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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.

Brugia malayi , a parasitic roundworm of humans, is colonized by the obligate intracellular bacterium, Wolbachia pipientis . The symbiosis between this nematode and bacterium is essential for nematode reproduction and long-term survival in a human host. Therefore, identifying molecular mechanisms required by Wolbachia to persist in and colonize B . malayi tissues will provide new essential information regarding the basic biology of this endosymbiosis. Wolbachia utilize a Type IV secretion system to translocate so-called “ effector” proteins into the cytosol of B . malayi cells to promote colonization of the eukaryotic host. However, the characterization of these Wolbachia secreted proteins has remained elusive due to the genetic intractability of both organisms. Strikingly, expression of the candidate Wolbachia Type IV-secreted effector protein, Wbm0076, in the surrogate eukaryotic cell model, Saccharomyces cerevisiae , resulted in the disruption of the yeast actin cytoskeleton and inhibition of endocytosis. Genetic analyses show that Wbm0076 is a member of the family of Wiskott-Aldrich syndrome proteins (WAS [p]), a well-conserved eukaryotic protein family required for the organization of actin skeletal structures. Thus, Wbm0076 likely plays a central role in the active cell-to-cell movement of Wolbachia throughout B . malayi tissues during nematode development. As most Wolbachia isolates sequenced to date encode at least partial orthologs of w Bm0076, we find it likely that the ability of Wolbachia to directly manipulate host actin dynamics is an essential requirement of all Wolbachia endosymbioses, independent of host cell species.

Parasitic nematodes that cause elephantiasis and river blindness threaten hundreds of millions of people in the developing world. We have sequenced the ∼90 megabase (Mb) genome of the human filarial parasite Brugia malayi and predict ∼11,500 protein coding genes in 71 Mb of robustly assembled sequence. Comparative analysis with the free-living, model nematode Caenorhabditis elegans revealed that, despite these genes having maintained little conservation of local synteny during ∼350 million years of evolution, they largely remain in linkage on chromosomal units. More than 100 conserved operons were identified. Analysis of the predicted proteome provides evidence for adaptations of B. malayi to niches in its human and vector hosts and insights into the molecular basis of a mutualistic relationship with its Wolbachia endosymbiont. These findings offer a foundation for rational drug design.

Thomas Nutman and colleagues report the draft genome of the filarial pathogen Loa loa , the African eyeworm. They also report coverage of two other filarial pathogens, Wuchereria bancrofti and Onchocerca volvulus . Unlike most filariae, L. loa lacks an obligate intracellular Wolbachia endosymbiont, and comparative genomic analyses suggest that the L. loa genome does not contain new metabolic synthesis or transport pathways compared to other filariae. Loa loa , the African eyeworm, is a major filarial pathogen of humans. Unlike most filariae, L. loa does not contain the obligate intracellular Wolbachia endosymbiont. We describe the 91.4-Mb genome of L. loa and that of the related filarial parasite Wuchereria bancrofti and predict 14,907 L. loa genes on the basis of microfilarial RNA sequencing. By comparing these genomes to that of another filarial parasite, Brugia malayi , and to those of several other nematodes, we demonstrate synteny among filariae but not with nonparasitic nematodes. The L. loa genome encodes many immunologically relevant genes, as well as protein kinases targeted by drugs currently approved for use in humans. Despite lacking Wolbachia , L. loa shows no new metabolic synthesis or transport capabilities compared to other filariae. These results suggest that the role of Wolbachia in filarial biology is more subtle than previously thought and reveal marked differences between parasitic and nonparasitic nematodes.

Lymphatic filariasis (LF) is a crippling and disfiguring parasitic condition. India accounts for 55% of the world’s LF burden. The filarial parasite Wuchereria bancrofti is known to cause 99.4% of the cases while, Brugia malayi accounts for 0.6% of the issue occurring mainly in some pockets of Odisha and Kerala states. The Balasore (Baleswar) district of Odisha has been a known focus of B. malayi transmission. We employed molecular xenomonitoring to detect filarial parasite DNA in vectors. In six selected villages, Gravid traps were used to collect Culex mosquitoes and hand catch method using aspirators was followed for collection of mansonioides. A total of 2903 mosquitoes comprising of Cx. quinquefasciatus (n = 2611; 89.94%), Cx. tritaeniorhynchus (n = 100; 3.44%), Mansonia annuliferea (n = 139; 4.78%) and Mansonia uniformis (n = 53; 1.82%) were collected from six endemic villages. The species wise mosquitoes were made into 118 pools, each with a maximum of 25 mosquitoes, dried and transported to the laboratory at VCRC, Puducherry. The mosquito pools were subjected to parasite DNA extraction, followed by Real-time PCR using LDR and HhaI probes to detect W. bancrofti and B. malayi infections, respectively. Seven pools (6.66%) of Cx. quinquefasciatus, showed infection with only W. bancrofti while none of the pools of other mosquito species showed infection with either W. bancrofti or B. malayi. Although the study area is endemic to B. malayi , none of the vectors of B. malayi was found with parasite infection. This study highlights the ongoing transmission of bancroftian filariasis in the study villages of Balasore district of Odisha and its implications for evaluating LF elimination programme.

Sex determination mechanisms often differ even between related species yet the evolution of sex chromosomes remains poorly understood in all but a few model organisms. Some nematodes such as Caenorhabditis elegans have an XO sex determination system while others, such as the filarial parasite Brugia malayi , have an XY mechanism. We present a complete B. malayi genome assembly and define Nigon elements shared with C. elegans , which we then map to the genomes of other filarial species and more distantly related nematodes. We find a remarkable plasticity in sex chromosome evolution with several distinct cases of neo-X and neo-Y formation, X-added regions, and conversion of autosomes to sex chromosomes from which we propose a model of chromosome evolution across different nematode clades. The phylum Nematoda offers a new and innovative system for gaining a deeper understanding of sex chromosome evolution. Many nematode worms, including Caenorhabditis elegans have XX/XO sex determination, while other species have XY. The authors use a new genome assembly of the filarial parasite Brugia malayi and published data to show that nematode sex chromosome evolution is highly plastic.

Glutamate-gated chloride channels (GluCls) are unique to invertebrates and are targeted by macrocyclic lactones. In this study, we cloned an AVR-14B GluCl subunit from adult Brugia malayi, a causative agent of lymphatic filariasis in humans. To elucidate this channel’s pharmacological properties, we used Xenopus laevis oocytes for expression and performed two-electrode voltage-clamp electrophysiology. The receptor was gated by the natural ligand L-glutamate (effective concentration, 50% [EC50 ] = 0.4 mM) and ivermectin (IVM; EC50 = 1.8 nM). We also characterized the effects of nodulisporic acid (NA) on Bma-AVR-14B and NA-produced dual effects on the receptor as an agonist and a type II positive allosteric modulator. Here we report characterization of the complex activity of NA on a nematode GluCl. Bma-AVR-14B demonstrated some unique pharmacological characteristics. IVM did not produce potentiation of L-glutamate–mediated responses but instead, reduced the channel’s sensitivity for the ligand. Further electrophysiological exploration showed that IVM (at a moderate concentration of 0.1 nM) functioned as an inhibitor of both agonist and positive allosteric modulatory effects of NA. This suggests that IVM and NA share a complex interaction. The pharmacological properties of Bma-AVR-14B indicate that the channel is an important target of IVM and NA. In addition, the unique electrophysiological characteristics of Bma-AVR-14B could explain the observed variation in drug sensitivities of various nematode parasites. We have also shown the inhibitory effects of IVM and NA on adult worm motility using Worminator. RNA interference (RNAi) knockdown suggests that AVR-14 plays a role in influencing locomotion in B. malayi.

Lymphatic filariasis (LF) is a neglected tropical disease affecting over 51 million people in 72 endemic countries. Causative agents of LF are mosquito-borne parasitic nematodes Wuchereria bancrofti , Brugia malayi , and Brugia timori . The adult parasites impact the integrity of lymphatic vessels and damage valves, leading to a remodeling of the lymphatic system and lymphatic dilation. Chronic infections can develop into severe clinical manifestations, primarily lymphedema, hydrocoele, and elephantiasis. Mechanistic studies on the underlying pathology due to the parasite are necessary to better manage human filariasis. Since parasite molecules, such as microRNAs (miRNAs), can be found in secreted extracellular vesicles (EVs) and are transported between parasite and host cells, we hypothesized that these could also play a role in the development of pathology in LF. In this study, we tested two B. malayi miRNAs previously detected in vitro in the culture media of microfilarial stages of worms. While one is Brugia -specific (bma-miR-5864) and the other nematode-specific (bma-miR-86), both miRNAs are secreted in high abundance. We first examined the in vitro response by transcriptomic profiling of human lymphatic endothelial cells to treatment with these miRNAs, which allowed us to identify genes involved in maintaining the integrity of the lymphatic endothelium. We then measured the effect of these miRNAs on the regulation of proteins necessary for cell integrity, demonstrating downregulation leading to a significant increase in the permeability of the endothelium monolayer. With this study we identify parasite miRNAs involved in undermining the integrity of endothelial cells, thus potentially contributing to the development of pathology. These findings could pave the way for a novel treatment strategy where the inhibition of parasite-secreted molecules could slow the progression of LF pathology. From a broader perspective, the miRNAs secreted by filarial parasites could potentially be used in the future for diagnosing and monitoring disease progression or treatment efficacy.

Filariae are parasitic nematodes that are transmitted to their definitive host as third-stage larvae by arthropod vectors like mosquitoes. Filariae cause diseases including: lymphatic filariasis with distressing and disturbing symptoms like elephantiasis; and river blindness. Filarial diseases affect millions of people in 73 countries throughout the topics and sub-tropics. The drugs available for mass drug administration, (ivermectin, albendazole and diethylcarbamazine), are ineffective against adult filariae (macrofilariae) at the registered dosing regimen; this generates a real and urgent need to identify effective macrofilaricides. Emodepside, a veterinary anthelmintic registered for treatment of nematode infections in cats and dogs, is reported to have macrofilaricidal effects. Here, we explore the mode of action of emodepside using adult Brugia malayi, one of the species that causes lymphatic filariasis. Whole-parasite motility measurement with Worminator and patch-clamp of single muscle cells show that emodepside potently inhibits motility by activating voltage-gated potassium channels and that the male is more sensitive than the female. RNAi knock down suggests that emodepside targets SLO-1 K channels. We expressed slo-1 isoforms, with alternatively spliced exons at the RCK1 (Regulator of Conductance of Potassium) domain, heterologously in Xenopus laevis oocytes. We discovered that the slo-1f isoform, found in muscles of males, is more sensitive to emodepside than the slo-1a isoform found in muscles of females; and selective RNAi of the slo-1a isoform in female worms increased emodepside potency. In Onchocerca volvulus, that causes river blindness, we found two isoforms in adult females with homology to Bma-SLO-1A and Bma-SLO-1F at the RCK1 domain. In silico modeling identified an emodepside binding pocket in the same RCK1 region of different species of filaria that is affected by these splice variations. Our observations show that emodepside has potent macrofilaricidal effects and alternative splicing in the RCK1 binding pocket affects potency. Therefore, the evaluation of potential sex-dependent effects of an anthelmintic compound is of importance to prevent any under-dosing of one or the other gender of nematodes once given to patients.

Brugia malayi is the most common cause of lymphatic filariasis (LF) in Indonesia. A zoophilic ecotype that infects both humans and animals occur in Belitung District in Indonesia. The district received five annual rounds of mass drug administration (MDA) between 2006 and 2010 and passed three transmission assessment surveys (TAS) in subsequent years. However, a survey in five villages in 2021 showed a microfilaria (Mf) prevalence of 2.1% in humans. The reappearance of B. malayi infection in humans may be due to reintroduction from animal reservoirs. The goal of this study was to determine B. malayi prevalence in potential reservoir hosts and to improve the identification of filarial Mf found in animals. Venous blood was collected from 291 cats, 41 dogs, and 163 crab-eating macaques (Macaca fascicularis) from areas with and without human B. malayi infection. B. malayi Mf were detected by microscopy in 1.4%, 7.3% and 13.5% of the samples, respectively. The geometric mean Mf density varied from 133 Mf/mL(dogs) to 255 Mf/mL (macaques). While Brugia Mf were easily differentiated from Dirofilaria Mf by microscopy, the morphological differentiation between B. malayi and B. pahangi was not reliable. qPCR detected B. malayi DNA in blood from 4.1% of cats, 2.4% dogs, and 13.5% macaques. In addition, infections or co-infection with B. pahangi (cats, dogs) or D. immitis (dogs) were detected. A novel Dirofilaria species was morphologically identified in 20.3% of macaques. Microscopy was less accurate for detection and species identification of Mf than qPCR. The presence of B. malayi Mf in animals represents a challenge for the elimination of LF in some areas in Indonesia. More research is needed to better understand B. malayi transmission between animals and humans in endemic areas like Belitung where routine MDA may not be sufficient to eliminate LF.