New insights into the natural history and pathology of bancroftian filariasis: implications for clinical management and filariasis control programmes

Travelers' tropical skin diseases: Challenges and interventions

Tropical regions receive a significant part of the traveling population. It is very important that health professionals are familiar with the main tropical skin diseases and able to advice patients appropriately. This article reviews the main tropical diseases of travelers, with an emphasis on diagnosis, management, and prevention. Among others, cutaneous larva migrans, myiasis, tungiasis, Chagas disease, Dengue fever, African trypanosomiasis, filariasis, and leishmaniasis are discussed. Increasing awareness among travelers and health care professionals can help reduce morbidity and mortality. Continued research on new drugs and vaccines is needed to reduce the risks of tropical diseases.

Translating Research into Reality: Elimination of Lymphatic Filariasis from Haiti

Research provides the essential foundation of disease elimination programs, including the global program to eliminate lymphatic filariasis (GPELF). The development and validation of new diagnostic tools and intervention strategies, critical steps in the evolution of GPELF, required a global effort. Lymphatic filariasis research in Haiti involved many partners and was directly linked to the development of the national elimination program and to the success achieved to date. Ongoing research efforts involving many partners will continue to be important in resolving the challenges faced by the program today in its final efforts to achieve elimination.

Economic Costs and Benefits of a Community-Based Lymphedema Management Program for Lymphatic Filariasis in Odisha State, India

Lymphatic filariasis afflicts 68 million people in 73 countries, including 17 million persons living with chronic lymphedema. The Global Programme to Eliminate Lymphatic Filariasis aims to stop new infections and to provide care for persons already affected, but morbidity management programs have been initiated in only 24 endemic countries. We examine the economic costs and benefits of alleviating chronic lymphedema and its effects through a simple limb-care program. For Khurda District, Odisha State, India, we estimated lifetime medical costs and earnings losses due to chronic lymphedema and acute dermatolymphangioadenitis (ADLA) with and without a community-based limb-care program. The program would reduce economic costs of lymphedema and ADLA over 60 years by 55%. Savings of US$1,648 for each affected person in the workforce are equivalent to 1,258 days of labor. Per-person savings are more than 130 times the per-person cost of the program. Chronic lymphedema and ADLA impose a substantial physical and economic burden on the population in filariasis-endemic areas. Low-cost programs for lymphedema management based on limb washing and topical medication for infection are effective in reducing the number of ADLA episodes and stopping progression of disabling and disfiguring lymphedema. With reduced disability, people are able to work longer hours, more days per year, and in more strenuous, higher-paying jobs, resulting in an important economic benefit to themselves, their families, and their communities. Mitigating the severity of lymphedema and ADLA also reduces out-of-pocket medical expense.

Autophagy protects monocytes from Wolbachia heat shock protein 60-induced apoptosis and senescence

Monocyte dysfunction by filarial antigens has been a major mechanism underlying immune evasion following hyporesponsiveness during patent lymphatic filariasis. Recent studies have initiated a paradigm shift to comprehend the immunological interactions of Wolbachia and its antigens in inflammation, apoptosis, lymphocyte anergy, etc. Here we showed that recombinant Wolbachia heat shock protein 60 (rWmhsp60) interacts with TLR-4 and induces apoptosis in monocytes of endemic normal but not in chronic patients. Higher levels of reactive oxygen species (ROS) induced after TLR-4 stimulation resulted in loss of mitochondrial membrane potential and caspase cascade activation, which are the plausible reason for apoptosis. Furthermore, release in ROS owing to TLR-4 signaling resulted in the activation of NF-κB p65 nuclear translocation which leads to inflammation and apoptosis via TNF receptor pathway following the increase in IL-6 and TNF-α level. Here for the first time, we report that in addition to apoptosis, rWmhsp60 antigen in filarial pathogenesis also induces molecular senescence in monocytes. Targeting TLR-4, therefore, presents a promising candidate for treating rWmhsp60-induced apoptosis and senescence. Strikingly, induction of autophagy by rapamycin detains TLR-4 in late endosomes and subverts TLR-4-rWmhsp60 interaction, thus protecting TLR-4–mediated apoptosis and senescence. Furthermore, rapamycin-induced monocytes were unresponsive to rWmhsp60, and activated lymphocytes following PHA stimulation. This study demonstrates that autophagy mediates the degradation of TLR-4 signaling and protects monocytes from rWmhsp60 induced apoptosis and senescence.

Despite knowing the significance of Wolbachia in helminth infections, our understanding of immunity and pathogenesis remains incomplete. Therefore, considering the gravity of the problem, the present study provides evidence that Wolbachia heat shock protein 60 induces apoptosis and senescence through TLR-4. Also, binding of rWmhsp60 to TLR-4 triggered caspase cascade activation following, ROS-mediated mitochondrial potential loss. Moreover, we found that nuclear translocation of NF-κB p65 was predominantly related to TLR-4 expression and resulted in apoptosis- and senescence-mediated inflammation via TNF-α and IL-6. Hence, we hypothesized that modifying TLR-4 expression may provide a plausible target for designing antiparasitic drugs. Here we have shown that induction of autophagy by rapamycin destabilizes TLR-4 expression and protects monocytes from rWmhsp60-induced apoptosis and senescence. In addition, rapamycin-induced monocytes were unresponsive to rWmhsp60 and triggered lymphocyte activation after PHA stimulation. Thus, synergistic usage of rapamycin with existing anti-filarial drugs might reduce the TLR-mediated inflammatory reactions following microfilaricidal treatment.

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.

Bancroftian filariasis in children and adolescents: clinical–pathological observations in 22 cases from an endemic area

In areas where bancroftian filariasis is endemic, the clinical manifestations of the disease, which are often very varied, appear most frequently during early adulthood or later. In consequence, very little attention, if any, has been given to the signs and symptoms of the disease in childhood. In an attempt to fill this gap, clinical and pathological observations were made, in Brazil, on 22 children (aged 2-15 years) who were infected with Wuchereria bancrofti. There was a predominance of lymph-node involvement. In all but three (14%) of the children (who had adult parasites in their intrascrotal lymphatic vessels), the adult worms were located in the afferent or efferent vessels of draining lymph nodes, predominantly in the inguinal region. None of the patients presented with distal lymphoedema, and the adenopathy was characterized by painless, localized, lymph-node enlargement, without signs of inflammation in the overlying skin. Histologically, the alterations in the lymphatic vessels and surrounding structures were similar to those described in adult patients, and depended essentially on adult-parasite viability. The localization of the adult worms in the paediatric cases was peculiar and distinct from that observed in adult patients, in whom the adult parasites are usually found in extra-nodal lymphatic vessels. In areas endemic for bancroftian filariasis, therefore, filarial infection should be considered as a possible cause of adenopathy. For the differential diagnosis of adenopathy in young patients from endemic areas, the authors recommend the use of ultrasound and other non-invasive diagnostic tools, as alternatives to excisional biopsies, which are often unnecessary in bancroftian filariasis.

Wolbachia heat shock protein 60 induces pro-inflammatory cytokines and apoptosis in monocytes in vitro

Recombinant Wolbachia heat shock protein 60 (rWmhsp60) induces gene expression of pro-inflammatory cytokines IL-1β, IL-6 and TNF-α in human monocytic cell line THP-1. In addition, it inhibits the phagocytic activity and does not alter the nitric oxide production by differentiated THP-1 macrophages, which corroborates with no significant change in inducible nitric oxide synthase gene expression in rWmhsp60 treated THP-1 monocytes. Further, 24 h stimulation of peripheral blood mononuclear cells from normal individuals by rWmhsp60 reveals that monocytes enter the late apoptotic stage, while lymphocytes do not show apoptosis. Thus these findings suggest that rWmhsp60 may contribute to inflammation mediated monocyte dysfunction in filarial pathogenesis.

Efficacy of home-based lymphoedema management in reducing acute attacks in subjects with lymphatic filariasis in Burkina Faso

One of the two main goals of the Global Programme to Eliminate Lymphatic Filariasis (LF) is to provide care for those suffering from the devastating clinical manifestations of this filarial infection. Among the 120 million infected people worldwide, up to 16 million have lymphoedema. The WHO strategy for managing lymphoedema is based on rigorous skin hygiene, exercise, antibiotics and antifungals when indicated. The aim is to reduce acute attacks of adenolymphangitis and cellulitis responsible for lymphoedema progression and disability. The objective of our study was to assess the effectiveness of home-based lymphoedema management implemented by the national health system of Burkina Faso. Any patient was eligible to participate in the study if suffering from LF-related lymphoedema of a lower limb at any stage, and receiving care as part of the health education and washing project between April 2005 and December 2007. The primary readout was the occurrence of an acute attack in the month preceding the consultation reported by the patient or observed by the care-giver. In all, 1089 patients were enrolled in the study. Before lymphoedema management intervention, 78.1% (95%CI: 75.5-80.5) of the patients had an acute attack in the month preceding the consultation; after four and half months of lymphoedema management, this was reduced to 39.1% (95%CI: 36.2-42.1). A reduction of acute attacks related to the number of consultations or related to the patients' age and gender was not observed. Our results suggest that the home-based lymphoedema management programme in the primary health care system of Burkina Faso is effective in reducing morbidity due to LF in the short-term (4.5 months). The lymphoedema management requires no additional human resources, but whether its effect can be sustained remains to be seen.

Parasitic infections and myositis

Infectious myositis may be caused by a wide variety of bacterial, fungal, viral, and parasitic agents. Parasitic myositis is most commonly a result of trichinosis, cystericercosis, or toxoplasmosis, but other parasites may be involved. A parasitic cause of myositis is suggested by history of residence or travel to endemic area and presence of eosinophilia. The diagnosis of parasitic myositis is suggested by the clinical picture and radiologic imaging, and the etiologic agent is confirmed by parasitologic, serologic, and molecular methods, together with histopathologic examination of tissue biopsies. Therapy is based on the clinical presentation and the underlying pathogen. Drug resistance should be put into consideration in different geographic areas, and it can be avoided through the proper use of anti-parasitic drugs.

Lack of evidence for the direct activation of endothelial cells by adult female and microfilarial excretory-secretory products

Lymphangiectasia (dilation of the lymphatic vessel (LV)) is pathognomonic for lymphatic filariasis. In both infected humans and animal models of infection, lymphangiectasia is not restricted to the site of the worm nest, but is found along the infected vessel. These observations argue that soluble products secreted by the worm could be mediating this effect by activating the lymphatic endothelial cells (LEC) lining the vessel. We tested the ability of filarial Excretory-Secretory products to activate LECs, but were unable to detect a direct effect of the Excretory-Secretory products on the activation of LEC as assessed by a variety of approaches including cellular proliferation, cell surface molecule expression and cytokine and growth factor production (although other mediators used as positive controls did induce these effects). Collectively, these results do not support the hypothesis that Excretory-Secretory products directly activate LECs.

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.

Filarial lymphedema is characterized by antigen-specific Th1 and th17 proinflammatory responses and a lack of regulatory T cells

Background

Lymphatic filariasis can be associated with development of serious pathology in the form of lymphedema, hydrocele, and elephantiasis in a subset of infected patients.

Methods and Findings

To elucidate the role of CD4⁺ T cell subsets in the development of lymphatic pathology, we examined specific sets of cytokines in individuals with filarial lymphedema in response to parasite antigen (BmA) and compared them with responses from asymptomatic infected individuals. We also examined expression patterns of Toll-like receptors (TLR1–10) and Nod-like receptors (Nod1, Nod2, and NALP3) in response to BmA. BmA induced significantly higher production of Th1-type cytokines—IFN-γ and TNF-α—in patients with lymphedema compared with asymptomatic individuals. Notably, expression of the Th17 family of cytokines—IL-17A, IL-17F, IL-21, and IL-23—was also significantly upregulated by BmA stimulation in lymphedema patients. In contrast, expression of Foxp3, GITR, TGFβ, and CTLA-4, known to be expressed by regulatory T cells, was significantly impaired in patients with lymphedema. BmA also induced significantly higher expression of TLR2, 4, 7, and 9 as well Nod1 and 2 mRNA in patients with lymphedema compared with asymptomatic controls.

Conclusion

Our findings implicate increased Th1/Th17 responses and decreased regulatory T cells as well as regulation of Toll- and Nod-like receptors in pathogenesis of filarial lymphedema.

Lymphatic filariasis afflicts over 120 million people worldwide. While the infection is mostly clinically asymptomatic, approximately 40 million people suffer from overt, morbid clinical pathology, characterized by swelling of the scrotal area and lower limbs (hydrocele and lymphedema). Host immunologic factors that determine susceptibility of this subset of individuals to clinically apparent disease is unknown. We addressed this issue by comparing the immunologic response of helper T (Th) cell subsets in lymphedema patients and clinically asymptomatic individuals. Four important subsets of Th cells (CD4⁺ T cells) are: Th1 cells, characterized by production of cytokines IL-2, IFN-γ, and TNF-α; Th2 cells, characterized by production of cytokines IL-4 and IL-13; Th17 cells, characterized by production of cytokines IL-17A, IL-17F, IL-21, and IL-22; and regulatory T cells (Tregs), characterized by the expression of transcription factor Foxp3, as well as other molecules such as GITR, TGFβ, and CTLA-4. We determined that Th1 and Th17 responses are significantly enhanced and Treg responses significantly impaired in lymphedema patients. This is accompanied by increased expression of pattern recognition receptors of the Toll and NOD family. Thus, approaches toward downregulating Th1 and Th17 responses and enhancing Treg responses would be beneficial in protecting against development of lymphatic disease.

[The complexity of the socioeconomic costs of lymphatic filariasis]

Lack of knowledge of the socioeconomic impact of various diseases is generally one of the biggest obstacles to obtaining funds for investment in applied research and for starting to implement control programs that are needed in developing countries. The authors analyze and emphasize important aspects of the complexity of quantifying the socioeconomic impact of lymphatic filariasis. They highlight the gaps that exist within some fields of knowledge and that these gaps have still not been properly explored with regard to individuals with this disease. They bring together the data in the literature and echoes from their own experience gained through caring for patients with Bancroftian infection and disease at a tertiary referral service (NEPAF--Filariasis Care, Research and Teaching Center, Recife, Brazil). The social impact, in its broadest sense, consists of strong indications of losses of quality of life among patients. Unfortunately, this is still poorly documented and, up to a certain point, very difficult to quantify because of the very particular social abandonment of the endemic communities.

[Aspects of the social realities of children and adolescents seen at a reference service for bancroftian filariasis in Recife, state of Pernambuco]

The authors report on aspects of the social realities of children and adolescents living in Jaboatão dos Guararapes, State of Pernambuco, who were diagnosed with Bancroftian filariasis infection and were treated at the Filariasis Teaching, Research and Care Center of the Federal University of Pernambuco (Health Sciences Center), which is a tertiary-level reference service for filariasis. The patients' housing conditions were quantified and classified as subhuman, with a direct relationship with the maintenance of Bancroftian filariasis transmission, and the authors highlight the need for political decisions regarding the implementation of basic sanitation projects.

[Hope Clubs as adjunct therapeutic measure in bancroftian filariasis endemic areas]

In 1997 the World Health Organization announced an ambitious project called the Global Program to Eliminate Lymphatic Filariasis, as a Public Health Problem. The program is based on two pillars: interruption of transmission and morbidity control. Experience in Recife, Brazil, an endemic area for bancroftian filariasis, showed that an innovative approach called Hope Clubs, can equip lymphedema patients with the skills, motivation, and enthusiasm to sustain effective, low-cost and convenient self-care to prevent acute skin bacterial episodes and milky urine in the case of chyluria carriers. They feel they are not alone, they regain their potential for productive work and are able to amplify these activities throughout filariasis-endemic communities.

Morbidity management in the Global Programme to Eliminate Lymphatic Filariasis: a review of the scientific literature

The Global Programme to Eliminate Lymphatic Filariasis (GPELF) has two major goals: to interrupt transmission of the parasite and to provide care for those who suffer the devastating clinical manifestations of the disease (morbidity control). This latter goal addresses three filariasis-related conditions: acute inflammatory episodes; lymphoedema; and hydrocele. Research during the last decade has confirmed the importance of bacteria as a cause of acute inflammatory episodes in filariasis-endemic areas, known as acute dermatolymphangioadenitis (ADLA). Current lymphoedema management strategies are based on the central role of ADLA as a trigger for lymphoedema progression. Simple intervention packages are in use that have resulted in dramatic reductions in ADLA rates, a lower prevalence of chronic inflammatory cells in the dermis and subdermis, and improvement in quality of life. During the past decade, the socioeconomic impact of ADLA and lymphoedema in filariasis-endemic areas has received increasing attention. Numerous operational research questions remain to be answered regarding how best to optimize, scale up, monitor, and evaluate lymphoedema management programmes. Of the clinical manifestations targeted by the GPELF, hydrocele has been the focus of the least attention. Basic information is lacking on the effectiveness and complications of hydrocele surgery and risk of post-operative hydrocele recurrence in filariasis-endemic areas. Data on the impact of mass administration of antifilarial drugs on filarial morbidity are inconsistent. Several studies report reductions in acute inflammatory episodes, lymphoedema, and/or hydrocele following mass drug administration, but other studies report no such association. Assessing the public health impact of mass treatment with antifilarial drugs is important for programme advocacy and morbidity control strategies. Thus, although our knowledge of filariasis-related morbidity and its treatment has expanded in recent years, much work remains to be done to address the needs of more than 40 million persons who suffer worldwide from these conditions.

Diethylcarbamazine (DEC)-medicated salt for community-based control of lymphatic filariasis

BACKGROUND

Mass treatment with diethylcarbamazine (DEC)-medicated salt has been used in a number of places as a control measure for lymphatic filariasis. We sought reliable evidence about its effect on lymphatic filariasis transmission.

OBJECTIVES

To evaluate the effects of DEC-medicated salt on infection with lymphatic nematodes in studies of individuals and communities.

SEARCH STRATEGY

In August 2006, we searched the Cochrane Infectious Disease Group Specialized Register, CENTRAL (The Cochrane Library 2006, Issue 3), MEDLINE, EMBASE, and LILACS. We also checked reference lists.

SELECTION CRITERIA

Studies of DEC-medicated salt in endemic populations or microfilaraemic individuals that reported on some measure of human infection before and after the intervention.

DATA COLLECTION AND ANALYSIS

Two authors assessed study eligibility and methodological quality. We calculated the percentage change in microfilariae prevalence and density, adult worm prevalence, disease rates, and vector infection and infectivity. We carried out meta-regression to explore the variability in percentage reduction in microfilariae prevalence between studies.

MAIN RESULTS

Twenty-one studies were included; two compared DEC-medicated salt with other forms of DEC, five had some control group, and 14 were before-and-after studies. Five were efficacy and safety studies of individuals who were all microfilaraemic at baseline; the rest studied endemic communities. Percentage reductions in microfilariae prevalence were large (43% to 100%) and consistent in most studies with high levels of coverage. Large reductions in microfilariae density were also observed, though most studies reported changes in microfilariae density only for people with microfilaraemia at baseline. Vector infection and infectivity also declined, but the samples were usually small. Changes in disease prevalence were inconclusive as most studies were not powered for this outcome. Adverse events seemed mild. Only two studies compared DEC-medicated salt with other forms of DEC (such as annual or standard 12-day dose), but in both performance of DEC-medicated salt was better.A few studies included longer term follow up (two to 19 years). Reductions in microfilariae prevalence, density, and vector infectivity were maintained over time. The DEC concentration in the salt and the duration of intervention were significant factors influencing the percentage reduction in microfilariae prevalence in these studies.

AUTHORS' CONCLUSIONS

DEC-medicated salt is an effective intervention when maintained with levels of coverage of at least 90% for at least six months. Further studies are required to assess the effects of continuous low-dose, DEC-medicated salt on adult worms, disease prevalence, and development of drug resistance.

Interdigital skin lesions of the lower limbs among patients with lymphoedema in an area endemic for bancroftian filariasis

OBJECTIVES

An estimated 15 million persons suffer from lymphoedema of the leg in filariasis-endemic areas of the world. A major factor in the progression of lymphoedema severity is the incidence of acute dermatolymphangioadenitis (ADLA), which is triggered by bacteria that gain entry through damaged skin, especially in the toe web spaces ('interdigital skin lesions'). Little is known about the epidemiology of these skin lesions or about patients' awareness of them.

METHODS

We interviewed and examined 119 patients (89% women) with lymphoedema of the leg in Recife, Brazil, an area endemic for bancroftian filariasis.

RESULTS

We detected 412 interdigital skin lesions in 115 (96.6%) patients (mean, 3.5 lesions per patient, range 0-8). The number of interdigital skin lesions was significantly associated with lymphoedema stage (P<0.001) and frequency of ADLA (P<0.0001). Only 20 (16.8%) patients detected their own interdigital skin lesions or considered them abnormal. Patients reported a mean of 3.6 ADLA episodes during the previous 12 months (range, 0-20); reported ADLA incidence was associated with lymphoedema stage (P<0.0001) and the number of interdigital skin lesions detected by the examining physician (P<0.0001).

CONCLUSIONS

These data suggest that interdigital skin lesions are a significant risk factor for ADLA and that persons with lymphoedema in filariasis-endemic areas are unaware of their presence or importance. Prevention of ADLA through prompt recognition and treatment of interdigital skin lesions will require that patients be taught to identify lesions, especially between the toes and to recognize them as abnormal.

Reliable and frequent detection of adult Wuchereria bancrofti in Ghanaian women by ultrasonography

Detection of adult Wuchereria bancrofti by ultrasonography of the scrotal region in men is a suitable diagnostic tool for lymphatic filariasis, whereas there are only a few case reports of adult filariae observed by ultrasonography in women. We examined 35 microfilaraemic women ultrasonographically in sites of the body suspected as locations for worm nests. In 15 women the 'filaria dance sign' (FDS) was detected in various locations, some being novel, such as adult worms within lymphatic vessels between muscular fibres of the thighs. The surprisingly high number of worm nests detectable in microfilaraemic women recommends ultrasonography for diagnosis and treatment efficacy monitoring of female patients infected with W. bancrofti.

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.

Lymphatic filariasis-specific immune responses in relation to lymphoedema grade and infection status. I. Cellular responses

The filariasis-specific cellular responsiveness was assessed in 109 adult individuals from a Wuchereria bancrofti-endemic area in north-east Tanzania. There were 9 study groups. Five groups of individuals were negative for microfilariae (mf) and specific circulating filarial antigen (CFA) and had leg lymphoedema of varying severity ranging from early to more advanced grades (pathology groups 1-5). Another group comprised individuals with mixed grades of lymphoedema and positive for mf and/or CFA (mixed pathology group). Three asymptomatic groups consisted of individuals without leg pathology but with different infection status: (i) CFA- and mf-negative individuals, (ii) CFA-positive but mf-negative individuals, and (iii) CFA- and mf-positive individuals. Peripheral blood mononuclear cells were collected and proliferative responsiveness and secretion of interleukin (IL)-4, IL-10 and gamma interferon (IFN gamma) were measured upon stimulation with a Brugia pahangi antigen. No distinct differences in responses were observed between the 5 uninfected pathology groups. Instead, responses were associated with infection status, with generally higher proliferative activity and higher levels of IL-4 and IFN gamma in uninfected as compared to infected individuals. High levels of IL-10 were observed in asymptomatic individuals without infection and in asymptomatic CFA-positive but mf-negative individuals. Asymptomatic individuals with mf had relatively low IL-10 levels. Groups presenting with chronic pathology generally had low levels of IL-10 independently of infection status. The findings thus give no immediate indication that the measured immunological parameters are related to progression of leg pathology. However, alternative interpretations are presented which suggest a possible role of immunological reactions in development of pathology in lymphatic filariasis.

Lymphatic filariasis: new insights into an old disease

Lymphatic filariasis has afflicted people in the tropical areas of the world for thousands of years but even up to comparatively recent times it has been poorly understood and its importance under recognised. In the last 2 decades or so there has been a flurry of activity in filariasis research, which has provided new insights into the global problem of filariasis, the pathogenesis of filarial disease, diagnosis and control.

Lymphatic filariasis-specific immune responses in relation to lymphoedema grade and infection status. II. Humoral responses

The filarial-specific humoral responses (IgG1, IgG2, IgG3, IgG4 and IgE) to a Brugia pahangi antigen was assessed in 9 groups of adult individuals from a Wuchereria bancrofti-endemic area in north-east Tanzania. In 5 of the groups, individuals were negative for microfilariae (mf) and circulating filarial antigen (CFA) and had leg lymphoedema of varying severity ranging from early to more advanced grades. A 6th group had mixed grades of lymphoedema and were actively infected with mf and/or CFA. Three groups of asymptomatic individuals with different infection status (mf+CFA+; mf-CFA+; mf-CFA-) were also included. No differences in the antibody levels were observed between the 5 uninfected pathology groups. However, groups with advanced lymphoedema had a significantly higher level of IgG3 as compared to groups with early lymphoedema. A decline in the IgG4/IgE ratios were observed when moving from groups with early to groups with more advanced lymphoedema, which could indicate that increasing levels of IgE relatively to IgG4 are associated with progression of pathology. When all study groups were compared, higher IgG4/IgE ratios were observed in infected groups than in uninfected groups. This could suggest that high levels of IgG4 relative to IgE protect the parasite, whereas the opposite may play a role in parasite killing. When relating IgG4/IgE ratios to levels of gamma interferon (IFN gamma), a clear inverse relationship was observed. Thus, high levels of IFN gamma were found in groups with low IgG4/IgE ratios (uninfected groups) and low levels of IFN gamma were found in groups with high IgG4/IgE ratios (infected groups). The relationship between cellular (IFN gamma) and humoral (IgG4/IgE ratios) responses and their possible role in parasite protection and killing, and in development of early lymphoedema, are discussed.

Progression of lymphatic vessel dilatation in the presence of living adult Wuchereria bancrofti

Bancroftian filariasis, a mosquito-transmitted disease commonly known as elephantiasis, is caused by infection with the parasite Wuchereria bancrofti. Infection with this parasite can induce a broad array of chronic debilitating and socially stigmatizing conditions, but the pathogenesis of this morbidity remains obscure. Recent evidence indicates that in filariasis-endemic areas the primary lesion is not lymphatic vessel obstruction but, rather, dilatation. To determine the extent to which lymphatic dilatation occurs in the presence of living adult W. bancrofti, we performed longitudinal ultrasonographic measurements in 80 men (mean age 24 years) in Brazil who had a total of 107 W. bancrofti nests detectable by ultrasound. Initial mean lymphatic vessel diameter at the site of the worms was 3.4 mm (range, 0.7-11.3), and was greater in men with 2 or more nests (3.9 mm) than in those with only one nest (3.0 mm, P = 0.003). During the study period (2-35 months, mean, 13.7), lymphatic vessel diameter increased at the site of 92 (86.0%) adult worm nests. Mean rate of increase of lymphatic vessel diameter was 1.2 mm per person-year (range, 0-0.93 mm per month). In a general linear model, no factors, including treatment with antifilarial drugs, were significantly associated with rate of vessel diameter increase. Thus, lymphatic vessel dilatation progress in the presence of living adult W. bancrofti; the rate of this progression is heterogeneous. These data suggest that lymphatic dilatation will continue to progress in most infected persons even after mass treatment with currently recommended antifilarial drugs. In addition to interrupting transmission, the global programme for elimination of lymphatic filariasis should address the potential for disease progression in persons who remain infected with adult W. bancrofti.

[Recommendations for the treatment of bancroftian filariasis in symptomless and diseased patients]

The goals of treatment for lymphatic filariasis are: to prevent, reverse, or halt progression of disease; and to interrupt transmission of the parasite. Selecting the appropriate therapy for the patient with lymphatic filariasis requires knowledge of the various clinical features of filarial disease and their pathogenesis. In the past, treatment of lymphatic filariasis has focused primarily on antiparasitic chemotherapy; however, for many of the acute and chronic manifestations of lymphatic filariasis, it is now clear that supportive or other forms of clinical care are even more important than antiparasitic medication in order to prevent worsening of the disease. Regardless of the clinical manifestations of filarial disease in a particular patient, the following three components of treatment should, in general, be considered: supportive or disease specific clinical care (including hygiene and diet), patient education and counseling and finally, antiparasitic chemotherapy with diethylcarbamazine (DEC) and/or the combination of DEC with ivermectin. The authors also describe the proportional efficacy of diethylcarbamazine and ivermectin, alone or in combination, for use in mass treatment aiming at transmission interruption and the use of hygiene as a public health approach for lymphedema prevention.

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.

Current status and future prospects of the Global Lymphatic Filariasis Programme

Lymphatic filariasis is recognized as one of the world's most disabling diseases. Adult lymphatic filarial nematodes live for several years; they infest the lymphatic and blood systems, and are transmitted via mosquito vectors. Acute and chronic disease can develop, manifesting as acute inflammation, hydrocoele, lymphoedema and elephantiasis. The development of a global programme for the elimination of lymphatic filariasis (focusing on disease caused by Wuchereria bancrofti) followed a resolution by the World Health Assembly in 1997 that endemic countries should develop programmes to eliminate lymphatic filariasis as a public health problem. This developed from an earlier recommendation by the International Task Force for Disease Eradication in 1993 that lymphatic filariasis was one of six diseases that could, in theory, be eradicated. Herein we review the current status and future prospects of the Global Lymphatic Filariasis Programme, which was launched in 2000.