Immunopathology of granuloma formation and fibrosis in schistosomiasis

In schistosomiasis the deposition of parasite ova within host tissues is the initial event in a complex pathophysiological cascade which is characterized by granuloma formation, and may terminate in fibrosis and related sequelae (Fig. 1). In spite of intensive study, the complex relationship between infection and morbidity remains poorly understood. In this article, Michael Phillips and Patrick Lammie review current concepts of the mechanisms of granuloma formation and its regulation in schistosome infections.

Factors associated with participation in a campaign of mass treatment against lymphatic filariasis, in Leogane, Haiti

In October 2000, to interrupt transmission of Wuchereria bancrofti, an intense health-education campaign followed by a mass drug administration (MDA) with diethylcarbamazine and albendazole was undertaken in Leogane, Haiti. Three months after the MDA, which was the first in the study area, a knowledge-attitude-practice (KAP) survey, with a cluster-sample design and probability sampling, was undertaken, to determine the existing knowledge of the local residents, their attitudes toward the MDA, and the possible reasons for non-compliance. Questionnaire-based interviews were used to explore the KAP of 304 subjects (one randomly chosen resident aged > 14 years from each selected household) in 33 communities. Most (93%) of the interviewees were aware of filariasis and 72% knew at least one clinical sign of the disease. Awareness of the MDA was high (91%). The most frequently mentioned sources of information were other people (56%) and radio announcements (33%). More than 80% of the respondents encouraged other people to take the drugs distributed in the MDA and 63% had been treated. The primary reasons given for failing to take the drugs were absenteeism during the distribution (17%), use of contraceptive drugs (12%) and pregnancy (11%). In a multivariate analysis, being male [odds ratio (OR) = 3.3; 95% confidence interval (CI) = 1.5-7.4], knowing that a mosquito transmits the disease (OR = 2.6; CI = 1.2-5.4), and having learned about the MDA through posters and banners (OR = 2.9; CI = 1.2-7.5) were found to be positively associated with taking the drugs. Information from such post-treatment surveys should be useful in developing better health communication for subsequent MDA.

Influence of infection with non-filarial helminths on the specificity of serological assays for antifilarial immunoglobulin G4

Serological assays based on the detection of immunoglobulin (Ig) G4 antibodies to crude filarial extracts are widely used for epidemiological and diagnostic purposes. We tested 195 samples collected in 1998 from an area of Brazil where filariasis is not endemic and 13 (6.7%) had levels of antifilarial IgG4 antibodies that were defined as positive. Both Strongyloides infection and the presence of Strongyloides antibody responses were associated with higher antifilarial antibody responses. None of the specimens had a positive response to the Brugia malayi recombinant antigen (Bm14). These data suggest that serodiagnostic assays based on the use of crude filarial antigens should be interpreted with caution because of the potential for cross-reactivity with Strongyloides.

Development and standardization of a rapid, PCR-based method for the detection of Wuchereria bancrofti in mosquitoes, for xenomonitoring the human prevalence of bancroftian filariasis

PCR has recently been studied as a promising tool for monitoring the progress of efforts to eliminate lymphatic filariasis. PCR can be used to test concurrently at least 30 pools, with as many as 40 mosquitoes in each pool, for the presence of filarial larvae. The SspI PCR assay for the detection of Wuchereria bancrofti DNA in pools of mosquitoes has been used since 1994 in a variety of laboratories worldwide. During that time, the original assay has been modified in these different laboratories and no standardized assay currently exists. In an effort to standardize and improve the assay, a meeting was held on 15-16 November 2001, at Emory University in Atlanta, with representatives from most of the laboratories currently using the assay. The first round of testing was designed to test the four most promising methods for DNA extraction from pools of mosquitoes. Two of the four methods stood out as clearly the best and these will be now optimised and evaluated in two further rounds of testing.

A community-based trial for the control of lymphatic filariasis and iodine deficiency using salt fortified with diethylcarbamazine and iodine

To evaluate the effectiveness of salt fortified with diethylcarbamazine (DEC) and iodine for elimination of Bancroftian filariasis and iodine deficiency, all consenting residents of Miton, Haiti (n = 1,932) were given salt fortified with 0.25% diethylcarbamazine and 25 ppm of iodine for one year. Wuchereria bancrofti microfilaria prevalence and intensity, antigenemia, and urinary iodine were measured before and one year after salt distribution began. To measure the effect of DEC-fortified salt on adult worm motility, 15 microfilaria-positive men were examined by ultrasound of the scrotal area. Entomologic surveys were conducted to determine the proportion of W. bancrofti-infected Culex quinquefasciatus. After one year of treatment, the prevalence and intensity of microfilaremia were both reduced by more than 95%, while antigenemia levels were reduced by 60%. The motility of adult worms, as detected by ultrasound, was decreased, but not significantly, by DEC-fortified salt. The proportion of vector mosquitoes carrying infective stage larvae decreased significantly from 2.3% in the nine months before the intervention to 0.2% in the last three-month follow-up period. Iodine deficiency, which had been moderate to severe, was eliminated after one year of iodized salt consumption. The DEC-fortified salt was well accepted by the community and reduced microfilaremia and transmission to low levels in the absence of reported side effects. Based on these results, salt cofortified with DEC and iodine should be considered as a concurrent intervention for lymphatic filariasis and iodine deficiency elimination programs.

Detection of serum IgG antibodies specific for Wolbachia surface protein in rhesus monkeys infected with Brugia malayi

The mechanism of lymphedema development in individuals with lymphatic filariasis is presently poorly understood. To investigate whether Wolbachia, symbiotic bacteria living within filarial nematodes, may be involved in disease progression, Wolbachia-specific immune responses were assayed in a group of Brugia malayi-infected rhesus monkeys. Serum IgG antibodies specific for a major Wolbachia surface protein (WSP) were detected in 2 of 12 infected monkeys. It is interesting that both of these monkeys developed lymphedema after becoming amicrofilaremic. WSP-specific antibody responses were temporally associated with increases in antifilarial IgG1 antibodies as well as lymphedema development. These findings suggest that Wolbachia may be important in understanding disease caused by filarial worms.

An analysis of the safety of the single dose, two drug regimens used in programmes to eliminate lymphatic filariasis

This review of the safety of the co-administration regimens to be used in programmes to eliminate lymphatic filariasis (albendazole + ivermectin or albendazole + diethylcarbamazine [DEC]) is based on 17 studies conducted in Sri Lanka, India, Haiti, Ghana, Tanzania, Kenya, Ecuador, the Philippines, Gabon, Papua New Guinea, and Bangladesh. The total data set comprises 90,635 subject exposures and includes individuals of all ages and both genders. Results are presented for hospital-based studies, laboratory studies, active surveillance of microfilaria-positive and microfilaria-negative individuals, and passive monitoring in both community-based studies and mass treatment programmes of individuals treated with albendazole (n = 1538), ivermectin (9822), DEC (576), albendazole + ivermectin (7470), albendazole + DEC (69,020), or placebo (1144). The most rigorous monitoring, which includes haematological and biochemical laboratory parameters pre- and post-treatment, provides no evidence that consistent changes are induced by any treatment; the majority of abnormalities appear to be sporadic, and the addition of albendazole to either ivermectin or DEC does not increase the frequency of abnormalities. Both DEC and ivermectin show, as expected, an adverse event profile compatible with the destruction of microfilariae. The addition of albendazole to either single-drug treatment regimen does not appear to increase the frequency or intensity of events seen with these microfilaricidal drugs when used alone. Direct observations indicated that the level of adverse events, both frequency and intensity, was correlated with the level of microfilaraemia. In non microfilaraemic individuals, who form 80-90% of the 'at risk' populations to be treated in most national public health programmes to eliminate lymphatic filariasis (LF), the event profile with the compounds alone or in combination does not differ significantly from that of placebo. Data on the use of ivermectin + albendazole in areas either of double infection (onchocerciasis and LF), or of loiais (with or without concurrent LF) are still inadequate and further studies are needed. Additional data are also recommended for populations infected with Brugia malayi, since most data thus far derive from populations infected with Wuchereria bancrofti.

Human T and B cell immunoreactivity to a recombinant 23-kDa Cryptosporidium parvum antigen

Cryptosporidial infection in humans results in parasite-specific IgG, IgM, and IgA antibody responses, but little is known of the cell-mediated immune responses to cryptosporidial antigens. In a convenience sample of 35 Haitian residents, there was a high level of cryptosporidial exposure (>90%) as determined by immunoblot reactivity of serum against cryptosporidial antigens. An attempt was made to determine if there was a relationship between antibody and T cell-mediated responses to recombinant Cp23 antigen and how this correlated with reactivity to crude sporozoite antigen preparations (SAg). T cell reactivity was greater against SAg (57%) than to Cp23 (34.3%) as measured by [3H]thymidine incorporation. Proliferative responses to Cp23 were significantly correlated with SAg responses. By enzyme-linked immunosorbent assay, most persons had IgG responses to both SAg (91.4%) and to recombinant Cp23 (88.5%). Antibody responses were greater among persons who exhibited T cell responses to SAg and Cp23. This study demonstrates that recombinant Cp23 antigen could be a useful antigen for detection of both antibody and cell-mediated responses in epidemiologic studies.

Cryptosporidium parvum-specific antibody responses among children residing in Milwaukee during the 1993 waterborne outbreak

A major gastroenteritis outbreak among >400,000 residents of Milwaukee, Wisconsin, in April 1993 was attributed to Cryptosporidium parvum oocysts in drinking water. Plasma specimens obtained from children (6 months to 12 years old) for routine blood lead level surveillance March-May 1993 were assayed by ELISA for levels of IgG antibody against the immunodominant Triton-17 and 27-kDa C. parvum antigens. Over a 5-week period, the seroprevalence for antibodies to the 2 antigens increased from 15% to 82% and from 17% to 87%, respectively, in samples from children living in southern ZIP code areas (n=218), whereas smaller increases (20% to 43% and 22% to 46%, respectively) were noted among samples from children living in northern ZIP code areas (n=335; P<.0001). The results demonstrate that C. parvum infection was much more widespread than previously appreciated and confirm that infection was associated with residence in the area served by the southern water treatment plant.

The immunodominant 17-kDa antigen from Cryptosporidium parvum is glycosylphosphatidylinositol-anchored

Cryptosporidium parvum is a protozoan parasite of the intestinal epithelium that has caused numerous outbreaks of diarrheal illness in humans. During our studies of the host immune response to C. parvum infection, we noted that two of the immunodominant surface antigens of the sporozoite stage of the parasite readily extract into Triton X-114. We recently cloned the immunodominant 17-kDa surface antigen and suggested that the carboxy-terminal peptide sequence may satisfy the requirements for GPI anchor addition. In the work presented here, we were able to show that the 17-kDa antigen could be metabolically labeled in vitro with tritiated ethanolamine and that the antigen contained myo-inositol. The antigen was cleaved by GPI-PLD but not by PI-PLC and it could be converted to a water soluble form by chemical deglycosylation. We suggest that the 17-kDa antigen is indeed GPI anchored and that the anchor contains an acylated inositol and either a lyso-acyl- or a diacyl-glycerol. We are currently working to determine what role the anchor may play in the human immune response to this antigen.

Enzyme immunoassay detection of antigen-specific immunoglobulin g antibodies in longitudinal serum samples from patients with cryptosporidiosis

Cryptosporidium parvum is a protozoan parasite that causes diarrheal illness in a wide range of mammalian hosts, including humans. Characteristic serum immunoglobulin G (IgG) antibody responses to antigens in the 27- and 17-kDa size ranges have been shown to develop after infection, and several enzyme-linked immunosorbent assay (ELISA) and Western blot assay formats have been used to measure these IgG levels in human serum. Using a collection of serial samples from laboratory-confirmed cryptosporidiosis patients, we compared the results obtained by using two new ELISAs with those obtained with two different Western blot assays. When assayed with the large-format Western blot, 97% of the 67 patients had a demonstrable antibody response on at least one occasion. The Cp23 ELISA correctly identified 93% of the samples that had a 27-kDa response by Western blot and 100% of the negative samples. The Triton antigen ELISA detected 77% of the samples that had a 17-kDa response by Western blot and 88% of the negative samples. The sensitivity of the Triton antigen assay was higher for samples collected between 16 and 92 days after the onset of symptoms (96%). The minigel-format Western blot did not compare favorably with the large-format blot for the detection of antibodies to the 27-kDa antigen (71% sensitivity). A half-life of about 12 weeks was estimated for antibodies to both the 27- and 17-kDa antigens. We believe the Cp23 and Triton antigen ELISAs will be useful in epidemiologic studies of the prevalence of Cryptosporidium infection in the population.

The Serologic response to Cryptosporidium in HIV-infected persons: implications for epidemiologic research

Advances in serologic assays for Cryptosporidium parvum have made serology an attractive surveillance tool. The sensitivity, specificity, and predictive value of these new assays for surveillance of immunocompromised populations, however, have not been reported. Using stored serum specimens collected for the San Francisco Men's Health Study, we conducted a case-control study with 11 clinically confirmed cases of cryptosporidiosis. Based on assays using a 27-kDa antigen (CP23), the serum specimens from cases had a median response immunoglobulin (Ig) G level following clinical diagnosis (1,334) and a net response (433, change in IgG level from baseline) that were significantly higher than their respective control values (329 and -32, Wilcoxon p value = 0.01). Receiver operator curves estimated a cutoff of 625 U as the optimal sensitivity (0.86 [0.37, 1.0]) and specificity (0.86 [0.37, 1.0]) for predicting Cryptosporidium infection. These data suggest that the enzyme-linked immunosorbent assay technique can be an effective epidemiologic tool to monitor Cryptosporidium infection in immunocompromised populations.

Short report: documentation of iodine deficiency in Haitian schoolchildren: implication for lymphatic filariasis elimination in Haiti

In this study we documented unexpected moderate-to-severe iodine deficiency in Haitian schoolchildren although they live in a coastal community where presumably they have access to iodine-containing seafood. This fact combined with the lack of an iodized salt supply and endemic lymphatic filariasis makes community distribution of diethylcarbamazine-fortified, iodized salt an attractive strategy for elimination of lymphatic filariasis and iodine deficiency disorders in this area of Haiti. Combining lymphatic filariasis elimination with other public health interventions is one strategy to increase its public health benefit and maximize the impact of limited public health resources.

Evaluation of the whole blood filariasis ICT test for short-term monitoring after antifilarial treatment

The immunochromatographic (ICT) filariasis test is a rapid screening tool that will be useful for defining the prevalence and distribution of Wuchereria bancrofti as part of the global program to eliminate lymphatic filariasis. To address questions about its usefulness for monitoring control programs, we used the ICT filariasis test to assess residual antigen levels following antifilarial treatment. Our results demonstrate that antigen levels persist in microfilaria-negative persons for up to three years after treatment. Different strategies for monitoring control programs may have to be considered.

Cloning of the immunodominant 17-kDa antigen from Cryptosporidium parvum

Infection with Cryptosporidium parvum causes a self-limiting diarrheal illness in immunocompetent humans and is associated with the development of a serum IgG antibody response dominated by the 27-kDa and 17-kDa parasite surface antigens. Antibodies against the 27-kDa and 17-kDa antigens may serve as useful markers for past infection in population-based studies of the risk factors associated with Cryptosporidium infection. A recombinant form of the 17-kDa antigen would be useful both in epidemiologic studies and in studies of the role of the humoral response in immunity. We have partially purified and sequenced the immunodominant 17-kDa surface antigen from sporozoites, and we have cloned a 975 bp open reading frame from C. parvum that includes all of the 17-kDa antigen peptide sequences. We show immunologic identity between a recombinant form of the protein and the native 17-kDa antigen. We conclude that the carboxy-terminal fragment of the cloned protein is the authentic 17-kDa antigen.

Detection by enzyme immunoassay of serum immunoglobulin G antibodies that recognize specific Cryptosporidium parvum antigens

Human infection with Cryptosporidium parvum usually elicits characteristic immunoglobulin G (IgG), IgA, and IgM antibody responses against two sporozoite surface antigens with apparent molecular masses of approximately 27 and 17 kDa. We have determined that these two antigens are actually complex families of related antigens. We have developed two new enzyme-linked immunosorbent assays (ELISAs) for the detection and quantitation of serum IgG antibodies against both antigens. The assays utilize a recombinant form of the 27-kDa antigen and a partially purified native fraction isolated from sonicated whole oocysts that contains 17-kDa antigen. An immunoblot assay previously developed in our laboratory served as the reference, or "gold standard," seroassay for the assessment of the new ELISAs. Positive responses with the recombinant-27-kDa-antigen ELISA were correlated with the immunoblot results for the 27-kDa antigen, with a sensitivity and specificity of 90 and 92%, respectively. Similarly, positive responses with the partially purified native-17-kDa-antigen ELISA correlated with the immunoblot results for the 17-kDa antigen, with a sensitivity and specificity of 90 and 94%, respectively. For both ELISAs the median IgG antibody levels for serum sets collected during outbreaks of waterborne C. parvum infection were at least 2.5-fold higher than the levels determined for a nonoutbreak set. Using the immunoblot as the "gold standard," the new ELISAs were more specific and, in the case of the 27-kDa-antigen ELISA, more sensitive than the crude oocyst antigen ELISA currently in use. These assays will be useful in future epidemiologic studies.

Cyclospora cayetanensis infections in Haiti: a common occurrence in the absence of watery diarrhea

Stool samples from a population-based cohort of mothers and children living in Leogane, Haiti were tested for Cyclospora cayetanensis from January 1997 through January 1998. Data on gastrointestinal symptoms were also collected. During the winter months of January to March, the infection was detected in 15-20% of the persons sampled. Most infections did not appear to be causing diarrhea and most infected persons had few oocysts detectable in concentrates of stool. The infection appears to have marked seasonality, with highest rates during the driest and coolest time of the year. It may be that in this tropical setting, high summer temperature is the critical environmental factor that influences the seasonality of infection. This study demonstrates that Cyclospora infections in Haiti are common in the general population.

Assessment of combined ivermectin and albendazole for treatment of intestinal helminth and Wuchereria bancrofti infections in Haitian schoolchildren

This randomized, placebo-controlled trial investigated the efficacy and nutritional benefit of combining chemotherapeutic treatment for intestinal helminths (albendazole) and lymphatic filariasis (ivermectin). Children were infected with Ascaris (29.2%), Trichuris (42.2%), and hookworm (6.9%), with 54.7% of children having one or more of these parasites. Wuchereria bancrofti microfilaria were found in 13.3% of the children. Children were randomly assigned to treatment with placebo, albendazole, ivermectin, or combined therapy. Combination treatment reduced the prevalence of Trichuris infections significantly more than either drug alone. Combination therapy also significantly reduced the prevalence and density of W. bancrofti microfilaremia compared with placebo or ivermectin alone. Only combination therapy resulted in significantly greater gains in height (hookworm-infected children) or weight (Trichuris-infected children) compared with the placebo group. Combined albendazole and ivermectin was a more efficacious treatment for intestinal helminth and W. bancrofti infections in children and resulted in nutritional benefits not found with either drug alone.

The antibody response to 27-, 17-, and 15-kDa Cryptosporidium antigens following experimental infection in humans

Previous studies have suggested that persons infected with Cryptosporidium parvum develop antibody responses to 27-, 17-, and 15-kDa C. parvum antigens. Studies of volunteers infected with Cryptosporidium species provided an opportunity to evaluate the relationship between antibody reactivity to these antigens and infection outcome. As monitored by immunoblot, increases in specific antibody reactivity were more prevalent among volunteers who developed signs and symptoms of cryptosporidiosis (n = 11) than among asymptomatic infected (n = 7; P = .05) or oocyst-negative volunteers (n = 11; P = .02). Volunteers with preexisting IgG antibody to the 27-kDa antigen excreted fewer oocysts than volunteers without this antibody (P = .003). IgG reactivity to the 17-kDa antigens and IgM reactivity to the 27-kDa antigens were higher at day 0 for asymptomatic infected persons than for those who developed symptoms (P = .03 and P = .04, respectively). These results suggest that characteristic antibody responses develop following C. parvum infection and that persons with preexisting antibodies may be less likely to develop illness.

Longitudinal analysis of the development of filarial infection and antifilarial immunity in a cohort of Haitian children

Longitudinal studies are being conducted in Leogane, Haiti to investigate the relationship between acquisition of filarial infection and development of antifilarial immunity as well as the impact of maternal infection on this relationship. Children (0-24 months of age) residing in Leogane were enrolled and were examined periodically to monitor parasitologic status and to collect serum for antigen and antifilarial antibody determinations. To examine the development of filarial antigenemia and antifilarial antibody responses in this cohort, serum samples were selected from a cross section of the population at two (n = 82) and four years of age (n = 76). Antigen prevalence increased from 6% among two-year-olds to more than 30% among four-year-olds, but in only one four-year-old child were microfilaria detected in a 20-microl smear. The proportion of antigen-positive children born to antigen-positive mothers was higher than the proportion of antigen-positive children born to antigen-negative mothers (9.8% versus 0% for two-year-olds; P = 0.15; and 39.6% versus 22.7% for four-year-olds; P = 0.18). Antifilarial IgG4 levels were significantly higher among antigen-positive children at both two and four years of age (P < 0.001). In analyses of paired samples, antifilarial IgG4 responses increased significantly more among children who acquired infection by four years of age than among children who remained antigen negative, whereas antifilarial IgG1 and IgG2 responses changed equally for antigen-positive and -negative children. Antifilarial antibody levels were not influenced by maternal infection status, but were significantly influenced by age, antigen status, and the neighborhood within the community. These results provide evidence that children acquire infection early in life and suggest that antifilarial antibody responses may peak in early childhood.

Wuchereria bancrofti in Kwale District, Coastal Kenya: patterns of focal distribution of infection, clinical manifestations and anti-filarial IgG responsiveness

A cross-sectional study of bancroftian filariasis was conducted in 2 adjacent communities, Mvumoni and Kilore in Muhaka, Kwale District. Wuchereria bancrofti infection, clinical manifestations and anti-filarial IgG responsiveness were determined before the long rains, a time coinciding with a low transmission season. The prevalence of microfilaraemia increased gradually with age and was significantly higher in Kilore (24%) than in Mvumoni (6.3%, P < 0.001). Similarly, the prevalence of antigenaemia increased with age and also was significantly higher in Kilore, 48.9% than in Mvumoni, 20.5% (P < 0.001). Hydrocele, funiculitis, lymphangitis and lymphadenitis were also significantly more common in Kilore than in Mvumoni. In comparing the 2 communities, levels of IgG4 responsiveness in antigen-positive persons were higher in Kilore than Mvumoni (P = 0.034), but this was related to higher antigen loads in persons in Kilore than in Mvumoni. In antigen-negative persons, anti-filarial antibodies of 3 IgG isotypes were significantly higher in Kilore than Mvumoni (P < 0.001, for IgG1, IgG2, IgG4). These results emphasize the highly focal nature of bancroftian filariasis in this setting and demonstrate that anti-filarial antibody levels are related to transmission intensity.

Enzyme-linked immunoelectrotransfer blot analysis of a cryptosporidiosis outbreak on a United States Coast Guard cutter

Symptoms consistent with an outbreak of cryptosporidiosis (diarrhea, vomiting, nausea, and abdominal cramps) occurred on a U.S. Coast Guard cutter within 0-18 days after the cutter filled its tanks with Milwaukee, Wisconsin city water in March 1993. At three-weeks postdocking (PD), the suspected water was removed, and serum samples and stool specimens were collected from 47 of the 58 crew members, as well as questionnaire data on their water consumption and symptoms aboard the cutter. At 10-weeks PD and/or at 28-weeks PD, additional serum specimens were collected. Intensitometric data from enzyme-linked immunoelectrotransfer blot (EITB) were obtained on IgA responses to a 17-kD antigen group, IgM responses to a 27-kD antigen group, and IgG responses to 27-, 17-, and 15-kD antigen groups extracted from oocysts. In addition, IgG responses to crude oocyst antigens were obtained by ELISA. Based on reported symptoms, EITB results, and stool examination, the crew members were classified as confirmed (10), probable (10), suspected (22), and noncases (16). Of the 10 confirmed cases (all symptomatic) and the 10 probable cases (eight symptomatic) whose stools were positive and negative, respectively, for Cryptosporidium oocysts by microscopy, all showed changes in EITB intensities to the antigen groups and were considered EITB positive. The remaining 38 crew members, 22 suspected cases (all symptomatic), and 16 noncases (all asymptomatic), if tested, had negative stool examinations and were considered EITB negative. Of the 10 confirmed cases, only four showed a significant change in IgG responses (P < 0.05) between three-weeks PD and follow-up serum specimens by ELISA. Crew members considered confirmed cases consumed significantly more water (P < or = 0.005) aboard the cutter than noncases. Crew members considered EITB positive consumed more water (P < or = 0.04) than crew members considered EITB negative while there was no significant difference in water consumption (P > or = 0.19) between crew members considered ELISA positive and ELISA negative. Using the EITB, the observation of changes in intensity of IgA responses to the 17-kD antigen group, IgM responses to the 27-kD antigen group, and IgG responses to the 27- 17-, and 15-kD antigen groups from C. parvum oocysts between acute and convalescent serum specimens appears useful for immunodiagnosis of Cryptosporidium infection and for prospective epidemiologic studies designed to monitor infection risk.

Clearance of Wuchereria bancrofti antigen after treatment with diethylcarbamazine or ivermectin

The present study was undertaken to assess the relationship between microfilarial clearance and clearance of circulating filarial antigen from the blood of Wuchereria bancrofti-infected persons following chemotherapy with either diethylcarbamazine or ivermectin. Patients received either 12 weekly doses of 6 mg/kg of diethylcarbamazine (DEC), a single dose of 6 mg/kg of DEC, a single dose of 420 microg/kg of ivermectin, or 20 microg/kg of ivermectin, followed by 6 mg/kg of DEC five days later. Microfilarial clearance was marked in all groups, but was significantly less in the single-dose DEC. In contrast, as monitored by the Og4C3 monoclonal anitbody assay, clearance of circulating filarial antigen was highly variable, not only between groups but within each group. As a result, there were few statistically significant differences in antigen clearance between groups. In no instance did the antigen level fall to zero, even in individuals that remained microfilaria negative during two or three years of follow-up. These results suggest that living adult worms persist in almost all persons treated with DEC and/or ivermectin.

The ICT Filariasis Test: A rapid-format antigen test for diagnosis of bancroftian filariasis

Antigen testing is now recognized as the method of choice for detection of Wuchereria bancrofti infections. Unlike tests that detect microfilariae, antigen tests can be performed with blood collected during the day or night. However, existing enzyme-linked immunosorbent assay (ELISA) tests for filarial antigenemia are difficult to perform in the field, and this has limited their use in endemic countries. In this article, Gary Weil, Patrick Lammie and Niggi Weiss review their experience with a new rapid-format filarial antigen test. They found that the ICT card test was very easy to perform and that it was comparable with ELISA for the detection of filarial antigen in sera from people with microfilaremia. The introduction now of an antigen test suitable for use in the field is especially timely, in that it may facilitate implementation of new strategies proposed by the World Health Organization for control and elimination of lymphatic filariasis.

Randomised placebo-controlled comparison of ivermectin and albendazole alone and in combination for Wuchereria bancrofti microfilaraemia in Haitian children

BACKGROUND

Lymphatic filariasis and intestinal helminth infections are important disorders in tropical areas. Periodic treatment with albendazole is now used in many school-based intestinal helminth-control programmes. However, few such programmes exist for lymphatic filariasis, despite evidence that single-dose treatment with ivermectin can greatly reduce the concentration of Wuchereria bancrofti microfilariae in the blood for months to years. We aimed to assess the potential for school-based control of lymphatic filariasis by investigating the efficacy and tolerability or combined ivermectin and albendazole in Haitian schoolchildren.

METHODS

In January, 1996, we collected 832 20 microL capillary blood samples for inclusion in a randomised controlled study from children aged 5-11 years, and examined them by microscopy for W bancrofti microfilariae. Infected children were randomly assigned treatment with placebo (n = 29), a single 200-400 micrograms/kg dose of ivermectin (mean, 273 micrograms/kg, n = 28), 400 mg albendazole (n = 29), or a combination of 200-400 micrograms/kg ivermectin and 400 mg albendazole (n = 24). Children with high concentrations of microfilariae in the blood were admitted to hospital and adverse reactions were monitored for 3-5 days, otherwise children were examined at school or during a visit to their home. 4 months after treatment, we examined blood samples again for microfilariae.

FINDINGS

113 microfilaraemic children were enrolled (mean age 7.8 years). 4 months after treatment, the proportion of children who remained positive for microfilariae was significantly lower in the ivermectin plus albendazole group (four [17%]), but there were no significant changes in the other three groups (20 [69%] placebo, 22 [76%] albendazole alone, 17 [61%] ivermectin alone remained positive; p = 0.004). Geometric mean microfilarial concentration decreased from 9.3 to 5.3 per 20 microL blood among children who received placebo; from 15.5 to 1.5 per 20 microL blood among those who received ivermectin only (p = 0.032); from 14.1 to 5.1 per 20 microL blood among those who received albendazole alone; and from 13.7 to 0.3 per 20 microL blood among those who received both ivermectin and albendazole (p = 0.0001). Systemic adverse reactions did not differ significantly between children who received ivermectin alone and those who were treated with ivermectin and albendazole [corrected].

INTERPRETATION

For children with W bancrofti microfilaraemia, combined treatment with ivermectin and albendazole was more effective than treatment with ivermectin only, with no measurable increase in severity of adverse reactions.

Investigation of the influence of maternal infection with Wuchereria bancrofti on the humoral and cellular responses of neonates to filarial antigens

Epidemiological data indicate that maternal filarial infection might be associated with increased susceptibility to filarial infection in offspring. To examine the influence of maternal infection on development of antifilarial immunity in neonates, paired cord and maternal sera and mononuclear cells were collected in an area where Wuchereria bancrofti infection is endemic. Anti-filarial humoral responses (IgG, IgM and IgE) non-parasite-specific humoral responses (total IgE), proliferation induced by filarial antigen and production of cytokines (interleukin-2, interleukin-4 and interferon-gamma) were all monitored. Few cord serum samples had detectable antifilarial IgM of IgE and neither these responses nor total IgE levels differed as a function of maternal infection status. Of cord-blood mononuclear cells assayed, a relatively small proportion exhibited reactivity to filarial antigens. Based on these limited responses to filarial antigens, few neonates display evidence of in-utero sensitization to filarial antigens.

Th1-like antifilarial immune responses predominate in antigen-negative persons

To characterize immune responses associated with the putatively immune state in bancroftian filariasis (that is, both microfilaria and antigen free), humoral and cellular responses were compared among antigen- and microfilaria-negative, antigen-positive and microfilaria-negative, and microfilaria-positive individuals. Antifilarial isotype levels were measured by enzyme-linked immunosorbent assay. Peripheral blood mononuclear cell responses were measured by proliferation, by bioassay for interleukin-2 (IL-2) and IL-10, and by reverse transcription-PCR for IL-4, IL-5, and gamma interferon. The absence of circulating filarial antigen was associated with Th1-like responses, including significantly higher proliferative (P < 0.001) and IL-2 (P = 0.008) responses and a higher prevalence of gamma interferon (0.02 < P < 0.1) responses. Significantly elevated antifilarial immunoglobulin G4 (IgG4) levels (P = 0.0035) were associated with antigenemia, whereas microfilaremia was associated with significantly decreased antifilarial IgG2 levels (P = 0.0014). IL-4 mRNA levels were not significantly different among the three groups; however, there was a subpopulation of microfilaremic individuals who did not make detectable levels of IL-4 mRNA and who produced low antifilarial IgG4 levels compared with those of individuals who had detectable levels of IL-4 mRNA. IL-5 mRNA levels also were not significantly different among groups; however, more microfilaremic individuals produced IL-5 mRNA in response to adult filarial antigens, and total parasite-specific IL-4 and IL-5 mRNA levels were significantly correlated (P = 0.05). Although longitudinal data are not currently available, the elevated Th1-like responses in antigen- and microfilaria-negative individuals are consistent with the hypothesis that these responses contribute to protection in putatively immune individuals.

Zoonotic Brugian lymphadenitis. An unusual case with florid monocytoid B-cell proliferation

Human infection with a zoonotic Brugia species in the United States is uncommon. Positive identification of the filarial nematode is required for histopathologic diagnosis. Many cases may go unrecognized because of the nonspecific clinical manifestations and the nondiagnostic histologic changes occurring in involved lymph nodes. A case of zoonotic Brugia lymphadenitis is described in a patient from Rhode Island, in which a small nongravid female worm was identified in a lymph node biopsy specimen. The lymph node also showed a spectrum of reaction changes including the presence of florid monocytoid B-cell proliferation, which has not been described in association with zoonotic Brugian filariasis.

A survey of knowledge, attitudes, and perceptions (KAPs) of lymphatic filariasis, elephantiasis, and hydrocele among residents in an endemic area in Haiti

To assess knowledge, attitudes, and perceptions about bancroftian filariasis, 104 residents of an endemic area in Haiti were interviewed. Questions focused on 1) whether people understood the relationship between infection and disease, 2) recognition of the role that mosquitoes play in transmission, 3) perceived importance of hydrocele and elephantiasis in relation to other recognized diseases, and 4) the willingness of the community to participate in a control program. Fewer than 50% of residents had heard of filariasis and only 6% of those surveyed knew that it was transmitted by mosquitoes. In contrast, all persons knew of the clinical conditions of hydrocele and elephantiasis. Hydrocele was thought to be caused by trauma (60%) or trapped gas (30%); elephantiasis by walking bare foot on soil or water (37%) or by use of ceremonial powder that had been sprinkled on the ground (23%). Of 76 respondents, 53% and 38% thought that hydrocele could be treated through surgery or a drug, respectively, whereas 86 respondents, 85% and 15% believed that either surgery or a drug could be used to treat elephantiasis. In this context, persons were not referring to a specific drug; rather, they believed a drug existed (possibly in some other country) that could cure these conditions. Hydrocele and elephantiasis ranked second to acquired immunodeficiency syndrome as perceived health problems, most likely because residents believed treatment for conditions such as malaria, intestinal worms, anemia, and diarrhea was easily obtained. Responses were influenced by age, sex, and symptoms, but none of these effects were statistically significant except that persons with hydrocele or elephantiasis were more likely to have sought treatment than persons without these conditions (P = 0.0006). The survey results indicate that awareness of the causes of disease, the relationship between infection and disease, and goals of treatment must be heightened through community-based education campaigns to increase the possibility of acceptance and support of control programs.

Immunopurification and measurement of IgE in serum samples from bancroftian filariasis patients

Patent infection with Wuchereria bancrofti is associated with increased levels of filaria-specific IgG4 and IgE. In vitro quantification of filaria-specific IgE is hampered by its small proportion in serum relative to other isotypes and by potential competition with IgG4 for the same epitopes on parasite antigens. To determine if IgG4 or other isotypes inhibit the detection of parasite-specific IgE, total IgE was affinity purified prior to filaria-specific IgE enzyme-linked immunosorbent assay. Briefly, anti-human IgE mouse monoclonal antibody 6H10 was coupled to Affigel, and 50 microliters of patient serum was incubated on microcolumns for 16 hr. Total IgE was eluted with 25 mM triethylamine (pH 11.2) and levels of total and filaria-specific IgE and total IgG4 were assessed in the filtrates and eluates. Sera from 14 patients with W. bancrofti microfilaremia (Mf+) and 17 amicrofilaremic patients with chronic pathology (CP) were assayed. Filtrates and eluates were devoid of IgE and IgG4, respectively. The average yield of total IgE in the eluates was 70% (SEM = 6.5; range 21-100%) of that measured in the serum. Antifilarial IgE levels in column eluates were significantly higher in serum samples from CP patients than Mf+ patients. Antibody inhibition of IgE was assessed by comparing the levels of anti-filarial IgE detected in eluates and serum. Evidence for antibody-mediated inhibition of IgE detection was obtained with 2/2 samples from Indian tropical pulmonary eosinophilia patients, but only 2/14 and 4/17 Mf+ and CP patients, respectively.

Reduced antifilarial IgG4 responsiveness in a subpopulation of microfilaremic persons

Antifilarial IgG4 is a marker of active filarial infection; however, 10% of microfilaremic persons may have low levels of antifilarial IgG4. To gain insight into how persons with microfilaremia with low antifilarial IgG4 levels (< 10 micrograms/mL) differ from those with high levels (> 170 micrograms/mL), total IgG4 and IgE and filaria-specific IgE, IgG1, and IgG2 were measured by ELISA in serum samples collected from 85 microfilaremic Haitians. Persons with lower levels of antifilarial IgG4 had significantly lower total IgG4 and total IgE (P < .01), lower levels of antifilarial IgG1, IgG2, and IgE (P < .01, = .03, and < .01, respectively), and higher antigenemia and microfilaremia (P < .01) than did persons with higher levels of antifilarial IgG4. Increased antigen loads in microfilaremic persons may be associated with a down-regulation of antibody production, which extends to all isotypes.

Acquisition and expression of humoral reactivity to antigens of infective stages of filarial larvae

Measurement of anti-larval responses in filaria-exposed populations may shed light on the natural history of exposure to Wuchereria bancrofti. Using serum samples obtained by a cross-sectional survey of 172 individuals from two neighbourhoods in Leogane, Haiti, antibody responses directed against infective stage filarial larvae (L3) were assayed by enzyme-linked immunosorbent assay (ELISA), immunofluorescence (IFA), and immunoblot for the presence of anti-larval antibodies. ELISA results indicated that virtually all members of both neighbourhoods mounted an anti-larval antibody response within the first five years of life, suggesting that exposure to infection is universal. In a multiple linear regression analysis that modelled antibody levels as a function of age, gender, microfilaria status, and neighbourhood (as a proxy for transmission intensity), isotype-specific antibody levels were found to be significantly influenced by both age and neighbourhood. Antibodies directed against the surface of L3 also were age-dependent; the prevalence of IgG antibodies detected by IFA was significantly higher in children than in adults. The prevalence of antibody recognition of 16.7 and 72.3 kDa L3 antigens on immunoblots was significantly greater for serum samples from microfilaraemic than amicrofilaraemic persons. These results suggest that antibody responses to larval antigens are influenced to varying degrees by age, transmission intensity, and microfilaraemia status.

Bancroftian filariasis: profile of serum antifilarial antibody and circulating parasite antigen

Forty-five serum specimens collected from persons living in a filaria-endemic community in Maili Nane, Coastal Kenya were analyzed by ELISA for levels of isotype specific antifilarial antibody and by Og4C3 ELISA for circulating parasite antigen. Mean levels of IgG1, IgG2, and IgG3 were lower in microfilaraemic persons than in amicrofilaraemic individuals. In contrast, mean levels of antifilarial IgG4 were significantly higher in microfilaraemic persons (p = 0.0374). Serum samples from all microfilaremic persons were positive for circulating antigen as were 15% of samples from amicrofilaremic and asymptomatic persons. The Og4C3 antigen assay may have value as a technique for identifying and targeting communities for control efforts.

Clinical, parasitologic, and immunologic observations of patients with hydrocele and elephantiasis in an area with endemic lymphatic filariasis

Hydrocele and elephantiasis, major clinical manifestations of bancroftian filariasis, are thought to share a common pathogenesis. The characteristics of 121 patients with hydrocele or elephantiasis in Leogane, Haiti, were compared: 39% of 57 men with hydrocele and 3% of 64 persons with lymphedema of the leg were microfilaria-positive (P < .001). Circulating filarial antigen, presumably from the adult worm, was detected in 15 (43%) microfilaria-negative men with hydrocele and 9 (15%) microfilaria-negative persons with leg edema (P = .004). Microfilaria-positive men had lower levels of filaria-specific IgG1 and hydroceles of significantly smaller volume and shorter duration than did microfilaria-negative men; hydrocele volume was inversely associated with microfilarial density (P = .001). In contrast, filarial antigen but not microfilariae was associated with filaria-specific IgG4 and decreased lymphocyte proliferation. Antigen status was not associated with severity of leg edema. In this filariasis-endemic area, men with hydrocele are more immunologically and parasitologically heterogeneous than are persons with elephantiasis.

Age-specific prevalence of antigenemia in a Wuchereria bancrofti-exposed population

Antigen detection assays serve as a useful adjunct to blood examinations for studies of filariasis, in terms of the diagnostic and epidemiologic information provided. We examined the utility of the Og4C3 antigen detection enzyme-linked immunosorbent assay for field studies and analyzed the distribution of Wuchereria bancrofti antigenemia in a Haitian population. Using serum samples collected following venipuncture, antigenemia levels were correlated with microfilaremia (P < 0.001). The microfilariae had a pronounced nocturnal periodicity while the sensitivity of the antigen assay was the same whether serum samples were collected during the day or at night. To determine whether the Og4C3 assay could be used in conjunction with fingerprick blood examinations, nocturnal blood surveys were conducted. Of 419 persons surveyed, 207 (49.4%) were antigen-positive with the Og4C3 assay. Serum specimens from all 121 microfilaremic individuals were antigen positive (100% sensitivity). The age prevalence of antigenemia increased from 24.5% for 1-5-year-old children to 70% for persons greater than 50 years of age. These results demonstrate that the Og4C3 assay is a sensitive tool for the detection of infection and raise questions about the expression of protective immunity in populations exposed to infection.

Differential proliferative and interleukin-10 responses to fractionated filarial antigens: preferential recognition by patients with chronic lymphatic dysfunction

To characterize filarial antigens that may be associated with the development of chronic lymphatic dysfunction in persons with lymphatic filariasis, T cell responsiveness to Brugia pahangi adult worm extracts and SDS-PAGE antigen fractions were examined among Haitians from an area in which Wuchereria bancrofti is endemic. Greater T cell proliferation and interleukin-10 (IL-10) production were observed in amicrofilaremic patients with hydrocele or elephantiasis than in amicrofilaremic or microfilaremic asymptomatic persons. Antigen fractions that stimulated the highest proliferative responses (in the 25-49 kDa range) and IL-10 production were not identical. Further separation of an immunodominant 30- to 38-kDa fraction by ion exchange high-pressure liquid chromatography identified several subfractions, including a 32-kDa protein band, that elicited T cell responses from patients with elephantiasis or hydrocele. By immunoblot, these patients also had markedly greater humoral reactivity to parasite antigens of approximately 52, 43, 32, and 30 kDa.

Maternal filarial infection — A persistent risk factor for microfilaremia in offspring?

The observation that children born to mothers that are infected with Wuchereria bancrofti ore more susceptible to filarial infection than those born to uninfected mothers, raises many questions, particularly regarding immune mechanisms. In this article, Allen Hightower, Patrick Lommie and Mark Eberhard discuss these issues and their implications for the epidemiology of filarial infection.

Zoonotic Brugia infection in western Michigan

A case of zoonotic lymphatic filariasis is reported from a resident of Michigan. Numerous sections of a small, nongravid female worm, measuring approximately 65 microns in diameter, were identified in histological preparations of an excised inguinal lymph node. Based on its location, small size, thin cuticle, small number of muscle cells, and paired uterine tubes, the worm was identified as a Brugia species, undoubtedly of zoonotic origin from the local animal population. The pathological response of the host to the parasite was one of hyperplastic lymph nodes with a focal granulomatous reaction. This is the first such case to be reported from Michigan and further expands the geographical range of states in which zoonotic Brugia infection have been reported.

Proliferative responsiveness of lymphocytes from Cryptosporidium parvum-exposed mice to two separate antigen fractions from oocysts

We assessed lymphoproliferative responsiveness of lymphocytes from the spleen and lymph nodes of inbred neonatal SWR/J H-2q mice at various times postinoculation (PI) using Cryptosporidium parvum oocysts. The lymphocytes were cultured in vitro with a water-soluble (SO) and a water-insoluble (IN) antigen fraction. The IN fraction was prepared by solubilizing particulates, the sediment obtained after centrifuging disrupted oocysts, in urea. Both fractions were characterized using silver stain and enzyme-linked immunoelectrotransfer blot (EITB) with hyperimmune rabbit anti-oocyst serum, monoclonal antibody specific to a 23-kD antigen, and serum from patients with symptoms of cryptosporidiosis. The EITB showed that the antigens in the IN fraction differed both quantitatively and qualitatively from those in the SO fraction. Lymphocytes from lymph nodes of exposed mice cultured with the SO fraction exhibited a significant (P < 0.05) and antigen-specific response compared with those from unexposed mice at days 10, 19, 22, and 28 PI. The response to the IN fraction of lymphocytes from lymph nodes of exposed mice was not as consistent as that to the SO fraction but showed a significant (P < 0.05) and antigen-specific response at days 10 and 19 PI. No significant response occurred when splenic lymphocytes were cultured with SO or IN fractions. These results show that lymphocytes from lymph nodes of mice exposed to Cryptosporidium parvum oocysts proliferate when cultured in vitro with soluble or particulate antigens prepared from oocysts.

Heterogeneity in filarial-specific immune responsiveness among patients with lymphatic obstruction

The relationship between chronic obstructive disease and antifilarial immune responsiveness was studied in the Haitian community of Leogane, where Wuchereria bancrofti is endemic. Differences in sex ratios and in the prevalence of microfilaremia were observed between patients with hydrocele and those with lymphedema or elephantiasis of the lower limb. Only 2 of 84 patients with limb involvement (74 women, 10 men) were microfilaremic compared with 25 of 42 men with hydrocele. Microfilaria-positive men with hydrocele had significantly lower IgG2 and proliferative responses to filarial antigen than did amicrofilaremic men with hydrocele or individuals with lymphedema or elephantiasis. Parasite-specific cellular responses of amicrofilaremic individuals with obstructive disease were greater, although not significantly so, than those of amicrofilaremic asymptomatic members of the community. These results are compatible with the hypothesis that development of obstructive disease of the lymphatics has an immune component in amicrofilaremic persons.

Transplacental transmission of Wuchereria bancrofti in Haitian women

To document the occurrence of transplacental transmission of microfilariae and to determine how frequently it occurred, umbilical cord blood samples and placental tissues were collected from 22 microfilaria-positive women in an area with endemic Wuchereria bancrofti. Microfilaria (mf) counts in the women ranged from 1 to 3,820 mf/ml. Microfilariae were detected in 2 placenta samples and a single cord blood sample. The positive cord blood sample and 1 of the positive placenta samples came from the same woman; no microfilariae were found in a finger prick sample taken from the infant 3 wk after delivery. Our results suggest that microfilariae cross the placenta in less than 10% of pregnancies of microfilaria-positive mothers. Furthermore, the microfilaria count of the mother does not seem to influence directly whether microfilariae are present in the placental blood pool. Although actual transfer of microfilariae to the fetus may occur infrequently, exposure to parasite antigens occurs with much greater frequency. The effect of in utero exposure to either microfilariae or parasite antigens may render newborns tolerant and explain why children born to infected mothers are almost 3 times more likely to become infected than are children born to uninfected women.

Comparative efficacy of clearing-dose and single high-dose ivermectin and diethylcarbamazine against Wuchereria bancrofti microfilaremia

To compare the efficacy and tolerability of various combinations of low- and high-dose ivermectin and diethylcarbamazine (DEC), 59 persons with Wuchereria bancrofti microfilaremia were enrolled in a double-blinded six-arm clinical trial in Leogane, Haiti. On day 1, study participants were treated with low clearing doses of ivermectin, DEC, or placebo; on day 5 they received 200-400 micrograms/kg of ivermectin or 6 mg/kg of DEC. Adverse reactions, which were generally mild, occurred more frequently with ivermectin than with DEC. One year after treatment, the geometric mean microfilarial density returned to 0.9% of pretreatment levels for persons who received a total of 420 micrograms/kg of ivermectin. This rate was significantly lower than 5.6% for persons who were treated with 220 micrograms/kg of ivermectin (P = 0.02) and 9.3% for those receiving 6 or 7 mg/kg of DEC (P = 0.006). Persons treated with a clearing dose of ivermectin followed by 6 mg/kg of DEC also had low microfilarial densities (1.7% of pretreatment levels), suggesting an additive or synergistic effect of the two drugs. The addition of a clearing dose neither reduced the severity of adverse reactions nor improved the efficacy of high-dose ivermectin. Community-based intervention trials are now warranted to determine the feasibility and effectiveness of mass chemotherapy with single high-dose ivermectin for the prevention and control of lymphatic filariasis.

Immunologic characterization of jird lymphocyte responsiveness to Brugia pahangi ribosomal protein S13

Ribosomal protein S13 of the nematode Brugia pahangi is recognized by B and T cells from parasite-infected animals. To identify helper T cell sites on the protein, 15 overlapping synthetic peptides spanning the entire molecule (Bp17.4) were tested for their ability to stimulate lymph node and spleen cells of peptide-immunized and recombinant antigen-immunized jirds. Lymph node cells from animals immunized with peptides 6, 8, 9, 13, and 14, corresponding to Bp17.4 amino acids (AA) 50-70, 70-90, 80-100, 120-140, and 130-150, respectively, showed strong and specific responses to the homologous peptide, while only those lymph node cells from jirds immunized with peptides 8, 9, 13, and 14 proliferated in response to Bp17.4. These results suggest the existence of at least two T cell epitopes. Lymph node cells from infected jirds also responded to these peptides and to Bp17.4 (80,000 cpm). In contrast to the lymph node cells, spleen cells from microfilaria-positive animals failed to mount significant responses to any of the peptides or to Bp17.4. Splenic T cell responsiveness was restored upon removal of nylon wool adherent cells, suggesting active regulation of Bp17.4 reactivity. In liquid-phase competitive inhibition immunoassays, peptides 1 (AA 1-30) and 6 (50-70) blocked antibody binding and, therefore, these regions contain conformational antibody-binding sites. This model system should prove useful for analyzing regulation of epitope-specific responses in experimental filariasis.