmission by releasing Wolbachia-transinfected mosquitoes. Titre regulation is a crucial aspect of Wolbachia biology. Higher titres can lead to stronger phenotypes and fidelity of transmission but can have a higher cost to the host. Since Wolbachia is maternally transmitted, its fitness depends on host fitness, and, therefore, its cost to the host may be under selection. Understanding how Wolbachia titres are regulated and other aspects of Wolbachia biology has been hampered by the lack of genetic tools. Here we developed a forward genetic screen to identify new Wolbachia over-proliferative mutant variants. We characterized in detail two new mutants, wMelPop2 and wMelOctoless, and show that the amplification or loss of the Octomom genomic region lead to over-proliferation. These results confirm previous data and expand on the complex role of this genomic region in the control of Wolbachia proliferation. Both new mutants shorten the host lifespan and increase antiviral protection. Moreover, we show that Wolbachia proliferation rate in Drosophila melanogaster depends on the interaction between Octomom copy number, the host developmental stage, and temperature. Our analysis also suggests that the life shortening and antiviral protection phenotypes of Wolbachia are dependent on different, but related, properties of the endosymbiont; the rate of proliferation and the titres near the time of infection, respectively. We also demonstrate the feasibility of a novel and unbiased experimental approach to study Wolbachia biology, which could be further adapted to characterize other genetically intractable bacterial endosymbionts.

Wolbachia: endosymbiont of onchocercid nematodes and their vectors

Background

Wolbachia is an obligate intracellular maternally transmitted, gram-negative bacterium which forms a spectrum of endosymbiotic relationships from parasitism to obligatory mutualism in a wide range of arthropods and onchocercid nematodes, respectively. In arthropods Wolbachia produces reproductive manipulations such as male killing, feminization, parthenogenesis and cytoplasmic incompatibility for its propagation and provides an additional fitness benefit for the host to protect against pathogens, whilst in onchocercid nematodes, apart from the mutual metabolic dependence, this bacterium is involved in moulting, embryogenesis, growth and survival of the host.

Methods

This review details the molecular data of Wolbachia and its effect on host biology, immunity, ecology and evolution, reproduction, endosymbiont-based treatment and control strategies exploited for filariasis. Relevant peer-reviewed scientic papers available in various authenticated scientific data bases were considered while writing the review.

Conclusions

The information presented provides an overview on Wolbachia biology and its use in the control and/or treatment of vectors, onchocercid nematodes and viral diseases of medical and veterinary importance. This offers the development of new approaches for the control of a variety of vector-borne diseases.

Graphic Abstract

The Eagle effect in the Wolbachia-worm symbiosis

Background

Onchocerciasis (river blindness) and lymphatic filariasis (elephantiasis) are two human neglected tropical diseases that cause major disabilities. Mass administration of drugs targeting the microfilarial stage has reduced transmission and eliminated these diseases in several countries but a macrofilaricidal drug that kills or sterilizes the adult worms is critically needed to eradicate the diseases. The causative agents of onchocerciasis and lymphatic filariasis are filarial worms that harbor the endosymbiotic bacterium Wolbachia. Because filarial worms depend on Wolbachia for reproduction and survival, drugs targeting Wolbachia hold great promise as a means to eliminate these diseases.

Methods

To better understand the relationship between Wolbachia and its worm host, adult Brugia pahangi were exposed to varying concentrations of doxycycline, minocycline, tetracycline and rifampicin in vitro and assessed for Wolbachia numbers and worm motility. Worm motility was monitored using the Worminator system, and Wolbachia titers were assessed by qPCR of the single copy gene wsp from Wolbachia and gst from Brugia to calculate IC₅₀s and in time course experiments. Confocal microscopy was also used to quantify Wolbachia located at the distal tip region of worm ovaries to assess the effects of antibiotic treatment in this region of the worm where Wolbachia are transmitted vertically to the microfilarial stage.

Results

Worms treated with higher concentrations of antibiotics had higher Wolbachia titers, i.e. as antibiotic concentrations increased there was a corresponding increase in Wolbachia titers. As the concentration of antibiotic increased, worms stopped moving and never recovered despite maintaining Wolbachia titers comparable to controls. Thus, worms were rendered moribund by the higher concentrations of antibiotics but Wolbachia persisted suggesting that these antibiotics may act directly on the worms at high concentration. Surprisingly, in contrast to these results, antibiotics given at low concentrations reduced Wolbachia titers.

Conclusion

Wolbachia in B. pahangi display a counterintuitive dose response known as the “Eagle effect.” This effect in Wolbachia suggests a common underlying mechanism that allows diverse bacterial and fungal species to persist despite exposure to high concentrations of antimicrobial compounds. To our knowledge this is the first report of this phenomenon occurring in an intracellular endosymbiont, Wolbachia, in its filarial host.

The Wolbachia Symbiont: Here, There and Everywhere

Wolbachia symbionts, first observed in the 1920s, are now known to be present in about 30-70% of tested arthropod species, in about half of tested filarial nematodes (including the majority of human filarial nematodes), and some plant-parasitic nematodes. In arthropods, they are generally viewed as parasites while in nematodes they appear to be mutualists although this demarcation is not absolute. Their presence in arthropods generally leads to reproductive anomalies, while in nematodes, they are generally required for worm development and reproduction. In mosquitos, Wolbachia inhibit RNA viral infections, leading to populational reductions in human RNA virus pathogens, whereas in filarial nematodes, their requirement for worm fertility and survival has been channeled into their use as drug targets for filariasis control. While much more research on these ubiquitous symbionts is needed, they are viewed as playing significant roles in biological processes, ranging from arthropod speciation to human health.

Modeling the metabolic interplay between a parasitic worm and its bacterial endosymbiont allows the identification of novel drug targets

The filarial nematode Brugia malayi represents a leading cause of disability in the developing world, causing lymphatic filariasis in nearly 40 million people. Currently available drugs are not well-suited to mass drug administration efforts, so new treatments are urgently required. One potential vulnerability is the endosymbiotic bacteria Wolbachia-present in many filariae-which is vital to the worm. Genome scale metabolic networks have been used to study prokaryotes and protists and have proven valuable in identifying therapeutic targets, but have only been applied to multicellular eukaryotic organisms more recently. Here, we present iDC625, the first compartmentalized metabolic model of a parasitic worm. We used this model to show how metabolic pathway usage allows the worm to adapt to different environments, and predict a set of 102 reactions essential to the survival of B. malayi. We validated three of those reactions with drug tests and demonstrated novel antifilarial properties for all three compounds.

The endosymbiont Wolbachia rebounds following antibiotic treatment

Antibiotic treatment has emerged as a promising strategy to sterilize and kill filarial nematodes due to their dependence on their endosymbiotic bacteria, Wolbachia. Several studies have shown that novel and FDA-approved antibiotics are efficacious at depleting the filarial nematodes of their endosymbiont, thus reducing female fecundity. However, it remains unclear if antibiotics can permanently deplete Wolbachia and cause sterility for the lifespan of the adult worms. Concerns about resistance arising from mass drug administration necessitate a careful exploration of potential Wolbachia recrudescence. In the present study, we investigated the long-term effects of the FDA-approved antibiotic, rifampicin, in the Brugia pahangi jird model of infection. Initially, rifampicin treatment depleted Wolbachia in adult worms and simultaneously impaired female worm fecundity. However, during an 8-month washout period, Wolbachia titers rebounded and embryogenesis returned to normal. Genome sequence analyses of Wolbachia revealed that despite the population bottleneck and recovery, no genetic changes occurred that could account for the rebound. Clusters of densely packed Wolbachia within the worm's ovarian tissues were observed by confocal microscopy and remained in worms treated with rifampicin, suggesting that they may serve as privileged sites that allow Wolbachia to persist in worms while treated with antibiotic. To our knowledge, these clusters have not been previously described and may be the source of the Wolbachia rebound.

The shutting down of the insulin pathway: a developmental window for Wolbachia load and feminization

Using the isopod Armadillidium vulgare as a case study, we review the significance of the "bacterial dosage model", which connects the expression of the extended phenotype to the rise of the Wolbachia load. In isopods, the Insulin-like Androgenic Gland hormone (IAG) induces male differentiation: Wolbachia feminizes males through insulin resistance, presumably through defunct insulin receptors. This should prevent an autocrine development of the androgenic glands so that females differentiate instead: feminization should translate as IAG silencing and increased Wolbachia load in the same developmental window. In line with the autocrine model, uninfected males expressed IAG from the first larval stage on, long before the androgenic gland primordia begin to differentiate, and exponentially throughout development. In contrast in infected males, expression fully stopped at stage 4 (juvenile), when male differentiation begins. This co-occurred with the only significant rise in the Wolbachia load throughout the life-stages. Concurrently, the raw expression of the bacterial Secretion Systems co-increased, but they were not over-expressed relative to the number of bacteria. The isopod model leads to formulate the "bacterial dosage model" throughout extended phenotypes as the conjunction between bacterial load as the mode of action, timing of multiplication (pre/post-zygotic), and site of action (soma vs. germen).

Novel anti-Wolbachia drugs, a new approach in the treatment and prevention of veterinary filariasis?

Filarial nematodes are tissue-dwelling parasitic worms that can cause a range of disfiguring pathologies in humans and potentially lethal infections of companion animals. The bacterial endosymbiont, Wolbachia, is present within most human and veterinary filarial pathogens, including the causative agent of heartworm disease, Dirofilaria immitis. Doxycycline-mediated drug targeting of Wolbachia leads to sterility, clearance of microfilariae and gradual death of adult filariae. This mode of action is attractive in the treatment of filariasis because it avoids severe host inflammatory adverse reactions invoked by rapid-killing anthelmintic agents. However, doxycycline needs to be taken for four weeks to exert curative activity. In this review, we discuss the evidence that Wolbachia drug targeting is efficacious in blocking filarial larval development as well as in the treatment of chronic filarial disease. We present the current portfolio of next-generation anti-Wolbachia candidates discovered through phenotypic screening of chemical libraries and validated in a range of in vitro and in vivo filarial infection models. Several novel chemotypes have been identified with selected narrow-spectrum anti-Wolbachia specificity and superior time-to-kill kinetics compared with doxycycline. We discuss the opportunities of developing these novel anti-Wolbachia agents as either cures, adjunct therapies or new preventatives for the treatment of veterinary filariasis.

Short-course quinazoline drug treatments are effective in the Litomosoides sigmodontis and Brugia pahangi jird models

The quinazolines CBR417 and CBR490 were previously shown to be potent anti-wolbachials that deplete Wolbachia endosymbionts of filarial nematodes and present promising pre-clinical candidates for human filarial diseases such as onchocerciasis. In the present study we tested both candidates in two models of chronic filarial infection, namely the Litomosoides sigmodontis and Brugia pahangi jird model and assessed their long-term effect on Wolbachia depletion, microfilariae counts and filarial embryogenesis 16−18 weeks after treatment initiation (wpt). Once per day (QD) oral treatment with CBR417 (50 mg/kg) for 4 days or twice per day (BID) with CBR490 (25 mg/kg) for 7 days during patent L. sigmodontis infection reduced the Wolbachia load by >99% and completely cleared peripheral microfilaremia from 10–14 wpt. Similarly, 7 days of QD treatments (40 mg/kg) with CBR417 or CBR490 cleared >99% of Wolbachia from B. pahangi and reduced peritoneal microfilariae counts by 93% in the case of CBR417 treatment. Transmission electron microscopy analysis indicated intensive damage to the B. pahangi ovaries following CBR417 treatment and in accordance filarial embryogenesis was inhibited in both models after CBR417 or CBR490 treatment. Suboptimal treatment regimens of CBR417 or CBR490 did not lead to a maintained reduction of the microfilariae and Wolbachia load. In conclusion, CBR417 or CBR490 are pre-clinical candidates for filarial diseases, which achieve long-term clearance of Wolbachia endosymbionts of filarial nematodes, inhibit filarial embryogenesis and clear microfilaremia with treatments as short as 7 days.

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CBR417 and CBR490 provide long-term effects in 2 chronic filaria jird models.

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CBR417 and CBR490 deplete >99% Wolbachia in B. pahangi and L. sigmodontis filariae.

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CBR417 and CBR490 clear L. sigmodontis microfilariae after 10–14 weeks.

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CBR417 and CBR490 inhibit filarial embryogenesis in both models.

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Suboptimal doses do not maintain reduction of microfilariae and Wolbachia.

Drug Repurposing of Bromodomain Inhibitors as Potential Novel Therapeutic Leads for Lymphatic Filariasis Guided by Multispecies Transcriptomics

The current treatment regimen for lymphatic filariasis is mostly microfilaricidal. In an effort to identify new drug candidates for lymphatic filariasis, we conducted a three-way transcriptomics/systems biology study of one of the causative agents of lymphatic filariasis, Brugia malayi, its Wolbachia endosymbiont wBm, and its vector host Aedes aegypti at 16 distinct B. malayi life stages. B. malayi upregulates the expression of bromodomain-containing proteins in the adult female, embryo, and microfilaria stages. In vitro, we find that the existing cancer therapeutic JQ1(+), which is a bromodomain and extraterminal protein inhibitor, has adulticidal activity in B. malayi.

To better understand the transcriptomic interplay of organisms associated with lymphatic filariasis, we conducted multispecies transcriptome sequencing (RNA-Seq) on the filarial nematode Brugia malayi, its Wolbachia endosymbiont wBm, and its laboratory vector Aedes aegypti across the entire B. malayi life cycle. In wBm, transcription of the noncoding 6S RNA suggests that it may be a regulator of bacterial cell growth, as its transcript levels correlate with bacterial replication rates. For A. aegypti, the transcriptional response reflects the stress that B. malayi infection exerts on the mosquito with indicators of increased energy demand. In B. malayi, expression modules associated with adult female samples consistently contained an overrepresentation of genes involved in chromatin remodeling, such as the bromodomain-containing proteins. All bromodomain-containing proteins encoded by B. malayi were observed to be upregulated in the adult female, embryo, and microfilaria life stages, including 2 members of the bromodomain and extraterminal (BET) protein family. The BET inhibitor JQ1(+), originally developed as a cancer therapeutic, caused lethality of adult worms in vitro, suggesting that it may be a potential therapeutic that can be repurposed for treating lymphatic filariasis.

IMPORTANCE The current treatment regimen for lymphatic filariasis is mostly microfilaricidal. In an effort to identify new drug candidates for lymphatic filariasis, we conducted a three-way transcriptomics/systems biology study of one of the causative agents of lymphatic filariasis, Brugia malayi, its Wolbachia endosymbiont wBm, and its vector host Aedes aegypti at 16 distinct B. malayi life stages. B. malayi upregulates the expression of bromodomain-containing proteins in the adult female, embryo, and microfilaria stages. In vitro, we find that the existing cancer therapeutic JQ1(+), which is a bromodomain and extraterminal protein inhibitor, has adulticidal activity in B. malayi.

Quantitative methods for assessing local and bodywide contributions to Wolbachia titer in maternal germline cells of Drosophila

Background

Little is known about how bacterial endosymbionts colonize host tissues. Because many insect endosymbionts are maternally transmitted, egg colonization is critical for endosymbiont success. Wolbachia bacteria, carried by approximately half of all insect species, provide an excellent model for characterizing endosymbiont infection dynamics. To date, technical limitations have precluded stepwise analysis of germline colonization by Wolbachia. It is not clear to what extent titer-altering effects are primarily mediated by growth rates of Wolbachia within cell lineages or migration of Wolbachia between cells.

Results

The objective of this work is to inform mechanisms of germline colonization through use of optimized methodology. The approaches are framed in terms of nutritional impacts on Wolbachia. Yeast-rich diets in particular have been shown to suppress Wolbachia titer in the Drosophila melanogaster germline. To determine the extent of Wolbachia sensitivity to diet, we optimized 3-dimensional, multi-stage quantification of Wolbachia titer in maternal germline cells. Technical and statistical validation confirmed the identity of Wolbachia in vivo, the reproducibility of Wolbachia quantification and the statistical power to detect these effects. The data from adult feeding experiments demonstrated that germline Wolbachia titer is distinctly sensitive to yeast-rich host diets in late oogenesis. To investigate the physiological basis for these nutritional impacts, we optimized methodology for absolute Wolbachia quantification by real-time qPCR. We found that yeast-rich diets exerted no significant effect on bodywide Wolbachia titer, although ovarian titers were significantly reduced. This suggests that host diets affects Wolbachia distribution between the soma and late stage germline cells. Notably, relative qPCR methods distorted apparent wsp abundance, due to altered host DNA copy number in yeast-rich conditions. This highlights the importance of absolute quantification data for testing mechanistic hypotheses.

Conclusions

We demonstrate that absolute quantification of Wolbachia, using well-controlled cytological and qPCR-based methods, creates new opportunities to determine how bacterial abundance within the germline relates to bacterial distribution within the body. This methodology can be applied to further test germline infection dynamics in response to chemical treatments, genetic conditions, new host/endosymbiont combinations, or potentially adapted to analyze other cell and tissue types.

Electronic supplementary material

The online version of this article (10.1186/s12866-019-1579-3) contains supplementary material, which is available to authorized users.

Pyruvate produced by Brugia spp. via glycolysis is essential for maintaining the mutualistic association between the parasite and its endosymbiont, Wolbachia

Human parasitic nematodes are the causative agents of lymphatic filariasis (elephantiasis) and onchocerciasis (river blindness), diseases that are endemic to more than 80 countries and that consistently rank in the top ten for the highest number of years lived with disability. These filarial nematodes have evolved an obligate mutualistic association with an intracellular bacterium, Wolbachia, a symbiont that is essential for the successful development, reproduction, and survival of adult filarial worms. Elimination of the bacteria causes adult worms to die, making Wolbachia a primary target for developing new interventional tools to combat filariases. To further explore Wolbachia as a promising indirect macrofilaricidal drug target, the essential cellular processes that define the symbiotic Wolbachia-host interactions need to be identified. Genomic analyses revealed that while filarial nematodes encode all the enzymes necessary for glycolysis, Wolbachia does not encode the genes for three glycolytic enzymes: hexokinase, 6-phosphofructokinase, and pyruvate kinase. These enzymes are necessary for converting glucose into pyruvate. Wolbachia, however, has the full complement of genes required for gluconeogenesis starting with pyruvate, and for energy metabolism via the tricarboxylic acid cycle. Therefore, we hypothesized that Wolbachia might depend on host glycolysis to maintain a mutualistic association with their parasitic host. We did conditional experiments in vitro that confirmed that glycolysis and its end-product, pyruvate, sustain this symbiotic relationship. Analysis of alternative sources of pyruvate within the worm indicated that the filarial lactate dehydrogenase could also regulate the local intracellular concentration of pyruvate in proximity to Wolbachia and thus help control bacterial growth via molecular interactions with the bacteria. Lastly, we have shown that the parasite's pyruvate kinase, the enzyme that performs the last step in glycolysis, could be a potential novel anti-filarial drug target. Establishing that glycolysis is an essential component of symbiosis in filarial worms could have a broader impact on research focused on other intracellular bacteria-host interactions where the role of glycolysis in supporting intracellular survival of bacteria has been reported.

In vivo kinetics of Wolbachia depletion by ABBV-4083 in L. sigmodontis adult worms and microfilariae

Depletion of Wolbachia endosymbionts of human pathogenic filariae using 4–6 weeks of doxycycline treatment can lead to permanent sterilization and adult filarial death. We investigated the anti-Wolbachia drug candidate ABBV-4083 in the Litomosoides sigmodontis rodent model to determine Wolbachia depletion kinetics with different regimens. Wolbachia reduction occurred in mice as early as 3 days after the initiation of ABBV-4083 treatment and continued throughout a 10-day treatment period. Importantly, Wolbachia levels continued to decline after a 5-day-treatment from 91.5% to 99.9% during a 3-week washout period. In jirds, two weeks of ABBV-4083 treatment (100mg/kg once-per-day) caused a >99.9% Wolbachia depletion in female adult worms, and the kinetics of Wolbachia depletion were recapitulated in peripheral blood microfilariae. Similar to Wolbachia depletion, inhibition of embryogenesis was time-dependent in ABBV-4083-treated jirds, leading to a complete lack of late embryonic stages (stretched microfilariae) and lack of peripheral microfilariae in 5/6 ABBV-4083-treated jirds by 14 weeks after treatment. Twice daily treatment in comparison to once daily treatment with ABBV-4083 did not significantly improve Wolbachia depletion. Moreover, up to 4 nonconsecutive daily treatments within a 14-dose regimen did not significantly erode Wolbachia depletion. Within the limitations of an animal model that does not fully recapitulate human filarial disease, our studies suggest that Wolbachia depletion should be assessed clinically no earlier than 3–4 weeks after the end of treatment, and that Wolbachia depletion in microfilariae may be a viable surrogate marker for the depletion within adult worms. Furthermore, strict daily adherence to the dosing regimen with anti-Wolbachia candidates may not be required, provided that the full regimen is subsequently completed.

Onchocerciasis and lymphatic filariasis represent debilitating neglected tropical diseases that are caused by parasitic filarial nematodes. Current efforts to eliminate onchocerciasis are hampered by the lack of drugs that lead to permanent sterilization of the adult worms or provide a macrofilaricidal effect, i.e. kill the adult worms. In the past, doxycycline has been shown to deplete Wolbachia endosymbionts of filarial nematodes, leading to permanent sterilization and macrofilaricidal efficacy in filariae causing both onchocerciasis and lymphatic filariasis. However, contraindications and a requirement for at least 4 weeks of doxycycline treatment impair its broader use, creating a need for drugs with a shorter treatment regimen and potentially fewer contraindications. ABBV-4083 is such an anti-Wolbachia candidate that was efficacious in several filarial animal models and has recently been tested in a phase 1 clinical trial. The present studies addressed several points that are important for subsequent phase 2 clinical trials, namely the comparison of once vs. twice-per-day treatments, the impact of missed treatments, and a comparison of the kinetics of Wolbachia depletion in adult worms and microfilariae, the latter of which has the potential to be a surrogate indicator to avoid the necessity of surgically removing nodules with adult worms at repeated time points.

Molecular Analysis of Canine Filaria and Its Wolbachia Endosymbionts in Domestic Dogs Collected from Two Animal University Hospitals in Bangkok Metropolitan Region, Thailand

Canine filariasis is caused by several nematode species, such as Dirofilaria immitis, Dirofilaria repens, Brugia pahangi, Brugia malayi, and Acanthocheilonema reconditum. Zoonotic filariasis is one of the world's neglected tropical diseases. Since 2000, the World Health Organization (WHO) has promoted a global filarial eradication program to eliminate filariasis by 2020. Apart from vector control strategies, the infection control of reservoir hosts is necessary for more effective filariasis control. In addition, many studies have reported that Wolbachia is necessary for the development, reproduction, and survival of the filarial nematode. Consequently, the use of antibiotics to kill Wolbachia in nematodes has now become an alternative strategy to control filariasis. Previously, a case of subconjunctival dirofilariasis caused by Dirofilaria spp. has been reported in a woman who resides in the center of Bangkok, Thailand. Therefore, our study aimed to principally demonstrate the presence of filarial nematodes and Wolbachia bacteria in blood collected from domestic dogs from the Bangkok Metropolitan Region, Thailand. A total of 57 blood samples from dogs with suspected dirofilariasis who had visited veterinary clinics in Bangkok were collected. The investigations for the presence of microfilaria were carried out by using both microscopic and molecular examinations. PCR was used as the molecular detection method for the filarial nematodes based on the COI and ITS1 regions. The demonstration of Wolbachia was performed using PCR to amplify the FtsZ gene. All positive samples by PCR were then cloned and sequenced. The results showed that the filarial nematodes were detected in 16 samples (28.07%) using microscopic examinations. The molecular detection of filarial species using COI-PCR revealed that 50 samples (87.72%) were positive; these consisted of 33 (57.89%), 13 (22.81%), and 4 (7.02%) samples for D. immitis, B. pahangi, and B. malayi, respectively. While the ITS1-PCR showed that 41 samples (71.93%) were positive-30 samples (52.63%) were identified as containing D. immitis and 11 samples (19.30%) were identified to have B. pahangi, whereas B. malayi was not detected. Forty-seven samples (82.45%) were positive for Wolbachia DNA and the phylogenetic tree of all positive Wolbachia was classified into the supergroup C clade. This study has established fundamental data on filariasis associated with Wolbachia infection in domestic dogs in the Bangkok Metropolitan Region. An extensive survey of dog blood samples would provide valuable epidemiologic data on potential zoonotic filariasis in Thailand. In addition, this information could be used for the future development of more effective prevention and control strategies for canine filariasis in Thailand.

Boron-Pleuromutilins as Anti- Wolbachia Agents with Potential for Treatment of Onchocerciasis and Lymphatic Filariasis

A series of pleuromutilins modified by introduction of a boron-containing heterocycle on C(14) of the polycyclic core are described. These analogs were found to be potent anti- Wolbachia antibiotics and, as such, may be useful in the treatment of filarial infections caused by Onchocerca volvulus, resulting in Onchocerciasis or river blindness, or Wuchereria bancrofti and Brugia malayi and related parasitic nematodes resulting in lymphatic filariasis. These two important neglected tropical diseases disproportionately impact patients in the developing world. The lead preclinical candidate compound containing 7-fluoro-6-oxybenzoxaborole (15, AN11251) was shown to have good in vitro anti- Wolbachia activity and physicochemical and pharmacokinetic properties providing high exposure in plasma. The lead was effective in reducing the Wolbachia load in filarial worms following oral administration to mice.

AWZ1066S, a highly specific anti-Wolbachia drug candidate for a short-course treatment of filariasis

Onchocerciasis (river blindness) and lymphatic filariasis (elephantiasis) are neglected tropical diseases that cause severe disability and affect more than 157 million people globally. Current control efforts are hindered by the lack of a safe macrofilaricidal drug that can eliminate the parasitic adult nematodes safely. A clinically validated approach for delivering macrofilaricidal activity is to target the Wolbachia bacterial endosymbiont of the causative nematodes. This first-in-class and highly potent and specific anti-Wolbachia preclinical candidate molecule, AWZ1066S, has the potential to significantly impact current global onchocerciasis and lymphatic filariasis elimination programs and reduce elimination time frames from decades to years.

Onchocerciasis and lymphatic filariasis are two neglected tropical diseases that together affect ∼157 million people and inflict severe disability. Both diseases are caused by parasitic filarial nematodes with elimination efforts constrained by the lack of a safe drug that can kill the adult filaria (macrofilaricide). Previous proof-of-concept human trials have demonstrated that depleting >90% of the essential nematode endosymbiont bacterium, Wolbachia, using antibiotics, can lead to permanent sterilization of adult female parasites and a safe macrofilaricidal outcome. AWZ1066S is a highly specific anti-Wolbachia candidate selected through a lead optimization program focused on balancing efficacy, safety and drug metabolism/pharmacokinetic (DMPK) features of a thienopyrimidine/quinazoline scaffold derived from phenotypic screening. AWZ1066S shows superior efficacy to existing anti-Wolbachia therapies in validated preclinical models of infection and has DMPK characteristics that are compatible with a short therapeutic regimen of 7 days or less. This candidate molecule is well-positioned for onward development and has the potential to make a significant impact on communities affected by filariasis.

Industrial scale high-throughput screening delivers multiple fast acting macrofilaricides

Nematodes causing lymphatic filariasis and onchocerciasis rely on their bacterial endosymbiont, Wolbachia, for survival and fecundity, making Wolbachia a promising therapeutic target. Here we perform a high-throughput screen of AstraZeneca’s 1.3 million in-house compound library and identify 5 novel chemotypes with faster in vitro kill rates (<2 days) than existing anti-Wolbachia drugs that cure onchocerciasis and lymphatic filariasis. This industrial scale anthelmintic neglected tropical disease (NTD) screening campaign is the result of a partnership between the Anti-Wolbachia consortium (A∙WOL) and AstraZeneca. The campaign was informed throughout by rational prioritisation and triage of compounds using cheminformatics to balance chemical diversity and drug like properties reducing the chance of attrition from the outset. Ongoing development of these multiple chemotypes, all with superior time-kill kinetics than registered antibiotics with anti-Wolbachia activity, has the potential to improve upon the current therapeutic options and deliver improved, safer and more selective macrofilaricidal drugs.

Parasitic nematodes causing onchocerciasis and lymphatic filariasis rely on a bacterial endosymbiont, Wolbachia, which is a validated therapeutic target. Here, Clare et al. perform a high-throughput screen of 1.3 million compounds and identify 5 chemotypes with faster kill rates than existing anti-Wolbachia drugs.

Growth kinetics of endosymbiont Wolbachia in the common bed bug, Cimex lectularius

The common bed bug, Cimex lectularius harbors the endosymbiotic microorganism, Wolbachia (wCle), in a gonad-associated bacteriome as an obligate nutritional mutualist. The obligatory nature of this association suggests that all individuals in C. lectularius populations would be infected with wCle. However, studies spanning the past several decades have reported variation in both infection frequency and relative abundance of wCle in field-collected samples of bed bugs. Since the growth kinetics of wCle is poorly understood, the objective of this study was to quantify wCle over the life cycle of two strains of C. lectularius. Our results highlight that wCle is dynamic during bed bug development, changing relative to life stage, intermolt stage, and blood-fed status. These results suggest new hypotheses about the coordination of Wolbachia growth and regression with its host's physiology and endocrine events. The observed quantitative modulation of wCle during the bed bug life cycle and during periods of starvation may explain the disparities in wCle infections reported in field-collected C. lectularius.

Polar cell fate stimulates Wolbachia intracellular growth

Bacteria are crucial partners in the development and evolution of vertebrates and invertebrates. A large fraction of insects harbor Wolbachia, bacterial endosymbionts that manipulate host reproduction to favor their spreading. Because they are maternally inherited, Wolbachia are under selective pressure to reach the female germline and infect the offspring. However, Wolbachia infection is not limited to the germline. Somatic cell types, including stem cell niches, have higher Wolbachia loads compared with the surrounding tissue. Here, we show a novel Wolbachia tropism to polar cells (PCs), specialized somatic cells in the Drosophila ovary. During oogenesis, all stages of PC development are easily visualized, facilitating the investigation of the kinetics of Wolbachia intracellular growth. Wolbachia accumulation is triggered by particular events of PC morphogenesis, including differentiation from progenitors and between stages 8 and 9 of oogenesis. Moreover, induction of ectopic PC fate is sufficient to promote Wolbachia accumulation. We found that Wolbachia PC tropism is evolutionarily conserved across most Drosophila species, but not in Culex mosquitos. These findings highlight the coordination of endosymbiont tropism with host development and cell differentiation.

Combinations of registered drugs reduce treatment times required to deplete Wolbachia in the Litomosoides sigmodontis mouse model

Filarial parasites can be targeted by antibiotic treatment due to their unique endosymbiotic relationship with Wolbachia bacteria. This finding has led to successful treatment strategies in both, human onchocerciasis and lymphatic filariasis. A 4–6 week treatment course using doxycycline results in long-term sterility and safe macrofilaricidal activity in humans. However, current treatment times and doxycycline contraindications in children and pregnant women preclude widespread administration of doxycycline in public health control programs; therefore, the search for shorter anti-wolbachial regimens is a focus of ongoing research. We have established an in vivo model for compound screening, using mice infected with Litomosoides sigmodontis. We could show that gold standard doxycycline treatment did not only deplete Wolbachia, it also resulted in a larval arrest. In this model, combinations of registered antibiotics were tested for their anti-wolbachial activity. Administration of rifamycins in combination with doxycycline for 7 days successfully depleted Wolbachia by > 2 log (>99% reduction) and thus resulted in a significant reduction of the treatment duration. Using a triple combination of a tetracycline (doxycycline or minocycline), a rifamycin and a fluoroquinolone (moxifloxacin) led to an even greater shortening of the treatment time. Testing all double combinations that could be derived from the triple combinations revealed that the combination of rifapentine (15mg/kg) and moxifloxacin (2 x 200mg/kg) showed the strongest reduction of treatment time in intraperitoneal and also oral administration routes. The rifapentine plus moxifloxacin combination was equivalent to the triple combination with additional doxycycline (>99% Wolbachia reduction). These investigations suggest that it is possible to shorten anti-wolbachial treatment times with combination treatments in order to achieve the target product profile (TPP) requirements for macrofilaricidal drugs of no more than 7–10 days of treatment.

Over the past years, more attention has been brought to neglected tropical diseases including lymphatic filariasis and onchocerciasis. The latter are caused by helminthic parasites and lead to chronic and debilitating symptoms and present a major health burden that also affects the economy of endemic countries. It has been suggested that disease elimination may be possible but an accelerated implementation of proven and cost-effective interventions are needed if the targets for elimination are to be achieved. Recently, an indirect mode of action has been identified, targeting bacterial Wolbachia endosymbionts within the filariae, which also kills the adult parasites, an advantage over the drug currently used for mass drug administration, i.e. ivermectin. Doxycycline has been successfully used in clinical trials, however due to its long regimen as well as restrictions of use in children and pregnant women new drugs or drug combinations are required that overcome these obstacles. Here, we present the filarial parasite Litomosoides sigmodontis as suitable model for the preclinical testing of anti-wolbachial drugs against filariae and show that combinations of already registered drugs with anti-wolbachial efficacy are able to reduce the treatment time dramatically.

Albendazole and antibiotics synergize to deliver short-course anti-Wolbachia curative treatments in preclinical models of filariasis

Filarial nematode infections, caused by Wuchereria bancrofti, Brugia malayi (elephantiasis), and Onchocerca volvulus (river blindness) infect 150 million of the world’s poorest populations and cause profound disability. Standard treatments require repetitive, long-term, mass drug administrations and have failed to interrupted transmission in certain sub-Saharan African regions. A drug cure using doxycycline, which targets the essential filarial endosymbiont Wolbachia, is clinically effective but programmatically challenging to implement due to long treatment durations and contraindications. Here we provide proof-of-concept of a radical improvement of targeting Wolbachia via identification of drug synergy between the anthelmintic albendazole and antibiotics. This synergy enables the shortening of treatment duration of macrofilaricidal anti-Wolbachia based treatments from 4 wk to 7 d with registered drugs ready for clinical testing.

Elimination of filariasis requires a macrofilaricide treatment that can be delivered within a 7-day period. Here we have identified a synergy between the anthelmintic albendazole (ABZ) and drugs depleting the filarial endosymbiont Wolbachia, a proven macrofilaricide target, which reduces treatment from several weeks to 7 days in preclinical models. ABZ had negligible effects on Wolbachia but synergized with minocycline or rifampicin (RIF) to deplete symbionts, block embryogenesis, and stop microfilariae production. Greater than 99% Wolbachia depletion following 7-day combination of RIF+ABZ also led to accelerated macrofilaricidal activity. Thus, we provide preclinical proof-of-concept of treatment shortening using antibiotic+ABZ combinations to deliver anti-Wolbachia sterilizing and macrofilaricidal effects. Our data are of immediate public health importance as RIF+ABZ are registered drugs and thus immediately implementable to deliver a 1-wk macrofilaricide. They also suggest that novel, more potent anti-Wolbachia drugs under development may be capable of delivering further treatment shortening, to days rather than weeks, if combined with benzimidazoles.

Reciprocal Interactions between Nematodes and Their Microbial Environments

Parasitic nematode infections are widespread in nature, affecting humans as well as wild, companion, and livestock animals. Most parasitic nematodes inhabit the intestines of their hosts living in close contact with the intestinal microbiota. Many species also have tissue migratory life stages in the absence of severe systemic inflammation of the host. Despite the close coexistence of helminths with numerous microbes, little is known concerning these interactions. While the environmental niche is considerably different, the free-living nematode Caenorhabditis elegans (C. elegans) is also found amongst a diverse microbiota, albeit on decaying organic matter. As a very well characterized model organism that has been intensively studied for several decades, C. elegans interactions with bacteria are much more deeply understood than those of their parasitic counterparts. The enormous breadth of understanding achieved by the C. elegans research community continues to inform many aspects of nematode parasitology. Here, we summarize what is known regarding parasitic nematode-bacterial interactions while comparing and contrasting this with information from work in C. elegans. This review highlights findings concerning responses to bacterial stimuli, antimicrobial peptides, and the reciprocal influences between nematodes and their environmental bacteria. Furthermore, the microbiota of nematodes as well as alterations in the intestinal microbiota of mammalian hosts by helminth infections are discussed.

Significant heterogeneity in Wolbachia copy number within and between populations of Onchocerca volvulus

BACKGROUND

Wolbachia are intracellular bacteria found in arthropods and several filarial nematode species. The filarial Wolbachia have been proposed to be involved in the immunopathology associated with onchocerciasis. Higher Wolbachia-to-nematode ratios have been reported in the savannah-ecotype compared to the forest-ecotype, and have been interpreted as consistent with a correlation between Wolbachia density and disease severity. However, factors such as geographic stratification and ivermectin drug exposure can lead to significant genetic heterogeneity in the nematode host populations, so we investigated whether Wolbachia copy number variation is also associated with these underlying factors.

METHODS

Genomic DNA was prepared from single adult nematodes representing forest and savannah ecotypes sampled from Togo, Ghana, Côte d'Ivoire and Mali. A qPCR assay was developed to measure the number of Wolbachia genome(s) per nematode genome. Next-generation sequencing (NGS) was also used to measure relative Wolbachia copy number, and independently verify the qPCR assay.

RESULTS

Significant variation was observed within the forest (range: 0.02 to 452.99; median: 10.58) and savannah (range: 0.01 to 1106.25; median: 9.10) ecotypes, however, no significant difference between ecotypes (P = 0.645) was observed; rather, strongly significant Wolbachia variation was observed within and between the nine study communities analysed (P = 0.021), independent of ecotype. Analysis of ivermectin-treated and untreated nematodes by qPCR showed no correlation (P = 0.869); however, an additional analysis of a subset of the nematodes by qPCR and NGS revealed a correlation between response to ivermectin treatment and Wolbachia copy number (P = 0.020).

CONCLUSIONS

This study demonstrates that extensive within and between population variation exists in the Wolbachia content of individual adult O. volvulus. The origin and functional significance of such variation (up to ~ 100,000-fold between worms; ~10 to 100-fold between communities) in the context of the proposed mutualistic relationship between the worms and the bacteria, and between the presence of Wolbachia and clinical outcome of infection, remains unclear. These data do not support a correlation between Wolbachia copy number and forest or savannah ecotype, and may have implications for the development of anti-Wolbachia drugs as a macrofilaricidal treatment of onchocerciasis. The biological significance of a correlation between variation in Wolbachia copy number and ivermectin response remains unexplained.

Defining Brugia malayi and Wolbachia symbiosis by stage-specific dual RNA-seq

Background

Filarial nematodes currently infect up to 54 million people worldwide, with millions more at risk for infection, representing the leading cause of disability in the developing world. Brugia malayi is one of the causative agents of lymphatic filariasis and remains the only human filarial parasite that can be maintained in small laboratory animals. Many filarial nematode species, including B. malayi, carry an obligate endosymbiont, the alpha-proteobacteria Wolbachia, which can be eliminated through antibiotic treatment. Elimination of the endosymbiont interferes with development, reproduction, and survival of the worms within the mamalian host, a clear indicator that the Wolbachia are crucial for survival of the parasite. Little is understood about the mechanism underlying this symbiosis.

Methodology/ Principle findings

To better understand the molecular interplay between these two organisms we profiled the transcriptomes of B. malayi and Wolbachia by dual RNA-seq across the life cycle of the parasite. This helped identify functional pathways involved in this essential symbiotic relationship provided by the co-expression of nematode and bacterial genes. We have identified significant stage-specific and gender-specific differential expression in Wolbachia during the nematode’s development. For example, during female worm development we find that Wolbachia upregulate genes involved in ATP production and purine biosynthesis, as well as genes involved in the oxidative stress response.

Conclusions/ Significance

This global transcriptional analysis has highlighted specific pathways to which both Wolbachia and B. malayi contribute concurrently over the life cycle of the parasite, paving the way for the development of novel intervention strategies.

Filarial nematodes currently infect millions of people worldwide and represent a leading cause of disability. Currently available medications are insufficient in reaching elimination of these parasites. Many filarial nematodes, including Brugia malayi, have an Achilles heel of sorts—that is their obligate symbiotic relationship with the bacteria Wolbachia. While it is known that the nematode and the bacteria are co-dependent, the molecular basis of this relationship remains poorly understood. Using deep sequencing, we profiled the transcriptomes of B. malayi and Wolbachia across the life cycle of the parasite to determine the functional pathways necessary for parasite survival provided by the co-expression of nematode and bacterial genes. Defining the mechanisms of endosymbiosis between these two organisms will allow for the exploitation of this relationship for the development of new intervention strategies.

Short-Course, High-Dose Rifampicin Achieves Wolbachia Depletion Predictive of Curative Outcomes in Preclinical Models of Lymphatic Filariasis and Onchocerciasis

Lymphatic filariasis (LF) and onchocerciasis are priority neglected tropical diseases targeted for elimination. The only safe drug treatment with substantial curative activity against the filarial nematodes responsible for LF (Brugia malayi, Wuchereria bancrofti) or onchocerciasis (Onchocerca volvulus) is doxycycline. The target of doxycycline is the essential endosymbiont, Wolbachia. Four to six weeks doxycycline therapy achieves >90% depletion of Wolbachia in worm tissues leading to blockade of embryogenesis, adult sterility and premature death 18-24 months post-treatment. Long treatment length and contraindications in children and pregnancy are obstacles to implementing doxycycline as a public health strategy. Here we determine, via preclinical infection models of Brugia malayi or Onchocerca ochengi that elevated exposures of orally-administered rifampicin can lead to Wolbachia depletions from filariae more rapidly than those achieved by doxycycline. Dose escalation of rifampicin achieves >90% Wolbachia depletion in time periods of 7 days in B. malayi and 14 days in O. ochengi. Using pharmacokinetic-pharmacodynamic modelling and mouse-human bridging analysis, we conclude that clinically relevant dose elevations of rifampicin, which have recently been determined as safe in humans, could be administered as short courses to filariasis target populations with potential to reduce anti-Wolbachia curative therapy times to between one and two weeks.

Genomic diversity in Onchocerca volvulus and its Wolbachia endosymbiont

Ongoing elimination efforts have altered the global distribution of Onchocerca volvulus, the agent of river blindness, and further population restructuring is expected as efforts continue. Therefore, a better understanding of population genetic processes and their effect on biogeography is needed to support elimination goals. We describe O. volvulus genome variation in 27 isolates from the early 1990s (before widespread mass treatment) from four distinct locales: Ecuador, Uganda, the West African forest and the West African savanna. We observed genetic substructuring between Ecuador and West Africa and between the West African forest and savanna bioclimes, with evidence of unidirectional gene flow from savanna to forest strains. We identified forest:savanna-discriminatory genomic regions and report a set of ancestry informative loci that can be used to differentiate between forest, savanna and admixed isolates, which has not previously been possible. We observed mito-nuclear discordance possibly stemming from incomplete lineage sorting. The catalogue of the nuclear, mitochondrial and endosymbiont DNA variants generated in this study will support future basic and translational onchocerciasis research, with particular relevance for ongoing control programmes, and boost efforts to characterize drug, vaccine and diagnostic targets.

Stage-specific Proteomes from Onchocerca ochengi, Sister Species of the Human River Blindness Parasite, Uncover Adaptations to a Nodular Lifestyle

Despite 40 years of control efforts, onchocerciasis (river blindness) remains one of the most important neglected tropical diseases, with 17 million people affected. The etiological agent, Onchocerca volvulus, is a filarial nematode with a complex lifecycle involving several distinct stages in the definitive host and blackfly vector. The challenges of obtaining sufficient material have prevented high-throughput studies and the development of novel strategies for disease control and diagnosis. Here, we utilize the closest relative of O. volvulus, the bovine parasite Onchocerca ochengi, to compare stage-specific proteomes and host-parasite interactions within the secretome. We identified a total of 4260 unique O. ochengi proteins from adult males and females, infective larvae, intrauterine microfilariae, and fluid from intradermal nodules. In addition, 135 proteins were detected from the obligate Wolbachia symbiont. Observed protein families that were enriched in all whole body extracts relative to the complete search database included immunoglobulin-domain proteins, whereas redox and detoxification enzymes and proteins involved in intracellular transport displayed stage-specific overrepresentation. Unexpectedly, the larval stages exhibited enrichment for several mitochondrial-related protein families, including members of peptidase family M16 and proteins which mediate mitochondrial fission and fusion. Quantification of proteins across the lifecycle using the Hi-3 approach supported these qualitative analyses. In nodule fluid, we identified 94 O. ochengi secreted proteins, including homologs of transforming growth factor-β and a second member of a novel 6-ShK toxin domain family, which was originally described from a model filarial nematode (Litomosoides sigmodontis). Strikingly, the 498 bovine proteins identified in nodule fluid were strongly dominated by antimicrobial proteins, especially cathelicidins. This first high-throughput analysis of an Onchocerca spp. proteome across the lifecycle highlights its profound complexity and emphasizes the extremely close relationship between O. ochengi and O. volvulus The insights presented here provide new candidates for vaccine development, drug targeting and diagnostic biomarkers.

Glucose and Glycogen Metabolism in Brugia malayi Is Associated with Wolbachia Symbiont Fitness

Wolbachia are endosymbiotic bacteria found in the majority of arthropods and filarial nematodes of medical and veterinary importance. They have evolved a wide range of symbiotic associations. In filarial nematodes that cause human lymphatic filariasis (Wuchereria bancrofti, Brugia malayi) or onchocerciasis (Onchocerca volvulus), Wolbachia are important for parasite development, reproduction and survival. The symbiotic bacteria rely in part on nutrients and energy sources provided by the host. Genomic analyses suggest that the strain of Wolbachia found in B. malayi (wBm) lacks the genes for two glycolytic enzymes—6-phosphofructokinase and pyruvate kinase—and is thus potentially unable to convert glucose into pyruvate, an important substrate for energy generation. The Wolbachia surface protein, wBm00432, is complexed to six B. malayi glycolytic enzymes, including aldolase. In this study we characterized two B. malayi aldolase isozymes and found that their expression is dependent on Wolbachia fitness and number. We confirmed by immuno-transmission electron microscopy that aldolase is associated with the Wolbachia surface. RNAi experiments suggested that aldolase-2 plays a significant role in both Wolbachia survival and embryogenesis in B. malayi. Treatment with doxycycline reduced Wolbachia fitness and increased the amount of both glucose and glycogen detected in the filarial parasite, indicating that glucose metabolism and glycogen storage in B. malayi are associated with Wolbachia fitness. This metabolic co-dependency between Wolbachia and its filarial nematode indicates that glycolysis could be a shared metabolic pathway between the bacteria and B. malayi, and thus a potential new target for anti-filarial therapy.

Minocycline as a re-purposed anti-Wolbachia macrofilaricide: superiority compared with doxycycline regimens in a murine infection model of human lymphatic filariasis

Lymphatic filariasis and onchocerciasis are parasitic helminth diseases, which cause severe morbidities such as elephantiasis, skin disease and blindness, presenting a major public health burden in endemic communities. The anti-Wolbachia consortium (A·WOL: http://www.a-wol.com/) has identified a number of registered antibiotics that target the endosymbiotic bacterium, Wolbachia, delivering macrofilaricidal activity. Here we use pharmacokinetics/pharmacodynamics (PK/PD) analysis to rationally develop an anti-Wolbachia chemotherapy by linking drug exposure to pharmacological effect. We compare the pharmacokinetics and anti-Wolbachia efficacy in a murine Brugia malayi model of minocycline versus doxycycline. Doxycycline exhibits superior PK in comparison to minocycline resulting in a 3-fold greater exposure in SCID mice. Monte-Carlo simulations confirmed that a bi-daily 25–40 mg/Kg regimen is bioequivalent to a clinically effective 100–200 mg/day dose for these tetracyclines. Pharmacodynamic studies showed that minocycline depletes Wolbachia more effectively than doxycycline (99.51% vs. 90.35%) after 28 day 25 mg/Kg bid regimens with a more potent block in microfilarial production. PK/PD analysis predicts that minocycline would be expected to be 1.7 fold more effective than doxycycline in man despite lower exposure in our infection models. Our findings warrant onward clinical investigations to examine the clinical efficacy of minocycline treatment regimens against lymphatic filariasis and onchocerciasis.

A histochemical study of the Nras/let-60 activity in filarial nematodes

BACKGROUND

Control and elimination of filarial pathogens is a central focus of major global health efforts directed at parasitic diseases of developing countries. Accomplishment of these goals would be markedly enhanced by the enhanced destruction of the adult stage of filariae. The identification of new, more quantitative biomarkers that correlate with mortality or chemotherapeutic damage to adult filariae, would greatly facilitate, for example, the development of new macrofilaricides.

METHODS

An immunocytochemical approach using an antibody against human Nras was used to identify and detect changes in the nematode homolog let-60 that is associated with cell growth and maintenance. Single Onchocerca volvulus nodules were removed from each of 13 patients treated with ivermectin (as part of a community-wide mass drug administration programme), and from each of 13 untreated individuals; these 26 nodules were stained with the anti-Nras antibody. The localization and degree of positivity of Nras/let-60 staining were assessed subjectively and compared between the two groups; the positivity of staining was also quantified, using image analysis, in a subgroup of these nodules. In addition, the specific morphological association between Nras/let-60 and the Wolbachia endosymbiont present in these parasites was also observed in 4 additional filarial species using an anti-Wolbachia surface protein (WSP) antibody under light and confocal microscopy.

RESULTS

Nras/let-60 is present in many structures within the adult female worms. A statistically significant decrease in the general staining intensity of Nras/let-60 was observed in adult female O. volvulus treated with ivermectin when compared with parasites from untreated patients. Nras/let-60 staining was frequently observed to be co-localized with WSP in O.volvulus, Brugia malayi, Litomosoides sigmodontis and Dirofilaria immitis. Nras/let60 is also present in Onchocerca ochengi.

CONCLUSION

Nras/let-60, as detected by immunocytochemical staining, is decreased in ivermectin-treated adult female O. volvulus relative to untreated control specimens, suggesting a suppressive effect of ivermectin on the overall biochemical activity of these parasites. Co-localization of Nras/let-60 and WSP suggests the possibility that the endosymbiont utilizes this nematode protein as part of a mutualistic relationship. Nras/let60 appears to be a useful biomarker for assessing the health of filariae.

Absence of Wolbachia endobacteria in Sri Lankan isolates of the nematode parasite of animals Setaria digitata

Setaria digitata is an animal filarial parasite with natural hosts of cattle and buffaloes that causes mild disease conditions. Infection of non-permissive hosts such as goats, sheep and horses, by this nematode can cause cerebrospinal nematodiasis that leads to lumbar paralysis and the eventual death of the animals and inflicts considerable economic losses on livestock farmers. Wolbachia are obligate mutualistic endosymbionts for some filarial nematodes and are currently being targeted for the control of diseases caused by these parasites. However, little is known about the occurrence of this endosymbiont in the Setariidae family. In this work, worms collected from infected cattle in Sri Lanka were morphologically identified as S. digitata and tested for the presence of Wolbachia by PCR screening using the WSP- and Wolbachia-specific 16S rRNA and multilocus sequence typing primers that were designed to amplify the gatB, coxA, hcpA, ftsZ and fbpA sequences of Wolbachia. The presence of endobacteria in S. digitata was also examined by whole-mount immunofluorescence staining of the parasites and transmission electron microscopic studies. These analyses did not produce evidence of presence of Wolbachia or any other endosymbiotic bacteria in S. digitata, whereas such evidence was found in Brugia malayi, which was used as a positive control in this study.

Concurrent transcriptional profiling of Dirofilaria immitis and its Wolbachia endosymbiont throughout the nematode life cycle reveals coordinated gene expression

Background

Dirofilaria immitis, or canine heartworm, is a filarial nematode parasite that infects dogs and other mammals worldwide. Current disease control relies on regular administration of anthelmintic preventives, however, relatively poor compliance and evidence of developing drug resistance could warrant alternative measures against D. immitis and related human filarial infections be taken. As with many other filarial nematodes, D. immitis contains Wolbachia, an obligate bacterial endosymbiont thought to be involved in providing certain critical metabolites to the nematode. Correlations between nematode and Wolbachia transcriptomes during development have not been examined. Therefore, we detailed the developmental transcriptome of both D. immitis and its Wolbachia (wDi) in order to gain a better understanding of parasite-endosymbiont interactions throughout the nematode life cycle.

Results

Over 215 million single-end 50 bp reads were generated from total RNA from D. immitis adult males and females, microfilariae (mf) and third and fourth-stage larvae (L3 and L4). We critically evaluated the transcriptomes of the various life cycle stages to reveal sex-biased transcriptional patterns, as well as transcriptional differences between larval stages that may be involved in larval maturation. Hierarchical clustering revealed both D. immitis and wDi transcriptional activity in the L3 stage is clearly distinct from other life cycle stages. Interestingly, a large proportion of both D. immitis and wDi genes display microfilarial-biased transcriptional patterns. Concurrent transcriptome sequencing identified potential molecular interactions between parasite and endosymbiont that are more prominent during certain life cycle stages. In support of metabolite provisioning between filarial nematodes and Wolbachia, the synthesis of the critical metabolite, heme, by wDi appears to be synchronized in a stage-specific manner (mf-specific) with the production of heme-binding proteins in D. immitis.

Conclusions

Our integrated transcriptomic study has highlighted interesting correlations between Wolbachia and D. immitis transcription throughout the life cycle and provided a resource that may be used for the development of novel intervention strategies, not only for the treatment and prevention of D. immitis infections, but of other closely related human parasites as well.

Electronic supplementary material

The online version of this article (doi:10.1186/1471-2164-15-1041) contains supplementary material, which is available to authorized users.

A murine macrofilaricide pre-clinical screening model for onchocerciasis and lymphatic filariasis

Background

New drugs effective against adult filariae (macrofilaricides) would accelerate the elimination of lymphatic filariasis and onchocerciasis. Anti-Onchocerca drug development is hampered by the lack of a facile model. We postulated that SCID mice could be developed as a fmacrofilaricide screening model.

Methods

The filaricides: albendazole (ABZ), diethylcarbamazine (DEC), flubendazole (FBZ), ivermectin (IVM) and the anti-Wolbachia macrofilaricide, minocycline (MIN) were tested in Brugia malayi (Bm)-parasitized BALB/c SCID mice vs vehicle control (VC). Responses were compared to BALB/c wild type (WT). Onchocerca ochengi male worms or onchocercomata were surgically implanted into BALB/c SCID, CB.17 SCID, BALB/c WT mice or Meriones gerbils. Survival was evaluated at 7–15 days. BALB/c SCID were tested to evaluate the responsiveness of pre-clinical macrofilaricides FBZ and rifapentine (RIFAP) against male Onchocerca.

Results

WT and SCID responded with >95% efficacy following ABZ or DEC treatments against Bm larvae (P < 0.0001). IVM was partially filaricidal against Bm larvae in WT and SCID (WT; 39.8%, P = 0.0356 and SCID; 56.7%, P = 0.026). SCID responded similarly to WT following IVM treatment of microfilaraemias (WT; 79%, P = 0.0194. SCID; 76%, P = 0.0473). FBZ induced a total macrofilaricidal response against adult Bm in WT and SCID (WT; P = 0.0067, SCID; P = 0.0071). MIN induced a >90% reduction in Bm Wolbachia burdens (P < 0.0001) and a blockade of microfilarial release (P = 0.0215) in SCID. Male Onchocerca survival was significantly higher in SCID vs WT mice, but not gerbils, after +15 days (60% vs 22% vs 39% P = 0.0475). Onchocercoma implants had engrafted into host tissues, with evidence of neovascularisation, after +7 days and yielded viable macro/microfilariae ex vivo. FBZ induced a macrofilaricidal effect in Onchocerca male implanted SCID at +5 weeks (FBZ; 1.67% vs VC; 43.81%, P = 0.0089). Wolbachia loads within male Onchocerca were reduced by 99% in implanted SCID receiving RIFAP for +2 weeks.

Conclusions

We have developed a ‘pan-filarial’ small animal research model that is sufficiently robust, with adequate capacity and throughput, to screen existing and future pre-clinical candidate macrofilaricides. Pilot data suggests a murine onchocercoma xenograft model is achievable.