The spectrum of disease in lymphatic filariasis

Lymphatic filariasis affects predominantly the poorer sector of a community, who can least afford to have the disease. According to an estimate by the World Health Organization in 1984, more than 90 million people are currently infected. It is postulated that the different disease manifestations of filariasis are caused by different host immune responses. An understanding of the clinical spectrum of lymphatic filariasis is essential for the effective treatment and control of the disease, and for correctly correlating clinical status with host immune responses. The disease should be divided into lymphatic filariasis caused by adult worms and occult filariasis due to hyper-responsiveness of the host against microfilariae. The acute stage of filariasis is characterized by episodic adenolymphangitis, followed by obstructive lesions one or more decades later. In brugian filariasis, adenolymphangitis is most commonly observed at the inguinal region, and elephantiasis predominantly involves the leg below the knee. In bancroftian filariasis, the lymphatics of the male genitalia are frequently affected, leading to epididymo-orchitis and hydrocele. Lymphatic filariasis runs an accelerated clinical course in previously unexposed adult migrants. Occult filariasis is not a disease of public health importance. It is characterized by lymphadenopathy, asthmatic bronchitis, hypereosinophilia, and an increase in the production of antibodies, especially immunoglobulin, against microfilarial antigens.

Antibody responses to human lymphatic filarial parasites

The lymphatic filarial parasites, Brugia and Wuchereria, continue to present an immunological puzzle, particularly with respect to the development of natural resistance or damaging disease. We have approached this question by examining humoral responses to a few defined antigens of selected interest from these parasites, using sera from each category in the spectrum of filarial disease. Many antigens, such as the major adult surface protein of Mr 29,000 (29K), appear to be recognized at all stages of infection, but two components show interesting patterns of differential recognition. A triplet of proteins of Mr 65-75K associated with the microfilarial surface is preferentially bound by serum from patent microfilaraemic infections, whereas an unrelated 75K protein has been found to react only with antibody from amicrofilaraemic individuals. In general, however, the data obtained so far emphasize the importance of undertaking an antigenic analysis at the level of single epitopes. Such studies are now under way using recombinant proteins expressed in bacterial hosts.

T-cell activation and the balance of antibody isotypes in human lymphatic filariasis

Human filarial infection presents a spectrum of clinical states with two major poles: asymptomatic microfilaraemia and amicrofilaraemic chronic disease. Microfilaremia is associated with a Th1-type tolerance, and maximal IgG4 antibodies, while elephantiasis patients react across a broad range of immune parameters. In this review, Rick Maizels and his colleagues discuss recent advances in the immunology of human filariasis and present a summary of their latest studies in an endemic area of Indonesia.

Specificity of predominant IgG4 antibodies to adult and microfilarial stages of Brugia malayi

Human infections with filarial nematodes such as Brugia malayi are accompanied by unusually high titres of parasite-specific IgG4 antibodies. We have compared the profile of antigens recognised by filarial-specific IgG1 and IgG4 isotypes by Western blotting. Serum samples were collected from 120 subjects exposed to Brugia malayi, divided into three groups of asymptomatic amicrofilaraemic (endemic normal), microfilaraemic, and elephantiasis patients. Antigen preparations were tested from both adult B. malayi parasites, and from microfilariae; 24 distinct bands were analysed from the former, and 19 from the latter. Both qualitative scoring for band reactivity, and densitometric scanning of major bands, were employed. The consistent result was one of high and preferential IgG4 reactivity to a set of low molecular weight bands, of 15, 17, 20, 31 and 33 kDa; most of the 19 other bands showed higher reactivity with IgG4. Analysis of Western blot patterns showed an overall tendency for stronger IgG4 responses in microfilaraemic cases, and higher IgG1 responses in elephantiasis patients, consistent with published studies using ELISA on unfractionated parasite extracts. This study has defined an array of filarial antigens from each stage, and relative levels of IgG4 recognition, which will be important in unravelling distinct immune responses to this complex parasite.

Antibody responses to filarial infective larvae are not dominated by the IgG4 isotype

The humoral immune response in humans to filarial parasites is generally dominated by the IgG4 isotype, when measured by ELISA against somatic adult worm extract. In contrast, as we report here, antibodies reactive to somatic extracts of infective larvae are more equally represented by IgG1 and IgG4. Moreover, binding to surface exposed epitopes in immunofluorescence on larval stages is mediated foremost by IgG1 and IgM, secondarily by IgG2 and IgG3, and very little by IgG4. Both anti-L3 surface and somatic antibodies are strongest in elephantiasis patients, and tend to increase with age. Antibody to the L3 surface is also present in most microfilaraemic individuals who bear no detectable antibodies to the surface of the microfilarial stage. These results demonstrate that a stage- and isotype-specific response is mounted to the L3 surface which should be considered as a possible mediator of concomitant immunity in filariasis.

Differential decline in filaria-specific IgG1, IgG4, and IgE antibodies in Brugia malayi-infected patients after diethylcarbamazine chemotherapy

In human filariasis, the predominant serum antibody is IgG4, accompanied by significant IgE production. The ratio of IgG4 to IgE is highest in asymptomatic microfilaremic carriers, while chronic disease is associated with elevated IgG1-3. The changes in isotypes following chemotherapy with diethylcarbamazine (DEC) were studied in 2 groups of Brugia malayi-infected patients from Sumatra and South Kalimantan, Indonesia. Similar results were obtained from each group. IgG4 levels decreased sharply (65%-78%) within 12 months. IgG1 levels declined in a less consistent and extreme manner, and levels of IgG2 and IgG3 declined only in patients with elephantiasis, who also had the highest initial levels of these antibodies. IgE responses were relatively stable to therapy in microfilaremic patients (7%-28% reduction) and showed only moderate decline (56% over 2 years) in elephantiasis patients. Active filarial infection is thus associated with specific IgG4 antibodies, but there is independent expression of the IgE and IgG4 isotypes in filariasis.

Specific T cell unresponsiveness in human filariasis: diversity in underlying mechanisms

In an attempt to overcome T cell unresponsiveness to filarial antigens, 65 individuals belonging to the three clinical groups of elephantiasis patients, microfilaraemics, and asymptomatic amicrofilaraemics who exhibited unresponsiveness to Brugia malayi adult worm antigen (BmA) were studied. Peripheral blood mononuclear cells were cocultured with antigen and one of the following reagents that have been reported to be effective in reconstituting T cell proliferation: interleukin-2 (IL-2), interleukin-7 (IL-7), anti-interleukin-4, anti-interleukin-10, anti-CD2, anti-CD27, anti-CD28, indomethacin, phorbol myristate acetate (PMA), or calcium ionophore (A23187). We were able to overcome antigen-specific unresponsiveness in only a minority of the individuals studied. Co-culture with IL-2, IL-7, indomethacin and PMA were the only conditions which resulted in enhanced proliferation to BmA in these individuals. In general, unresponsiveness in elephantiasis patients was easier to reverse than in other clinical groups: in 50% of elephantiasis patients, in 12.5% of microfilaraemics and in 20% of asymptomatic amicrofilaraemics. The results indicate that more than one distinct immunological mechanism may account for the antigen-specific unresponsiveness in individuals exposed to and infected with brugian filariasis.

Differential antibody isotype reactivity to specific antigens in human lymphatic filariasis: gp15/400 preferentially induces immunoglobulin E (IgE), IgG4, and IgG2

Lymphatic filarial infection in humans is associated with a strong skewing of the immune response towards the TH2 arm, with prominent interleukin 4-producing cells and elevated levels of immunoglobulin G4 (IgG4) and IgE antibodies in peripheral blood. To determine how such a generalized TH2 imbalance governs responses to individual parasite antigens, the profiles of isotypes of antibodies to two recombinant proteins of Brugia spp. were studied. One molecule was the C-terminal portion of the filarial heat shock protein 70 (Bpa-26), representative of a cytoplasmic protein, and the second antigen was a single unit of the tandem repeats of a Brugia polypeptide (BpL-4), a secreted product which is prominently exposed to the immune system. Serum samples from 146 individuals resident in areas in which brugian filariasis is endemic were used, and it was found that whereas the levels of IgG1 and IgG3 responses to both Bpa-26 and BpL-4 were high, IgG4 and IgE antibodies to only BpL-4, not to Bpa-26, were prominent. Thus, an antigen which is chronically exposed to the immune system elicited a TH2-dependent isotype switch, as manifested by increased IgG4 and IgE responses. Moreover, IgG4 and IgE responses to BpL-4 showed a strong negative association, suggesting that mediators other than interleukin 4 must be responsible for such differential regulation of these two isotypes. When the data were analyzed as a function of clinical status, a striking association between elevated levels of IgG3 antibodies to Bpa-26 and manifestation of chronic obstructive disease was found; elephantiasis patients showed significantly higher levels of IgG3 antibodies to Bpa-26 than microfilaremics and asymptomatic amicrofilaremics. This indicates that an imbalance of isotypes of antibodies to particular filarial antigens might play a role in the pathogenesis of chronic disease.

HLA and elephantiasis in lymphatic filariasis

Lymphatic filariasis presents a spectrum of manifestations with infection-free asymptomatics at one end and elephantiasis at the other. In order to determine if any HLA antigens are associated with the development of elephantiasis, we compared the HLA frequencies in 55 elephantiasis patients with those in 40 controls consisting of individuals older than 45 years of age without any signs of elephantiasis. The only significant difference in class I antigen frequencies was observed for B27, which was present in 11% of the patients and absent in the controls. More differences were observed in HLA class II antigen frequencies. Both DR3 and the 2B3 epitope (on DQ6, DQ8, and DQ9 molecules) were significantly decreased in patients with elephantiasis whereas the DQ5 frequency was significantly higher in patients than in controls. Analysis of specific antibody isotype profiles revealed that DQ5-positive individuals had increased levels of antifilarial IgG3, an isotype known to be involved in tissue damage. These data suggest that HLA class II genes may control the course of Brugian filariasis by influencing the T-cell-dependent antibody repertoire.

Elevated cellular immune responses and interferon-gamma release after long-term diethylcarbamazine treatment of patients with human lymphatic filariasis

Cellular immune responses to filarial antigens were examined in persons before and 1 year after beginning treatment with diethylcarbamazine (DEC). The subjects (17 microfilaremics, 13 asymptomatic amicrofilaremics, and 13 with elephantiasis) had not responded to Brgia malayi adult worm antigen (BmA) before chemotherapy. T cell proliferative responses to BmA improved significantly after therapy in the 3 clinical groups (P < .05) but was highest in the elephantiasis patients and asymptomatic amicrofilareimics. Cytokine release profiles after stimulation with parasite antigen were analyzed. Production of interferon (IFN)-gamma by BmA-stimulated mononuclear cells increased significantly after DEC treatment (geometric mean, 39.6-55.7 U/mL; P < .05), largely due to improved responses in elephantiasis patients and asymptomatic amicrofilaremics. In contrast, BmA-induced interleukin (IL)-4 release did not change significantly in these same patients after treatment. Thus, both microfilaremic and amicrofilaremic infections with B. malayi are associated with similar down-regulation of proliferative T cell function and IFN-gamma release.

A polymerase chain reaction assay for the detection of Brugia malayi in blood

There is need for sensitive, rapid, species-specific diagnosis of Brugia filarial parasites because traditional methods are tedious and time-consuming, with little guarantee of species specificity. A polymerase chain reaction (PCR)-based assay was developed using the Hha I family of highly repeated DNA sequences from Brugia. The assay was tested on 124 human blood samples collected in a field study in Indonesia. These included 66 microfilaria-positive samples from patients in an area endemic for Brugia, 30 from healthy individuals from the same endemic area, and 28 from healthy individuals from a nonendemic area. Twenty-eight blood samples collected in a village in French Polynesia endemic for Wuchereria bancrofti, but not B. malayi, were also tested. The blood samples were screened using the traditional blood smear and membrane filtration methods, which served as the gold standards to which the PCR assay was compared. The samples were digested with proteinase K, extracted with phenol and chloroform, and dialyzed. A fraction of the dialyzed product was used in PCRs using Hha I-specific primers. The PCR assay correctly identified all of the microfilaria-positive samples as PCR positive and all of the nonendemic samples as PCR negative. Additionally, 26 of 30 samples from healthy individuals in the endemic area were also identified as PCR negative, while four were PCR positive. It is likely that these four individuals had very low-level or cryptic infections, and that the PCR assay detected circulating DNA released from dead filariae. The results indicate that the Hha I PCR detection system is rapid, species-specific, and sensitive.

Elevated levels of T cell activation antigen CD27 and increased interleukin-4 production in human lymphatic filariasis

To assess the immunological changes occurring during filarial infection with or without elephantiasis, 145 patients in different clinical groups from an endemic area in Indonesia were compared with respect to plasma levels of both soluble CD25 (sCD25) and sCD27; interleukin-4 (IL-4) and interferon-gamma release by peripheral blood mononuclear cells was also measured in a smaller subset of individuals. Levels of sCD27 were significantly elevated in elephantiasis and microfilaremic patients compared with endemic normals (p < 0.002), whereas sCD25 levels remained low in microfilaremics and was only slightly elevated in elephantiasis patients compared with endemic normals (p < 0.02). As activated T cell populations release both sCD27 and sCD25, these findings imply that there is filarial-driven activation of a T cell subset that releases sCD27 rather than sCD25. The expansion of a particular T cell population by filarial parasites is further suggested by the enhancement in both IL-4-producing and CD4+CD27-T cells in PBMC from elephantiasis and microfilaremic patients compared with endemic normals. More detailed characterization and comparison of CD27-lymphocytes from these individuals may identify mechanisms involved in the pathogenesis of lymphatic filariasis.

Primary structure of and immunoglobulin E response to the repeat subunit of gp15/400 from human lymphatic filarial parasites

We have isolated and sequenced clones encoding the repeated subunit of the surface-associated glycoprotein gp15/400 from the two nematode species predominantly responsible for lymphatic filariasis in humans: Brugia malayi and Wuchereria bancrofti. The amino acid sequence of the 15-kDa subunit, derived from the nucleotide sequence of the gene fragment from B. malayi, is identical to that previously reported for B. pahangi, whereas the derived W. bancrofti protein sequence differs in only 7 of 132 residues. The identity of the protein in the two Brugia species allowed us to use a recombinant from B. pahangi to examine the serological response of adult Indonesian subjects infected with B. malayi. The polymerase chain reaction-amplified subunit was expressed in Escherichia coli via the pDS56/RBS11 plasmid and purified by nickel-chelating chromatography. A significant proportion of individuals produced antigen-specific immunoglobulin E (IgE). This was most pronounced in the individuals with elephantiasis, with 14 of 15 showing elevated titers and a mean of 3.2 ng of specific IgE ml-1. Only 2 of 15 microfilaremic individuals possessed elevated titers of specific IgE, with a mean of 0.045 ng ml-1 for the group as a whole. Asymptomatic amicrofilaremic residents showed approximately equal numbers of responders (defined as having a value in the radioimmunoassay greater than two standard deviations above controls) and nonresponders, with a group mean of 1.2 ng of antigen-specific IgE ml-1.

Differential expression of IgE and IgG4 specific antibody responses in asymptomatic and chronic human filariasis

A population of 164 adult individuals resident in an area endemic for Brugia malayi lymphatic filariasis has been studied for humoral immune responses to filarial parasites. Antibody levels to Ag extracted from adult worms were determined for each of the IgG subclasses, for IgM and for IgE. The dominant isotype of antifilarial antibody was IgG4, which represented 88% of total IgG in asymptomatic microfilaremics, most of whom possessed 100 to 1000 micrograms/ml of specific antibody of this subclass (geometric mean 762 micrograms/ml). Patients with chronic disease (elephantiasis), who were generally amicrofilaremic, had substantially higher levels of IgG1, IgG2, and IgG3, but a 3.4-fold lower geometric mean level of specific IgG4 (222 micrograms/ml) than asymptomatics with or without microfilaremia. In contrast, specific IgE antibody levels in cases of elephantiasis were on average 4.5 times higher than those found in the asymptomatic carrier state. The majority of microfilaremics were therefore typified by extremely high specific IgG4 concentrations and relatively low IgE reactivities, whereas clinical cases tended to show the reverse relationship. The possible roles of these isotypes and the implications of changing IgG4/IgE balances in disease are discussed.

Differential expression of IgE and IgG4 specific antibody responses in asymptomatic and chronic human filariasis

A population of 164 adult individuals resident in an area endemic for Brugia malayi lymphatic filariasis has been studied for humoral immune responses to filarial parasites. Antibody levels to Ag extracted from adult worms were determined for each of the IgG subclasses, for IgM and for IgE. The dominant isotype of antifilarial antibody was IgG4, which represented 88% of total IgG in asymptomatic microfilaremics, most of whom possessed 100 to 1000 micrograms/ml of specific antibody of this subclass (geometric mean 762 micrograms/ml). Patients with chronic disease (elephantiasis), who were generally amicrofilaremic, had substantially higher levels of IgG1, IgG2, and IgG3, but a 3.4-fold lower geometric mean level of specific IgG4 (222 micrograms/ml) than asymptomatics with or without microfilaremia. In contrast, specific IgE antibody levels in cases of elephantiasis were on average 4.5 times higher than those found in the asymptomatic carrier state. The majority of microfilaremics were therefore typified by extremely high specific IgG4 concentrations and relatively low IgE reactivities, whereas clinical cases tended to show the reverse relationship. The possible roles of these isotypes and the implications of changing IgG4/IgE balances in disease are discussed.

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.

Ivermectin and diethylcarbamazine trials in leaf monkeys (Presbytis cristatus) infected with Wuchereria kalimantani

Clinical trials of Ivermectin in single oral doses of 200, 400, and 1,000 mg/kg body weight or in multiple doses of 200 mg/kg body weight for 5 consecutive days were performed in leaf monkeys (Presbytis cristatus) infected with Wuchereria kalimantani. Optimal microfilaricidal effect occurred at 200 mg/kg body weight. The drug was less effective than diethylcarbamazine in this animal model for human filariasis but had no adverse effects.

Towards a filariasis-free community: evaluation of filariasis control over an eleven year period in Flores, Indonesia

A population of 202 residents in an area endemic for Brugia timori lymphatic filariasis was treated in a diethylcarbamazine control programme commencing in 1977. All individuals were treated twice with diethylcarbamazine on a mass basis with additional selected treatment for cases with manifestations of infection. Clinical features of lymphatic filariasis were recorded annually until 1982, and the population re-assessed in 1988, six years after the completion of chemotherapy. Microfilarial counts were made on each occasion, and circulating filarial antigen levels measured for 1982 and 1988. The results showed a dramatic and sustained reduction in the rate of elephantiasis and adenolymphangitic disease, and of circulating antigenaemia, and the prevalence of microfilaraemia was reduced to zero by the end of the study.

Secreted antigens of filarial nematodes: a survey and characterization of in vitro excreted/secreted products of adult Brugia malayi

We report here a broad analysis of the excretory/secretory (E/S) products of adult Brugia malayi, collected by in-vitro cultivation of the parasite. Culture media and conditions were optimized, and non-essential amino acids were found to be crucial for efficient protein synthesis under cell- and serum-free culture conditions. A close correlation was found between total protein secretion, phosphorylcholine-bearing antigen release and lactate production on each day of culture, indicating that E/S molecules are actively secreted. Parasites cultured in vitro take 2-3 days to adjust to the new environment, and show peak levels of secretion at days 3 and 4. The active secretion of phosphorylcholine by the parasite therefore justifies the measurement of this molecule as an indication of active infection, possibly reflecting total worm burdens. By comparing metabolically labelled E/S from male and female worms, several molecules of low mol. wt, namely 10,000, 13,000, 14,000 and 22,000, together with high mol. wt components of above 12,000 were found to be female specific. Tracing the origin of the E/S products, several molecules were also found to be associated with the surface. Among these, there are at least two glycoproteins, 29,000 and 51,000 of which the 29,000 molecule is a major surface protein. The immunogenicity of the E/S was examined and antigenic cross-reactivity was found with sera from most filarial infections but not with non-filarial nematodiases such as hookworm or Trichinella. However, two molecules of low mol. wt, 15,000 and 19,000, were not recognized by anti-Onchocerca sera and appeared to be potential Brugia-specific diagnostic molecules. Possible functional roles of the adult E/S products were examined but we could find no evidence of protease activity in the E/S or glutathione S-transferase activity in either the E/S or in whole somatic extract.

Heat shock cognate 70 is a prominent immunogen in Brugian filariasis

A cDNA expression library constructed from RNA derived from adult stage Brugia pahangi (mixed sexes) was screened with pooled sera from chronic, amicrofilaremic cases of human lymphatic filariasis from the Indonesian island of Tanjungpinang, where Brugia malayi is endemic. Polyclonal antisera raised to purified beta-galactosidase fusion proteins from two of the most highly reactive clones identified a protein of Mr 70,000 in all stages examined (microfilariae, L3 and adults) of both B. malayi and Brugia pahangi. Derivation of the amino acid sequence from these two overlapping cDNAs identified the encoded protein as a member of the heat shock protein 70 family, and showed the closest similarity to the constitutively expressed "heat shock cognate 70" (hsc70) protein. Hybridization of hsc70 cDNAs to RNA and DNA from B. pahangi under stringent conditions identified a major transcript of 2.4 kb and revealed the existence of a family of related genes. In vitro culture of larval stages of B. pahangi at elevated temperatures (43 degrees C) resulted in increased expression of hsc70, and a classic heat shock response in which five proteins (mr 18,500, 22,000, 62,000, 70,000, and 85,000) were exclusively synthesized in microfilariae. Analysis of cross-reactivities by Western blotting implied that antibody generated by infection with B. malayi was directed at filarial-specific determinants of Brugia hsc70. However, ELISA with recombinant fusion proteins for both Plasmodium falciparum and Schistosoma mansoni hsc70 indicated that some individuals with Brugian or Bancroftian filariasis did produce antibodies which cross-reacted with plasmodial and schistosomal homologs. Thus filarial-specific antibody responses were not generated in all individuals, indicating that this molecule would not be suitable for diagnostic purposes. ELISA with a purified beta-galactosidase fusion protein from B. pahangi showed antibody responses to hsc70 across the clinical spectrum of filariasis. Alignment of the derived amino acid sequences from B. pahangi, P. falciparum, S. mansoni and rat hsc70 homologs, and comparison of the immunologic reactivity of the products of the two cDNA clones by Western blotting and ELISA suggested that these determinants were located primarily at the C terminus of the protein.

Heat shock cognate 70 is a prominent immunogen in Brugian filariasis

A cDNA expression library constructed from RNA derived from adult stage Brugia pahangi (mixed sexes) was screened with pooled sera from chronic, amicrofilaremic cases of human lymphatic filariasis from the Indonesian island of Tanjungpinang, where Brugia malayi is endemic. Polyclonal antisera raised to purified beta-galactosidase fusion proteins from two of the most highly reactive clones identified a protein of Mr 70,000 in all stages examined (microfilariae, L3 and adults) of both B. malayi and Brugia pahangi. Derivation of the amino acid sequence from these two overlapping cDNAs identified the encoded protein as a member of the heat shock protein 70 family, and showed the closest similarity to the constitutively expressed "heat shock cognate 70" (hsc70) protein. Hybridization of hsc70 cDNAs to RNA and DNA from B. pahangi under stringent conditions identified a major transcript of 2.4 kb and revealed the existence of a family of related genes. In vitro culture of larval stages of B. pahangi at elevated temperatures (43 degrees C) resulted in increased expression of hsc70, and a classic heat shock response in which five proteins (mr 18,500, 22,000, 62,000, 70,000, and 85,000) were exclusively synthesized in microfilariae. Analysis of cross-reactivities by Western blotting implied that antibody generated by infection with B. malayi was directed at filarial-specific determinants of Brugia hsc70. However, ELISA with recombinant fusion proteins for both Plasmodium falciparum and Schistosoma mansoni hsc70 indicated that some individuals with Brugian or Bancroftian filariasis did produce antibodies which cross-reacted with plasmodial and schistosomal homologs. Thus filarial-specific antibody responses were not generated in all individuals, indicating that this molecule would not be suitable for diagnostic purposes. ELISA with a purified beta-galactosidase fusion protein from B. pahangi showed antibody responses to hsc70 across the clinical spectrum of filariasis. Alignment of the derived amino acid sequences from B. pahangi, P. falciparum, S. mansoni and rat hsc70 homologs, and comparison of the immunologic reactivity of the products of the two cDNA clones by Western blotting and ELISA suggested that these determinants were located primarily at the C terminus of the protein.

Identification, synthesis and immunogenicity of cuticular collagens from the filarial nematodes Brugia malayi and Brugia pahangi

The major structural proteins of the cuticle of the filarial nematode parasites Brugia malayi and Brugia pahangi were identified by extrinsic iodination and sensitivity to clostridial collagenase. At least 16 acidic components were identified in adult worms by 2-dimensional electrophoresis, with molecular weights ranging from 35,000 to 160,000. These proteins appear to be cross-linked by disulphide bonds, and localised in the basal and inner cortical layers of the cuticle. The outer cortex, containing the epicuticle, is insoluble in 1% sodium dodecyl sulphate and 5% 2-mercaptoethanol, and can be isolated free of cellular material. Despite their inaccessibility to the immune system in intact worms, antibodies to the cuticular collagens are provoked in humans infected with a variety of filarial parasites. Immunological cross-reactivity was demonstrated between a 35 kDa component and human type IV (basement membrane) collagen. Autoantibodies to type IV collagen were detected in a number of individuals with lymphatic filariasis, although no correlation could be drawn with observed pathology. Synthesis of cuticular collagens is discontinuous, occurs at negligible levels in mature adult male worms, and does not appear to involve the production of small molecular weight precursors, in contrast to Caenorhabditis elegans. Hybridisation with a heterologous cDNA probe coding for the alpha 2 chain of chicken type 1 collagen suggests that they are encoded by a multigene family.

Circulating antibodies and antigens in Presbytis monkeys infected with the filarial parasite Wuchereria bancrofti

Levels of circulating filarial antigen, and humoral antibody to other defined antigenic targets, were measured over the course of experimental infection of three Presbytis cristatus monkeys with Wuchereria bancrofti. Circulating antigen levels, measured with an anti-phosphorylcholine monoclonal antibody, varied widely although all animals were positive for some period of the infection. Circulating antigen levels tended to be inversely related to the titre of anti-phosphorylcholine antibody, and this trend was maintained even following acid dissociation and inactivation of immune complexed host antibody. Other antibody specificities were measured by Western blotting against somatic proteins and immunoprecipitation of surface antigens. Amongst somatic antigens, targets between 14,000 and 200,000 daltons were recognised by monkey antibodies, but no correlation with infection status could be discerned. Likewise when measuring the response to the 29,000 dalton major adult surface glycoprotein, one animal produced a rapid response but the others did not recognise it until late in infection. In general, the experimental findings are characterised by wide variability between individuals, as may perhaps be expected in a primate host for a human spectral disease.

[Discrimination of geographic strains of periodic Brugia malayi by the cuticular ornamentation of the male]

A comparative study of five periodic human strains of Brugia malayi, originating from India, China, Korea, Malaysia and Indonesia, is given. This morphological analysis is based on males; the "standard" characters (oesophagus, papillae, spicules...) appear identical. On the contrary, the cuticular ornamentation of the posterior region--which is composed of the area rugosa and of a system of bosses and constitutes a secondary non-skid copulatory apparatus--differs following the geographical origin of the strain. A key is given, based on this character. 1(2) At 800-1,200 micron from the tip of tail, numerous cuticular bosses present on the right side of the body (fig. 2 and 8 B). 2(1) At 800-1,200 micron from the tip of tail, cuticular bosses absent or scarce on the right side of the body (fig. 8 D). 3(4) At 1,800-1,200 micron from the tip of tail (fig. 4), scarce and slightly projecting cuticular bosses on the dorsal side of the body contrasting with well projecting lateral cuticular bosses (fig. 9 E and F). Anterior extremity of the area rugosa made by a few stripes of tiny bosses linked transversally (fig. 9 A). 4(3) At 1,800-2,200 micron, numerous cuticular bosses on the dorsal side of the body (figs. 5, 6 and 7). Anterior extremity of the area rugosa made by the stripes of longitudinal rods (fig. 9C). 5(6) Oblong transversally stretched cuticular bosses on the dorsal and left sides of the body, anteriorly to the area rugosa (fig. 5); big oblong bosses on the left side (fig. 9 B). Transversal wrinkles and stripes of rods absent on the dorsal side of the body. 6(5) Round cuticular bosses on the dorsal and left sides of the body anteriorly to the area rugosa (figs. 6 and 7): no big oblong bosses on the left side. Transversal wrinkles or stripes of rods present on the dorsal side of the body (fig. 9 D). Nomenclaturally, such differences could be used in defining different taxa, but it could be useful to perform "blind determination" (material without labelling), to study conveniently the morphology of microfilariae (often an excellent indication for speciation in that group of Nematodes) and, evenly, to proceed to parallel studies on isoenzymes. However, whatever could be the taxonomical conclusion, the differences observed in Brugia malayi originating from different regions appear to the sufficient to consider the existence of four distinct diseases.

Monoclonal antibody to a unique surface epitope of the human filaria Brugia malayi identifies infective larvae in mosquito vectors

We describe properties of an IgM monoclonal antibody (NEB-D1E5) raised against the human filarial parasite Brugia malayi. The antibody reacts with a stage- and species-specific determinant located on the surface of the infective-stage larva, as determined by indirect immunofluorescence. To use this reagent in epidemiological field studies, we developed an enzyme-linked immunoassay with which B. malayi larvae can be differentiated from other filarial parasites in mosquito vectors, including the morphologically indistinguishable parasite of animals Brugia pahangi. The immunoenzyme assay was 91-94% specific and 90-97% sensitive when performed on infected mosquitoes. In the absence of mosquito tissue, the levels of specificity and sensitivity increased to 100% and 97.5-100%, respectively. Binding of antibody to the surface of living larvae was abrogated by treatment of the worms with the enzymes pronase and proteinase K and with the detergents Triton X-100, octyl beta-D-glucopyranoside, and 3-[(3-cholamidopropyl)dimethylammonio]-1-propanesulphonate (CHAPS). In contrast, treatment with trypsin, endoglycosidase-F, O-Glycanase, N-Glycanase, lipase, various phospholipases, boiling, 2-mercaptoethanol at 37 degrees C, or periodate did not reduce the antigenicity of the larval surface to antibody NEB-D1E5. These results suggest that the species-specific epitope is a peptide domain attached to a hydrophobic anchoring residue.

Periodicity studies of Brugia malayi in Indonesia: recent findings and a modified classification of the parasite

We have recently reinvestigated the position of Brugia malayi in Indonesia. Periodicity patterns of microfilariae from several endemic areas were mathematically determined. We have also designed a simple method to quantify microfilaria periodicities in these studies. To determine whether periodicity patterns of microfilariae were stable, repeated studies were performed in the same individual or community. Other biological features of the parasite were also investigated. The parasite from each isolate was taxonomically identified as B. malayi. It could be classified into two distinct biological types, one nocturnally periodic and the other aperiodic, nocturnally subperiodic, or nocturnally periodic. We therefore propose to modify Wilson's classification, using the biological behaviour of the parasite in animals as the discriminating feature, and classify the two types as zoophilic and anthropophilic B. malayi.

Antigenic characterization of adult Wuchereria bancrofti filarial nematodes

Adult Wuchereria bancrofti were recovered from infected Presbytis cristatus monkeys and radio-isotope labelled extrinsically with 125I and in vitro with [35S]methionine. 125I labelling of the surface of adult W. bancrofti permitted a comparison between the major surface antigens of this species and those from the related lymphatic filariae, Brugia malayi and B. pahangi. All species bear a prominent Mr 29,000 surface antigen but among the differences observed were the strongly labelled molecules with Mr 58,000 and 67,000 in W. bancrofti which are extremely faint in the Brugia species. The [35S]methionine label was effectively incorporated into somatic parasite proteins in vitro although it was not possible to identify any secreted proteins in this way. The antigenicity of these products was investigated using a variety of sera from homologous and heterologous infections and the immunoprecipitation patterns highlighted particular differences between somatic proteins of male and female worms. One secreted antigen was detected, however, by virtue of its phosphorylcholine epitopes, in the culture medium of mixed adult worms; medium from male W. bancrofti adults was negative although homogenates of either sex of adult W. bancrofti were strongly positive in the same system.

Secreted and surface antigens from larval stages of Wuchereria bancrofti, the major human lymphatic filarial parasite

Antigenic proteins of microfilariae and infective larvae of Wuchereria bancrofti have been identified by intrinsic and extrinsic radiolabelling, and specific immunoprecipitation with sera from filarial patients. From 125I surface-labelling experiments, the most prominent antigen on both stages is of relative molecular mass (Mr) 17 000, while a molecule of similar size is both synthesized and released in vitro following labelling with [35S]methionine. A second similarity between the two stages is the production and secretion of a Mr 21 000 component, which is, however, not detected on the worm surfaces. A series of additional proteins from larval W. bancrofti are described from each parasite compartment (secreted, surface and somatic) and the antigenicity and specificity of these components explored with serum from patients with filariasis due to W. bancrofti or Brugia species, and with onchocerciasis. Among additional molecules released in vitro we have found a Mr 51 000 antigen from both stages, and also several proteins which are not recognised by antibody from human filarial patients.

Molecular characterization of antigens of lymphatic filarial parasites

Three species of filarial worms,Wuchereria bancrofti, Brugia malayiandBrugia timori, are the causative agents of lymphatic filariasis in man, defined by the characteristic tropism of adult worms of each species for the afferent lymphatics. Reproductive activity leads to the release of large numbers of microfilariae, which circulate in the vascular system, and upon ingestion by an appropriate mosquito vector, develop through to infective third-stage larvae (L3) within 10–14 days. After a subsequent bloodmeal, the infective larvae enter the definitive host via the wound and mature to the adult stage over several months, involving two moults, during which the entire nematode exoskeleton (cuticle) is replaced.

Combined low dosage and short term standard dose treatment with diethylcarbamazine to control Timorian filariasis

A combined weekly low dosage and short term standard dose treatment with diethylcarbamazine (DEC) to control Timorian filariasis is described. Weekly low dosage DEC was distributed by the village chief to all villagers for 6 months. The dosage of DEC was 50 mg weekly for group A, and 100 mg for group B. Children below 10 years of age received half the adult dose. Following the initial phase of low dosage treatment, 5 mg DEC/kg was distributed by one of us to all villagers for 6 consecutive days. The results of treatment were evaluated approximately one year later. There was no difference between the results of treatment with 50 mg DEC weekly compared to the 100 mg dosage. The microfilaria, adenolymphangitis and lymphoedema rates decreased drastically in both groups, similar to the results of our previous studies. Side reactions during low dosage and standard dose treatment of DEC were characteristically mild.

Adverse reactions to a single dose of diethylcarbamazine in patients with Brugia malayi infection in Riau Province, West Indonesia

A study on the adverse reactions, occurring after treating microfilaremic patients infected with B. malayi, revealed that all reacted to a single oral dose of DEC (5 mg/kg). The major reactions were fever, headache, anorexia, abdominal pain, muscle and joint pains, nausea and vomiting. There seemed to be no association between the time of fever onset and microfilarial density, but the number of cases observed was too small to make any firm conclusion. There was a tendency for more severe reactions to occur in patients with higher microfilaria counts. Local reactions, probably due to destruction of adult worms, were seen in 3 patients. The reactions were serious enough to necessitate the patients spending approximately 48 hours in bed.

Diagnosis and treatment of lymphatic filariasis

The lymphatic filariases, Wuchereria bancrofti, Brugia malayi, and B. timori, infect nearly 100 million people throughout the tropics, but mainly in Africa and southeast Asia. Over 900 million people live in endemic, areas at risk to the infection. The filarial parasites reproduce slowly, whereas their mosquito vectors are quickly-reproducing opportunists. Thus, although vector control can reduce the risk of transmission, the parasite itself would seem a more vulnerable target for prolonged attack. In this article, Felix Partono discusses the clinical diagnosis of f lariasis and argues that the disease can be effectively controlled by attacking the parasites in infected communities, using diethyl-carbamazine (DEC) as the drug of choice.

Treatment of elephantiasis in a community with timorian filariasis

To elucidate the issue of lymphoedema and elephantiasis in our previous reports, all data on the two clinical conditions have been reviewed and analysed. The various characteristics of the swelling are described and factors that may influence the outcome of treatment with diethylcarbamazine (DEC) analysed. The results showed that all cases with lymphoedema could be treated with DEC, irrespective of the size of the swelling, and that in most cases the swelling disappeared within one year. On the other hand, it required at least two to four years for most swelling to disappear in people with elephantiasis. Elephantiasis of the arms was easier to treat than of the legs. Bilateral elephantiasis of the legs were more difficult to treat than unilateral elephantiasis. Elephantiasis of less than three to five years' duration were easier to treat than that of longer duration. Individuals with a higher grade of elephantiasis were more difficult to treat than those with a lower grade of elephantiasis. The age and sex of patients did not influence the outcome of treatment.

Low dosage diethylcarbamazine administered by villagers for the control of timorian filariasis

The results of mass treatment using low dosage diethylcarbamazine (DEC) in three small villages in West Flores, Indonesia, endemic for Brugia timori are described. DEC was distributed on a weekly basis by motivated persons in the community to nearly all villagers for 18 months. An educational programme was developed which focused on describing the relationship between microfilaraemia, vector and disease manifestations, the danger of repeated attacks of adenolymphangitis, and the efficiency of DEC in eliminating the parasites and attacks. During the consolidation phase motivated persons were assigned to treat promptly all cases with acute filariasis and to distribute DEC to all new residents. With this programme the microfilaria rates decreased to very low levels, even as detected by the use of membrane filtration techniques. The adenolymphangitis rates also decreased. An unexpected bonus was the cure of "elephantiasis" in many people. Mild side effects attributed to DEC were encountered only during the first few weeks of treatment.

Cross-reactive surface antigens on three stages of Brugia malayi, B. pahangi and B. timori

Surface antigens of three stages of three species of the filarial nematode genus Brugia have been analysed by radio-iodination and immunoprecipitation. These surface antigens have been shown to be characteristic for each stage by polyacrylamide gel electrophoresis. For example, infective larvae and adult worms have relatively complex patterns while microfilariae have few bands which are not found when other stages are radio-isotope labelled by the same technique. The surface antigens of Brugia malayi, B. timori and B. pahangi adult worms are all closely homologous, as are the surface antigens of infective larvae of the same three species, and of microfilariae of B. malayi and B. pahangi. Immunoprecipitation revealed that antibody raised in mice against one stage or species reacted with surface antigens from other stages and species. For example, sera raised against B. pahangi male adults reacted strongly with surface antigens from all three species. This cross-reactivity was dominant despite the apparent stage-specificity of the surface pattern seen on SDS-PAGE analysis. Moreover, in cross-immunization experiments, infective larvae were able to stimulate a secondary antibody response in mice previously primed with microfilarial surface antigens. The major microfilarial surface antigens (of mol. wt 65-70 000 Daltons) were recognized by serum antibody from microfilariae-, infective larvae- or adult-infected animals. Thus, although the dominant antigens from each stage are of different molecular weight, cross-reactions with stage-specific antisera suggest that there must be shared epitopes on Brugia surface antigens from each stage. Such shared antigenic determinants dominate the immune response, although other evidence, including the differences in molecular weight, indicates the existence of stage- and species-specific components.

Antigenic analysis of Brugia timori, a filarial nematode of man: initial characterization by surface radioiodination and evaluation of diagnostic potential

The antigenic composition of Brugia timori has been investigated with surface labelling techniques and defined sets of parasite molecules have been identified on infective larvae, adult worms and microfilariae. Iodinated preparations from all three stages were assessed for immunodiagnostic potential with a small number of serum samples from human filariasis patients. In these tests, reaction with infective larval antigen was the clearest indicator of infection. Reactivity to microfilarial antigens however, correlated poorly with incidence of infection. These experiments show that levels of anti-parasite antibody appear to increase as filarial disease becomes more severe. In contrast to some reports, antibody to microfilarial surface antigens is present in sera from several patients with circulating microfilariae. The immunodiagnostic potential of these tests is indicated by the detection of a few individuals who have high levels of antibody but no outward signs of infection.

Antigen-specific suppressor T lymphocytes in human lymphatic filariasis

Immune responses to parasite antigens are much lower in patients with microfilaremia than in persons with other manifestations of brugian filariasis. To determine whether hyporeactivity is associated with changes in populations of lymphocytes that regulate immune responses, we quantitated helper and suppressor T cells in the blood of patients infected with Brugia malayi. Increased numbers of suppressor T cells were present in 15 of 17 patients with microfilaremia and in six of 11 patients with elephantiasis. This increase correlated with hyporeactivity to filarial antigens but not to nonparasite antigens. Removal of suppressor T cells activated in vivo or in vitro improved reactivity to filarial antigens. These results suggest that immunosuppression induced by filarial parasites is a possible mechanism of survival of these organisms in an immunocompetent host.

The long term effects of repeated diethylcarbamazine administration with special reference to microfilaraemia and elephantiasis

The result of mass treatment with 50 mg diethylcarbamazine (DEC) per kg body weight followed by two annual selective retreatments in an area highly endemic for Brugia timori infections are described. The criteria for selective re-treatment are simple and practical for use in rural areas. An education programme was developed which focused on describing the relationship between adenolymphangitis and filarial infections, the danger of repeated attacks and the efficiency of DEC in eliminating these attacks. Motivated persons in the community were charged with the responsibility of promptly treating all cases with acute clinical manifestations. With this programme the microfilaria rate by finger prick decreased from 24% to 0%, and by Nuclepore filtration from 30% to 5%. The adenolymphangitis rate decreased from 46% to 11% and the "elephantiasis' rate from 17% to 4%.

Further studies on the development of Wuchereria bancrofti in laboratory animals

In an attempt to obtain a small animal laboratory model for Wuchereria bancrofti Mongolian gerbils and hamsters were infected with third-stage larvae of strains of the parasite from Indonesia and China. Gerbils were necropsied at 7 to 591 days and larvae recovered up to 219 days. The third molt occurred on or before 10 days and worms found after 14 days were in the fourth stage. More worms were recovered early in the infection (7 to 30 days) than in older infections. The worms were usually recovered from the testes, pelt and carcass and heart and lungs. An adult male worm was recovered on one occasion from the lung of a gerbil at 92 days. The parasite was also found to develop in hamsters with results similar to those in gerbils. Gerbils and hamsters were given antithymocyte sera before and after infection and more worms were recovered and the worms larger in size in some treated animals. Continued studies with geographic strains of W. bancrofti in various animals should be encouraged in order to find a small laboratory animal model for the parasite.

A study on vectors of Bancroftian filariasis in West Flores, Indonesia

A brief survey was conducted in a filariaendemic village of Robek, West Flores, Indonesia, to identify the mosquito fauna, to determine the vector of W. bancrofti, and to update information on the bionomics of An. subpictus. A total of 6 genera and 22 species were collected. Five species of culicines collected, have not been previously recorded from Flores. Dissections of wild caught mosquitoes consisted of 592 anophelines, and 70 culicines did not reveal any filarial infection. An. subpictus was a potential vector of bancroftian filariasis in the Robek area, as 11.3% of this species that fed on carriers were found to harbour W. bancrofti larvae. Larvae of An. subpictus were collected in lagoons, rice fields, swamps and ground pools. Breeding sites are exposed to sunlight, contain fresh or brackish water, with or withour vegetation. They have been found primarily associated with An. aconitus, An. annularis, An. barbirostris, Cx. vishnui and Cx. bitaeniorhynchus. The time for a female to become fully engorged with human blood is 3-10 minutes. This species is a night biter, attacking man and animals from twilight to dawn. Its peak of biting activity is between 0100-0300 hrs.

Human intestinal parasites in Karakuak, West Flores, Indonesia and the effect of treatment with mebendazole and pyrantel pamoate

A survey for intestinal parasites and mass-treatment with a combination of mebendazole and pyrantel pamoate were conducted in Karakuak, West Flores in 1977. A total of 198 stool specimens from 104 males and 94 females ranging in age from less than 1 to 70 years were examined and 72% harbored one or more intestinal parasites. Ascaris lumbricoides (43%) and Entamoeba histolytica (21%) were the most common, followed by Entamoeba coli (19%), hookworm (18%), Iodamoeba bütschlii (8%), Giardia lamblia (5%) and Trichuris trichiura (4%). Other intestinal parasites infrequently found were: Entamoeba hartmanni (2%), Chilomastix mesnili (2%), Endolimax nana (1%), Enterobius vermicularis (1%) and a heterophyid sp. (1%). A combination of mebendazole base at 200 mg/day and pyrantel pamoate salt at 60 mg/day for three consecutive days was 100% effective.

Experimental transmission of Wuchereria bancrofti to monkeys

Infective larvae of Wuchereria bancrofti from laboratory-raised Culex pipiens fatigans and Aedes togoi mosquitoes fed on human volunteers in Jakarta, Indonesia (J strain) and Kinmen Island, China (K strain) were introduced into Taiwan monkeys (Macaca cyclopis) by subcutaneous inoculation, by foot puncture, or by permitting infected mosquitoes to feed weekly on the monkeys. Some animals were splenectomized and others were treated with varying regimens of immunosuppressants. Necropsy was done on monkeys that died or were killed and the entire bodies were examined for worms. A total of 78 monkeys (43 males and 35 females) were exposed to infection and parasites were found in 29% of the females and 63% of males. In infections of 38 days or less worms were recovered from the testes of males and the pelt, carcass and lymph nodes of both sexes, but after 42 days of infection most worms were in the testes of males, and a few were recovered from lymph nodes and carcasses of females. Worms recovered at 8-11 days were third-stage, those found between 14 and 38 days fourth-stage, and ones found between 42 and 103 days were young adults. After 148 days most were adults and microfilariae were seen in the uteri of female worms at 160 days and later. The parasites continued to grow in size with time. Microfilariae were detected in the blood of nine monkeys between 8 and 18 months and the patent period varied from 5-21 months. Microfilarial densities were low and erratic, and periodicity could not be determined. The effectiveness of methods of administering infections and the value of various treatment regimens seem uncertain; monkey antilymphocytic sera, however, appeared to have some influence. Parasites were found in 36% of the Taiwan monkeys given the J strain and 54% of those given the K strain. A limited number of M. mulatta (3), M.irus (fascicularis) (3) and Aotus trivirgatus (4) were also given infective larvae and adult W. bancrofti were recovered from the testes of one male M. mulatta and one male M. irus; uterine microfilariae were found in one female worm from the latter monkey. A. trivirgatus were negative. Low numbers of infective larvae recovered from mosquitoes fed on patent monkeys were introduced intermittently into seven clean monkeys and one became microfilaremic between 11 and 17 months postinoculation.

A simple method to control Brugia timori by diethylcarbamazine administration

The results of mass treatment using 50 mg diethylcarbamazine per kg body-weight followed one year later by short term selective re-treatment in a highly endemic area of Brugia timori are described. The criteria for selection of re-treatment are simple and practical for use in rural areas. The microfilaria rate by finger prick decreased from 24% to 0 and by Nuclepore filtration from 30% to 2.5%. The disease rates were also affected favourably. 88% of persons receiving the drug reacted to treatment, this percentage slightly exceeding the total filarial infection rate (71%). The prevalence, onset, duration and nature of side reactions are briefly discussed and related to the presence of microfilaraemia and disease manifestations among the study population.