Current status and future prospects of the Global Lymphatic Filariasis Programme

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.

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.

An Integrated Approach to Identify New Anti-Filarial Leads to Treat River Blindness, a Neglected Tropical Disease

Filarial worms cause multiple debilitating diseases in millions of people worldwide, including river blindness. Currently available drugs reduce transmission by killing larvae (microfilariae), but there are no effective cures targeting the adult parasites (macrofilaricides) which survive and reproduce in the host for very long periods. To identify effective macrofilaricides, we carried out phenotypic screening of a library of 2121 approved drugs for clinical use against adult Brugia pahangi and prioritized the hits for further studies by integrating those results with a computational prioritization of drugs and associated targets. This resulted in the identification of 18 hits with anti-macrofilaricidal activity, of which two classes, azoles and aspartic protease inhibitors, were further expanded upon. Follow up screening against Onchocerca spp. (adult Onchocerca ochengi and pre-adult O. volvulus) confirmed activity for 13 drugs (the majority having IC50 < 10 μM), and a counter screen of a subset against L. loa microfilariae showed the potential to identify selective drugs that prevent adverse events when co-infected individuals are treated. Stage specific activity was also observed. Many of these drugs are amenable to structural optimization, and also have known canonical targets, making them promising candidates for further optimization that can lead to identifying and characterizing novel anti-macrofilarial drugs.

The use of molecular xenomonitoring for surveillance of mosquito-borne diseases

The scientific community recognizes that molecular xenomonitoring (MX) can allow infected mosquitoes to serve as a proxy for human infection in vector-borne disease surveillance, but developing reliable MX systems for programmatic use has been challenging. The primary aim of this article is to examine the available evidence to recommend how MX can best be used for various purposes. Although much of the literature published within the last 20 years focuses on using MX for lymphatic filariasis elimination, a growing body of evidence supports its use in early warning systems for emerging infectious diseases (EIDs). An MX system design must consider the goal and target (e.g. diseases targeted for elimination versus EIDs), mosquito and pathogen characteristics, and context (e.g. setting and health system). MX is currently used as a 'supplement' to human surveillance and will not be considered as a 'replacement' until the correlation between pathogen-infection rates in human and mosquito populations is better understood. Establishing such relationships may not be feasible in elimination scenarios, due to increasingly dwindling human infection prevalence after successful control, but may still be possible for EIDs and in integrated disease surveillance systems. This article is part of the theme issue 'Novel control strategies for mosquito-borne diseases'.

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.

Immunological evaluation of fusion protein of Brugia malayi abundant larval protein transcript-2 (BmALT-2) and Tuftsin in experimental mice model

Introduction

Filariasis, a neglected tropical helminth disease needs vaccine besides mass drug administration for its successful eradication.

Methods

An attempt was made to produce a fusion protein (P-TUFT-ALT-2) of abundant larval transcript protein-2 and Tuftsin to enhance its immunogenicity. The fusion construct was expressed in Pichia pastoris, a nonexpensive commercial expression system. This study focused on the evaluation of immunological response produced by P-TUFT-ALT-2 in Balb/c mice.

Result and discussion

P-TUFT-ALT-2 showed an enhanced IgG peak titre compared to E. coli expressed E-ALT-2 and P. pastoris expressed P-ALT-2. IgG2b, IgG2a and IgG1 production were predominant indicating a balanced Th1/Th2 response. P-TUFT-ALT-2 also induced about 28% and 9.5% higher splenocyte proliferation over control and E-ALT-2 respectively. Splenocytes produced predominant IFN-γ followed by IL-5, IL-2 and IL-10 specifying a balanced Th1/Th2 response. P-TUFT-ALT-2 showed 55% to 80% with an average of 65% cytotoxicity in B. malayi L3 larvae in in vitro ADCC assay.

Conclusion

This experiment validates P-TUFT-ALT-2 as a potential vaccine candidate for human lymphatic filariasis.

Cloning, large-scale production and characterization of fusion protein (P-TUFT-ALT-2) of Brugian abundant larval transcript-2 with tuftsin in Pichia pastoris

Lymphatic filariasis is a "disease of poor people" due to a large section of affected people with economic backwardness. Therefore, successful elimination of this disease requires a cost-effective prophylactic agent such as vaccine along with conventional drugs. The Abundant Larval Transcript-2 (BmALT-2) protein of Brugia malayi has been recognized as the most potential vaccine candidate. Tuftsin, a tetra-peptide immunopotentiator has already shown the enhanced immunogenicity of various vaccine antigens in earlier studies. This study deals with the development of tuft-alt-2 fusion construct and a suitable culture condition for its large-scale production in Pichia pastoris. The recombinant P. pastoris/tuft-alt-2 with 9-11 copies of the gene construct exhibited the highest expression level. The molecular weight of P-TUFT-ALT-2 was determined as 28 kDa in SDS-PAGE including 3 kDa due to glycosylation. The dry cell biomass was 57.4 gL^-1 in the bioreactor. The P-TUFT-ALT-2 expression was measured as about 35 mg L^-1, which was 102% higher than flask culture. The P-TUFT-ALT-2 produced the highest 65,000 IgG peak titer in Balb/c mice. Moreover, P-TUFT-ALT-2 exhibited about 9.46% higher splenocyte proliferation than E. coli expressed E-ALT-2 alone. The enhanced secreted production of P-TUFT-ALT-2 in bioreactor would step up its commercialization as an inexpensive commercial vaccine for human lymphatic filariasis.

Elucidation of immunological response and its regulatory network by P-TUFT-ALT-2: a promising fusion protein vaccine for human lymphatic filariasis

Human lymphatic filariasis, a mosquito-borne neglected tropical parasitic disease, needs an early development of prophylactic agents such as a vaccine for its successful elimination. Our earlier study suggested the enhanced immunological response by fusion protein (P-TUFT-ALT-2) of Tuftsin and ALT-2 in a mice model. We cultured human peripheral blood mononuclear cells (PBMCs) and treated cells with Escherichia coli-expressed ALT-2 (E-ALT-2) and P-TUFT-ALT-2. Real-time polymerase chain reaction was performed to identify the mRNA copy number of various cytokine and transcription factor genes. The recombinant vaccine candidate was also validated for humans by immunoreactivity with human sera samples of natural infection. In this study, P-TUFT-ALT-2 stimulated 12% higher PBMC proliferation in endemic normal (EN) individuals than E-ALT-2 alone. There was enhanced production of IFN γ, IL-2, IL-5 and IL-12, indicating a balanced Th1/Th2 response. However, higher expression of IL-5 and lower IL-4 validate the humoral response through an IL-5-dependent manner. Also, high level of IL-17 indicates a strong Th/Treg regulation over T-cell activation. The upregulated T-bet might have enhanced IFN-γ production, whereas GATA-3 was supposed to enhance IL-5 expression. The fusion protein also exhibited 15-16% higher reactivity with EN clinical sera, exposing the upregulation of IgG1 and IgM in natural infection. The higher reactivity of P-TUFT-ALT-2 with sera of natural infection (EN) was validated indirectly by B-cell activation through various cytokines and regulatory genes produced from different T cells. Thus, these findings endorse P-TUFT-ALT-2 as a potential vaccine candidate for human lymphatic filariasis.

In search of a potential diagnostic tool for molecular characterization of lymphatic filariasis

Lymphatic filariasis (LF) is a chronic disease and is caused by the parasites Wuchereria bancrofti (W. bancrofti), Brugia malayi (B. malayi) and Brugia timori (B. timori). In the present study, Setaria cervi (S. cervi), a bovine filarial parasite has been used. Previously, it has been reported that the S. cervi shares some common proteins and antigenic determinants with that of human filarial parasite. The larval stages of filarial species usually cannot be identified by classical morphology. Hence, molecular characterization allows the identification of the parasites throughout all their developmental stages. The genomic DNA of S. cervi adult were isolated and estimated spectrophotometrically for the quantitative presence of DNA content. Screening of DNA sequences from filarial DNA GenBank and Expressed Sequence Tags (EST's) were performed for homologous sequences and then multiple sequence alignment was executed. The conserved sequences from multiple sequence alignment were used for In Silico primer designing. The successfully designed primers were used further in PCR amplifications. Therefore, in search of a promising diagnostic tool few genes were identified to be conserved in the human and bovine filariasis and these novel primers deigned may help to develop a promising diagnostic tool for identification of lymphatic filariasis.

Potential involvement of Brugia malayi cysteine proteases in the maintenance of the endosymbiotic relationship with Wolbachia

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Bm-cpl-3 and Bm-cpl-6 are involved during development and endosymbiosis.

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In tetracycline-treated worms Bm-cpl-3 and -6 are regulated in a bimodal pattern.

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Reduction in Bm-cpl-3 and -6 levels resulted in hindered microfilarial development.

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Reduction in Bm-cpl-3 and -6 levels resulted in reduced Wolbachia DNA levels.

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These enzymes might be strong drug target candidates.

Brugia malayi, a parasitic nematode that causes lymphatic filariasis, harbors endosymbiotic intracellular bacteria, Wolbachia, that are required for the development and reproduction of the worm. The essential nature of this endosymbiosis led to the development of anti-Wolbachia chemotherapeutic approaches for the treatment of human filarial infections. Our study is aimed at identifying specific proteins that play a critical role in this endosymbiotic relationship leading to the identification of potential targets in the adult worms. Filarial cysteine proteases are known to be involved in molting and embryogenesis, processes shown to also be Wolbachia dependent. Based on the observation that cysteine protease transcripts are differentially regulated in response to tetracycline treatment, we focused on defining their role in symbiosis. We observe a bimodal regulation pattern of transcripts encoding cysteine proteases when in vitro tetracycline treated worms were examined. Using tetracycline-treated infertile female worms and purified embryos we established that the first peak of the bimodal pattern corresponds to embryonic transcripts while the second takes place within the hypodermis of the adult worms. Localization studies of the native proteins corresponding to Bm-cpl-3 and Bm-cpl-6 indicate that they are present in the area surrounding Wolbachia, and, in some cases, the proteins appear localized within the bacteria. Both proteins were also found in the inner bodies of microfilariae. The possible role of these cysteine proteases during development and endosymbiosis was further characterized using RNAi. Reduction in Bm-cpl-3 and Bm-cpl-6 transcript levels was accompanied by hindered microfilarial development and release, and reduced Wolbachia DNA levels, making these enzymes strong drug target candidates.

Diversity and expression of microRNAs in the filarial parasite, Brugia malayi

Human filarial parasites infect an estimated 120 million people in 80 countries worldwide causing blindness and the gross disfigurement of limbs and genitals. An understanding of RNA-mediated regulatory pathways in these parasites may open new avenues for treatment. Toward this goal, small RNAs from Brugia malayi adult females, males and microfilariae were cloned for deep-sequencing. From ∼30 million sequencing reads, 145 miRNAs were identified in the B. malayi genome. Some microRNAs were validated using the p19 RNA binding protein and qPCR. B. malayi miRNAs segregate into 99 families each defined by a unique seed sequence. Sixty-one of the miRNA families are highly conserved with homologues in arthropods, vertebrates and helminths. Of those miRNAs not highly conserved, homologues of 20 B. malayi miRNA families were found in vertebrates. Nine B. malayi miRNA families appear to be filarial-specific as orthologues were not found in other organisms. The miR-2 family is the largest in B. malayi with 11 members. Analysis of the sequences shows that six members result from a recent expansion of the family. Library comparisons found that 1/3 of the B. malayi miRNAs are differentially expressed. For example, miR-71 is 5–7X more highly expressed in microfilariae than adults. Studies suggest that in C.elegans, miR-71 may enhance longevity by targeting the DAF-2 pathway. Characterization of B. malayi miRNAs and their targets will enhance our understanding of their regulatory pathways in filariads and aid in the search for novel therapeutics.

New strategies to combat filariasis

Two of the major filarial infections, lymphatic filariasis (LF) and onchocerciasis, affect 150 million people, while 1 billion living in endemic areas are at risk of infection. Public health programs to control these infections have successfully existed for years and have evolved from activities driven by the WHO into global programs with public-private partnerships. Currently, these programs use yearly mass application of drugs that mainly kill the larval stages (the microfilariae), with the aim of preventing uptake by the transmitting insect vectors and thus, to block transmission and reduce the infections to such levels that in 15-30 years from now, they will no longer pose a public health problem. While the programs have been very successful in general, there are drawbacks such as coverage being too low within the population, reappearance of infection by migration of infected people into controlled areas, targeting of a stage (the microfilaria) that does not induce pathology in LF and thus lowers compliance, and the potential development of drug resistance, first indications of which have been clearly observed in onchocerciasis. In addition, even without drawbacks, program scopes are not the eradication of filarial infections, which is, however, an ultimate goal of control activities. There is therefore an unequivocal call for the development of higher efficient, complementary chemotherapeutical approaches that lead to a long-lasting reduction of the pathology-inducing worm stages; that is, microfilariae in onchocerciasis and adult worms in LF, or to a macrofilaricidal effect. The recent discovery that depletion of Wolbachia endosymbionts by tetracycline antibiotics leads to long-lasting sterility of adult female worms in onchocerciasis and a macrofilaricidal effect in LF fulfils these requirements. Successful regimens have already been published and agreed upon for use by expert panels. While these regimens are still too long for mass application, the antiwolbachial chemotherapy can currently be applied in the form of a suitable doxycycline regimen for 6 weeks for the treatment of individuals, and exploited in the future for the development of new drugs suitable for mass application. In addition, first data suggest that Wolbachia may also be major mediators of lymphangiogenesis and that their depletion is associated with reduction of lymph vessel-specific vascular endothelial growth factors and reduced lymph vessel size.

Socioeconomic burden of lymphatic filariasis in Georgetown, Guyana

OBJECTIVE

To assess the socioeconomic impact of lymphatic filariasis (LF) in Guyana.

METHODS

Observational, cross-sectional study of 50 persons with chronic LF attending the Filariasis Clinic who were selected as the cases; and 50 persons with chronic skin conditions but no chronic LF, attending the Skin Clinic who were selected as the controls. The two groups were assessed using semi-structured interviews.

RESULTS

Socioeconomic impact was statistically significant, especially with respect to 'having to change jobs' and experiencing major emotional and financial changes (P < 0.05). Fifty-six per cent of cases reported a major change since their diagnosis, whereas only 32% of controls did. Cases were less likely to be able to dress themselves and walk inside and outside the house than controls; they were three times more likely to spend money on transportation than controls (OR, 3.04 95% CI 1.11, 8.44).

CONCLUSION

Patients with chronic LF face a considerable burden, which should be addressed as part of the Elimination Programme. One way in which this can be done is to provide free transportation for patients with chronic LF to and from Filariasis Clinics.

Cloning and characterization of high mobility group box protein 1 (HMGB1) of Wuchereria bancrofti and Brugia malayi

A human homologue of high mobility group box 1 (HMGB1) protein was cloned and characterized from the human filarial parasites Wuchereria bancrofti and Brugia malayi. Sequence analysis showed that W. bancrofti HMGB1 (WbHMGB1) and B. malayi HMGB1 (BmHMGB1) proteins share 99 % sequence identity. Filarial HMGB1 showed typical architectural sequence characteristics of HMGB family of proteins and consisted of only a single HMG box domain that had significant sequence similarity to the pro-inflammatory B box domain of human HMGB1. When incubated with mouse peritoneal macrophages and human promyelocytic leukemia cells, rBmHMGB1 induced secretion of significant levels of pro-inflammatory cytokines such as TNF-α, GM-CSF, and IL-6. Functional analysis also showed that the filarial HMGB1 proteins can bind to supercoiled DNA similar to other HMG family of proteins. BmHMGB1 protein is expressed in the adult and microfilarial stages of the parasite and is found in the excretory secretions of the live parasites. These findings suggest that filarial HMGB1 may have a significant role in lymphatic pathology associated with lymphatic filariasis.

Characterization of cofactor-independent phosphoglycerate mutase isoform-1 (Wb-iPGM) gene: a drug and diagnostic target from human lymphatic filarial parasite, Wuchereria bancrofti

The inter-conversion of 3-phosphoglycerate and 2-phosphoglycerate during glycolysis and gluconeogenesis in filarial nematodes, is catalyzed by a co-factor-independent phosphoglycerate mutase (iPGM). The gene encoding iPGM isoform-1 was amplified from Wuchereria bancrofti, the major causative agent of human lymphatic filariasis. Partial genomic DNA (gDNA) fragment of the gene was also amplified from periodic and sub-periodic forms of W. bancrofti and Brugia malayi and sequenced. The Wb-iPGM isoform-1 gene encodes an ORF of 515 amino acids and is found to share 99.4%, 96.0%, and 64.0% amino acid sequence identity with iPGM of B. malayi, Onchocerca volvulus, and Caenorhabditis elegans, respectively. Serine and all the other 13 amino acid residues involved in the catalytic function of iPGM are highly conserved. Further comparison of iPGM nucleotide and amino acid sequences of Wolbachia of B. malayi with Wb-iPGM showed 41% and 54.4% similarity, respectively. The analysis of partial genomic and amino acid sequences and phylogenetic tree of Wb-iPGM indicated that this gene, apart from being a potential drug target, could provide diagnostic, taxonomical, and evolutionary markers. This is the first report of the characterization of iPGM gene from W. bancrofti.

Filaria monitoring visualization system: a geographical information system-based application to manage lymphatic filariasis in Andhra Pradesh, India

Among various public health diseases, filariasis constitutes a major public health problem in India, wherein an estimated 553.7 million people are at risk of infection. The aim of this article is to present a spatial mapping and analysis of filariasis data over a 3-year period (2004-2007) from Karimnagar, Chittoor, East and West Godavari districts of Andhra Pradesh, India. The data include epidemiological and entomological studies (i.e., infection rate, infectivity rate, mosquito per man hour, and microfilaria rate). These parameters were customized on Geographical Information System (GIS) platform and developed filaria monitoring visualization system (FMVS) for identifying the endemic/risk areas of filariasis among these four districts. GIS map for filariasis transmission from the study areas was created and stratified into different spatial entities like low, medium, and high risk zones. On the basis of the data and FMVS maps, it was demonstrated that filariasis remained unevenly distributed within the districts. Balancing the intervention coverage in different villages with overall mass drug administration and continued promotion of the proper use of control measures are necessary for further reduction of filarial cases in these districts.

Lymphatic filariasis mapping by immunochromatographic test cards and baseline microfilaria survey prior to mass drug administration in Sierra Leone

Background

National mapping of lymphatic filariasis (LF) was conducted using Immunochromatographic tests (ICT) in 2005 to determine endemicity and geographic spread of the disease. A baseline microfilaria survey was then conducted to determine LF prevalence and microfilaria intensity.

Methods

In 2005 1,982 persons of 15 years and over from 14 health districts were selected and fingertip blood samples were tested with ICT cards. In 2007-8 blood samples were taken between 10 p.m. and 2 a.m. and examined for microfilaria (mf) from 9,288 persons from 16 sentinel sites representing each district and 2 additional sites for districts with populations over 500,000 (Bo and Kenema).

Results

The overall LF prevalence by ICT cards was 21% (males 28%, females 15%). All districts had a prevalence of Wuchereria bancrofti antigen > 1%. Distribution of LF prevalence showed a strong spatial correlation pattern with high prevalence in a large area in the northeast gradually decreasing to a relatively low prevalence in the southwest coast. High prevalence was found in the northeast, Bombali (52%), Koinadugu (46%), Tonkolili (37%) and Kono (30%). Low prevalence was found in the southwest, Bonthe (3%) and Pujehun (4%). The mf prevalence was higher in the northeast: Bombali, 6.7%, Koinadugu 5.7%, Port Loko 4.4% and Kono 2.4%. Overall there was a significant difference in mf prevalence by gender: males 2.9%, females 1.8% (p = 0.0002) and within districts in Kailahun, Kono, Port Loko, Moyamba and Koinadugu (all p < 0.05). The mf prevalence was higher in people > 20 years (2.5%) than in people ≤ 20 years (1.7%) (p = 0.043). The overall arithmetic mean mf density was 50.30 mf/ml among mf-positive individuals and 1.19 mf/ml in the population examined which varied significantly between districts.

Conclusions

The ICT results showed that LF was endemic nationwide and that preventive chemotherapy (PCT) was justified across the country. Both the ICT and microfilaraemia surveys found that prevalence was greater in males than females. The increase in microfilaraemia prevalence by age was evident when grouped as ≤ 20 versus > 20 years demonstrating early exposure. Baseline LF microfilaria load will be used to monitor PCT program progress.

Towards novel antifilarial drugs: challenges and recent developments

Filariasis is caused by thread-like nematode worms, classified according to their presence in the vertebrate host. The cutaneous group includes Onchocerca volvulus, Loa loa and Mansonella streptocerca; the lymphatic group includes Wuchereria bancrofti, Brugia malayi and Brugia timori and the body cavity group includes Mansonella perstans and Mansonella ozzardi. Lymphatic filariasis, a mosquito-borne disease, is one of the most prevalent diseases in tropical and subtropical countries and is accompanied by a number of pathological conditions. In recent years, there has been rapid progress in filariasis research, which has provided new insights into the pathogenesis of filarial disease, diagnosis, chemotherapy, the host–parasite relationship and the genomics of the parasite. Together, these insights are assisting the identification of novel drug targets and the discovery of antifilarial agents and candidate vaccine molecules. This review discusses the antifilarial activity of various chemical entities, the merits and demerits of antifilarial drugs currently in use, their mechanisms of action, in addition to antifilarial drug targets and their validation.

Human thelaziasis, Europe

Thelazia callipaeda eyeworm is a nematode transmitted by drosophilid flies to carnivores in Europe. It has also been reported in the Far East in humans. We report T. callipaeda infection in 4 human patients in Italy and France.

The geographical distribution of lymphatic filariasis infection in Malawi

Mapping distribution of lymphatic filariasis (LF) is a prerequisite for planning national elimination programmes. Results from a nation wide mapping survey for lymphatic filariasis (LF) in Malawi are presented. Thirty-five villages were sampled from 23 districts excluding three districts (Karonga, Chikwawa and Nsanje) that had already been mapped and Likoma, an Island, where access was not possible in the time frame of the survey. Antigenaemia prevalence [based on immunochromatographic card tests (ICT)] ranged from 0% to 35.9%. Villages from the western side of the country and distant from the lake tended to be of lower prevalence. The exception was a village in Mchinji district on the Malawi-Zambia border where a prevalence of 18.2% was found. In contrast villages from lake shore districts [Salima, Mangochi, Balaka and Ntcheu (Bwanje valley)] and Phalombe had prevalences of over 20%.

A national map is developed which incorporates data from surveys in Karonga, Chikwawa and Nsanje districts, carried out in 2000. There is a marked decline in prevalence with increasing altitude. Further analysis revealed a strong negative correlation (R² = 0.7 p < 0.001) between altitude and prevalence. These results suggest that the lake shore, Phalombe plain and the lower Shire valley will be priority areas for the Malawi LF elimination programme. Implications of these findings as regards implementing a national LF elimination programme in Malawi are discussed.

Delivery strategy of mass annual single dose DEC administration to eliminate lymphatic filariasis in the urban areas of Pondicherry, South India: 5 years of experience

BACKGROUND

The recommended strategy for elimination of Lymphatic filariasis is single-dose, once-yearly mass treatment with anti-filarial drugs and the program is in operation on a national level in India. Rate of coverage and consumption is the most crucial factor in the success of Mass Drug Administration (MDA) program. In spite of massive efforts, the program demonstrated sub-optimal coverage and consumption in urban areas than rural. The involvement of Anganwadi workers (AWWs) of the Integrated Child Development Scheme (ICDS) as communicators and drug distributors was attempted to enhance the coverage and consumption in urban areas and the results presented here.

METHODS

An annual single dose MDA program was launched under the auspices of Freedom From Filariasis (FFF) program in Pondicherry, India, in the year 1997 and continued for five years. A questionnaire survey was carried out following all the treatment rounds (TRs) for assessing coverage of distribution and consumption Five percent of randomly selected households constituted the sample. All the members available in the selected household at the time of interview formed the respondent of the study.

RESULTS

The coverage of drug distribution during the TRs varied from 74.3 to 95.4 percent and consumption rate from 52.9 to 78.8. Among the respondents, 71% were aware of the MDA program and the source of information for 62.8% of them was through personal communication by the AWW. It was observed that 33.2% of the respondents who accepted the drug did so based on the trust on the AWW as a government representative. The main reason for non-consumption in all TRs was fear of side reaction (25.4 - 42.2%).

CONCLUSION

The delivery-strategy of health information and Diethylcarbamazine (DEC) drug to the urban community using the AWWs could achieve relatively higher coverage and consumption than reported in other urban areas. In order to achieve the optimum level, it is imperative to equip the AWWs with current knowledge and skills, and design innovative Information, Education and Communication (IEC) campaign to target the less compliant groups. The beneficial effect of this delivery strategy may be used in similar urban settings to achieve the elimination of LF.

Brugia malayi Adult Low Molecular Weight IgG4-Reactive Antigens Induce Differential Cytokine Response in Lymphocytes of Endemic Normal and Asymptomatic Microfilariae Carriers In Vitro

To characterize putatively protective immune response in bancroftian filariasis, Th1/Th2 cytokine profile induced in peripheral blood mononuclear cells (PBMCs) of endemic normal (EN) and asymptomatic microfilaremic (ASM) individuals were studied using different molecular weight fractions of Brugia malayi adult soluble antigens (BmA), which are differentially recognized by IgG4 antibodies present in their sera. Infection free and putatively immune individuals living in a filaria endemic area were identified and included in the present study as EN only after careful longitudinal follow up for three years. It was observed that the low molecular weight antigens present in Fr4 and Fr5 induced differential cytokine response; EN individuals showed a strong Th1 bias whereas ASM individuals showed a strong Th2 bias even though both the groups produced Th1 cytokines, albeit of different quantity, when a nonhelminthic antigen like H37Rv whole cell lysate was used. Since antigens present in Fr5 induced a highly polarized response, they should be examined for their diagnostic potential in lymphatic filariasis.

Determination of the prevalence of lymphatic filariasis among migrant workers in Kuwait by detecting circulating filarial antigen

The main objective of this study was to determine the prevalence of filarial infection among migrant workers in Kuwait. The study was conducted from April 2000 to November 2003. A total of 1050 migrant workers (>90 % from the Indian subcontinent) from filarial endemic countries and 260 individuals residing in Kuwait as controls (50 healthy Kuwaiti blood donors, 50 microfilaria-negative individuals from endemic areas and 160 patients with other parasitic infections) were screened for filarial infection. All specimens were tested for microfilaraemia by microscopy of nucleopore-filtered blood (NFB) and detection of circulating filarial antigen (CFA) by an immunochromatographic test (ICT) and the TropBio assay. The overall prevalence of filarial antigenaemia was 18·3 % (192 individuals) using the ICT and 20·3 % (213 individuals) using the TropBio assay. Thirty-two cases (3 %) of Wuchereria bancrofti were detected by microscopy and the mean microfilaria count in these cases was 816 microfilariae ml−1. CFA was detected only in two of the 260 control subjects. Statistical analysis to calculate the sensitivity, specificity and prevalence of infection was carried out using maximum-likelihood statistical methods. The overall sensitivity and specificity of the ICT and TropBio assay to detect CFA were comparable. Compared with NFB microscopy, the sensitivity of the ICT was 93·8 % and specificity ranged from 84 to 100 %. The sensitivity and specificity of the TropBio assay were 90·1 and 100 %, respectively. However, the ICT failed to detect CFA in two cases with a microfilarial load of <20 microfilariae ml−1. In conclusion, the prevalence of filarial infection among the migrant workers in Kuwait was 18·3 % as determined by the ICT.

New initiatives against Africa's worms

Since 1999, the funding available for the control of diseases of poverty (neglected diseases) has increased mainly due to leverage resulting from donations by the Bill and Melinda Gates Foundation and loans from the World Bank. Many countries have embarked on control programmes on a national scale due to drug donations by pharmaceutical companies through vertical programmes. The Schistosomiasis Control Initiative has expanded its operations to cover six countries in sub-Saharan Africa, but overlap of treatments between different vertical programmes is now a reality, and so care is needed to ensure that too many different drugs are not given together. Dialogue between programme managers has increased, and integration of some programmes may offer chances of synergy.

Mass chemotherapy options to control lymphatic filariasis: a systematic review

Understanding the efficacy of microfilaricidal drugs is important in guiding the global programme for the elimination of lymphatic filariasis as a public-health problem. We did a systematic review of the available literature to determine which currently available drug intervention most effectively decreases circulating Wuchereria bancrofti microfilaria in individuals and populations. 57 randomised studies of drug efficacy were identified. Data were combined and compared using weighted mean effect estimates taking into account the longitudinal nature of the data. Combined treatment with diethylcarbamazine plus ivermectin, diethylcarbamazine plus albendazole, and ivermectin plus albendazole resulted in average microfilarial intensity decreases that were 0.7%, 4.6%, and 12.7% of the pre-treatment values, respectively. Drug combinations containing diethylcarbamazine were the most effective against microfilarial prevalence and intensity relative to single drugs or other combinations. The relative efficacies of drug combinations have not been well documented from existing studies and therefore limit the application of evidenced-based recommendations for chemotherapy-based interventions to control lymphatic filariasis. These results provide valuable estimates of drug effect using existing data, but highlight the need for more comprehensive comparative drug studies.

Modeling analysis of GST (glutathione-S-transferases) from Wuchereria bancrofti and Brugia malayi

GST (glutathione S-transferases) are a family of detoxification enzymes that catalyze the conjugation of reduced GSH (glutathione) to xenobiotic (endogenous electrophilic) compounds. GST from Wb (Wuchereria bancrofti) and Bm (Brugia malayi) are significantly different from human GST in sequence and structure. Thus, Wb-GST and Bm-GST are potential chemotherapeutic targets for anti-filarial treatment. Comparison of modeled Wb and Bm GST with human GST show structural difference between them. Analysis of the active site residues for the binding of electrophilic co-substrates provides insight towards the design of parasite specific GST inhibitors.

Observations on false positive reactions in the rapid NOW Filariasis card test

The NOW Filariasis card test is a useful tool for rapid field diagnosis of Wuchereria bancrofti infection, based on detection of specific circulating filarial antigen (CFA) in the patients' blood. Concern has been raised that a high proportion of infection negative individuals develop false positive reactions in these tests when the test cards are left for a prolonged period before being examined. We carried out a survey in an endemic Tanzanian village to investigate this phenomenon. Individuals who were positive in the NOW Filariasis test at 10 min after specimen application were also positive in the TropBio ELISA for CFA, and thus appeared to be truly positive. Many of the test cards that were negative at 10 min developed a positive line later, but these lines appeared to be falsely positive when the TropBio test was used as the gold standard. Close examination revealed that true and false positivity lines could be distinguished on their shape and colour. The study thus reaffirmed that test cards should be read after 10 min to avoid false positives, but it also indicated that experienced test card users should be able to make a correct diagnosis even at a later time.

The role of endosymbiotic Wolbachia bacteria in filarial disease

In this review, we describe the pathogenic role of Wolbachia endosymbiotic bacteria in filarial diseases, focusing on the host innate immune responses to filarial and Wolbachia products. A description of the host pathogen recognition and early inflammatory responses including TLR4-mediated signalling, chemokine and cytokine responses and inflammatory cell recruitment is provided from human studies and from animal models of filarial disease. Finally, the impact of the discovery and characterization of Wolbachia on filarial research and treatment programmes is discussed.

Impact of long-term ivermectin (Mectizan) on Wuchereria bancrofti and Mansonella perstans infections in Burkina Faso: strategic and policy implications

Parasitological and clinical surveys were used to determine the long-term impact of ivermectin on the prevalence of Wuchereria bancrofti and Mansonella perstans filarial infections, when the drug was given under community-directed-treatment strategies for onchocerciasis control. The study was undertaken in 11 communities in south-western Burkina Faso. Six of the villages investigated had been treated with ivermectin at least once a year for five of 6 years, with a mean coverage of approximately 65% in each round. The other five, adjacent villages, which were matched with the ivermectin-treated communities by size, ethnicity and social and economic activities, had never been treated because they were not endemic for onchocerciasis. Each subject was checked by the microscopical examination of a smear of 'night' blood, by measurement of the level of circulating antigens from adult W. bancrofti, and by clinical examination for hydrocele (if male) and lymphoedema. The prevalences of lymphoedema and hydrocele in the treated villages were similar to those in the untreated. The prevalences and intensities of W. bancrofti and M. perstans microfilaraemia were, however, significantly lower in the ivermectin-treated communities. The implications of this study are discussed in relation to the old Onchocerciasis Control Programme (OCP) and to the ongoing African Programme for Onchocerciasis (APOC), where extensive and sustained ivermectin distribution is planned through community-based treatment programmes. As with onchocerciasis in Africa, the success of annual treatments to control lymphatic filariasis will depend not only on the number of regular rounds of treatment given but on adequate coverages being achieved in each round. Wherever ivermectin is being distributed alone, for onchocerciasis control, its impact on other filarial infections, notably W. bancrofti, should be evaluated routinely. Any opportunity to add donated albendazole to such distributions should be taken, both to limit the transmission of W. bancrofti and for the wider public-health benefits.

Control of filarial infections: not the beginning of the end, but more research is needed

PURPOSE OF REVIEW

Infections with the filarial nematodes affect more than 150 million people mainly in the tropics. The very successful efforts to control filarial infections, however, have to be sustained by new tools that require long-term commitment to research. This review, focusing on reports from 2002 and 2003, highlights recent advances in research on immunology, understanding of pathogenesis and drug development in lymphatic filariasis and onchocerciasis research with potential relevance to the generation of new tools for control.

RECENT FINDINGS

Dramatic improvement has been achieved in the control of lymphatic filariasis and onchocerciasis by vector control and mass treatment with microfilaricidal drugs. Additional tools that could help in regional elimination or, ultimately, eradication of filariasis may arise from the development of new drugs or a vaccine. Research into the immune responses mediating protection or pathology has provided new insights into the pathways that lead to effector function and immunosuppression, such as T regulatory responses, as well as into genetic predispositions from the host's side, and to the identification of vaccine candidates that show protection in animal models. Recognition of the role the Wolbachia endosymbionts may play in activating the innate immune system has altered our understanding of immunopathology of filariasis and adverse reactions to microfilaricidal drugs. Wolbachia spp. have also proven to be suitable targets for the development of a long-term sterilizing or potentially macrofilaricidal drug.

SUMMARY

This review summarizes recent developments in the control of filariasis, in particular lymphatic filariasis and onchocerciasis, as well as in modern research into the immunity of filariasis and new drug development that could lead to additional tools necessary for sustained success in filariasis control.

Cloning and biochemical characterization of blisterase, a subtilisin-like convertase from the filarial parasite, Onchocerca volvulus

Blisterase is a subtilisin-like proprotein convertase of nematodes. The enzyme is named after the blistered cuticle found in Caenorhabditis elegans with the bli-4 e937 mutation. The critical role of the enzyme in cuticle production makes it a potential drug target for parasitic nematodes. We have cloned and expressed blisterase from the parasitic nematode Onchocerca volvulus, a major cause of blindness in Africa. The catalytic domain of the protease exhibits 84% identity with the corresponding domain of its closest homologue, C. elegans blisterase. O. volvulus blisterase expressed in insect cells has maximal activity in 1 mm calcium at neutral pH. The protease is inhibited by EDTA, the suicide substrate decanoyl-RVKR-chloromethylketone, alpha1-antitrypsin Portland and by its own propeptide. Substrate assays with fluorescent peptides show that O. volvulus blisterase requires a P4 arginine and a basic amino acid at P1 for cleavage. The kcat of blisterase on the peptide substrate, t-butyloxycarbonyl-RVRR-4-methylcoumaryl-7-amide was determined to be 0.018 s-1. In vitro cleavage studies with the nematode polyprotein antigen demonstrated that blisterase cleaved at tetrabasic (RRKR) but not at dibasic (KR) sites. This report describes the first biochemical characterization of the nematode specific protease, blisterase.

Thioredoxin from Brugia malayi: defining a 16-kilodalton class of thioredoxins from nematodes

Thioredoxins are a family of small redox proteins that undergo NADPH-dependent reduction by thioredoxin reductase. This results in a supply of reducing equivalents that cells use in a wide variety of biological reactions, which include maintaining reduced forms of the enzymes important for protection against damage from high-energy oxygen radicals, the regulation of transcription factor activity, and the inhibition of apoptosis. Here we report on a new member of the thioredoxin family of proteins from the filarial nematode Brugia malayi, Bm-TRX-1, which defines a new subclass of 16-kDa thioredoxins that occur widely in nematodes, including Caenorhabditis elegans. In addition to being larger than the thioredoxins found in mammalian and bacterial species, the putative active site sequence of Bm-TRX-1, WCPPC, does not conform to the highly conserved WCGPC reported for thioredoxins from mammals to bacteria. Interestingly, an allelic form of Bm-TRX-1 was identified with an active site sequence WCPQC, which appears to be unique to the thioredoxins from filarial species. Bm-TRX-1 was between 98% and 35% identical to thioredoxins from other nematodes and approximately 20% identical to the thioredoxins from mammals and Escherichia coli. Bm-TRX-1 was constitutively transcribed throughout the B. malayi life cycle, and Bm-TRX protein was detectable in somatic extracts and excretory-secretory products from adults and microfilariae. Recombinant Bm-TRX-1 had thiodisulfide reductase activity, as measured by the reduction of insulin, and protected DNA from the nicking activity of oxygen radicals. Overexpression of Bm-TRX-1 in a human monocyte cell line negatively regulated tumor necrosis factor alpha-induced p38 mitogen-activated protein kinase activity, suggesting a possible role of the 16-kDa Bm-TRX-1 in immunomodulation.

Wolbachia in the inflammatory pathogenesis of human filariasis

Filarial nematodes cause some of the most debilitating diseases in tropical medicine. Recent studies, however, have implicated the parasites' endosymbiotic Wolbachia bacteria, rather than the nematode, as the cause of inflammatory-mediated filarial disease. Soluble extracts of a variety of filarial species stimulate innate inflammatory responses, which are absent or reduced when using extracts derived from species either devoid of bacteria, or those cleared of bacteria by antibiotics. Characterization of the molecular nature of the bacterial derived inflammatory stimulus points toward an endotoxin-like activity that is dependent on the pattern recognition receptors CD14 and TLR4 and can be inhibited by lipid A antagonists. TLR4 dependent inflammation has been shown to occur in the systemic inflammatory adverse reaction to Brugia malayi following anti-filarial chemotherapy and in the development of neutrophil-mediated ocular inflammation in a mouse model of river blindness. The development of acute and severe inflammatory responses in people infected with Brugia malayi and Onchocerca volvulus is associated with the release of Wolbachia into the blood following death or damage of the worms after anti-filarial chemotherapy. Together these studies suggest that Wolbachia are the principal cause of acute inflammatory filarial disease. Accumulated exposure to acute episodes of inflammation may also underlie the development of chronic filarial pathology. The use of antibiotic therapy to target Wolbachia of filarial parasites may therefore provide a means to prevent the development of filarial pathology.

Lymphatic filariasis in the Karonga district of northern Malawi: a prevalence survey

In Malawi, two main foci of lymphatic filariasis (LF) are known to exist: one in the south, in the Shire valley, and the other in the north, along the Songwe River, on the border with Tanzania. There have been no formal surveys in the Songwe area since the 1960s but an opportunity arose in 2000-2001 to map LF in this area, in the context of a leprosy survey that formed part of the follow-up of a large leprosy and tuberculosis vaccine trial. Overall 687 immunochromatographic (ICT) tests were carried out. Wuchereria bancrofti antigenaemia was found in > 25% of adults in each of the 12 villages sampled (four in the Songwe area and eight in the rest of the Karonga district), with village prevalences varying from 28%-58%. Of the 685 adult male residents of the Songwe area who were each given full-body clinical examinations, 80 (11.7%) were identified as cases of hydrocele. Lymphoedema was found in seven (1.0%) of these adult males and in 29 (3.7%) of the 769 adult female residents of the Songwe area who were also examined. Microfilariae were detected in 33 (30.8%) of the 107 thick smears of night-blood samples that were made from individuals with positive ICT cards. The W. bancrofti infection focus in Karonga district is therefore wider than was previously known. This has important implications for the implementation and eventual impact of LF-control activities in this area.

Update on Lymphatic Filarial Infections

Filarial infections remain significant causes of disability in tropical areas worldwide. However, insights into the developmental and molecular biology of the parasite and the immunobiology of the host response to infection have advanced our understanding, even as progress is being made towards implementing eradication programs. This article summarizes some of the recent advances in the understanding of filarial biology and parasite immune evasion mechanisms, and reviews those newer aspects of diagnosis and treatment most relevant to clinicians.

A new approach to the treatment of filariasis

The symbiosis of filarial nematodes and intracellular Wolbachia bacteria has recently been exploited as a target for antibiotic therapy of filariasis. Antibiotic treatment of filarial nematodes results in sterility and inhibits larval development and adult worm viability. In the first trial on human onchocerciasis depletion of bacteria following treatment with doxycycline resulted in a complete and long-term block of embryogenesis. Bacteria are unable to repopulate nematode tissues up to 18 months after depletion, suggesting these effects may be permanent. Following ivermectin treatment, individuals given antibiotic therapy showed sustained reductions in skin microfilariae, with the majority of people remaining microfilarial negative 12-18 months after treatment. Since Wolbachia also contribute to the inflammatory pathogenesis of filarial disease, antibiotic therapy could, in addition to effects on worm fertility or viability, prevent the onset or development of filarial pathology.

Lymphatic filariasis: new insights and prospects for control

Although lymphatic filariasis remains among the major causes of disability among the tropical infectious diseases, dramatic advances have been made in the approach to its diagnosis, epidemiology and treatment, in our understanding of the molecular composition of the parasites that cause these infections, and in the factors underlying the pathology seen. Superimposing the tools of modern epidemiology, immunology, and molecular biology on field-based clinical trials has allowed the emergence of the concept of elimination of lymphatic filariasis. Much of the important new research emphasizes parasite development in the context of the host response, the importance of both the adult worm and other factors in the pathogenesis of lymphatic filarial disease, the role the Wolbachia endosymbiont holds as both a target for drug treatment and in inducing post-treatment reactions, and the various principles underlying the implementation of control programs.