Filarial Disease Research Articles

A new insight into the pathogenesis of filarial disease.

Filariasis is a major public health problem throughout many regions of the tropics. The disease is caused by several species of filarial nematode including Wuchereria bancrofti and Brugia malayi, the agents of lymphatic filariasis, and Onchocerca volvulus, the cause of 'riverblindness'. Disease caused by these worms varies depending on the tissue location of the parasite, and is associated with episodes of acute and chronic inflammation. These pathologies, including elephantiasis and blindness, rank among the most disabling in the world. Studies aimed at characterizing the molecular nature of the inflammatory stimuli derived from filarial nematodes uncovered a long forgotten secret, their symbiont Wolbachia. LPS-like molecules from these intracellular bacteria are responsible for potent inflammatory responses from macrophages and in animal models of filarial disease. Wolbachia has also been associated with severe inflammatory reactions to filarial chemotherapy, being released into the blood following the death of the parasite. Recent studies in animal models even implicate Wolbachia in the onset of lymphodema and blindness. Taken together these studies suggest a major role for Wolbachia in the pathogenesis of filarial disease. It may be possible, through the use of antibiotic therapy, to clear worms of their bacteria, in the hope that this will prevent the onset and development of filarial pathology.

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.

Sequencing and analysis of a 63 kb bacterial artificial chromosome insert from the Wolbachia endosymbiont of the human filarial parasite Brugia malayi

Wolbachia endosymbiotic bacteria are widespread in filarial nematodes and are directly involved in the immune response of the host. In addition, antibiotics which disrupt Wolbachia interfere with filarial nematode development thus, Wolbachia provide an excellent target for control of filariasis. A 63.1 kb bacterial artificial chromosome insert, from the Wolbachia endosymbiont of the human filarial parasite Brugia malayi, has been sequenced using the New England Biolabs Inc. Genome Priming System™ transposition kit in conjunction with primer walking methods. The bacterial artificial chromosome insert contains approximately 57 potential ORFs which have been compared by individual protein BLAST analysis with the 35 published complete microbial genomes in the Comprehensive Microbial Resource database at The Institute for Genomic Research and in the NCBI GenBank database, as well as to data from 22 incomplete genomes from the DOE Joint Genome Institute. Twenty five of the putative ORFs have significant similarity to genes from the α-proteobacteria Rickettsia prowazekii, the most closely related completed genome, as well as to the newly sequenced α-proteobacteria endosymbiont Sinorhizobium meliloti. The bacterial artificial chromosome insert sequence however has little conserved synteny with the R. prowazekii and S. meliloti genomes. Significant sequence similarity was also found in comparisons with the currently available sequence data from the Wolbachia endosymbiont of Drosophila melanogaster. Analysis of this bacterial artificial chromosome insert provides useful gene density and comparative genomic data that will contribute to whole genome sequencing of Wolbachia from the B. malayi host. This will also lead to a better understanding of the interactions between the endosymbiont and its host and will offer novel approaches and drug targets for elimination of filarial disease.

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.

A simple and quick method for enhanced detection of specific IgE in serum from lymphatic filariasis patients

A new simple and quick technique, using a suspension of protein A agarose beads to absorb IgG4 from sera prior to determination of filarial-specific IgE in ELISA, is presented. The optimal ratio between serum and absorbant was determined by absorbing fixed volumes of sera from individuals from a Wuchereria bancrofti endemic area with different volumes of the protein A agarose bead suspension and testing supernatants for filaria-specific IgG4 and IgE. The effect of absorption on measured IgG4 and IgE intensities in sera from various categories of individuals from the endemic area was thereafter examined. Overall, absorption resulted in a 96.5% decrease in mean ELISA OD values for IgG4 and a 41.6% increase in mean ELISA OD values for IgE. Higher increases in IgE measurements were seen with sera from circulating filarial antigen (CFA) negative individuals (64.7%), microfilaria (mf) negative individuals (56.1%) and individuals with chronic filarial disease (62.7%) than with sera from individuals who were CFA positive (23.4%), mf positive (10.0%), or without chronic disease (36.5%). These differences indicate that the degree to which IgE detection in unabsorbed serum is blocked by IgG4 varies with infection and disease status. Absorption of IgG4 from serum with a protein A agarose bead suspension prior to measurement of specific IgE is a useful alternative to conventional gel column absorption methods, particularly when processing many samples.

Wolbachia bacteria in filarial immunity and disease.

Lymphatic filarial nematodes are infected with endosymbiotic Wolbachia bacteria. Lipopolysaccharide from these bacteria is the major activator of innate inflammatory responses induced directly by the parasite. Here, we propose a mechanism by which Wolbachia initiates acute inflammatory responses associated with death of parasites, leading to acute filarial lymphangitis and adverse reactions to antifilarial chemotherapy. We also speculate that repeated exposure to acute inflammatory responses and the chronic release of bacteria, results in damage to infected lymphatics and desensitization of the innate immune system. These events will result in an increased susceptibility to opportunistic infections, which cause acute dermatolymphangitis associated with lymphoedema and elephantiasis. The recognition of the contribution of endosymbiotic bacteria to filarial disease could be exploited for clinical intervention by the targeting of bacteria with antibiotics in an attempt to reduce the development of filarial pathology.

Evaluation of sevafilachek immunoassays and rapid ICT-filariasis test for detection of bancroftian filariasis.

A comparative analysis was made on the utility of SEVAFILACHEK-stick based immunoassays and commercially available ICT-filariasis test to detect active infection in different groups of bancroftian filariasis. The SEVAFILACHEK immunoassays were found to be useful to detect filarial infection in microfilaraemia and in a significant number of clinical filarial cases with acute, chronic and occult clinical manifestations. In the clinical cases, microfilariae are not usually detected in peripheral circulation. Employing SEVAFILACHEK assays 6 and 5 of the 7 samples of patients with chronic filarial disease, and 6 and 5 of 6 microfilaraemic cases gave positivity for filarial IgG antibodies and antigen respectively. Four of the 6 occult filarial samples were positive for antibodies and antigen. Filarial antigen was detected by ICT-filariasis test in blood samples of all the 6 microfilariaemic cases, 1 chronic filarial and 2 occult filarial samples. The main advantage of ICT assay is its rapid format and convenience for field use.

One in the eye for river blindness

This Journal Club article also appears in Trends in ParasitologyChemotherapy is the principal intervention in the control of filariasis. For Onchocerca volvulus, the species responsible for ‘river blindness’, the current approach is to treat with ivermectin (Mectizan), a drug highly effective at clearing the juvenile microfilarial stage of the parasite, which lives in the skin awaiting transmission by the blackfly vector. Unfortunately, Mectizan has no effect on the survival of adult worms, which can live for a decade or more in subcutaneous nodules, giving birth to millions of microfilariae. Consequently, treatment has to be repeated on an annual basis for several years and cover sufficient numbers of people to have any hope of interrupting transmission. For years, scientists have been searching for that elusive drug that can kill or permanently sterilize the long-lived adult nematodes, but with little success. Recently, a new target for anti-filarial chemotherapy has emerged from the revelation that intracellular Wolbachia bacteria have evolved an obligate symbiosis with their nematode hosts. Treatment of filarial nematodes with the antibiotics tetracycline or rifampicin leads to the depletion of Wolbachia, and results in long-term sterility and inhibition of worm development and viability. In the few years since this discovery, the first clinical trial to test the effect of antibiotics on the depletion of Wolbachia in human onchocerciasis has been completed in Ghana 1xDepletion of Wolbachia endobacteria in Onchocerca volvulus by doxycycline and microfilaridermia after ivermectin treatment. Hoerauf, A. et al. Lancet. 2001; 357: 1415–1416Abstract | Full Text | Full Text PDF | PubMed | Scopus (167)See all

In Wuchereria bancrofti filariasis, asymptomatic microfilaraemia does not progress to amicrofilaraemic lymphatic disease.

In lymphatic filariasis due to Wuchereria bancrofti infections, the relationship between the natural course of infection and development of clinical disease remains controversial. The two hypotheses that are widely considered are (1) microfilaraemia represents an early stage of infection which progresses to amicrofilaraemic clinical disease and (2) microfilaraemia and clinical disease are two sequentially unrelated independent entities of the filarial infection and disease. Aim To determine whether microfilaraemic individuals develop lymphatic disease. The study was conducted in Sri Lanka during the period 1982 to 1998. There were two components, firstly a cross-sectional study and then a longitudinal study. Microfilaraemia was determined by microscopic examination of night blood films. Microfilaraemia associated anti-filarial antibodies were determined by ELISA. Clinical examinations were performed to determine if the test subjects had evidence of acute and chronic lymphoedema. Two major observations were made. First, the incidence and development of adenolymphangitis and lymphoedema in microfilaraemic individuals were very rare and these subjects maintained asymptomatic microfilaraemic status for very long periods of time. Second, in contrast to microfilaraemic subjects, the incidence and development of lymphangitis and lymphoedema were significantly higher in amicrofilaraemic anti-filarial antibody-positive subjects. Microfilaraemia does not represent a precondition to development of clinical disease (except male genital involvement).

Sir Patrick Manson. Father of tropical medicine.

Sir Patrick Manson. Illustration by Venita Jay, MD, FRCPC. I the obscurity of Amoy, South China, a lone Scotsman working with the most humble medical resources uncovered the remarkable mystery of filariasis. He not only enriched the world of medicine with numerous contributions on several tropical diseases, but also initiated a new era of thinking that winged arthropods may be associated with the spread of disease in man. In 1899, his pioneering efforts led to the establishment of a new discipline in medicine and the founding of the London School of Tropical Medicine. The lone Scotsman was Patrick Manson (1844–1922), who was born in Aberdeenshire, Scotland, the second in a family of 9 children. At the age of 15 years, he was apprenticed to an ironmaster’s firm in Aberdeen, but a breakdown in health prevented him from continuing this pursuit. The young Manson therefore turned to medicine at Aberdeen University, and passed his final examinations by the age of 20. By regulation, he had to be 21 years old to obtain his medical degree. Manson’s thesis on the internal carotid artery was his first paper, written while he was a medical officer at the Durham Lunatic Asylum; for this work he was awarded his MD in Aberdeen. In 1866, Manson traveled to Formosa, as medical officer to the Chinese Imperial Maritime Customs. Thus started a lifelong connection with the tropics and tropical diseases. After 5 years in Formosa, he was transferred to Amoy, China, where he would live for 13 years. Manson was in charge of a hospital for seamen and another missionary hospital. Practicing medicine in these areas was not easy for a Westerner at the time, but the persistent Manson slowly won the trust of the local population. Besides his busy medical practice, which included many surgical operations, Manson devoted his spare time to his passion, research on filaria. Manson’s scientific inquiries were aided only by his extraordinary will and curiosity, and his microscope. Filarial disease, which causes the disfiguring elephantiasis, was highly prevalent in Manson’s patient population in Amoy. Surgery was necessary in advanced cases, but the local population initially resisted his efforts. By an un-

Inflammatory responses induced by the filarial nematode Brugia malayi are mediated by lipopolysaccharide-like activity from endosymbiotic Wolbachia bacteria.

The pathogenesis of filarial disease is characterized by acute and chronic inflammation. Inflammatory responses are thought to be generated by either the parasite, the immune response, or opportunistic infection. We show that soluble extracts of the human filarial parasite Brugia malayi can induce potent inflammatory responses, including tumor necrosis factor (TNF)-alpha, interleukin (IL)-1beta, and nitric oxide (NO) from macrophages. The active component is heat stable, reacts positively in the Limulus amebocyte lysate assay, and can be inhibited by polymyxin B. TNF-alpha, IL-1beta, and NO responses were not induced in macrophages from lipopolysaccharide (LPS)-nonresponsive C3H/HeJ mice. The production of TNF-alpha after chemotherapy of microfilariae was also only detected in LPS-responsive C3H/HeN mice, suggesting that signaling through the Toll-like receptor 4 (TLR4) is necessary for these responses. We also show that CD14 is required for optimal TNF-alpha responses at low concentrations. Together, these results suggest that extracts of B. malayi contain bacterial LPS. Extracts from the rodent filaria, Acanthocheilonema viteae, which is not infected with the endosymbiotic Wolbachia bacteria found in the majority of filarial parasites, failed to induce any inflammatory responses from macrophages, suggesting that the source of bacterial LPS in extracts of B. malayi is the Wolbachia endosymbiont. Wolbachia extracts derived from a mosquito cell line induced similar LPS-dependent TNF-alpha and NO responses from C3H/HeN macrophages, which were eliminated after tetracycline treatment of the bacteria. Thus, Wolbachia LPS may be one of the major mediators of inflammatory pathogenesis in filarial nematode disease.

Development of rapid assessment procedures for the delimitation of lymphatic filariasis-endemic areas.

Lymphatic filariasis caused by Wuchereria bancrofti is a major public health problem in 73 tropical and subtropical countries including India. Delimitation of endemic areas is essential to plan control operations. The current method of night blood survey (NBS) for delimitation is cumbersome, time-consuming and expensive. Therefore, there is a need to develop assessment procedures which can rapidly delimit endemic areas. For this purpose we evaluated three procedures: direct interviewing of key informants using structured questionnaires, an indirect method of a self-administered questionnaires to key informants and physical examination by health workers for the presence of chronic filarial disease. Thirty rural communities in a filariasis-endemic region in Cuddalore district in Tamil Nadu State in southern India constituted the study population. The determination of filariasis endemicity in the village communities assessed by the above procedures was compared in terms of rapidity, specificity, sensitivity and cost with the microfilaria rate and disease rate obtained by night blood sample survey and clinical examination by physicians. Prevalence score, control preference score and weighted mean number of cases with filarial disease per village were calculated using the key informant questionnaire techniques. While the prevalence and control preference score showed low sensitivity and moderate specificity, weighted mean number of cases showed high sensitivity and moderate specificity in identifying endemic villages. The prevalence of disease as determined by the physical examination of a sample population by health workers was highly sensitive in identifying communities endemic for filariasis. The degree of association between the disease rates estimated by physician and trained health workers was significant (r = 0.56; P < 0.05). These observations suggest that the weighted mean number of cases per village obtained through key informant techniques may be considered at a primary level to crudely identify endemic areas, followed by physical examination by health workers for filariasis, since it is relatively cheap and rapid.

Extralymphatic disease due to bancroftian filariasis.

Infection with Wuchereria bancrofti, Brugia malayi, or B. timori not only affects the structure and function of lymphatic vessels but is also associated with extralymphatic pathology and disease. Because it is now possible to detect living adult worms by ultrasonography, much emphasis is placed on lymphatic pathology. However, the finding of renal damage in asymptomatic microfilaremic carriers has led to increased recognition of the importance of extralymphatic clinical manifestation in bancroftian filariasis. The authors present a number of clinical syndromes that may be manifestations of extralymphatic filarial disease and discuss possible mechanisms that cause these conditions. The main purpose of this paper is to raise the awareness of students and physicians of the prevalence and the importance of extralymphatic disease in bancroftian filariasis so that it is diagnosed and treated properly and also to alert for the need of additional research in this area.

Longitudinal Cellular Immune Responses in Asymptomatic and Symptomatic Brugia malayi-Infected Indian Leaf Monkey Presbytis entellus

To investigate the cell-mediated immune (CMI) responses of the host during the development of acute filarial disease manifestations, we studied the sequential changes in CD4+ and CD8+ T-cell subsets, leukocyte migration inhibition (LMI) response to Brugia malayi adult worm antigen, and concanavalin-A (ConA) and filarial antigen-induced lymphocyte transformation (LT) in the Indian leaf monkey (Presbytis entellus)-B. malayi model. Filarial infection was established in monkeys by subcutaneous inoculations of infective larvae (L3) (700-1,250 L3/monkey) in multiple doses, and the infected monkeys were categorized as symptomatic (Sym) and asymptomatic (Asym) depending on whether or not acute clinical manifestations were shown by them. In Sym monkeys, LMI response to homologous adult parasite antigen was significantly suppressed as compared to Asym monkeys. In Asym monkeys, LMI response varied among the animals; 2 showed an increase throughout the study period and 2 showed suppression at different time points. When compared with Asym monkeys, CD8+ T cells in Sym monkeys showed a trend of significant increase after day 180 postinoculation (PI). CD4+ T cells remained within the normal range till day 300 (PI), after which they showed a marginal increase. ConA-stimulated LT was suppressed in Asym monkeys from day 60 PI. Antigen-stimulated LT was unresponsive in both Asym and Sym animals. Thus, the host's LT response to ConA is suppressed in Asym animals, and alteration in CD8+ T-cell number and LMI response in Sym monkeys may be involved in the development of the acute disease manifestations in this model.

Epifil: a dynamic model of infection and disease in lymphatic filariasis.

The lack of a quantitative framework that describes the dynamic relationships between infection and morbidity has constrained efforts aimed at the community-level control of lymphatic filariasis. In this paper, we describe the development and validation of EPIFIL, a dynamic model of filariasis infection intensity and chronic disease. Infection dynamics are modeled using the well established immigration-death formulation, incorporating the acquisition of immunity to infective larvae over time. The dynamics of disease (lymphodema and hydrocele) are modeled as a catalytic function of a variety of factors, including worm load and the impact of immunopathological responses. The model was parameterized using age-stratified data collected from a Bancroftian filariasis endemic area in Pondicherry in southern India. The fitted parameters suggest that a relatively simple model including only acquired immunity to infection and irreversible progression to disease can satisfactorily explain the observed infection and disease patterns. Disease progression is assumed to be a consequence of worm induced damage and to occur at a high rate for hydrocele and a low rate for lymphodema. This suggests that immunopathology involvement may not be a necessary component of observed age-disease profiles. These findings support a central role for worm burden in the initiation and progression of chronic filarial disease.

Short report: total serum levels of the nitric oxide derivatives nitrite/nitrate during microfilarial clearance in human filarial disease.

Nitric oxide (NO) has recently been shown to be cytotoxic to both microfilariae and adult Brugia malayi in vitro and in a murine model, as well against Onchocerca lienalis microfilariae in vitro. We studied the kinetics of nitrite/nitrate, both stable end products of NO, by high-pressure liquid chromatography during microfilaricidal chemotherapy in four filariasis (three Loa loa, and one Onchocerca volvulus) patients. High serum levels of nitrite/nitrate were released during microfilarial clearance and sustained elevated levels were observed six months after chemotherapy, suggesting a role of NO in the elimination of microfilariae in human filariasis.

Epidemiological pattern of lymphatic filariasis in children living in endemic areas

Lymphatic filariasis still represents a major public health problem in the city of Recife. In spite of the fact that previous surveys had already shown high frequency of microfilaraemia in pediatric population, the prevalence of filarial disease and the microfilaraemic pattern of this group were unknown. This paper describes the clinical-epidemiological pattern of filariasis in children and adolescents living in two highly endemic areas of Recife. The parasitological survey was done through a census carried out between December 1990 and July 1991. Thick drop technique (45 micro l) was performed on a total of 1,464 children and adolescents between the ages of 5 and 14, of whom 967 were submitted to clinical examination. Positive cases had their blood recollected (60 micro l) to measure the microfilaraemic density. The microfilaraemia prevalence was 6.4 %. In the age groups of 5 to 9 and 10 to 14 a microfilaraemia prevalence of respectively 4.6% and 8.3% was observed. The microfilaraemic density varied from 3 to 864 microfilariae per 60 microl of blood, there having been no statistically significant difference between the sexes and age groups (p<0.05). 6 cases (0.6 %) of acute filarial disease and 11 of chronic filarial disease (1.1%) were identified, hydrocele being the principal manifestation found. Lymphadenopathy was found in 22% of the children, statistical association with microfilaraemia being observed (p<0.001). The results of the parasitological survey show the strong presence of children in the contingent of microfilaraemic individuals, indicating an early and intense exposure to filariasis in the population studied.

T-Lymphocytes from Individuals with Filarial Inflammatory Disease Have Increased Transendothelial Migrationin Vitro

Thein vitrotransendothelial migration of circulating filarial antigen-specific T-cells was examined inWuchereria bancroftiinfection. Circulating T-cells from individuals with filaria-induced lymphatic pathology (LP) had significantly greater migration through unstimulated HUVEC monolayers than did T-cells from asymptomatic infected (MF) individuals (P= 0.04). In contrast to the MF individuals where no effect was seen, transendothelial migration of 48-hr filarial antigen stimulated T-cells from LP individuals was significantly (P= 0.01) greater than migration of 48-hr media-stimulated T-cells. In six of seven patients examined, inhibition of the VLA-4/VCAM-1 pathway resulted in greater than 50% inhibition of transendothelial migration of T-cells.

Lymphatic filariasis on the coast of Ghana

Parasitological, clinical and entomological surveys for lymphatic filariasis were carried out in 6 villages and 3 towns on the coast of Ghana. Few or no filarial infections were observed in the towns or in the villages east of Accra. However, Wuchereria bancrofti microfilaraemia was common in the 4 western villages, with overall prevalences of 9.2%–25.4% and overall microfilariae (mf) geometric mean intensities of 321–1172 mf/mL of blood. In the same villages, hydrocele affected 8.5%–27.9% of adult males (aged ⩾20 years), and 5.6%–6.6% of adult individuals had elephantiasis (mainly of the legs). In general, the patterns of filarial infection and disease in the endemic villages resembled those observed in endemic villages in the coastal part of East Africa, with the exception that in the Ghanaian focus more females than males were affected by elephantiasis. Entomological surveys revealed that Anopheles gambioe s.l. and A. funestus were vectors of filariasis in the endemic villages. Only negligible prevalences of microfilaraemia were observed in town communities located close to highly endemic villages. Control of filariasis in this area is difficult with presently available measures, and new control tools, especially development of new drug regimens for mass treatment, are greatly needed.