A new approach to the treatment of filariasis

Targeting a microbiota Wolbachian aminoacyl-tRNA synthetase to block its pathogenic host

The interplay between humans and their microbiome is crucial for various physiological processes, including nutrient absorption, immune defense, and maintaining homeostasis. Microbiome alterations can directly contribute to diseases or heighten their likelihood. This relationship extends beyond humans; microbiota play vital roles in other organisms, including eukaryotic pathogens causing severe diseases. Notably, Wolbachia, a bacterial microbiota, is essential for parasitic worms responsible for lymphatic filariasis and onchocerciasis, devastating human illnesses. Given the lack of rapid cures for these infections and the limitations of current treatments, new drugs are imperative. Here, we disrupt Wolbachia's symbiosis with pathogens using boron-based compounds targeting an unprecedented Wolbachia enzyme, leucyl-tRNA synthetase (LeuRS), effectively inhibiting its growth. Through a compound demonstrating anti-Wolbachia efficacy in infected cells, we use biophysical experiments and x-ray crystallography to elucidate the mechanism behind Wolbachia LeuRS inhibition. We reveal that these compounds form adenosine-based adducts inhibiting protein synthesis. Overall, our study underscores the potential of disrupting key microbiota to control infections.

Miniature spatial transcriptomics for studying parasite-endosymbiont relationships at the micro scale

Several important human infectious diseases are caused by microscale-sized parasitic nematodes like filarial worms. Filarial worms have their own spatial tissue organization; to uncover this tissue structure, we need methods that can spatially resolve these miniature specimens. Most filarial worms evolved a mutualistic association with endosymbiotic bacteria Wolbachia. However, the mechanisms underlying the dependency of filarial worms on the fitness of these bacteria remain unknown. As Wolbachia is essential for the development, reproduction, and survival of filarial worms, we spatially explored how Wolbachia interacts with the worm's reproductive system by performing a spatial characterization using Spatial Transcriptomics (ST) across a posterior region containing reproductive tissue and developing embryos of adult female Brugia malayi worms. We provide a proof-of-concept for miniature-ST to explore spatial gene expression patterns in small sample types, demonstrating the method's ability to uncover nuanced tissue region expression patterns, observe the spatial localization of key B. malayi - Wolbachia pathway genes, and co-localize the B. malayi spatial transcriptome in Wolbachia tissue regions, also under antibiotic treatment. We envision our approach will open up new avenues for the study of infectious diseases caused by micro-scale parasitic worms.

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.

Onchocerciasis (river blindness) - more than a century of research and control

This review summarises more than a century of research on onchocerciasis, also known as river blindness, and its control. River blindness is an infection caused by the tissue filaria Onchocerca volvulus affecting the skin, subcutaneous tissue and eyes and leading to blindness in a minority of infected persons. The parasite is transmitted by its intermediate hosts Simulium spp. which breed in rivers. Featured are history and milestones in onchocerciasis research and control, state-of-the-art data on the parasite, its endobacteria Wolbachia, on the vectors, previous and current prevalence of the infection, its diagnostics, the interaction between the parasite and its host, immune responses and the pathology of onchocerciasis. Detailed information is documented on the time course of control programmes in the afflicted countries in Africa and the Americas, a long road from previous programmes to current successes in control of the transmission of this infectious disease. By development, adjustment and optimization of the control measures, transmission by the vector has been interrupted in foci of countries in the Americas, in Uganda, in Sudan and elsewhere, followed by onchocerciasis eliminations. The current state and future perspectives for control, elimination and eradication within the next 20-30 years are described and discussed. This review contributes to a deeper comprehension of this disease by a tissue-dwelling filaria and it will be helpful in efforts to control and eliminate other filarial infections.

Macrofilaricides: An Unmet Medical Need for Filarial Diseases

Neglected parasitic helminth diseases such as onchocerciasis and lymphatic filariasis affect an estimated 145 million people worldwide, creating a serious health burden in endemic areas such as sub-Saharan Africa and India. Although these diseases are not usually lethal, these filarial nematodes, transmitted by blood-feeding insect vectors, cause severe debilitation and cause chronic disability to infected individuals. The adult worms can reproduce from 5 to up to 14 years, releasing millions of microfilariae, juvenile worms, over an infected individual's lifetime. The current treatments for controlling human filarial infections is focused on killing microfilariae, the earliest larval stage. Currently, there is an unmet medical need for treatments consisting of a macrofilaricidal regimen, one that targets the adult stage of the parasite, to increase the rate of elimination, allow for safe use in coendemic regions of Onchocerca volvulus and Loa loa, and to provide a rapid method to resolve reinfections. Herein, recent approaches for targeting human filarial diseases are discussed, including direct acting agents to target parasitic nematodes and antibacterial approaches to target the endosymbiotic bacteria, Wolbachia.

Development and validation of an Onchocerca ochengi adult male worm gerbil model for macrofilaricidal drug screening

BACKGROUND

Onchocerciasis currently afflicts an estimated 15 million people and is the second leading infectious cause of blindness world-wide. The development of a macrofilaricide to cure the disease has been hindered by the lack of appropriate small laboratory animal models. This study therefore, was aimed at developing and validating the Mongolian gerbil, as an Onchocerca ochengi (the closest in phylogeny to O. volvulus) adult male worm model.

METHODOLOGY/PRINCIPAL FINDINGS

Mongolian gerbils (Meriones unguiculatus) were each implanted with 20 O. ochengi male worms (collected from infected cattle), in the peritoneum. Following drug or placebo treatments, the implanted worms were recovered from the animals and analyzed for burden, motility and viability. Worm recovery in control gerbils was on average 35%, with 89% of the worms being 100% motile. Treatment of the gerbils implanted with male worms with flubendazole (FBZ) resulted in a significant reduction (p = 0.0021) in worm burden (6.0% versus 27.8% in the control animals); all recovered worms from the treated group had 0% worm motility versus 91.1% motility in control animals. FBZ treatment had similar results even after four different experiments. Using this model, we tested a related drug, oxfendazole (OFZ), and found it to also significantly (p = 0.0097) affect worm motility (22.7% versus 95.0% in the control group).

CONCLUSIONS/SIGNIFICANCE

We have developed and validated a novel gerbil O. ochengi adult male worm model for testing new macrofilaricidal drugs in vivo. It was also used to determine the efficacy of oxfendazole in vivo.

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.

AmiD Is a Novel Peptidoglycan Amidase in Wolbachia Endosymbionts of Drosophila melanogaster

Wolbachia endobacteria are obligate intracellular bacteria with a highly reduced genome infecting many arthropod and filarial species, in which they manipulate arthropod reproduction to increase their transmission and are essential for nematode development and survival. The Wolbachia genome encodes all enzymes required for the synthesis of the cell wall building block lipid II, although a peptidoglycan-like structure has not been detected. Despite the ability to synthesize lipid II, Wolbachia from arthropods and nematodes have only a subset of genes encoding enzymes involved in the periplasmic processing of lipid II and peptidoglycan recycling, with arthropods having two more than nematodes. We functionally analyzed the activity of the putative cell wall hydrolase AmiD from the Wolbachia endosymbiont of Drosophila melanogaster, an enzyme not encoded by the nematode endobacteria. Wolbachia AmiD has Zn²⁺-dependent amidase activity and cleaves intact peptidoglycan, monomeric lipid II and anhydromuropeptides, substrates that are generated during bacterial growth. AmiD may have been maintained in arthropod Wolbachia to avoid host immune recognition by degrading cell wall fragments in the periplasm. This is the first description of a wolbachial lipid II processing enzyme putatively expressed in the periplasm.

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.

Humans from Wuchereria bancrofti endemic area elicit substantial immune response to proteins of the filarial parasite Brugia malayi and its endosymbiont Wolbachia

BACKGROUND

In the past, immune responses to several Brugia malayi immunodominant antigens have been characterized in filaria-infected populations; however, little is known regarding Wolbachia proteins. We earlier cloned and characterized few B. malayi (trehalose-6-phosphate phosphatase, Bm-TPP and heavy chain myosin, BmAF-Myo) and Wolbachia (translation initiation factor-1, Wol Tl IF-1 and NAD⁺-dependent DNA ligase, wBm-LigA) proteins and investigated the immune responses, which they triggered in animal models. The current study emphasizes on immunological characteristics of these proteins in three major categories of filarial endemic zones: endemic normal (EN, asymptomatic, amicrofilaraemic; putatively immune), microfilariae carriers (MF, asymptomatic but microfilaraemic), and chronic filarial patients (CP, symptomatic and mostly amicrofilaraemic).

METHODS

Immunoblotting and ELISA were carried out to measure IgG and isotype antibodies against these recombinant proteins in various clinical categories. Involvement of serum antibodies in infective larvae killing was assessed by antibody-dependent cellular adhesion and cytotoxicity assay. Cellular immune response was investigated by in vitro proliferation of peripheral blood mononuclear cells (PBMCs) and reactive oxygen species (ROS) generation in these cells after stimulation.

RESULTS

Immune responses of EN and CP displayed almost similar level of IgG to Wol Tl IF-1 while other three proteins had higher serum IgG in EN individuals only. Specific IgA, IgG1, IgG3 and IgM to Bm-TPP were high in EN subjects, while BmAF-Myo additionally showed elevated IgG2. Enhanced IgA and IgG3 were detected in both EN and CP individuals in response to Wol Tl IF-1 antigen, but IgG1 and IgM were high only in EN individuals. wBm-LigA and BmAF-Myo exhibited almost similar pattern of antibody responses. PBMC isolated from EN subjects exhibited higher proliferation and ROS generation when stimulated with all three proteins except for Wol Tl IF-1.

CONCLUSIONS

Overall, these findings display high immunogenicity of all four proteins in human subjects and revealed that the EN population was exposed to both B. malayi and Wolbachia proteins simultaneously. In addition, immune responses to Wol Tl IF-1 suggest possible role of this factor in Wolbachia-induced pathological responses while immune responses to other three proteins suggest that these can be explored further as vaccine candidates.

Burden of lymphatic filariasis morbidity in an area of low endemicity in Brazil

The Global Programme to Eliminate Lymphatic Filariasis has two main components: interrupting transmission of lymphatic filariasis (LF) and managing morbidity and preventing disability. However, interventions to prevent and manage LF-related disabilities in endemic communities have been of limited extent. The aim of this study was to describe the prevalence of morbidity and its correlation with filarial infection, thereby filling a gap that existed regarding the data on morbidity in Brazil. Presence of Wuchereria bancrofti microfilaria was investigated using the thick smear technique. Information on parasitosis-related clinical manifestations was obtained using a questionnaire applied by community health agents with previous training and capacitation to know about and identify the disease. To analyze correlations, Pearson's correlation coefficient was used with the corresponding statistical significance test. 23,673 individuals were investigated: 323 presented microfilaremia (1.36%) and 741 (3.13%) had clinical complaints that were attributable to LF. Acute dermatolymphangioadenitis (ADLA) was the most prevalent condition (2.2%). Lymphedema, ADLA and chyluria were more commonly reported among female patients. There were positive associations between all the clinical complaints reported and filarial infection. Hydrocele presented the most strongly positive association (r=0.699; p<0.001). The present study showed that there is an association between clinical condition reported and the rate of infection among people living in an area of low endemicity for LF. It contributes data that might provide support for healthcare systems and thus optimize disease management, through incorporating surveillance measures directed towards preventing disability and reducing the psychosocial and economic impact of the disease on poor populations living in areas endemic for LF.

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.

Essential proteins and possible therapeutic targets of Wolbachia endosymbiont and development of FiloBase--a comprehensive drug target database for Lymphatic filariasis

Lymphatic filariasis (Lf) is one of the oldest and most debilitating tropical diseases. Millions of people are suffering from this prevalent disease. It is estimated to infect over 120 million people in at least 80 nations of the world through the tropical and subtropical regions. More than one billion people are in danger of getting affected with this life-threatening disease. Several studies were suggested its emerging limitations and resistance towards the available drugs and therapeutic targets for Lf. Therefore, better medicine and drug targets are in demand. We took an initiative to identify the essential proteins of Wolbachia endosymbiont of Brugia malayi, which are indispensable for their survival and non-homologous to human host proteins. In this current study, we have used proteome subtractive approach to screen the possible therapeutic targets for wBm. In addition, numerous literatures were mined in the hunt for potential drug targets, drugs, epitopes, crystal structures, and expressed sequence tag (EST) sequences for filarial causing nematodes. Data obtained from our study were presented in a user friendly database named FiloBase. We hope that information stored in this database may be used for further research and drug development process against filariasis. URL: http://filobase.bicpu.edu.in.

Relationship between oral declaration on adherence to ivermectin treatment and parasitological indicators of onchocerciasis in an area of persistent transmission despite a decade of mass drug administration in Cameroon

Background

Onchocerciasis control for years has been based on mass drug administration (MDA) with ivermectin (IVM). Adherence to IVM repeated treatment has recently been shown to be a confounding factor for onchocerciasis elimination precisely in rain forest areas where transmission continues and Loa loa co-exists with Onchocerca volvulus. In this study, participants’ oral declarations were used as proxy to determine the relationship between adherence to IVM treatment and parasitological indicators of onchocerciasis in the rain forest area of Cameroon with more than a decade of MDA.

Methods

Participants were recruited based on their IVM intake profile with the aid of a semi-structured questionnaire. Parasitological examinations (skin sniping and nodule palpation) were done on eligible candidates. Parasitological indicators were calculated and correlated to IVM intake profile.

Results

Of 2,364 people examined, 15.5 % had never taken IVM. The majority (40.4 %) had taken the drug 1–3 times while only 18 % had taken ≥ 7 times. Mf and nodule prevalence rates were still high at 47 %, 95 % CI [44.9–49.0 %] and 36.4 %, 95 % CI [34.4–38.3 %] respectively. There was a treatment-dependent reduction in microfilaria prevalence (r_s =−0.986, P = 0.01) and intensity (r_s =−0.96, P = 0.01). The highest mf prevalence (59.7 %) was found in the zero treatment group and the lowest (33.9 %) in the ≥ 7 times treatment group (OR = 2.8; 95 % CI [2.09–3.74]; P < 0.001). Adults with ≥ 7 times IVM intake were 2.99 times more likely to have individuals with no microfilaria compared to the zero treatment group (OR = 2.99; 95 % CI [2.19–4.08], P < 0.0001). There was no clear correlation between treatment and nodule prevalence and intensity.

Conclusion

Adherence to ivermectin treatment is not adequate in this rain forest area where L. loa co-exists with O. volvulus. The prevalence and intensity of onchocerciasis remained high in individuals with zero IVM intake after more than a decade of MDA. Our findings show that using parasitological indicators, reduction in prevalence is IVM intake-dependent and that participants’ oral declaration of treatment adherence could be relied upon for impact studies. The findings are discussed in the context of challenges for the elimination of onchocerciasis in this rain forest area.

Homology modeling of NAD+-dependent DNA ligase of the Wolbachia endosymbiont of Brugia malayi and its drug target potential using dispiro-cycloalkanones

Lymphatic filarial nematodes maintain a mutualistic relationship with the endosymbiont Wolbachia. Depletion of Wolbachia produces profound defects in nematode development, fertility, and viability and thus has great promise as a novel approach for treating filarial diseases. NAD(+)-dependent DNA ligase is an essential enzyme of DNA replication, repair, and recombination. Therefore, in the present study, the antifilarial drug target potential of the NAD(+)-dependent DNA ligase of the Wolbachia symbiont of Brugia malayi (wBm-LigA) was investigated using dispiro-cycloalkanone compounds. Dispiro-cycloalkanone specifically inhibited the nick-closing and cohesive-end ligation activities of the enzyme without inhibiting human or T4 DNA ligase. The mode of inhibition was competitive with the NAD(+) cofactor. Docking studies also revealed the interaction of these compounds with the active site of the target enzyme. The adverse effects of these inhibitors were observed on adult and microfilarial stages of B. malayi in vitro, and the most active compounds were further monitored in vivo in jirds and mastomys rodent models. Compounds 1, 2, and 5 had severe adverse effects in vitro on the motility of both adult worms and microfilariae at low concentrations. Compound 2 was the best inhibitor, with the lowest 50% inhibitory concentration (IC50) (1.02 μM), followed by compound 5 (IC50, 2.3 μM) and compound 1 (IC50, 2.9 μM). These compounds also exhibited the same adverse effect on adult worms and microfilariae in vivo (P < 0.05). These compounds also tremendously reduced the wolbachial load, as evident by quantitative real-time PCR (P < 0.05). wBm-LigA thus shows great promise as an antifilarial drug target, and dispiro-cycloalkanone compounds show great promise as antifilarial lead candidates.

Situation analysis of parasitological and entomological indices of onchocerciasis transmission in three drainage basins of the rain forest of South West Cameroon after a decade of ivermectin treatment

BACKGROUND

Community-Directed Treatment with Ivermectin (CDTI) is the main strategy adopted by the African Programme for Onchocerciasis control (APOC). Recent reports from onchocerciasis endemic areas of savannah zones have demonstrated the feasibility of disease elimination through CDTI. Such information is lacking in rain forest zones. In this study, we investigated the parasitological and entomological indices of onchocerciasis transmission in three drainage basins in the rain forest area of Cameroon [after over a decade of CDTI]. River basins differed in terms of river number and their flow rates; and were characterized by high pre-control prevalence rates (60-98%).

METHODS

Nodule palpation and skin snipping were carried out in the study communities to determine the nodule rates, microfilarial prevalences and intensity. Simulium flies were caught at capture points and dissected to determine the biting, parous, infection and infective rates and the transmission potential.

RESULTS

The highest mean microfilaria (mf) prevalence was recorded in the Meme (52.7%), followed by Mungo (41.0%) and Manyu drainage basin (33.0%). The same trend was seen with nodule prevalence between the drainage basins. Twenty-three (23/39) communities (among which 13 in the Meme) still had mf prevalence above 40%. All the communities surveyed had community microfilarial loads (CMFL) below 10 mf/skin snip (ss). The infection was more intense in the Mungo and Meme. The intensity of infection was still high in younger individuals and children less than 10 years of age. Transmission potentials as high as 1211.7 infective larvae/person/month were found in some of the study communities. Entomological indices followed the same trend as the parasitological indices in the three river basins with the Meme having the highest values.

CONCLUSION

When compared with pre-control data, results of the present study show that after over a decade of CDTI, the burden of onchocerciasis has reduced. However, transmission is still going on in this study site where loiasis and onchocerciasis are co-endemic and where ecological factors strongly favour the onchocerciasis transmission. The possible reasons for this persistent and differential transmission despite over a decade of control efforts using ivermectin are discussed.

Identification and ultrastructural characterization of the Wolbachia symbiont in Litomosoides chagasfilhoi

BACKGROUND

Filarial nematodes are arthropod-transmitted parasites of vertebrates that affect more than 150 million people around the world and remain a major public health problem throughout tropical and subtropical regions. Despite the importance of these nematodes, the current treatment strategies are not efficient in eliminating the parasite. The main strategy of control is based on chemotherapy with diethylcarbamazine, albendazole and ivermectin. In the 1970s, it was found that some filarids possess endosymbiotic bacteria that are important for the development, survival and infectivity of the nematodes. These bacteria belong to the genus Wolbachia, which is a widespread and abundant intracellular symbiont in worms. Knowledge about the structure of the bacteria and their relationship with their nematode hosts may allow new perspectives for the control of filarial nematodes.

METHODS

In this study, we used transmission electron microscopy combined with three-dimensional approaches to observe the structure of the endosymbiont of the filarial nematode Litomosoides chagasfilhoi, an experimental model for the study of lymphatic filariasis. In addition, the bacterium was classified based on PCR analyses.

RESULTS

The bacterium was mainly found in the hypodermis and in the female reproductive system in close association with host cell structures, such as the nucleus and endoplasmic reticulum. Our ultrastructural data also showed that the symbiont envelope is composed of two membrane units and is enclosed in a cytoplasmic vacuole, the symbiosome. Molecular data revealed that the bacterium of L. chagasfilhoi shares 100% identity with the Wolbachia endosymbiont of Litomosoides galizai.

CONCLUSIONS

Here we described ultrastructural aspects of the relationship of the Wolbachia with the filarial nematode Litomosoides chagasfilhoi and the findings lead us to consider this relationship as a mutualistic symbiosis.

Wolbachia translation initiation factor-1 is copiously expressed by the adult, microfilariae and infective larvae of Brugia malayi and competitively inhibited by tetracycline

The intracellular alphaproteobacteria, Wolbachia, is considered to be a future antimacrofilarial drug target as it is obligatory for filarial endurance. Characterizing wolbachial proteins is necessary to understand wolbachial mechanisms and also for discovering new drug entities. Translation initiation factor-1 (Tl IF-1) is an indispensable prokaryotic factor concerned with bacterial viability. This factor is prioritized as one of the most potent antibacterial drug target. To investigate its role in filarial biology, recombinant Wol Tl IF-1 was purified on metal ion column. The factor was found folded in its monomeric native conformation, and contained a buried fluorophore. Molecular modeling revealed that the factor belonged to the Oligomer Binding family, and consisted of the highly conserved S1 domain with 81.6% of the amino acids occupying the allowed regions in Ramachandran plot. In addition, Wol Tl IF-1 exhibited selective binding to the 30S ribosomal subunit, which declined progressively with tetracycline addition. Tetracycline perturbs interaction of Thr18 and Asn32 of the factor with ribosomal protein S4. The factor was immune-localized in adult, microfilariae (Mf) and infective larvae (L3) of Brugia malayi by immunoblotting. High expression was also observed in Wolbachia within B. malayi Mf, L3 and female adult parasite along the gravid uteri by the confocal microscopy. Therefore, Wol Tl IF-1 appears to be an essential Wolbachia factor whose inhibition leads to extensive cell apoptosis and premature killing of adult worms, validating the antifilarial potential of the factor.

Wolbachia transcription elongation factor "Wol GreA" interacts with α2ββ'σ subunits of RNA polymerase through its dimeric C-terminal domain

OBJECTIVES

Wolbachia, an endosymbiont of filarial nematode, is considered a promising target for therapy against lymphatic filariasis. Transcription elongation factor GreA is an essential factor that mediates transcriptional transition from abortive initiation to productive elongation by stimulating the escape of RNA polymerase (RNAP) from native prokaryotic promoters. Upon screening of 6257 essential bacterial genes, 57 were suggested as potential future drug targets, and GreA is among these. The current study emphasized the characterization of Wol GreA with its domains.

METHODOLOGY/PRINCIPAL FINDINGS

Biophysical characterization of Wol GreA with its N-terminal domain (NTD) and C-terminal domain (CTD) was performed with fluorimetry, size exclusion chromatography, and chemical cross-linking. Filter trap and far western blotting were used to determine the domain responsible for the interaction with α2ββ'σ subunits of RNAP. Protein-protein docking studies were done to explore residual interaction of RNAP with Wol GreA. The factor and its domains were found to be biochemically active. Size exclusion and chemical cross-linking studies revealed that Wol GreA and CTD exist in a dimeric conformation while NTD subsists in monomeric conformation. Asp120, Val121, Ser122, Lys123, and Ser134 are the residues of CTD through which monomers of Wol GreA interact and shape into a dimeric conformation. Filter trap, far western blotting, and protein-protein docking studies revealed that dimeric CTD of Wol GreA through Lys82, Ser98, Asp104, Ser105, Glu106, Tyr109, Glu116, Asp120, Val121, Ser122, Ser127, Ser129, Lys140, Glu143, Val147, Ser151, Glu153, and Phe163 residues exclusively participates in binding with α2ββ'σ subunits of polymerase.

CONCLUSIONS/SIGNIFICANCE

To the best of our knowledge, this research is the first documentation of the residual mode of action in wolbachial mutualist. Therefore, findings may be crucial to understanding the transcription mechanism of this α-proteobacteria and in deciphering the role of Wol GreA in filarial development.

Filamentation temperature-sensitive protein Z (FtsZ) of Wolbachia, endosymbiont of Wuchereria bancrofti: a potential target for anti-filarial chemotherapy

Lymphatic filariasis (LF) is a leading cause of morbidity in the tropical world. It is caused by the filarial parasites Wuchereria bancrofti, Brugia malayi and Brugia timori and transmitted by vector mosquitoes. Currently a programme for the elimination of LF, Global programme for Elimination of Lymphatic Filariasis (GPELF), is underway with the strategy of mass administration of single dose of diethylcarbamazine or ivermectin, in combination with an anthelmintic drug, albendazole. However, antifilarial drugs used in the programme are only microfilaricidal but not or only partially macrofilaricidal. Hence, there is a need to identify new targets for developing antifilarial drugs. Filarial parasites harbor rickettsial endosymbionts, Wolbachia sp., which play an important role in their biology and hence are considered as potential targets for antifilarial chemotherapy development. In this study, one of the cell division proteins of Wolbachia of the major lymphatic filarial parasite, W. bancrofti, viz., filamentation temperature-sensitive protein Z (FtsZ), was explored as a drug target. The gene coding for FtsZ protein was amplified from the genomic DNA of W. bancrofti, cloned and sequenced. The derived amino acid sequence of the gene revealed that FtsZ protein is 396 amino acids long and contained the tubulin motif (GGGTGTG) involved in GTP binding and the GTP hydrolyzing motif (NLDFAD). The FtsZ gene of endosymbiont showed limited sequence homology, but exhibited functional homology with β-tubulin of its host, W. bancrofti, as it had both the functional motifs and conserved amino acids that are critical for enzymatic activity. β-tubulin is the target for the anti-helminthic activity of albendazole and since FtsZ shares functional homology with, β-tubulin it may also be sensitive to albendazole. Therefore, the effect of albendazole was tested against Wolbachia occurring in mosquitoes instead of filarial parasites as the drug has lethal effect on the latter. Third instar larvae of Culex quinquefasciatus were treated with 0.25mg/ml of albendazole (test) or tetracycline (positive control) in the rearing medium for different intervals and tested for the presence of Wolbachia by FtsZ PCR. All the treated larvae were negative for the presence of the FtsZ band, whereas all the control larvae were positive. The findings of the study, thus indicated that FtsZ is sensitive to albendazole. In view of this albendazole appears to have dual targets; FtsZ in Wolbachia and β-tubulin in W. bancrofti. Further, the functional domain of the gene was assessed for polymorphism among recombinant clones representing 120 W. bancrofti parasites, prevalent across wide geographic areas of India and found to be highly conserved among them. Since it is highly conserved and plays an important role in Wolbachia cell division it appears to be a potential target for anti-filarial chemotherapy development.

Wolbachia filarial interactions

Wolbachia pipientis is a widespread intracellular bacterial symbiont of arthropods and is common in insects. One of their more exotic and unexpected hosts is the filarial nematodes, notable for the parasites responsible for onchocerciasis (river blindness), lymphatic filariasis (elephantiasis) and dirofilariasis (heartworm). Wolbachia are only present in a subgroup of the filarial nematodes and do not extend to other groups of nematodes either parasitic or free-living. In the medically and veterinary important species that host Wolbachia, the symbiont has become an essential partner to key biological processes in the life of the nematode to the point where antibiotic elimination of the bacteria leads to a potent and effective anti-filarial drug treatment. We review the cellular and molecular basis of Wolbachia filarial interactions and highlight the key processes provided by the endosymbiont upon which the nematodes have become entirely dependent. This dependency is primarily restricted to periods of the lifecycle with heavy metabolic demands including growth and development of larval stages and embryogenesis in the adult female. Also, the longevity of filarial parasites is compromised following depletion of the symbiont, which for the first time has delivered a safe and effective treatment to kill adult parasites with antibiotics.

Molecular characterization of NAD+-dependent DNA ligase from Wolbachia endosymbiont of lymphatic filarial parasite Brugia malayi

The lymphatic filarial parasite, Brugia malayi contains Wolbachia endobacteria that are essential for development, viability and fertility of the parasite. Therefore, wolbachial proteins have been currently seen as the potential antifilarial drug targets. NAD(+)-dependent DNA ligase is characterized as a promising drug target in several organisms due to its crucial, indispensable role in DNA replication, recombination and DNA repair. We report here the cloning, expression and purification of NAD(+)-dependent DNA ligase of Wolbachia endosymbiont of B. malayi (wBm-LigA) for its molecular characterization. wBm-LigA has all the domains that are present in nearly all the eubacterial NAD(+)-dependent DNA ligases such as N-terminal adenylation domain, OB fold, helix-hairpin-helix (HhH) and BRCT domain except zinc-binding tetracysteine domain. The purified recombinant protein (683-amino acid) was found to be biochemically active and was present in its native form as revealed by the circular dichroism and fluorescence spectra. The purified recombinant enzyme was able to catalyze intramolecular strand joining on a nicked DNA as well as intermolecular joining of the cohesive ends of BstEII restricted lamda DNA in an in vitro assay. The enzyme was localized in the various life-stages of B. malayi parasites by immunoblotting and high enzyme expression was observed in Wolbachia within B. malayi microfilariae and female adult parasites along the hypodermal chords and in the gravid portion as evident by the confocal microscopy. Ours is the first report on this enzyme of Wolbachia and these findings would assist in validating the antifilarial drug target potential of wBm-LigA in future studies.

Cloning and sequence analysis of partial genomic DNA coding for HtrA-type serine protease of Wolbachia from human lymphatic filarial parasite, Wuchereria bancrofti

Background:

Periplasmic serine proteases of HtrA type of Wolbachia have been shown to play a role in the pathogenesis of filarial disease.

Aims:

This study was aimed to sequence Wb-HtrA serine protease and analyze its phylogenetic position by comparing with other filarial and non-filarial nematode homologs.

Materials and Methods:

Partial HtrA gene fragment was amplified from DNA isolated from periodic and sub-periodic Wuchereria bancrofti parasites collected from Pondicherry and Nicobar islands, respectively. The amplicons were sequenced, and sequence homology and phylogenetic relationship with other filarial and non-filarial nematodes were analyzed.

Results:

Partial orthologue of HtrA-type serine protease from Wolbachia of W. bancrofti was amplified, cloned and sequenced. The deduced amino acid sequence exhibited 87%, 81% and 74% identity with the homologous Wolbachia proteases identified from Brugia malayi, Onchocerca volvulus and Drosophila melanogaster, respectively. The Wb-HtrA has arthologues in several proteobacteria with very high homology and hence is highly conserved not only among Wolbachia of filarial parasites but also across proteobacteria. The phylogenetic tree constructed using Neighbor-Joining method showed two main clusters: cluster-I containing bacteria that dwell in diverse habitats such as soil, fresh and marine waters and plants and cluster-II comprising Anaplasma sp. and Erlichia, and Wolbachia endosymbionts of insects and nematodes, in distinct groups.

Conclusions:

HtrA-type serine protease from Wolbachia of W. bancrofti is highly conserved among filarial parasites. It will be of interest to know whether filarial Wolbachia HtrA type of serine protease might influence apoptosis and lymphatic epithelium, thereby playing a role in the filarial pathogenesis. Such information will be useful for identifying targets for the development of newer drugs for filariasis treatment, especially for preventing lymphatic pathology.

Lymphatics, tertiary lymphoid organs and the granulomas of Crohn's disease: an immunohistochemical study

BACKGROUND

Case studies in the past repeatedly suggested that the fundamental alteration in Crohn's disease occurs in the regional lymphatics of the intestine.

AIM

To evaluate the lymphatic inflammation in Crohn's disease, and to characterise lymphoid aggregates and granulomas in and surrounding lymphatics and blood vasculature.

METHODS

Forty-eight tissue blocks from 24 Crohn's disease patients and 23 tissue blocks from 23 control patients were selected. Tissue sections were immunostained with a lymphatic endothelial cell marker (D2-40), a marker for blood vasculature (FVIII), and markers for T cells (CD3), B cells (CD20) and macrophages (CD68).

RESULTS

Lymphangiectasia and lymphocytic perilymphangitis were demonstrated in all 24 patients, lymphocyte-obstructed lymphatics in seven patients, granuloma-obstructed lymphatics in nine patients and inflammatory lymphoid follicles in all 24 patients. Free-standing granulomas occurred in 19 patients, and in three further patients granulomas were in or attached to blood vascular units.

CONCLUSIONS

This study, employing immunohistochemistry, revealed, better than standard microscopy, the association of inflammation, granulomas and tertiary lymphoid follicles or organs with the lymphatic vasculature in Crohn's disease. Disease in some patients was characterised by perilymphangitis and lymphoid follicular inflammation and in others by granulomas, some of which totally obstructed lymphatics. These findings have aetiological, therapeutic and prognostic implications.

Human subcutaneous dirofilariasis in India: a report of three cases with brief review of literature

Human subcutaneous dirofilariasis is a rare infection caused by filarial worms of the genus Dirofilaria. The parasites are transmitted to man by mosquitoes and the infection is manifested as subcutaneous nodules. Excision of the lesion is both diagnostic and therapeutic. Hereby we report three cases of human subcutaneous dirofilariasis. The worms were sent to our department for identification over a period of four years (2006-2009). Of these three patients, two men and one woman were between 15 and 45 years of age. In two cases, the infection manifested as a nodule on face, in one case near lower eyelid and in the other on the cheek, while in the third case as an itchy nodule on the abdomen. It is emphasized that both clinicians and microbiologists should have an increased awareness of this entity and include dirofilariasis in the differential diagnosis of patients presenting with subcutaneous nodules.

Identifying sub-optimal responses to ivermectin in the treatment of River Blindness

Identification of drug resistance before it becomes a public health concern requires a clear distinction between what constitutes a normal and a suboptimal treatment response. A novel method of analyzing drug efficacy studies in human helminthiases is proposed and used to investigate recent claims of atypical responses to ivermectin in the treatment of River Blindness. The variability in the rate at which Onchocerca volvulus microfilariae repopulate host's skin following ivermectin treatment is quantified using an individual-based onchocerciasis mathematical model. The model estimates a single skin repopulation rate for every host sampled, allowing reports of suboptimal responses to be statistically compared with responses from populations with no prior exposure to ivermectin. Statistically faster rates of skin repopulation were observed in 3 Ghanaian villages (treated 12-17 times), despite the wide variability in repopulation rates observed in ivermectin-naïve populations. Another village previously thought to have high rates of skin repopulation was shown to be indistinguishable from the normal treatment response. The model is used to generate testable hypotheses to identify whether atypical rates of skin repopulation by microfilariae could result from low treatment coverage alone or provide evidence of decreased ivermectin efficacy. Further work linking phenotypic poor responses to treatment with parasite molecular genetics markers will be required to confirm drug resistance. Limitations of the skin-snipping method for estimating parasite load indicates that changes in the distribution of microfilarial repopulation rates, rather than their absolute values, maybe a more sensitive indicator of emerging ivermectin resistance.

The ubiquitous and varied role of infection in the lives of animals and plants

Parasitic and symbiotic infections are major forces governing the life histories of plant and animal hosts-a fact that is ever more evident because of recent findings emanating from diverse subdisciplines of biology. Yet, infectious organisms have been relatively little investigated by biologists who study natural populations. Now that new molecular and computational tools allow us to differentiate and track microscopic infectious agents in nature, we are beginning to establish a better appreciation of their effects on larger, more familiar organisms. This special issue on the ecological and evolutionary consequences of infection for plants and animals is based on the annual Vice Presidential Symposium at the meeting of the American Society of Naturalists held in Knoxville, Tennessee, in the summer of 2001.

Cloning, expression, purification and characterization of a DsbA-like protein from Wolbachia pipientis

Wolbachia pipientis are obligate endosymbionts that infect a wide range of insect and other arthropod species. They act as reproductive parasites by manipulating the host reproduction machinery to enhance their own transmission. This unusual phenotype is thought to be a consequence of the actions of secreted Wolbachia proteins that are likely to contain disulfide bonds to stabilize the protein structure. In bacteria, the introduction or isomerization of disulfide bonds in proteins is catalyzed by Dsb proteins. The Wolbachia genome encodes two proteins, alpha-DsbA1 and alpha-DsbA2, that might catalyze these steps. In this work we focussed on the 234 residue protein alpha-DsbA1; the gene was cloned and expressed in Escherichia coli, the protein was purified and its identity confirmed by mass spectrometry. The sequence identity of alpha-DsbA1 for both dithiol oxidants (E. coli DsbA, 12%) and disulfide isomerases (E. coli DsbC, 14%) is similar. We therefore sought to establish whether alpha-DsbA1 is an oxidant or an isomerase based on functional activity. The purified alpha-DsbA1 was active in an oxidoreductase assay but had little isomerase activity, indicating that alpha-DsbA1 is DsbA-like rather than DsbC-like. This work represents the first successful example of the characterization of a recombinant Wolbachia protein. Purified alpha-DsbA1 will now be used in further functional studies to identify protein substrates that could help explain the molecular basis for the unusual Wolbachia phenotypes, and in structural studies to explore its relationship to other disulfide oxidoreductase proteins.

River blindness: a success story under threat?

The success of the Onchocerciasis Control Programme is undeniable and exemplary, say the authors, but it is too early to claim victory against river blindness.

Tapping the nucleotide pool of the host: novel nucleotide carrier proteins of Protochlamydia amoebophila

Protochlamydia amoebophila UWE25 is related to the Chlamydiaceae comprising major pathogens of humans, but thrives as obligate intracellular symbiont in the protozoan host Acanthamoeba sp. The genome of P. amoebophila encodes five paralogous carrier proteins belonging to the nucleotide transporter (NTT) family. Here we report on three P. amoebophila NTT isoforms, PamNTT2, PamNTT3 and PamNTT5, which possess several conserved amino acid residues known to be critical for nucleotide transport. We demonstrated that these carrier proteins are able to transport nucleotides, although substrate specificities and mode of transport differ in an unexpected manner and are unique among known NTTs. PamNTT2 is a counter exchange transporter exhibiting submillimolar apparent affinities for all four RNA nucleotides, PamNTT3 catalyses an unidirectional proton-coupled transport confined to UTP, whereas PamNTT5 mediates a proton-energized GTP and ATP import. All NTT genes of P. amoebophila are transcribed during intracellular multiplication in acanthamoebae. The biochemical characterization of all five NTT proteins from P. amoebophila in this and previous studies uncovered that these metabolically impaired bacteria are intimately connected with their host cell's metabolism in a surprisingly complex manner.

Differential display of genes expressed in the filarial nematode Litomosoides sigmodontis reveals a putative phosphate permease up-regulated after depletion of Wolbachia endobacteria

Mutualist symbiotic Wolbachia endobacteria are found in most filarial nematodes. Wolbachia are essential for embryogenesis and for larval development into adults, and thus represent a new target for anti-filarial drug development. Tetracycline antibiotics deplete Wolbachia in animal model filaria Litomosoides sigmodontis and Brugia pahangi, as well as in the human parasites Brugia malayi, Onchocerca volvulus and Wuchereria bancrofti. Very little is known about the molecular details of the symbiotic interaction between Wolbachia and filarial nematodes. Nematode genes that respond to anti-Wolbachia antibiotic treatment may play important roles in the symbiosis. Differential display PCR was used to detect several candidate genes that are up-regulated after 3, 6, 15, 30 and 36 days of tetracycline treatment. One of these genes, Ls-ppe-1, was similar to a family of phosphate permeases, and had putative orthologues in O. volvulus and B. malayi. Ls-ppe-1 steady-state mRNA levels were elevated by day 3-6 of treatment, and remained elevated through to 70 days post-treatment. In Caenorhabditis elegans, the knockdown of a homologous phosphate permease results in embryonic lethality, with the production of degenerating embryos, a phenotype also seen in filarial nematodes after depletion of Wolbachia with tetracycline. The potential role of Ls-ppe-1 in the nematode-bacterial symbiosis is discussed.

Ectoparasitic infestations

Ectoparasitic infestations are highly prevalent in resource-poor populations throughout the world and are associated with considerable morbidity. Reliable data on the epidemiology, immunology, and therapy of ectoparasitic infestations and on the biology of the parasites remain scarce. The control of parasitic skin diseases, such as scabies, pediculosis, tungiasis, myiasis, and cutaneous larva migrans in endemic areas remains a challenge. Using appropriate study designs, it is imperative to increase further the knowledge on the various aspects of the parasites and the infestations they cause.

Widespread prevalence of wolbachia in laboratory stocks and the implications for Drosophila research

Wolbachia is an intracellular microbe harbored by a wide variety of arthropods (including Drosophila) and filarial nematodes. Employing several different strategies including male killing, induced parthenogenesis, cytoplasmic incompatibility, and feminization, and acting by as-yet-unknown mechanisms, Wolbachia alters host reproduction to increase its representation within a population. Wolbachia is closely associated with gametic incompatibility but also interacts with Drosophila in other, little understood ways. We report here significant and widespread infection of Wolbachia within laboratory stocks and its real and potential impact on Drosophila research. We describe the results of a survey indicating that approximately 30% of stocks currently housed at the Bloomington Drosophila Stock Center are infected with Wolbachia. Cells of both reproductive tissues and numerous somatic organs harbor Wolbachia and display considerable variation in infection levels within and between both tissue types. These results are discussed from the perspective of Wolbachia's potential confounding effects on both host fitness and phenotypic analyses. In addition to this cautionary message, the infection status of stock centers may provide further opportunities to study the genetic basis of host/symbiosis.

Wolbachia Genomes: Insights into an Intracellular Lifestyle

The genome sequence of the Wolbachia endosymbiont that infects the nematode Brugia malayi has recently been determined together with three partial Wolbachia genomes from different Drosophila species. These data along with the previously published Wolbachia genome from Drosophila melanogaster provide new insights into how this endosymbiont has managed to become so successful.

Macrofilaricidal activity after doxycycline treatment of Wuchereria bancrofti: a double-blind, randomised placebo-controlled trial

BACKGROUND

Wolbachia endosymbionts of filarial nematodes are vital for larval development and adult-worm fertility and viability. This essential dependency on the bacterium for survival of the parasites has provided a new approach to treat filariasis with antibiotics. We used this strategy to investigate the effects of doxycycline treatment on the major cause of lymphatic filariasis, Wuchereria bancrofti.

METHODS

We undertook a double-blind, randomised, placebo-controlled field trial of doxycycline (200 mg per day) for 8 weeks in 72 individuals infected with W bancrofti from Kimang'a village, Pangani, Tanzania. Participants were randomly assigned by block randomisation to receive capsules of doxycycline (n=34) or placebo (n=38). We assessed treatment efficacy by monitoring microfilaraemia, antigenaemia, and ultrasound detection of adult worms. Follow-up assessments were done at 5, 8, 11, and 14 months after the start of treatment. Analysis was per protocol.

FINDINGS

One person from the doxycycline group died from HIV infection. Five (doxycycline) and 11 (placebo) individuals were absent at the time of ultrasound analysis. Doxycycline treatment almost completely eliminated microfilaraemia at 8-14 months' follow-up (for all timepoints p<0.001). Ultrasonography detected adult worms in only six (22%) of 27 individuals treated with doxycycline compared with 24 (88%) of 27 with placebo at 14 months after the start of treatment (p<0.0001). At the same timepoint, filarial antigenaemia in the doxycycline group fell to about half of that before treatment (p=0.015). Adverse events were few and mild.

INTERPRETATION

An 8-week course of doxycycline is a safe and well-tolerated treatment for lymphatic filariasis with significant activity against adult worms and microfilaraemia.

The Wolbachia genome of Brugia malayi: endosymbiont evolution within a human pathogenic nematode

Complete genome DNA sequence and analysis is presented for Wolbachia, the obligate alpha-proteobacterial endosymbiont required for fertility and survival of the human filarial parasitic nematode Brugia malayi. Although, quantitatively, the genome is even more degraded than those of closely related Rickettsia species, Wolbachia has retained more intact metabolic pathways. The ability to provide riboflavin, flavin adenine dinucleotide, heme, and nucleotides is likely to be Wolbachia's principal contribution to the mutualistic relationship, whereas the host nematode likely supplies amino acids required for Wolbachia growth. Genome comparison of the Wolbachia endosymbiont of B. malayi (wBm) with the Wolbachia endosymbiont of Drosophila melanogaster (wMel) shows that they share similar metabolic trends, although their genomes show a high degree of genome shuffling. In contrast to wMel, wBm contains no prophage and has a reduced level of repeated DNA. Both Wolbachia have lost a considerable number of membrane biogenesis genes that apparently make them unable to synthesize lipid A, the usual component of proteobacterial membranes. However, differences in their peptidoglycan structures may reflect the mutualistic lifestyle of wBm in contrast to the parasitic lifestyle of wMel. The smaller genome size of wBm, relative to wMel, may reflect the loss of genes required for infecting host cells and avoiding host defense systems. Analysis of this first sequenced endosymbiont genome from a filarial nematode provides insight into endosymbiont evolution and additionally provides new potential targets for elimination of cutaneous and lymphatic human filarial disease.

Analysis of this Wolbachia genome, which resides within filarial parasites, offers insight into endosymbiont evolution and the promise of new strategies for the elimination of human filarial disease

Analysis of Sarcoptes scabiei finds no evidence of infection with Wolbachia

The endosymbiont Wolbachia has been detected in a range of filarial nematodes and parasitic mites and is known to affect host reproductive compatibility and potentially evolutionary processes. PCR of Wolbachia surface protein (wsp), ftsZ and 16SrRNA genes from individual Sarcoptes scabiei mites obtained from a series of individual hosts, and database searches of an S. scabiei var. hominis EST library failed to detect Wolbachia genes. Therefore, Wolbachia appears not to be involved in the genetic subdivision observed between varieties of host-associated S. scabiei or, involved in the inflammatory disease pathogenesis of scabies unlike its activity in filarial infection.

Wolbachia.Bacterial Endosymbionts of Filarial Nematodes

Filarial nematodes are important helminth parasites of the tropics and a leading cause of global disability. They include species responsible for onchocerciasis, lymphatic filariasis and dirofilariasis. A unique feature of these nematodes is their dependency upon a symbiotic intracellular bacterium, Wolbachia, which is essential for normal development and fertility. Advances in our understanding of the symbiosis of Wolbachia bacteria with filarial nematodes have made rapid progress in recent years. Here we summarise our current understanding of the evolution of the symbiotic association together with insights into the functional basis of the interaction derived from genomic analysis. Also we discuss the contribution of Wolbachia to inflammatory-mediated pathogenesis and adverse reactions to anti-filarial drugs and describe the outcome of recent field trials using antibiotics as a promising new tool for the treatment of filarial infection and disease.

Construction of bacterial artificial chromosome libraries from the parasitic nematode Brugia malayi and physical mapping of the genome of its Wolbachia endosymbiont

The parasitic nematode, Brugia malayi, causes lymphatic filariasis in humans, which in severe cases leads to the condition known as elephantiasis. The parasite contains an endosymbiotic alpha-proteobacterium of the genus Wolbachia that is required for normal worm development and fecundity and is also implicated in the pathology associated with infections by these filarial nematodes. Bacterial artificial chromosome libraries were constructed from B. malayi DNA and provide over 11-fold coverage of the nematode genome. Wolbachia genomic fragments were simultaneously cloned into the libraries giving over 5-fold coverage of the 1.1 Mb bacterial genome. A physical framework for the Wolbachia genome was developed by construction of a plasmid library enriched for Wolbachia DNA as a source of sequences to hybridise to high-density bacterial artificial chromosome colony filters. Bacterial artificial chromosome end sequencing provided additional Wolbachia probe sequences to facilitate assembly of a contig that spanned the entire genome. The Wolbachia sequences provided a marker approximately every 10 kb. Four rare-cutting restriction endonucleases were used to restriction map the genome to a resolution of approximately 60 kb and demonstrate concordance between the bacterial artificial chromosome clones and native Wolbachia genomic DNA. Comparison of Wolbachia sequences to public databases using BLAST algorithms under stringent conditions allowed confident prediction of 69 Wolbachia peptide functions and two rRNA genes. Comparison to closely related complete genomes revealed that while most sequences had orthologs in the genome of the Wolbachia endosymbiont from Drosophila melanogaster, there was no evidence for long-range synteny. Rather, there were a few cases of short-range conservation of gene order extending over regions of less than 10 kb. The molecular scaffold produced for the genome of the Wolbachia from B. malayi forms the basis of a genomic sequencing effort for this bacterium, circumventing the difficult challenge of purifying sufficient endosymbiont DNA from a tropical parasite for a whole genome shotgun sequencing strategy.

The bacterial catalase from filarial DNA preparations derives from common pseudomonad contaminants and not from Wolbachia endosymbionts

Wolbachia are obligatory endosymbionts in many species of filarial nematodes. Certain bacterial molecules induce antibody responses in mammalian hosts infected with filariae, while others activate inflammatory responses that contribute to pathology. These findings, coupled with antibiotic studies demonstrating the dependence of filarial embryogenesis on the presence of Wolbachia, have intensified research on Wolbachia-nematode interactions, and the effects of Wolbachia molecules on the mammalian immune system. By amplification and sequencing of 16S rDNA and catalase sequences, we show that filarial DNA samples prepared from nematodes collected under typical conditions are frequently contaminated with Pseudomonas DNA. Analysis of a published DNA fragment containing a catalase attributed to the Wolbachia of Onchocerca volvulus showed it to be most like Pseudomonas, both in terms of sequence similarity and genomic organization. Additionally, there was no obvious catalase in either of two available Wolbachia genome sequences. Contamination of filarial DNA with bacterial sequences other than Wolbachia can complicate studies of the role of these symbionts in filarial biology.

Population dynamics of Wolbachia bacterial endosymbionts in Brugia malayi

The human filarial nematode Brugia malayi contains an endosymbiotic bacterium, Wolbachia. We used real-time quantitative polymerase chain reaction (QPCR) and microscopy to investigate the population dynamics of the bacterium-nematode association. Two Wolbachia (wsp and ftsZ) and one nematode (gst) genes were amplified from all life-cycle stages of B. malayi and results expressed as gene copies per worm and as Wolbachia/nematode ratios. Since the genes were single copy and there was one genome per Wolbachia, the gene copy numbers were equivalent to the numbers of bacteria. These were similar in microfilariae and the mosquito-borne larval stages (L2 and L3), with the lowest ratios of Wolbachia/nematode DNA. However, within 7 days of infection of the mammalian host, bacteria had increased 600-fold and the bacteria/worm ratio was the highest of all life-cycle stages. The rapid multiplication continued throughout L4 development, so that the major period of bacterial population growth occurred within 4 weeks of infection of the definitive host. Microscopy confirmed that there were few bacteria in mosquito-derived L3 but many, in large groups, in L4 collected 9 and 21 days after infection. In adult male worms up to 15 months of age, the bacterial populations were maintained, whilst in females, bacteria numbers increased as the worms matured and as the ovary and embryonic larval stages became infected. These results support the hypothesis that the bacteria are essential for larval development in the mammalian host and for the long-term survival of adult worms.