New tools for diagnosis and monitoring of bancroftian filariasis parasitism: The polynesian experience

Detection of anti-filarial antibody among hydrocele patients living in an endemic area for filariasis

Background:

The knowledge of the current prevalence of lymphatic filariasis and its transmission will be helpful in its elimination. Thus, the present study is aimed to determine its prevalence among hydrocele patients which is a common presentation in chronically infected cases.

Materials and Methods:

One hundred patients suffering from hydrocele admitted to the surgical ward were included in the study. Blood samples were collected from the patients during the day hours for the detection of anti-filarial antibody and during night hours to detect the presence of microfilaria by smear examination. Blood samples were also collected from the family member attending the ward along with the patients to determine the presence of anti-filarial antibodies. Serum IgE level and eosinophil count were also determined in the patients showing a positive result for the anti-filarial antibody test.

Results:

Out of 100 hydrocele patients, 21% patients showed anti-filarial antibody card test positive with maximum patients belonging to age group of 20–40 years. Microfilaria was detected in 5% of the hydrocele patients, whereas none of the family members showed positive anti-filarial antibody test. Serum IgE level and eosinophil count were more than 1000 ng/ml and 500/mm³, respectively.

Conclusions:

The study has found a high prevalence of filariasis among hydrocele patients. It is suggested that more studies are needed to know the real time prevalence of the cases showing manifestations of the filariasis in the acute stage which will help the eradication program to formulate new strategies.

Mathematical modelling of lymphatic filariasis elimination programmes in India: required duration of mass drug administration and post-treatment level of infection indicators

Background

India has made great progress towards the elimination of lymphatic filariasis. By 2015, most endemic districts had completed at least five annual rounds of mass drug administration (MDA). The next challenge is to determine when MDA can be stopped. We performed a simulation study with the individual-based model LYMFASIM to help clarify this.

Methods

We used a model-variant for Indian settings. We considered different hypotheses on detectability of antigenaemia (Ag) in relation to underlying adult worm burden, choosing the most likely hypothesis by comparing the model predicted association between community-level microfilaraemia (Mf) and antigenaemia (Ag) prevalence levels to observed data (collated from literature). Next, we estimated how long MDA must be continued in order to achieve elimination in different transmission settings and what Mf and Ag prevalence may still remain 1 year after the last required MDA round. The robustness of key-outcomes was assessed in a sensitivity analysis.

Results

Our model matched observed data qualitatively well when we assumed an Ag detection rate of 50 % for single worm infections, which increases with the number of adult worms (modelled by relating detection to the presence of female worms). The required duration of annual MDA increased with higher baseline endemicity and lower coverage (varying between 2 and 12 rounds), while the remaining residual infection 1 year after the last required treatment declined with transmission intensity. For low and high transmission settings, the median residual infection levels were 1.0 % and 0.4 % (Mf prevalence in the 5+ population), and 3.5 % and 2.0 % (Ag prevalence in 6–7 year-old children).

Conclusion

To achieve elimination in high transmission settings, MDA must be continued longer and infection levels must be reduced to lower levels than in low-endemic communities. Although our simulations were for Indian settings, qualitatively similar patterns are also expected in other areas. This should be taken into account in decision algorithms to define whether MDA can be interrupted. Transmission assessment surveys should ideally be targeted to communities with the highest pre-control transmission levels, to minimize the risk of programme failure.

Electronic supplementary material

The online version of this article (doi:10.1186/s13071-016-1768-y) contains supplementary material, which is available to authorized users.

Further evidence of the cross-reactivity of the Binax NOW® Filariasis ICT cards to non-Wuchereria bancrofti filariae: experimental studies with Loa loa and Onchocerca ochengi

Background

The immunochromatographic test (ICT) for lymphatic filariasis is a serological test designed for unequivocal detection of circulating Wuchereria bancrofti antigen. It was validated and promoted by WHO as the primary diagnostic tool for mapping and impact monitoring for disease elimination following interventions. The initial tests for specificity and sensitivity were based on samples collected in areas free of loiasis and the results suggested a near 100 % specificity for W. bancrofti. The possibility of cross-reactivity with non-Wuchereria bancrofti antigens was not investigated until recently, when false positive results were observed in three independent studies carried out in Central Africa. Associations were demonstrated between ICT positivity and Loa loa microfilaraemia, but it was not clearly established if these false positive results were due to L. loa or can be extended to other filarial nematodes. This study brought further evidences of the cross-reactivity of ICT card with L. loa and Onchocerca ochengi (related to O. volvulus parasite) using in vivo and in vitro systems.

Methods

Two filarial/host experimental systems (L. loa-baboon and O. ochengi-cattle) and the in vitro maintenance of different stages (microfilariae, infective larvae and adult worm) of the two filariae were used in three experiments per filarial species. First, whole blood and sera samples were prepared from venous blood of patent baboons and cattle, and applied on ICT cards to detect circulating filarial antigens. Secondly, larval stages of L. loa and O. ochengi as well as O. ochengi adult males were maintained in vitro. Culture supernatants were collected and applied on ICT cards after 6, 12 and 24 h of in vitro maintenance. Finally, total worm extracts (TWE) were prepared using L. loa microfilariae (Mf) and O. ochengi microfilariae, infective larvae and adult male worms. TWE were also tested on ICT cards. For each experiment, control assays (whole blood and sera from uninfected babon/cattle, culture medium and extraction buffer) were performed.

Results

Positive ICT results were obtained with whole blood and sera of L. loa microfilaremic baboons, culture supernatants of L. loa Mf and infective larvae as well as with L. loa Mf protein extracts. In contrast, negative ICT results were observed with whole blood and sera from the O. ochengi-cattle system. Surprisingly, culture supernatant of O. ochengi adult males and total worm extracts (Mf, infective larvae and adult worm) were positive to the test.

Conclusions

This study has provided further evidence of L. loa cross-reactivity for the ICT card. All stages of L. loa seem capable of inducing the cross-reactivity. Onchocerca ochengi. can also induce cross-reactivity in vitro, but this is less likely in vivo due to the location of parasite. The availability of the parasite proteins in the blood stream determines the magnitude of the cross-reactivity. The cross-reactivity of the ICT card to these non-W. bancrofti filariae poses some doubts to the reliability and validity of the current map of LF of Central Africa that was generated using this diagnostic tool.

Electronic supplementary material

The online version of this article (doi:10.1186/s13071-016-1556-8) contains supplementary material, which is available to authorized users.

Circulating filarial antigen detection in brugian filariasis

Human lymphatic filariasis (LF) is a major cause of disability globally. The success of global elimination programmes for LF depends upon effectiveness of tools for diagnosis and treatment. In this study on stage-specific antigen detection in brugian filariasis, L3, adult worm (AW) and microfilarial antigenaemia were detected in around 90-95% of microfilariae carriers (MF group), 50-70% of adenolymphangitis (ADL) patients, 10-25% of chronic pathology (CP) patients and 10-15% of endemic normal (EN) controls. The sensitivity of the circulating filarial antigen (CFA) detection in serum samples from MF group was up to 95%. In sera from ADL patients, unexpectedly, less antigen reactivity was observed. In CP group all the CFA positive individuals were from CP grade I and II only and none from grade III or IV, suggesting that with chronicity the AWs lose fecundity and start to disintegrate and die. Amongst EN subject, 10-15% had CFA indicating that few of them harbour filarial AWs, thus they might not be truly immune as has been conventionally believed. The specificity for antigen detection was 100% when tested with sera from various other protozoan and non-filarial helminthic infections.

Immunoepidemiology of Wuchereria bancrofti infection in two East African communities: antibodies to the microfilarial sheath and their role in regulating host microfilaraemia

The response pattern of specific antibodies to the microfilarial sheath (sheath-Ab) of the mosquito-borne filarial parasite Wuchereria bancrofti was investigated in individuals from two East African communities with different levels of endemicity. Individuals from both communities presented a strong inverse relationship between positivity for sheath-Ab and being positive for microfilariae (mf) and circulating filarial antigens (CFA). The prevalence of sheath-Ab positivity was highest in young individuals, but peaked at a younger age in the high (1-14 years) than the low (15-19 years) endemicity community. IgG1, IgG2, IgG3 and IgE intensities to a crude adult filarial worm antigen were higher, and IgG4 intensities were lower, in sheath-Ab positive than in sheath-Ab negative individuals, probably reflecting the infection status of individuals. From the study it appears that individuals become sheath-Ab positive before mf and/or CFA can be detected in the peripheral blood, and only after later disappearance of sheath-Ab from the circulation can CFA and mf be diagnosed. In light of the findings, possible roles of the distinct sheath-Ab in the host-parasite relationship are discussed, and a hypothesis is proposed which suggests that sheath-Ab play an important role in the regulation of host microfilaraemia.

Production, purification and diagnostic application of filarial recombinant protein WbSXP-1 expressed in salt inducible Escherichia coli

Wuchereria bancrofti protein WbSXP-1 was identified and established as a potential candidate for the diagnosis of lymphatic filariasis. For the economic production of rWbSXP-1, osmotically (salt) inducible Escherichia coli GJ1158 was preferred. Cultivation and expression was optimized in 3 L airlift bioreactor (ALB) and was successfully extended to 30 L ALB. Purification of rWbSXP-1 his-tag protein was optimized in technical scale using FPLC and the maximal recovery of rWbSXP-1 with significant level of purity was achieved using the combination of IMAC and gel filtration. Quality criteria for immuno-reactivity of purified rWbSXP-1 were established for diagnostic applications. Enhancement of sensitivity in rapid diagnostic format was optimized to effectively detect weak to strong antibody reactivity in individuals exposed to lymphatic filariasis. Performance of the rapid format during field evaluation was successful. The accelerated stability assessment of the rapid format satisfied the requirements of WHO-cGMP norms. This investigation presents a successful technical scale production and purification of rWbSXP-1 considering the future industrial application and an enhanced rapid flow through antibody assay for the diagnosis of human lymphatic filariasis.

Vector control complements mass drug administration against bancroftian filariasis in Tirukoilur, India

OBJECTIVE

To determine the role of vector control in further decreasing the transmission of bancroftian filariasis achieved by mass drug administration and the long-term impact on filariometric indices.

METHODS

Three rounds of annual mass drug administration, with diethylcarbamazine and ivermectin, were complemented by vector control (mainly using polystyrene beads) in villages of Tirukoilur, south India, during 1995-99. Subsequently, drug administration is being carried out with diethylcarbamazine and albendazole or diethylcarbamazine alone. We evaluated the impact of mass drug administration used alone or in conjunction with vector control (from 1995 to 2005) on vector transmission indices (such as transmission intensity index, monthly biting rate, monthly transmission potential and annual transmission potential). We analysed data on filarial infection in the community to estimate the prevalence of microfilaraemia and antigenaemia using chi2 analysis and Fisher's exact test.

FINDINGS

Vector density greatly decreased in villages where vector control was used as an adjunct to mass drug administration and almost no infective mosquitoes were found in the small numbers still remaining. Filarial antigenaemia was low and continued to decrease significantly in the age group 15-25 years in villages receiving mass drug administration with vector control in contrast to villages receiving only mass drug administration.

CONCLUSION

The gains of mass drug administration were sustained only with the integration of vector control measures. We advocate the incorporation of vector control in the Global Programme to Eliminate Lymphatic Filariasis as it can potentially decrease the time required for eliminating lymphatic filariasis.

Mathematical models and lymphatic filariasis control: monitoring and evaluating interventions

Monitoring and evaluation are crucially important to the scientific management of any mass parasite control programme. Monitoring enables the effectiveness of implemented actions to be assessed and necessary adaptations to be identified; it also determines when management objectives are achieved. Parasite transmission models can provide a scientific template for informing the optimal design of such monitoring programmes. Here, we illustrate the usefulness of using a model-based approach for monitoring and evaluating anti-parasite interventions and discuss issues that need addressing. We focus on the use of such an approach for the control and/or elimination of the vector-borne parasitic disease, lymphatic filariasis.

Soluble cellular adhesion molecules, selectins, VEGF and endothelin-1 in patients with Wuchereria bancrofti infection and association with clinical status

Lymphatic filariasis, a mosquito-transmitted disease commonly known as Bancroftian filariasis, is characterized by debilitating pathology linked to the progression of lymphoedema to a chronic state of elephantiasis. We performed longitudinal measurements of endothelial adhesion and angiogenic molecules in 63 Polynesian patients living in an hyperendemic focus of Wuchereria bancrofti. Decreased serum concentrations of soluble (s-) L selectin (CD62L) were noticed in sera of of patients with chronic conditions (hydrocele and elephantiasis). Chyluria was associated with increased vascular endothelial growth factor (VEGF) levels, whereas elephantiasis presented a high endothelin-1 (ET-1) profile. By contrast, increased serum concentrations of soluble intercellular (sICAM-1, CD54), but not of vascular cell (sVCAM-1, CD106), adhesion molecules were observed in sera of patients with bacterial lymphangitis used as controls. These trends are consistent with the increased permeability of vascular structures, a major clinical feature observed in acute lymphatic pathology (of bacterial or filarial origin), and of fundamental differences in the pathogenesis of hydrocele and elephantiasis. Using markers correlated with the clinical status (high ET-1 and VEGF levels for elephantiasis and chyluria, respectively; low CD62L levels for hydrocoele and elephantiasis) it should be possible to monitor disease progression in lymphatic filariasis.

Observations on false positive reactions in the rapid NOW Filariasis card test

The NOW Filariasis card test is a useful tool for rapid field diagnosis of Wuchereria bancrofti infection, based on detection of specific circulating filarial antigen (CFA) in the patients' blood. Concern has been raised that a high proportion of infection negative individuals develop false positive reactions in these tests when the test cards are left for a prolonged period before being examined. We carried out a survey in an endemic Tanzanian village to investigate this phenomenon. Individuals who were positive in the NOW Filariasis test at 10 min after specimen application were also positive in the TropBio ELISA for CFA, and thus appeared to be truly positive. Many of the test cards that were negative at 10 min developed a positive line later, but these lines appeared to be falsely positive when the TropBio test was used as the gold standard. Close examination revealed that true and false positivity lines could be distinguished on their shape and colour. The study thus reaffirmed that test cards should be read after 10 min to avoid false positives, but it also indicated that experienced test card users should be able to make a correct diagnosis even at a later time.

Mapping of lymphatic filariasis in Nepal

BACKGROUND: Human infection with Wuchereria bancrofti causes a disabling parasitic disease known as lymphatic filariasis, which is a major public health and socio-economic problem in many parts of the world. At the onset of the study, little was known of the distribution of filariasis and its current importance as a public health problem in Nepal. METHODS: Epidemiological mapping was undertaken to determine the prevalence of infection by Wuchereria bancrofti in 37 districts of Nepal between July to December 2001. The study population above 15 years of age was selected, and the immunochromatographic test (ICT Filariasis) was used to screen for circulating filarial antigen (CFA). RESULTS: The overall prevalence of lymphatic filariasis from a 4,488-sample population was 13% and 33/37 districts were found to be endemic. On the basis of geographical data, the highest number of cases was found at altitudes between 500-700 m; however, a substantial number of infected individuals were found in the highly populated Kathmandu valley, at altitudes between 900-1,500 metres where transmission appears to take place. Prevalence rates above 20% were found in 11 districts (with the highest rate of 40%), 6-19% were found in 15 districts, and 0.1-5% were in 7 districts.Information on people's knowledge, attitudes and behaviour towards filariasis was also collected by means of a structured questionnaire, which is presented and discussed in the study. CONCLUSIONS: This is the most extensive study of lymphatic filariasis undertaken to date in Nepal. The study indicates that the prevalence of infection is far greater that was previously reported and that lymphatic filariasis should be a much higher health priority than currently given.

Antigenemia is associated with low antibody response to carbohydrate determinants of a filarial surface antigen

The IgG response to a filarial surface antigen (DssdI) was evaluated in circulating antigen (Og4C3 test) positive and negative individuals from the Wuchereria bancrofti endemic region of Orissa, India. Circulating filarial antigen (CFA) positive individuals exhibited depressed antibody levels to DssdI and individuals with high antibody levels were invariably CFA negative. Low IgG levels to DssdI are associated with CFA positivity irrespective of microfilaraemia and clinical status. Thus asymptomatic microfilaraemic individuals with antigen positivity exhibited low IgG levels similar to symptomatic (chronic filariasis with elephantiasis, hydrocele) or asymptomatic amicrofilaraemic individuals with antigenemia. Western blot analysis revealed a band of approximately 210 kDa reactive with CFA-negative, but not with CFA-positive sera. DssdI was subjected to mild periodate oxidation to investigate the role of carbohydrate epitopes. The treatment considerably reduced the antigenic recognition of DssdI, stressing the immunodominance of carbohydrate residues of DssdI in infection-free individuals. In contrast, individuals with active infection failed to produce such antibodies to filarial surface carbohydrates.

The influence of the mass administration of diethylcarbamazine, alone or with albendazole, on the prevalence of filarial antigenaemia

The current Indian campaign for the elimination of lymphatic filariasis is largely based on mass drug administration (MDA). As part of this campaign, villagers in the Tirukoilur and Mugaiyur 'blocks' (i.e. revenue units) of Villupuram district, in Tamil Nadu, India, were treated with diethylcarbamazine (DEC), either alone (Mugaiyur) or with albendazole (Tirukoilur), in March 2001. The efficacy of treatment, in each of the two treatment arms, was evaluated by determining the percentages of the subjects who were carrying antigen from adult Wuchereria bancrofti before, 6 months and 12 months after the MDA. In a cross-sectional survey at each time-point, commercial, immunochromatographic tests were used to check 1000-1200, randomly selected, young residents (aged 2-25 years) of 18 index villages for the antigen; at least 300 villagers aged 2-9 years and at least 170 aged 10-25 years from each treatment arm were screened in each survey. Before the MDA, 12.7% of the subjects aged 2-9 years and 23.6% of those aged 10-25 years were found to be positive for the filarial antigen. Although only about 50% of villagers aged 2-9 years were successfully treated, MDA (with DEC alone or DEC plus albendazole) led to a significant (28.7%) reduction in the prevalence of antigenaemia in this age-group 6 months later (P<0.05). Although, the prevalences of antigenaemia among those aged 2-9 years were higher 12 months post-treatment than 6 months post-treatment, they were still lower (by 16%-23%) than those observed pre-treatment. The addition of albendazole to the DEC treatment appeared to offer no additional benefit in terms of the prevalence of antigenaemia in children aged <10 years; in fact, the use of DEC alone produced a slightly greater reduction in the prevalence of antigenaemia than the use of both DEC and albendazole. In the block given MDA based on both DEC and albendazole, the prevalences of antigenaemia among the villagers aged 10-25 years were 19.4% and 16.6% lower 6 and 12 months post-treatment, respectively, than observed pre-treatment. Curiously, in the block given DEC alone, the prevalences in this age-group were higher at both post-treatment follow-ups (by 17.4% at 6 months and 35.1% at 12 months) than observed pre-treatment. In concurrent experimental studies, high drug compliance (90%) among young children (aged 2-5 years) led to a pronounced (62.6%) reduction in the prevalence of antigenaemia after one MDA. In follow-up studies of those found antigen-positive, 40% of those aged 2-9 years but only 23% of those aged 10-25 years cleared their antigenaemias after three (annual) MDA. To maximize the benefits of MDA, greater efforts should be made to increase treatment coverage among young children.

Cellular immune responses of filaria (Litomosoides sigmodontis) infected BALB/c mice detected on the level of cytokine transcription

Cellular immune responses of BALB/c mice infected with 80 or 160 L3 of Litomosoides sigmodontis were studied over a period of 200 days postinfection (p.i.) by stimulating spleen cells with specific microfilariae and adult antigens and Concanavalin A (Con A). Effects were determined as the level of transcription of cytokine genes [interleukin (IL)-2, interferon (IFN)-gamma, IL-4, IL-5, IL-10, IL-13] employing a semiquantitative reverse transcriptase-polymerase chain reaction technique. Con A stimulation resulted in generally enhanced transcription levels in infected animals. Exposure to filarial antigens stimulated T cells of infected animals dependent on time p.i. There was a general strong response in the early prepatency (24 days p.i.), a temporary almost complete downregulation of cytokine gene transcription except IL-10 towards the end of prepatency (45 days p.i.), and subsequently strong reactions particularly concerning IFN-gamma and IL-13 during patency and postpatency. The dose of infection as well as the mode of antigenic stimulation had generally only small effects on the cytokine gene transcription: following the same type of kinetics, infection with 160 L3 as well as the use of microfilarial antigen generally induced lower levels of cytokine gene transcription compared with infection with 80 L3 and stimulation with female antigen, respectively.

Lymphatic filariasis: an infection of childhood

Lymphatic filariasis (LF), already recognized as a widespread, seriously handicapping disease of adults, was generally thought to occur only sporadically in children. New, highly sensitive diagnostic tests (antigen detection, ultrasound examination) now reveal, however, that LF is first acquired in childhood, often with as many as one-third of children infected before age 5. Initial damage to the lymphatic system by the parasites generally remains subclinical for years or gives rise only to non-specific presentations of adenitis/adenopathy; however, especially after puberty the characteristic clinical features of the adult disease syndromes (lymphoedema, hydrocoele) manifest themselves. Recognizing that LF disease starts its development in childhood has immediate practical implications both for management and prevention of the disease in individual patients and for the broader public health efforts to overcome all childhood illnesses. For the new World Health Organization (WHO)-supported, public-/private-sector collaboration (Global Alliance) to eliminate LF through once-yearly drug treatment, this recognition means that children will be not only the principal beneficiaries of LF elimination but also a population particularly important to target in order for the programme to achieve its twin goals of interrupting transmission and preventing disease.

The impact of 34 years of massive DEC chemotherapy on Wuchereria bancrofti infection and transmission: the Maupiti cohort

Semi-annual mass DEC chemotherapy combined with vector control at the beginning of the programme, has been administered on the remote island of Maupiti (French Polynesia) since 1955 (except two periods in 1960-67 and 1970-74). The results of two surveys in 1985 and 1989, reporting 0% microfilaraemia, led to the hope that the eradication of lymphatic filariasis had been achieved. We combined parasitological criteria (microfilaraemia by membrane filtration), immunological (antigenaemia and serum levels of specific IgG antibodies) and molecular (PCR-based evaluation of infection in mosquitoes) techniques and found only good control of the parasite: We found residual microfilaraemia in 0.4% of the sample (mean level in carriers: 101.2 mf/ml), antigenaemia in 4.6% (mean level in positive persons: 714.4 units/ml) and specific IgG in 21.6% (including in one very young child). In addition, an infection rate of 1.4% was calculated in the Aedes polynesiensis vector population. These data, obtained in 1997 just before a hurricane, were partially confirmed in 1999 (0.1% of infection rate in the vector). Together with the possibility of some resistance to DEC, various epidemiological factors critical for the eradication of lymphatic filariasis are discussed.

Screening of army soldiers for Wuchereria bancrofti infection in the metropolitan Recife region, Brazil: implications for epidemiological surveillance

Between 1989 and 1995, blood surveys were performed for Wuchereria bancrofti infection in several barracks of the Brazilian army in the metropolitan Recife region. For initial screening, 60 microliters of capillary blood were examined for microfilaria. All men who tested positive had microfilaria quantified by filtration of venous blood through a polycarbonate membrane. Of 23,773 men screened, 585 (2.5%) had microfilaria (mf). Microfilarial density ranged from < 1-8706 mf/ml of blood. Thirteen individuals had ultra-low microfilarial densities (1 mf/11 ml of blood). Characterization of 174 autochthonous cases made it possible to map 8 new districts in 4 cities within metropolitan Recife region where transmission of W. bancrofti was previously unknown. Routine screening of soldiers in the military may provide important surveillance data for national programmes to eliminate transmission of W. bancrofti.

Simple blood-spot sampling with nested polymerase chain reaction detection for epidemiology studies on Brugia malayi

In the absence of a suitable Brugia malayi antigen detection assay, PCR remains one of the more sensitive alternatives to Giemsa-stained thick blood films for B. malayi detection. The need for refrigerated storage and transportation of blood has limited the use of PCR for large-scale epidemiology studies in remote endemic areas. Here we report simple finger-prick blood-spot collection, a one-tube DNA template extraction method and the development of a B. malayi-specific nested PCR assay. The assay was tested on 145 field samples and was positive for all 30 microscopy-positive samples and for an additional 13 samples which were microscopy-negative.

Comparative evaluation of three new tools for diagnosis of bancroftian filariasis based on detection of specific circulating antigens

Three new and commercially available tools for diagnosis of Wuchereria bancrofti infections based on detection of specific circulating antigens were evaluated and compared in the same group of individuals from a highly endemic village in southern Ghana. The tests were: (1) the ICT card test for serum specimens; (2) the TropBio ELISA test for serum specimens; and (3) the TropBio ELISA test for filter-paper specimens. A high degree of positive/negative response similarity was observed for the 3 tests, and the sensitivity for detecting microfilaraemic cases was 100% for all tests. The antigen levels measured in the TropBio serum test and the TropBio filter-paper test were statistically significantly correlated. Among antigen-positive endemic individuals the antigen levels in these 2 tests furthermore showed a positive association with the microfilarial intensity, but a statistical significant correlation was seen only for the filter-paper version of the test. The results are promising for the use of the 3 tests as diagnostic tools in bancroftian filariasis.

The significance of guinea worm infection in the immunological diagnosis of onchocerciasis and bancroftian filariasis

Infections with Dracunculus medinensis frequently occur in the same geographical area as infections with Onchocerca volvulus and Wuchereria bancrofti. This study analysed the significance of D. medinensis infections for the specificity and sensitivity of available tests for antibody-based diagnosis of onchocerciasis (using individual recombinant clones OV-10, OV-11 and OV-16, and the OV-7/OV-10/OV-16 tri-cocktail, in an enzyme-linked immunosorbent assay) and for circulating antigen-based diagnosis of bancroftian filariasis (using the TropBio and the ICT card tests). Some immunological cross-reactivity was observed with all tests. When using individual recombinant O.volvulus antigens, the highest assay indices were obtained for clone OV-10, and the lowest for clone OV-16. Testing the serum responses against the tri-cocktail of recombinant antigens did not notably improve the assay indices. Two of 40 serum samples from individuals with patent dracunculiasis gave a false positive response in the ICT test and one of these was also positive in the TropBio test. Possible implications of applying these diagnostic assays in areas endemic for dracunculiasis are discussed.

The immunodominant Brugia malayi paramyosin as a marker of current infection with Wuchereria bancrofti adult worms

The full-length cDNA sequence encoding Brugia malayi L3 paramyosin has been isolated by immunoscreening a cDNA library with a mouse antiserum raised against Wuchereria bancrofti L3 infective larvae. A recombinant truncated form of paramyosin was expressed as a glutathione S-transferase fusion protein and used to evaluate humoral responses of adults from a W. bancrofti-endemic area in French Polynesia according to their parasitological status. Immunoglobulin G4 (IgG4) preferentially bound to paramyosin in W. bancrofti-parasitized individuals, in contrast to unparasitized individuals, who harbored neither microfilaria nor Og4C3 adult worm circulating antigen. Reduction of the anti-paramyosin IgG4 titer following combined chemotherapy with diethylcarbamazine and ivermectin was significantly correlated with a reduction in the adult worm burden. This indicates that the presence of paramyosin-reactive IgG4 is associated with the presence of parasites and that reduction can be used as an immunological marker for W. bancrofti clearance.