Clinical Filariasis Research Articles

The relationship between infection and disease in Wuchereria bancrofti infection in Ghana

The relationship between infection and clinical disease in Wuchereria bancrofti infection was investigated in a community-based study in different endemic areas in Ghana. At the individual level, there was no association between acute adenolymphangitis and infection (microfilaraemia) status.There was a negative association between infection status and lymphoedema/elephantiasis, but a positive association with hydrocele; however, the intensity of infection was negatively associated with both elephantiasis and hydrocele. The community prevalence of infection was strongly associated with the prevalence of clinical filariasis (especially hydrocele). There was a strong positive association between the prevalence of infection in males and the odds of a case of hydrocele being microfilaraemic, suggesting that there is no acquired immunity to reinfection in cases of hydrocele. The pathophysiologies of elephantiasis and hydrocele may therefore differ from one another, and require further investigation.

Differences in the frequency of cytokine-producing cells in antigenemic and nonantigenemic individuals with bancroftian filariasis.

Individuals with clinical manifestations of lymphatic filariasis may be currently infected or not. Twenty-five individuals from a Wuchereria bancrofti-endemic area of Brazil were classified as being asymptomatic microfilaremic individuals, antigenemic individuals with clinical filariasis, or nonantigenemic individuals with clinical filariasis. Intracellular cytokine staining of mitogen-stimulated peripheral blood mononuclear cells (PBMC) showed that the frequency of either gamma interferon (IFN-gamma)- or interleukin-4 (IL-4)-producing cells was higher in the nonantigenemic individuals with clinical filariasis than in the asymptomatic microfilaremic individuals (geometric means, 22.1 versus 10.7% [P = 0.02] and 2.9 versus 1.4% [P = 0.01], respectively). When the asymptomatic microfilaremic individuals and antigenemic individuals with clinical filariasis were grouped together to constitute all actively infected individuals, the frequency of IFN-gamma-producing cells was also lower than in the nonantigenemic individuals with clinical filariasis (P = 0.04). Likewise, the frequency of IL-4-producing cells in the actively infected individuals was also lower than in the nonantigenemic individuals with clinical filariasis (P = 0.02). No differences in the frequency of IFN-gamma-, IL-4-, or IL-5-producing cells in purified CD4 T lymphocytes were found among the groups. These findings suggest that the presence of antigenemia, which is an indicator of current active infection, is closely associated with the frequency of IFN-gamma- and IL-4-producing cells in lymphatic filariasis. The differences found in the frequency of cytokine-producing cells among the three groups appear to be due to a subset of cells other than CD4 T cells.

The presence or absence of active infection, not clinical status, is most closely associated with cytokine responses in lymphatic filariasis.

Twenty-eight Brazilians from an area in which Wuchereria bancrofti is endemic were classified as asymptomatic microfilaremic or having clinical filariasis with active infection or without current active infection. Total accumulation of antigen-specific interleukin (IL)-4 and IL-5 in 48 h peripheral blood mononuclear cell supernatants was not significantly different between groups. However, when cytokine kinetics were examined, responses segregated according to infection status. Sustained production of IL-4 and IL-5 beyond the first 24 h of stimulation and production of interferon-gamma were seen only in the group with clinical filariasis without active infection. CD8 T cells were the major source of IL-5 production in this group, while CD8 production of IL-5 was undetectable in any subject with active infection (asymptomatic microfilaremic or with clinical filariasis and active infection). These findings indicate that active infection, rather than clinical status, is most closely associated with cytokine patterns in lymphatic filariasis.

Diagnostic potential of fractionated Brugia malayi microfilarial excretory/secretory antigen for bancroftian filariasis

Due to the non-availability of sufficient parasite material from Wuchereria bancrofti, a heterologous filarial antigen from Brugia malayi has been investigated for the diagnosis of bancroftian filariasis. B. malayi microfilarial excretory/secretory antigen (BmmfES) effectively inhibited the binding of circulating filarial antigen fractions (CFA2-1,9,11 and 12) from microfilaraemic cases, and of W. bancrofti microfilarial excretory/ secretory antigen, to the immunoglobulin G (IgG) fraction of anti-filarial serum immunoglobulins. BmmfES was separated by ion-exchange chromatography on DEAE cellulose into 2 fractions, BmE DE1 and BmE DE2. BmE DE1 was marginally superior to whole BmmfES and BmE DE2 in detecting filarial IgG antibodies in human sera. 230 human sera from different groups of patients were screened against BmE DE1, which detected specific IgG in 83% of sera from microfilaraemic donors, 83% of sera from patients with clinical filariasis, 17% of sera from normal residents of an endemic area, and in none of the sera from persons living in a non-endemic area. The assay system using BmE DE1, with a sensitivity of 83% and specificity of 83%, should be very useful in detecting microfilaraemia, particularly in active clinical infections where the parasite is usually not seen.

Community diagnosis of Bancroftian filariasis

The objective of this study was to find the best tests for efficiently estimating the true prevalence of Bancroftian filariasis in endemic areas. The study population comprised 427 people over 10 years of age in an endemic village in Egypt. Four tests were evaluated; a standardized clinical examination, night blood examinations for microfilariae (50 μL thick films and 1 mL membrane filtration), and a test for circulating filarial antigen. 191 subjects (44·75%) had at least one positive test and were considered to have filariasis. The sensitivities of clinical examination, thick films, membrane filtration and antigen testing for filariasis were 16%, 50%, 64%, and 88%, respectively. Relative to membrane filtration of night blood, the filarial antigen test had a sensitivity of 97·5%, a positive predictive power of 71%, and a negative predictive power of 99%. None of the blood tests was a sensitive indicator of clinical filariasis; 69% of clinical cases were negative in all 3 blood tests and would have been missed if clinical examinations had not been done. Therefore, we recommend a combination of clinical examination and the filarial antigen test (with optional examination for microfilariae of those with positive antigen tests) for community diagnosis of Bancroftian filariasis in endemic areas.

Diagnostic utility of fractionated urinary filarial antigen

Urinary filarial antigen isolated from urine samples of microfilaraemic patients was analysed for its antigenic activity by immunoblotting and enzyme linked immunosorbent assay techniques. SDS-PAGE fractionation of urinary filarial antigen showed 11 protein bands, of which two showed reactivity with immunoglobulin-G fraction of filarial serum immunoglobulin in immunoblotting. Antigenic analysis of SDS-PAGE fractions of urinary filarial antigen by inhibition enzyme linked immunosorbent assay using filarial serum immunoglobulin-G andWuchereria bancrofti microfilarial excretory-secretory antigen revealed 3 fractions, numbers 5, 6 and 9 with significant activity. In indirect enzyme linked immunosorbent assay using fractions 5 and 6, filarial immunoglobulin-G antibody was detected in about 90% of microfilaraemics, 80% clinical filariasis and 20% of endemic normal individuals. Further, there was no phosphorylcholine epitope in these fractions. Fractions 5 and 6 can be a candidate antigens for the immunodiagnosis of filariasis.

T cell responsiveness correlates differentially with antibody isotype levels in clinical and asymptomatic filariasis.

To establish the relationships among T and B cell responses, active infection, and clinical manifestations in lymphatic filariasis, filarial-specific lymphocyte proliferation, IgG antibody isotypes, and IgE levels were determined in an exposed population: 31 asymptomatic amicrofilaremics, 43 microfilaremics, 12 symptomatic amicrofilaremics, and 52 elephantiasis patients. Lymphocyte proliferation was higher in elephantiasis patients and asymptomatic amicrofilaremics than in microfilaremics (P < .004). A proportion of asymptomatic amicrofilaremics (32%), elephantiasis patients (37%), and symptomatic amicrofilaremics (58%) showed antigen-specific lymphocyte unresponsiveness, and lymphocyte proliferation to filarial antigens correlated negatively with specific IgG4 levels (rho = -0.315, P < .001). As elevated specific IgG4 is an indicator of active infection, it is argued that active infection may result in lymphocyte hyporesponsiveness irrespective of clinical category. Of those with elevated specific IgE levels and high T cell proliferative responses, 70% had elephantiasis, suggesting these factors have a role in pathology. However, the existence of a proportion of elephantiasis patients with low anti-filarial IgE and T cell unresponsiveness to filarial antigens suggests that elephantiasis can be caused by distinct processes.

Correlation between the preferred biting site of Culex quinquefasciatus and the region of the body affected by clinical filariasis.

Entomological and filariasis surveys were conducted simultaneously in a rural and an urban environment in West Bengal from September 1986 to August 1987. The aim of the surveys was to see if any correlation existed between the preferred biting site of Culex quinquefasciatus, the filarial vector, and the region of the body affected by clinical filariasis. Significantly more mosquitoes (> 55%) attacked the thighs, legs and feet of human volunteers than other sites on their bodies, whether the volunteers were indoors or outdoors, in rural or urban environments. Significantly more patients had clinical filariasis of these lower body parts than of the upper parts. The vector's preferred biting sites and the anatomical sites most affected by clinical filariasis were therefore the same.

Analysis of human sera for filarial IgM antibody using antigen fractions isolated from immune complexes

Filarial IgM antibody response to various antigenic fractions isolated from immune complexes by SDS-PAGE viz., IC-2, IC-4, IC-7, and IC-9, was studied by ELISA. The IgM antibody response to almost all antigenic fractions was seen more in microfilaraemic group compared to the clinical filariasis group. The antibody response to IC-9 antigen fraction as compared to other fractions was found significantly higher in microfilaraemic patients than in patients with clinical manifestations. Ninety percent of microfilariae carriers and 75% of clinical filarial patients have shown IgM isotype to IC-9 antigen. Studies with various lectins have revealed the Con A binding nature of IC-9 antigen. This study suggests that IC-9 antigen could be another candidate antigen in the immunodiagnosis of lymphatic filariasis.

Evaluation of a Monoclonal-Antibody Based Antigen Assay for Diagnosis of Wuchereria Bancrofti Infection in Egypt

Conventional methods for diagnosis of Wuchereria bancrofti infection are insensitive and often impractical because of the need for night blood collections. A sensitive and specific antigen detection assay has been developed for W. bancrofti, which is based on a monoclonal antibody (AD12) that binds to a repeated epitope on a 200 kDa adult worm excretion product present in sera from infected humans. The only formal evaluation of this assay to date was performed with sera from India. In the present study, we have evaluated the performance of the AD12 antigen assay in two laboratories with sera collected in endemic and non-endemic areas in Egypt. Antigen was detected in 57 of 59 (97%) sera from microfilaremic subjects, and in 22 of 139 asymptomatic and amicrofilaremic subjects who reside in a highly endemic area. Antigen titers were significantly correlated with microfilaria counts (r = 0.41, P less than 0.01). Filarial antigen was not detected in most sera from amicrofilaremic subjects with clinical filariasis. Comparative antigen test results obtained from laboratories in Cairo and St. Louis agreed in 170 of 173 sera tested. Filarial antigen was not detected in sera from Egyptians with no history of residence in filaria-endemic areas. Specifically, nonendemic sera from patients with other parasitic infections (schistosomiasis, fascioliasis, ascariasis, etc.) were uniformly negative in the assay. We conclude that the AD12 filarial antigen assay is sensitive and specific for W. bancrofti infection in Egypt.

The occurrence of loiasis, mansonellosis and wuchereriasis in the Jarawa River Valley, Central Nigeria

In a study to assess the status of filariasis in the Jarawa River Valley of the savanna area of Nigeria, 940 self-selected residents from 10 villages were examined between March 1984 and April 1987. Overall results showed 105 (11.2%) had microfilaraemia and/or clinical signs of filariasis. Sixty-four (6.8%) and 20 (2.1%) persons, respectively, were infected with Mansonella perstans and Loa loa microfilariae (mff). Four of the 28 villagers examined had Wuchereria bancrofti mff in their night blood samples whereas 17 (1.8%) of all residents surveyed had clinical filariasis mainly due to lympho-obstructive manifestations: hydrocele ( n=11, 64.7%); enlargement of the inguinal nodes ( n=8, 47.1%) and elephantiasis ( n=2, 11.8%).

IgG antibody subclasses in human filariasis. Differential subclass recognition of parasite antigens correlates with different clinical manifestations of infection.

The four subclasses of IgG are distinct in structure, function, and degree of participation in the antibody response to complex antigens. Looking for differential responsiveness of potential pathogenetic significance, we have analyzed both quantitatively and qualitatively the filaria-specific IgG subclass responses of 20 patients with lymphatic filariasis presenting either with chronic lymphatic obstructive pathology and elephantiasis (CP) or with asymptomatic microfilaremia (MF). Subclass-specific monoclonal antibodies were used in an enzyme-linked immunosorbent assay to study IgG filarial antibodies quantitatively and in immunoblot analyses to determine qualitatively the subclass antibody specificities. Quantitatively, the most significant differences among patient groups were in levels of IgG4, which were more than 17 times higher in MF patients (geometric mean, 64.7 micrograms/ml) than in those with CP (mean, 3.7 micrograms/ml). When qualitative analyses were done on the same sera, major differences were noted, particularly in the recognition profiles of the IgG1, IgG3, and IgG4 responses. IgG1 and IgG3 responses to antigens were seen especially to antigens with m.w. greater than 68,000 in all patients with elephantiasis, whereas MF patients showed most of their reactivity to antigens less than 68,000. For IgG4, the MF patients showed prominent recognition of antigens throughout the entire range of m.w., whereas those with CP had very little IgG4 recognition of antigens of any m.w. Interestingly, this relationship was essentially reversed in the IgG3 antibody responses (especially to antigens greater than 68,000) and, to a lesser extent, the IgG1 responses. These findings demonstrate correlations of potential cause/effect significance between IgG4 antibody responsiveness and the immunomodulated asymptomatic MF form of clinical filariasis and between IgG3/IgG1 antibody responsiveness and the clinical presentation of CP.

A monoclonal antibody-based enzyme immunoassay for detecting parasite antigenemia in bancroftian filariasis.

We evaluated a monoclonal antibody-based enzyme immunoassay for detecting soluble parasite antigen in sera collected in an area in South India endemic for Wuchereria bancrofti. Filarial antigen was detected in sera from 56 of 57 microfilaremic patients, 9 of 64 aminofilaremic patients with clinical filariasis, and 11 of 70 endemic controls. Antigen was not detected in sera from patients from nonendemic areas who had a variety of other filarial and nonfilarial helminth infections. Parasite antigen titers were significantly correlated with microfilarial counts in night blood smears (r = .64, P less than .01). Negative antigen tests in patients with clinical filariasis may be explained in part by antibody-mediated clearance of circulating antigen. Antibodies to circulating W. bancrofti antigen were detected in 41 of 55 antigen-negative sera from patients with clinical filariasis. Despite this limitation, detecting parasite antigen by enzyme immunoassay provides significant advantages over previously available methods for diagnosing active W. bancrofti infection.

Detection of Circulating Parasite Antigen in Bancroftian Filariasis by Counterimmunoelectrophoresis

We used counterimmunoelectrophoresis (CIEP) with rabbit antibodies to Dirofilaria immitis and Brugia malayi to detect soluble filarial antigen in sera collected in a Wuchereria bancrofti-endemic area in South India. Filarial antigen was detected in 38 of 38 sera from microfilaremic patients, 3 of 48 sera from amicrofilaremic patients with lymphatic pathology, and 3 of 5 sera from former microfilaria carriers with negative blood examinations 6 months or more after diethylcarbamazine therapy. One of 32 endemic control sera, 0 of 35 nonendemic sera, and 0 of 20 B. malayi sera were positive. Antigenemia was equally detectable in sera collected at night or during the day (when microfilariae are absent from the blood). Parasite antigen was also detected in the urine of patients with positive serum tests. Antibodies to circulating filarial antigen (also detected by CIEP) were absent in all but 2 antigen-positive sera but present in 22 of 45 antigen-negative sera from clinical filariasis patients and in 9 of 31 antigen-negative sera from endemic controls. Parasite antigen detection by CIEP appears to be a sensitive, specific, and practical diagnostic test for active W. bancrofti infection.

Evaluation of fractionatedWuchereria bancrofti microfilarial excretory-secretory antigens for diagnosis of bancroftian filariasis by enzyme linked immunosorbent assay

TheWuchereria bancrofti microfilarial excretory-secretory antigens were fractionated into ES1, ES2, ES3 and ES4 by ultra-membrane filtration and evaluated for their diagnostic utility by enzyme linked immunosorbent assay. Three of the four fractions showed antigenic activity (ES2, ES3 and ES4). The antigen fractions ES2 and ES4 were highly active in the detection of filarial IgM antibody in clinical filariasis and microfilaraemia respectively. The chemical characterization of the ES2 and ES4 antigen fractions showed that they were glycoproteins

Selective primary health care: strategies for the control of disease in the developing world. VII. Filariasis.

At least 250 million people throughout the world are infected with filariae, and the number of such persons is increasing. Three species infect humans: Wuchereria bancrofti, Brugia malayi, and Brugia timori. The peak of microfilarial density in the blood usually occurs nocturnally. Transmission of filariasis is remarkably inefficient. In an endemic area, approximately 100,000 mosquito bites yearly are required for production of each new case of microfilaremia. Only a small proportion of those infected suffer any ill effects from these worms. Clinical filariasis can present with acute inflammation such as lymphangitis and lymphadenitis and with chronic lymphatic obstruction such as hydrocele and lymphedema of the limbs. Measures available for potential control include the widespread usage of mosquito nets, vector control, and chemotherapy with diethylcarbamazine. Unfortunately, the efficacy of the first of these is untested and the latter two are inadequate. More research is required on vector control, assessment of new drugs, and the development of vaccines.

IgE responses in human filariasis. I. Quantitation of filaria-specific IgE.

We have developed a noncompetitive solid phase radioimmunoassay to quantitate human IgE antibodies against soluble adult antigens of Brugia malayi (B.m.), a filarial parasite, in sera of patients with various forms of clinical filariasis in Madras, India. A single reference serum was shown to contain 23 micrograms/ml of B.m.-specific IgE by depletion analysis and was used as a standard serum throughout the study. The levels of specific IgE ranged in the patients sera from 2 to 23,000 ng/ml. When these individuals were divided into clinical groups, the individuals with tropical pulmonary eosinophilia had the highest levels (mean = 8630 ng/ml) and were significantly higher than all the other groups (p less than 0.001). The lowest levels were seen in patients with circulating microfilariae (mean = 30.5 ng/ml). Patients exhibiting lymphatic obstruction (i.e., chronic pathology group) had levels slightly higher than microfilaremics (mean = 68 ng/ml) but were not significantly different (p less than 0.1). Surprisingly, individuals living in endemic areas but who had no clinical signs of filariasis also showed appreciable levels of B.m.-specific IgE (mean = 55 ng/ml). The B.m.-specific IgE represented 0.1 to 48% of the total IgE. High percentages of specific IgE may be responsible for evoking allergic symptomatology in patients with tropical pulmonary eosinophilia.

Studies on human filariasis in Malaysia: the application of an indirect hemagglutination technique for immunodiagnosis.

The indirect hemagglutination (IHA) test done with turkey red cells was applied to 173 serum samples obtained from patients and persons exposed to Wuchereria bancrofti and Brugia malayi in endemic areas of Peninsular Malaysia. A crude extract of adult worms of the rat filaria, Breinlia booliati, was used as the antigen. When a titer of 1:16 was taken as negative, positive IHA test rates in sera from microfilaria-negative persons in endemic areas, microfilaremic cases, and patients with clinical filariasis were 13%, 75%, and 80%, respectively. Results of the IHA test correlated well with results obtained with the indirect fluorescent technique.

Immunodiagnosis of human filariasis by counterimmunoelectrophoresis using Litomosoides carinii antigens.

The presence of precipitin antibody and soluble circulating antigen was demonstrated in sera of individuals with clinical filariasis by counterimmunoelectrophoresis. Antigens derived from Litomosoides carinii and antisera raised in rabbits to the adult worm antigens were used for the detection of antibody and antigen in human sera. Of 35 subjects, 2 had microfilariae in the peripheral blood, 9 soluble circulating antigen, 19 antibody in sera, and 6 had both antigen and antibody. It suggests that 5.7% of cases diagnosed as bancroftian filariasis by parasitological examination can be increased to 62.8% by serological means.

Filariasis in The Sudan

Cases of bancroftian filariasis are reported from 2 areas in the east and west of The Sudan. Previously the disease has been known only in a small area in the central Sudan. The co-existence of onchocerciasis and bancroftian filariasis in eastern Sudan is described and the association of onchocerciasis and loaisis with clinical filariasis is discussed.