Update on Lymphatic Filarial Infections

Unraveling the Dynamics of Human Filarial Infections: Immunological Responses, Host Manifestations, and Pathogen Biology

Lymphatic filariasis (LF), or elephantiasis, is a neglected tropical disease caused by filarial worms, primarily Wuchereria bancrofti, transmitted through mosquito bites. It often begins in childhood but may not show symptoms until later, leaving many individuals asymptomatic for long periods. LF disrupts the lymphatic system, causing severe swelling in the limbs and genitals, leading to deformities and disabilities. The World Health Organization estimates that around 51 million people are affected globally, with 36 million suffering from chronic conditions like lymphedema and hydrocele. In 2021, approximately 882.5 million people in 44 countries required preventive chemotherapy, making LF the second leading parasitic cause of disability, significantly impacting socioeconomic status. The immune response to filarial parasites is complex, involving both innate and adaptive immune cells. A key feature of LF immunology is the antigen-specific Th2 response, expansion of IL-10-producing CD4+ T cells, and a muted Th1 response. This T cell hypo-responsiveness is crucial for sustaining long-term infections with high parasite densities. While the correlates of protective immunity are not fully understood-due in part to a lack of suitable animal models-T cells, particularly CD4+ Th2 cells, and B cells, play essential roles in immune protection. Moreover, host immune responses contribute to the disease's pathological manifestations. A failure to induce T cell hypo-responsiveness can lead to exaggerated inflammatory conditions such as lymphedema, hydrocele, and elephantiasis. Filarial infections also induce bystander effects on various immune responses, impacting responses to other infectious agents. This intricate immune interplay offers valuable insights into the regulation of immune responses to chronic infections. This review explores recent immunological research on lymphatic filarial worms, highlighting their effects on both innate and adaptive immune responses in humans and the mechanisms underlying this neglected tropical disease.

Modified Combined Physiological and Debulking Procedure for Lower Limb Lymphedema to Achieve Both Immediate and Sustained Results in Lymphedema

A 17-year-old girl presented with bilateral lower limb lymphedema since 3 years. Lymphedema in the right leg was Grade III, not pitting and not reducing in size after limb elevation. She hailed from a tribal community. Considering her young age, a single-stage operative procedure for her lymphedematous leg was followed, as she was not prepared for a multistaged operation. However, this operative procedure needed to be a combination of both, debulking and physiological procedures, so as to give her immediate limb girth reduction as well as reduction in recurrence, as seen with debulking procedures. We report a newer technique that could achieve both goals.

Filarial infection during pregnancy has profound consequences on immune response and disease outcome in children: A birth cohort study

Background

Current Global Program to Eliminate Lymphatic Filariasis (GPELF) that prohibits pregnant mothers and children below two years of age from coverage targeted interruption of transmission after 5–6 rounds of annual mass drug administration (MDA). However, after more than 10 rounds of MDA in India the target has not been achieved, which poses challenge to the researchers and policy makers. Several studies have shown that in utero exposure to maternal filarial infections plays certain role in determining the susceptibility and disease outcome in children. But the mechanism of which has not been studied extensively. Therefore the present study was undertaken to understand the mechanism of immune modulation in children born to filarial infected mother in a MDA ongoing area.

Methodology and principal finding

To our knowledge this is the first study to conduct both cellular and humoral immunological assays and follow up the children until older age in a W bancrofti endemic area,where the microfilariae (Mf) rate has come down to <1% after 10 rounds of MDA. A total 57 (32: born to infected, 25: born to uninfected mother) children were followed up. The infection status of children was measured by presence of Mf and circulating filarial antigen (CFA) assay. Filaria specific IgG1, IgG2, IgG3 and IgG4 responses were measured by ELISA. Plasma level of IL-10 and IFN-γ were evaluated by using commercially available ELISA kit. The study reveals a high rate of acquisition of filarial infection among the children born to infected mother compared to uninfected mothers. A significantly high level of IgG1 and IgG4 was observed in children born to infected mother, whereas high level of IgG3 was marked in children born to uninfected mother. Significantly high level of IL-10 positively correlated with IgG4 have been observed in infected children born to infected mother, while high level of IFN-γ positively correlated with IgG3 was found in infection free children born to mother free from infection at the time of pregnancy. Moreover a negative correlation between IL-10 and IFN-γ has been observed only among the infected children born to infected mother.

Significance conclusion

The study shows a causal association between maternal filarial infection and impaired or altered immune response in children more susceptible to filarial infection during early childhood. As lymphatic damage that commences in childhood during asymptomatic stage has major implications from public health point of view, understanding maternal programming of the newborn immune system could provide a basis for interventions promoting child health by implementing MDA campaigns towards all women of childbearing age and young children in achieving the target of global elimination of LF.

Lymphatic filariasis (LF) has been targeted for elimination by 2020 through a major global initiative. The elimination strategy mainly aims to interrupt the transmission, or spread of infection, through annual mass drug administration (MDA) to entire at-risk population except the pregnant women and children below two years of age. Nevertheless, evidence exists that maternal W bancrofti infection during pregnancy can increase the susceptibility of the offspring to such infection during early childhood, the precise mechanism of which is not clear. Therefore in this study we have made an attempt to elucidate the mechanism of alteration of the foetal immunity due to maternal filarial infection, which may help developing strategy to strengthen the elimination programme. It is known that regulatory T cells are responsible for development of hyporesponsiveness, a condition that supports parasite growth and maternal filarial infection influences the development of T-regulatory cells from infancy to early childhood. Since T-reg cell can induce the production of regulatory cytokine IL-10 that often implicated in induction of IgG4 and we have observed an increased level of IL-10 / IgG4 and decreased levels of IFN- γ/ IgG3 in cord blood of infected mothers, we have thought that the modulation that takes place in utero affects the immune response and eventually disease outcome in early childhood. In order to prove our hypothesis, we have followed up a cohort of 57 children born to infected and uninfected mother in a MDA ongoing area of Odisha, India, where we have found a high rate of acquisition of filarial infection by children born to infected mother. Moreover a significantly high as well as a positive correlation between IgG4 and IL-10 levels in children born to infected mother during early childhood indicates that IL-10 and IgG4 contribute to immune modulation that starts during the period of gestation and continues till the early childhood helping the filarial parasites to evade destruction by their host’s immune system. In contrast a high level of IFN-γ and IgG3 in infection free children irrespective of infection status of mother shows the protective mechanism against the parasite. Additionally the correlation between antibodies and cytokines indicates that susceptibility to filarial infection during early childhood is due to the in utero modulation of T and B responses. Our findings highlights that every effort should be made to advance implementation policies and continue the focus to use the currently available anti-filarial drugs to prevent filarial infection before pregnancy as well as early childhood to achieve the target on time.

Setaria digitata in advancing our knowledge of human lymphatic filariasis

Setaria digitata is a filarial parasite that causes fatal cerebrospinal nematodiasis in goats, sheep and horses, resulting in substantial economic losses in animal husbandry in the tropics. Due to its close resemblance to Wuchereria bancrofti, this nematode is also frequently used as a model organism to study human lymphatic filariasis. This review highlights numerous insights into the morphological, histological, biochemical, immunological and genetic aspects of S. digitata that have broadened our understanding towards the control and eradication of filarial diseases.

A qualitative study of the perceptions, practices and socio-psychological suffering related to chronic brugian filariasis in Kerala, southern India

Lymphatic filariasis is a major health problem in many parts of the tropical world. Although the disease itself is rarely fatal, the disability caused by the swollen extremities, the acute attacks of adenolymphangitis and the consequent sufferings of those afflicted are considerable. The economic burden imposed by lymphatic filariasis is not fully quantified and information on the social and psychological problems caused by the disease is scanty. Semi-structured interviews were therefore used, in southern India, to assess the perceptions, practices and socio-psychological problems of 127 patients with brugian filariasis. The patients were aware of the causative factors and the precautions to be taken to prevent progression of the disease. However, depression and loss of job opportunities were common in the study population. Patients also complained that the disease eroded their standing in the community and diminished their prospects of marriage. Awareness of these factors will be of help in planning suitable disability-management packages, including the rehabilitation of those who find it difficult to carry on with their existing jobs because of the severity of their disease.

Treatment-seeking behavior and treatment practices of lymphatic filariasis patients with lymphoedema in the Colombo district, Sri Lanka

This cross-sectional, descriptive study describes the treatment-seeking behavior of 413 lymphoedema patients attending 2 filariasis clinics in the Colombo district, Sri Lanka. A pretested, interviewer-administered questionnaire obtained information regarding sources and types of treatment taken, time taken for diagnosis, and details regarding diethylcarbamazine citrate (DEC) treatment. There was a mean delay of 2.37 years (SD 1.37) in diagnosing filariasis after the first appearance of limb swelling. General practitioners were the most frequent first-contact health care providers and the most visited source overall, followed by government hospitals and Ayurvedic practitioners. Approximately 95% of patients were on DEC treatment ranging from 10 days to 43 years (mean 2.5 years SD +/- 1.1). Sixty-one percent of patients reported always having taken the recommended DEC course. Nonsteroidal anti-inflammatory drugs, diuretics, and antibiotics were liberally prescribed. Approximately 97% had sought treatment from a medical practitioner for an acute adenolymphangitis attack. Despite the area being endemic for filariasis, there was a delay in treatment and inappropriate use of DEC in patients with chronic filarial lymphoedema.

Animal models for the molecular and mechanistic study of lymphatic biology and disease

The development of animal model systems for the study of the lymphatic system has resulted in an explosion of information regarding the mechanisms governing lymphatic development and the diseases associated with lymphatic dysfunction. Animal studies have led to a new molecular model of embryonic lymphatic vascular development, and have provided insight into the pathophysiology of both inherited and acquired lymphatic insufficiency. It has become apparent, however, that the importance of the lymphatic system to human disease extends, beyond its role in lymphedema, to many other diverse pathologic processes, including, very notably, inflammation and tumor lymphangiogenesis. Here, we have undertaken a systematic review of the models as they relate to molecular and functional characterization of the development, maturation, genetics, heritable and acquired diseases, and neoplastic implications of the lymphatic system. The translation of these advances into therapies for human diseases associated with lymphatic dysfunction will require the continued study of the lymphatic system through robust animal disease models that simulate their human counterparts.

Orthologues of the Drosophila melanogaster E75 molting control gene in the filarial parasites Brugia malayi and Dirofilaria immitis

Filarial parasites cause debilitating diseases in humans and domesticated animals. Brugia malayi and Dirofilaria immitis are transmitted by mosquitoes and infect humans and dogs, respectively. Their life cycle is punctuated by a series of cuticular molts as they move between different hosts and tissues. An understanding of the genetic basis for these developmental transitions may suggest potential targets for vaccines or chemotherapeutics. Nuclear receptor (NR) proteins have been implicated in molting in the free-living nematode Caenorhabditis elegans and have well characterized roles in molting during larval development of Drosophila melanogaster. For example, the D. melanogaster E75 (NR1D3) NR gene is required for molting and metamorphosis, as well as egg chamber development in adult females. We have identified Bm-nhr-11and Di-nhr-6, B. malayi and D. immitis orthologues of E75. Both genes encode canonical nuclear receptor proteins, are developmentally regulated, and are expressed in a sex-specific manner in adults.

Cytochemical characterization of the third-stage larva of Wuchereria bancrofti (Nematoda: Filarioidea)

In the present paper, we report the results we obtained using several cytochemical techniques to analyze the infective larva of Wuchereria bancrofti. An imidazole osmium tetroxide solution was used to visualize unsaturated fatty acids. A highly contrasted material forming a continuous structure was observed on the larval surface and over the epicuticle. A strong reaction was observed on the esophagus and also on the inner secreted material. Carbohydrates containing vic-glycol groups were not observed on the cuticle of the third-stage larva of W. bancrofti submitted to the Thiéry technique. Using a panel of eight gold-labeled lectins, we found that the cuticle exhibited slight labeling with all lectins used, indicating residues of N-acetyl-D: -glucosamine, N-acetyl-galactosamine, D: -galactose, D: -manose, and L: -fucose. Surface anionic sites were visualized by using cationized ferritin particles. Treatment with trypsin partially inhibited the reaction, whereas the treatment with chondroitinase ABC, a specific enzyme for glycosaminoglycans, completely abolished the labeling with cationic particles.

Effectiveness of two annual, single-dose mass drug administrations of diethylcarbamazine alone or in combination with albendazole on soil-transmitted helminthiasis in filariasis elimination programme

A longitudinal community-trial on the control of soil-transmitted helminths (STHs), as part of a lymphatic filariasis elimination campaign, was taken up in two revenue blocks of southern India in the years 2001 and 2002 to assess the impact of two annual single-dose mass drug administration (MDA) of diethylcarbamazine (DEC) + albendazole (ALB) with that of DEC alone. The prevalences and intensities of STHs were studied among cross-sectional samples of school children aged 9-10 years by using the Kato-Katz technique at baseline and 11 months after each MDA. The combined drug mass treatment produced a higher reduction in the prevalence (RIP) (51-77%) and the egg reduction rate (ERR) (92-98%) compared with 12-15% RIP and 58-62% ERR of DEC alone mass treatment. The effect of two-drug therapy after two annual treatments was relatively long lasting as shown by RIP and ERR indicating that the reinfection rates were relatively lower in this approach than single-drug therapy. This study demonstrates that mass drug co-administration of DEC + ALB in Global Programme for Elimination of Lymphatic Filariasis (GPELF) targeted at the community had a synergistic and sustainable effect against soil-transmitted helminthiasis and provided considerable 'beyond filariasis' benefits. The additional advantages accrued to the community underscore the importance of scaling-up GPELF to cover the entire population at risk.

Multicentre laboratory evaluation of Brugia Rapid dipstick test for detection of brugian filariasis

A multicentre evaluation of the Brugia Rapid dipstick test was performed using 1263 serum samples in four international laboratories, i.e. T.D. Medical College (TDMC, India), National Institutes of Health (NIH, USA), Swiss Tropical Institute (STI, Switzerland) and Leiden University Medical Centre (LUMC, Netherlands). In comparison with microscopy, the dipstick demonstrated sensitivities of 97.2% (70 of 72) at TDMC, 91.6% (175 of 191) at LUMC and 100% (six of six) at STI. Sera of chronic patients showed a positivity rate of 11.3% (19 of 168) and 61.2% (71of 116) at TDMC and LUMC, respectively. All 266 sera of non-endemic normals from STI, NIH and LUMC tested negative with the dipstick. At LUMC, sera of 'endemic normals' (amicrofilaraemics with no clinical disease) from an area with approximately 35% microfilaria positivity showed 60.8% positive results (31 of 51), thus demonstrating the likelihood of many cryptic infections occurring in this population. Specificities of the test with Onchocerca volvulus sera were 98.8% (80 of 81) and 100% (10 of 10) at the NIH and STI, respectively; while specificity with Loa loa sera at the NIH was 84.6% (44 of 52). At the STI, the dipstick test also demonstrated 100% specificity when tested with 75 sera from various protozoan and helminthic infections.