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

Step towards elimination of Wuchereria bancrofti in Southwest Tanzania 10 years after mass drug administration with Albendazole and Ivermectin

Background

Lymphatic filariasis is a mosquito transmitted parasitic infection in tropical regions. Annual mass treatment with ivermectin and albendazole is used for transmission control of Wuchereria bancrofti, the infective agent of lymphatic filariasis in many African countries, including Tanzania.

Methodology

In a general population study in Southwest Tanzania, individuals were tested for circulating filarial antigen, an indicator of W. bancrofti adult worm burden in 2009 before mass drug administration commenced in that area. Seven annual rounds with ivermectin and albendazole were given between 2009 and 2015 with a population coverage of over 70%. Participants of the previous study took part in a follow-up activity in 2019 to measure the effect of this governmental activity.

Findings

One thousand two hundred and ninety nine inhabitants of Kyela district in Southwest Tanzania aged 14 to 65 years who had participated in the study activities in 2009 were revisited in 2010/11 and 2019. Among this group, the prevalence of lymphatic filariasis of the 14–65 years olds in 2009 was 35.1%. A follow-up evaluation in 2010/11 had shown a reduction to 27.7%. In 2019, after 7 years of annual treatment and an additional three years of surveillance, the prevalence had dropped to 1.7%, demonstrating successful treatment by the national control programme. Risk factors for W. bancrofti-infection were the occupation as farmer, male sex, and older age. Most infected individuals in the 2019 follow-up study already had a positive test for filarial antigen in 2009 and/or 2010/11.

Conclusions

This data supports the findings of the Tanzanian Neglected Tropical Disease Control Programme (NTDCP), who conducted Transmission Assessment Surveys and found an impressive reduction in the prevalence of LF in children. Our results complement this data by showing a similar decrease in prevalence of LF in the adult population in the same area. The elimination of LF seems achievable in the near future.

Membrane Technology for Rapid Point-of-Care Diagnostics for Parasitic Neglected Tropical Diseases

Parasitic neglected tropical diseases (NTDs) affect over one billion people worldwide, with individuals from communities in low-socioeconomic areas being most at risk and suffering the most. Disease management programs are hindered by the lack of infrastructure and resources for clinical sample collection, storage, and transport and a dearth of sensitive diagnostic methods that are inexpensive as well as accurate. Many diagnostic tests and tools have been developed for the parasitic NTDs, but the collection and storage of clinical samples for molecular and immunological diagnosis can be expensive due to storage, transport, and reagent costs, making these procedures untenable in most areas of endemicity. The application of membrane technology, which involves the use of specific membranes for either sample collection and storage or diagnostic procedures, can streamline this process, allowing for long-term sample storage at room temperature. Membrane technology can be used in serology-based diagnostic assays and for nucleic acid purification prior to molecular analysis. This facilitates the development of relatively simple and rapid procedures, although some of these methods, mainly due to costs, lack accessibility in low-socioeconomic regions of endemicity. New immunological procedures and nucleic acid storage, purification, and diagnostics protocols that are simple, rapid, accurate, and cost-effective must be developed as countries progress control efforts toward the elimination of the parasitic NTDs.

Relative Performance and Predictive Values of Plasma and Dried Blood Spots with Filter Paper Sampling Techniques and Dilutions of the Lymphatic Filariasis Og4C3 Antigen ELISA for Samples from Myanmar

Diagnostic testing of blood samples for parasite antigen Og4C3 is used to assess Wuchereria bancrofti in endemic populations. However, the Tropbio ELISA recommends that plasma and dried blood spots (DBS) prepared using filter paper be used at different dilutions, making it uncertain whether these two methods and dilutions give similar results, especially at low levels of residual infection or resurgence during the post-program phase. We compared results obtained using samples of plasma and DBS taken simultaneously from 104 young adults in Myanmar in 2014, of whom 50 (48.1%) were positive for filariasis antigen by rapid antigen test. Results from DBS tests at recommended dilution were significantly lower than results from plasma tested at recommended dilution, with comparisons between plasma and DBS at unmatched dilutions yielding low sensitivity and negative predictive values of 60.0% and 70.6% respectively. While collection of capillary blood on DBS is cheaper and easier to perform than collecting plasma or serum, and does not need to be stored frozen, dilutions between different versions of the test must be reconciled or an adjustment factor applied.

Scope of detectability of circulating antigens of human lymphatic filarial parasite Wuchereria bancrofti with smaller amount of serum by Og4C3 assay: its application in lymphatic filariasis elimination programme

Filarial antigen detection is an appropriate epidemiological indicator for mapping lymphatic filariasis and impact evaluation of filariasis elimination programme in view of low sensitivity of parasite detection. Monoclonal antibody-based Og4C3 immunological test requires 100 µl serum, which is difficult to collect by finger prick method during community based surveys. Hence, we tested lesser volume of serum compared to standard volume of 100 µl to compare its sensitivity and specificity in detecting the circulating filarial antigens. Blood samples were collected from individuals who tested positive [with titer groups 4 (border line positives), 6 (medium positives), and 8 (high positives)] and negative (titre group 3) for Og4C3 assay. Different volumes of serum samples were used to make-up required volume (100 µl) with appropriate dilutions and subjected to Og4C3 assay. The results showed that known negative samples tested negative at all the serum volumes tested. All positives (titer groups 6 and 8) showed positivity at all reduced volumes of serum sample. However one of the medium positive sample showed negative reaction in 5 µl volume of serum and two of the border line positives showed negative at all the serum volume tested. The results thus showed as less as 15 µl serum is adequate for use in Og4C3 assay. So the test can be performed without losing its sensitivity even with 5 µl serum samples at high titre of antigen (titre group 8) and 15 µl for other groups and this method has scope in programme evaluation.

Real-time PCR detection of the HhaI tandem DNA repeat in pre- and post-patent Brugia malayi Infections: a study in Indonesian transmigrants

BACKGROUND

Lymphatic filariasis caused by Wuchereria bancrofti or Brugia spp. is a public health problem in developing countries. To monitor bancroftian filariasis infections, Circulating Filarial Antigen (CFA) test is commonly used, but for brugian infections only microfilariae (Mf) microscopy and indirect IgG4 antibody analyses are available. Improved diagnostics for detecting latent infections are required.

METHODS

An optimized real-time PCR targeting the brugian HhaI repeat was validated with plasma from microfilariae negative Mongolian gerbils (jirds) infected with B. malayi. Plasma samples from microfilaremic patients infected with B. malayi or W. bancrofti were used as positive and negative controls, respectively. PCR results of plasma samples from a transmigrant population in a B. malayi endemic area were compared to those of life-long residents in the same endemic area; and to IgG4 serology results from the same population. To discriminate between active infections and larval exposure a threshold was determined by correlation and Receiver-Operating Characteristics (ROC) curve analyses.

RESULTS

The PCR detected HhaI in pre-patent (56 dpi) B. malayi infected jirds and B. malayi Mf-positive patients from Central Sulawesi, Indonesia. HhaI was also detected in 9/9 elephantiasis patients. In South Sulawesi 87.4% of the transmigrants and life-long residents (94% Mf-negative) were HhaI PCR positive. Based on ROC-curve analysis a threshold for active infections was set to >53 HhaI copies/μl (AUC: 0.854).

CONCLUSIONS

The results demonstrate that the HhaI PCR detects brugian infections with greater sensitivity than the IgG4 test, most notably in Mf-negative patients (i.e. pre-patent or latent infections).

New strategies to combat filariasis

Two of the major filarial infections, lymphatic filariasis (LF) and onchocerciasis, affect 150 million people, while 1 billion living in endemic areas are at risk of infection. Public health programs to control these infections have successfully existed for years and have evolved from activities driven by the WHO into global programs with public-private partnerships. Currently, these programs use yearly mass application of drugs that mainly kill the larval stages (the microfilariae), with the aim of preventing uptake by the transmitting insect vectors and thus, to block transmission and reduce the infections to such levels that in 15-30 years from now, they will no longer pose a public health problem. While the programs have been very successful in general, there are drawbacks such as coverage being too low within the population, reappearance of infection by migration of infected people into controlled areas, targeting of a stage (the microfilaria) that does not induce pathology in LF and thus lowers compliance, and the potential development of drug resistance, first indications of which have been clearly observed in onchocerciasis. In addition, even without drawbacks, program scopes are not the eradication of filarial infections, which is, however, an ultimate goal of control activities. There is therefore an unequivocal call for the development of higher efficient, complementary chemotherapeutical approaches that lead to a long-lasting reduction of the pathology-inducing worm stages; that is, microfilariae in onchocerciasis and adult worms in LF, or to a macrofilaricidal effect. The recent discovery that depletion of Wolbachia endosymbionts by tetracycline antibiotics leads to long-lasting sterility of adult female worms in onchocerciasis and a macrofilaricidal effect in LF fulfils these requirements. Successful regimens have already been published and agreed upon for use by expert panels. While these regimens are still too long for mass application, the antiwolbachial chemotherapy can currently be applied in the form of a suitable doxycycline regimen for 6 weeks for the treatment of individuals, and exploited in the future for the development of new drugs suitable for mass application. In addition, first data suggest that Wolbachia may also be major mediators of lymphangiogenesis and that their depletion is associated with reduction of lymph vessel-specific vascular endothelial growth factors and reduced lymph vessel size.

Semi-quantitative scoring of an immunochromatographic test for circulating filarial antigen

Abstract. The value of a semi-quantitative scoring of the filarial antigen test (Binax Now Filariasis card test, ICT) results was evaluated during a field survey in the Republic of Congo. One hundred and thirty-four (134) of 774 tests (17.3%) were clearly positive and were scored 1, 2, or 3; and 11 (1.4%) had questionable results. Wuchereria bancrofti microfilariae (mf) were detected in 41 of those 133 individuals with an ICT test score ≥ 1 who also had a night blood smear; none of the 11 individuals with questionable ICT results harbored night mf. Cuzick's test showed a significant trend for higher microfilarial densities in groups with higher ICT scores (P < 0.001). The ICT scores were also significantly correlated with blood mf counts. Because filarial antigen levels provide an indication of adult worm infection intensity, our results suggest that semi-quantitative reading of the ICT may be useful for grading the intensity of filarial infections in individuals and populations.

Lymphatic filariasis control in Tanzania: effect of six rounds of mass drug administration with ivermectin and albendazole on infection and transmission

Background

Control of lymphatic filariasis (LF) in most countries of sub-Saharan Africa is based on annual mass drug administration (MDA) with a combination of ivermectin and albendazole, in order to interrupt transmission. We present findings from a detailed study on the effect of six rounds of MDA with this drug combination as implemented by the National Lymphatic Filariasis Elimination Programme (NLFEP) in a highly endemic rural area of north-eastern Tanzania.

Methods

The effect of treatment on transmission and human infection was monitored in a community- and a school-based study during an 8-year period (one pre-intervention and 7 post-intervention years) from 2003 to 2011.

Results

Before intervention, 24.5% of the community population had microfilariae (mf) in the blood, 53.3% had circulating filarial antigens (CFA) and 78.9% had specific antibodies to the recombinant filarial antigen Bm14. One year after the sixth MDA, these values had decreased considerably to 2.7%, 19.6% and 27.5%, respectively. During the same period, the CFA prevalence among new intakes of Standard 1 pupils in 10 primary schools decreased from 25.2% to 5.6%. In line with this, transmission by the three vectors (Anopheles gambiae, An. funestus and Culex quinquefasciatus) as determined by dissection declined sharply (overall vector infectivity rate by 99.3% and mean monthly transmission potential by 99.2% between pre-intervention and fifth post-intervention period). A major shift in vector species composition, from predominantly anopheline to almost exclusively culicine was observed over the years. This may be largely unrelated to the MDAs but may have important implications for the epidemiology of LF in the area.

Conclusions

Six MDAs caused considerable decrease in all the measured indices for transmission and human infection. In spite of this, indices were still relatively high in the late period of the study, and it may take a long time to reach the recommended cut-off levels for interruption of transmission unless extra efforts are made. These should include increased engagement of the target population in the control activities, to ensure higher treatment coverage. It is expected that the recent initiative to distribute insecticide impregnated bed nets to every household in the area will also contribute towards reaching the goal of successful LF elimination.

Immuno–parasitological assessment of bancroftian filariasis in a highly endemic area along the River Sabaki, in Malindi district, Kenya

Lymphatic filariasis is endemic in the coastal areas of Kenya, with four major foci identified in the early 1970s. The prevalence and intensity of Wuchereria bancrofti infection, together with antifilarial antibody responses, were assessed in a historically highly endemic focus along the River Sabaki, in Malindi district. The prevalences of microfilaraemia and antigenaemia (detected by Og4C3 ELISA) were >20% and >40%, respectively, and both increased steadily with age. The high prevalences of antifilarial IgG1 (86%) and IgG4 (91%) responses indicate that most people living in this setting are exposed to W. bancrofti infection. The children investigated had higher levels of antifilarial IgG1 than the adults. The results of this study, based on a battery of currently available parasitological and immunological methods, provide an epidemiological update on lymphatic filariasis on the northern Kenyan coast. They show that the River Sabaki area is still an important focus for bancroftian filariasis and highlight the importance of implementing an elimination programme, to interrupt the transmission of W. bancrofti in all areas of endemicity in Kenya. The detailed baseline data collected in the River Sabaki area make the communities studied ideal as sentinel sites for epidemiological monitoring and the evaluation of the impact of mass drug administrations to eliminate lymphatic filariasis.

Elevated adaptive immune responses are associated with latent infections of Wuchereria bancrofti

In order to guarantee the fulfillment of their complex lifecycle, adult filarial nematodes release millions of microfilariae (MF), which are taken up by mosquito vectors. The current strategy to eliminate lymphatic filariasis as a public health problem focuses upon interrupting this transmission through annual mass drug administration (MDA). It remains unclear however, how many rounds of MDA are required to achieve low enough levels of MF to cease transmission. Interestingly, with the development of further diagnostic tools a relatively neglected cohort of asymptomatic (non-lymphedema) amicrofilaremic (latent) individuals has become apparent. Indeed, epidemiological studies have suggested that there are equal numbers of patent (MF⁺) and latent individuals. Since the latter represent a roadblock for transmission, we studied differences in immune responses of infected asymptomatic male individuals (n = 159) presenting either patent (n = 92 MF⁺) or latent (n = 67 MF⁻) manifestations of Wuchereria bancrofti. These individuals were selected on the basis of MF, circulating filarial antigen in plasma and detectable worm nests. Immunological profiles of either Th1/Th17, Th2, regulatory or innate responses were determined after stimulation of freshly isolated PBMCs with either filarial-specific extract or bystander stimuli. In addition, levels of total and filarial-specific antibodies, both IgG subclasses and IgE, were ascertained from plasma. Results from these individuals were compared with those from 22 healthy volunteers from the same endemic area. Interestingly, we observed that in contrast to MF⁺ patients, latent infected individuals had lower numbers of worm nests and increased adaptive immune responses including antigen-specific IL-5. These data highlight the immunosuppressive status of MF⁺ individuals, regardless of age or clinical hydrocele and reveal immunological profiles associated with latency and immune-mediated suppression of parasite transmission.

The tropical helminth infection lymphatic filariasis affects more than 120 million people worldwide and is considered a major public health concern. Over 90% of infections are elicited by Wucheria bancrofti and adult worms reside in the lymphatic system releasing millions of microfilariae (MF), which periodically circulate in the blood. New diagnostic tools have provided a method to determine asymptomatic patients that are amicrofilaremic: a subset of individuals that have so far been neglected but are of special interest since these patients represent a dead end in terms of parasite transmission. Therefore, we were interested in determining whether the absence of MF was associated with distinct immunological profiles and observed that indeed responses in MF⁺ patients were dampened. From the viewpoint of the helminth such overall suppression of immune responses may facilitate MF transmission. Latent individuals however, presented elevated filarial specific responses and extrapolating these findings to the host provides novel insight into possible protective mechanisms which either actively hinders the release of MF from worms or their travel to the periphery. Further research into these aspects may broaden the range of strategies currently employed to reduce transmission and in turn eliminate bancroftian filariasis.

Immunoepidemiology of Wuchereria bancrofti infection: parasite transmission intensity, filaria-specific antibodies, and host immunity in two East African communities

We compared the age profiles of infection and specific antibody intensities in two communities with different transmission levels in East Africa to examine the contribution of humoral responses to human immunity to the vector-borne helminth Wuchereria bancrofti. The worm intensities were higher and exhibited a nonlinear age pattern in a high-transmission community, Masaika, in contrast to the low but linearly increasing age infection profile observed for a low-transmission community, Kingwede. The mean levels of specific immunoglobulin G1 (IgG1), IgG2, IgG4, and IgE were also higher in Masaika, but intriguingly, the IgG3 response was higher in Kingwede. The age-antibody patterns differed in the two communities but in a manner apparently contrary to a role in acquired immunity when the data were assessed using simple correlation methods. By contrast, multivariate analyses showed that the antibody response to infection may be classified into three types and that two of these types, a IgG3-type response and a response measuring a trade-off in host production of IgG4 and IgG3 versus production of IgG1, IgG2, and IgE, had a negative effect on Wuchereria circulating antigen levels in a manner that supported a role for these responses in the generation of acquired immunity to infection. Mathematical modeling supported the conclusions drawn from empirical data analyses that variations in both transmission and worm intensity can explain community differences in the age profiles and impacts of these antibody response types. This study showed that parasite-specific antibody responses may be associated with the generation of acquired immunity to human filarial infection but in a form which is dependent on worm transmission intensity and interactions between immune components.

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.

Detection of filarial antigen and antibody in serum and hydrocele fluid of 100 patients of hydrocele

AIM

The present study was carried out to detect an association between isolated non-communicable hydrocoele and filariasis and to provide awareness to positive patients regarding sequel and advising methods for the reduction of morbidity.

METHODS

Blood samples and hydrocoele fluids were used to detect filarial antigen and antibody by ICT Kit, Trop-bio kit and Sevafilachek Kit. These were followed by statistical evaluation by chi2 test.

RESULTS

14% of cases were positive for filarial antigen and antibody in hydrocoele patient serum, while 15% of cases were positive for filarial antigen and antibody in the serum of non-hydrocoele patients.

CONCLUSION

Probability is less than 0.05, which is statistically significant.

The effect of eight half-yearly single-dose treatments with DEC on Wuchereria bancrofti circulating antigenaemia

The effect of eight half-yearly treatment rounds with diethylcarbamazine (DEC; 6mg/kg bodyweight) on Wuchereria bancrofti-specific circulating filarial antigen (CFA), a marker of adult worm infection, was followed in 79 individuals who were CFA-positive before start of treatment. Half of these were also microfilariae (mf)-positive. Microfilaraemia decreased rapidly after onset of treatment and became undetectable after four treatments. Circulating antigenaemia also decreased progressively, but at a much slower rate. After two, four and eight treatment rounds, the mean CFA intensity was reduced by 81, 94 and 98%, and the prevalence of CFA positivity was 85, 66 and 57%, compared with pre-treatment, respectively. CFA clearance rates were negatively related to pre-treatment CFA intensities, and were higher among pre-treatment mf-negative individuals than among pre-treatment mf-positive individuals. Even among patients who had pre-treatment CFA intensities above the upper measuring level (32000antigen units), and who continued to have intensities above this level after treatment, a decrease in post-treatment CFA intensities was obvious from a continuous decrease in ELISA optical density values. Repeated DEC therapy thus appears to have a slow but profound and persistent macrofilaricidal effect, which in the long run may be beneficial to populations undergoing DEC-based control interventions by reducing the probability of future morbidity development.

Lymphatic filariasis in Ghana: establishing the potential for an urban cycle of transmission

Lymphatic filariasis is a significant public health and economic problem in many tropical and sub-tropical regions. Unplanned urbanization leading to a lack of proper sanitary conditions has resulted in an increase in the urban-based transmission of a number of vector-borne diseases, including lymphatic filariasis. It has been well established that lymphatic filariasis is endemic in rural areas of Ghana. The goal of this study was to determine if there is a potential of establishing urban transmission cycles in Ghana's major cities. We clinically and immunologically assessed 625 individuals from the three major urban areas (Bawku, Bolgatanga and Secondi/Takoradi), finding that the prevalence of infection with Wuchereria bancrofti ranged from 0 to 12.5%. The results of a polymerase chain reaction based analysis of mosquitoes collected from these areas suggested that there is a low but detectable prevalence of mosquitoes infected with W. bancrofti. We conclude that there may be a potential for an established urban transmission of lymphatic filariasis in Ghana.

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.

The effect of single dose ivermectin alone or in combination with albendazole on Wuchereria bancrofti infection in primary school children in Tanzania

Examination of 1829 children from 6 primary schools in coastal Tanzania revealed overall Wuchereria bancrofti microfilaria (mf) and circulating filarial antigen (CFA) prevalences of 17.3% and 43.7%, respectively. A randomized double-blind field trial with a single dose of ivermectin (150-200 microg/kg body weight) alone or in combination with albendazole (400 mg) was subsequently carried out among these children. Both treatment regimens resulted in a considerable decrease in mean mf intensities, with overall reductions being slightly but statistically significantly higher for the combination than for ivermectin alone. The difference in effect between the two treatment regimens was most pronounced at 6 months, whereas it was minor at 12 months after treatment. The relative effect of treatment on mean CFA units was less pronounced than on mf. For both treatment regimens, reductions in CFA intensity appeared to be higher in children who were both CFA and mf positive before treatment, which may suggest that treatment mainly affected the survival and/or production of mf, rather than the survival of adult worms. New cases of infection appeared after treatment with both regimens among the pre-treatment mf and CFA negative children. Adverse reactions were few and mild in both groups, and mainly reported from pre-treatment mf and CFA positive children. The alarmingly high prevalence of W. bancrofti infection in primary school children highlights the importance of also determining the reversibility of already acquired early lesions, and the development of new measures and strategies to specifically protect children from later developing clinical disease.

Field evaluation of the whole blood immunochromatographic test for rapid bancroftian filariasis diagnosis in the northeast of Brazil

This study evaluated the whole blood immunochromatographic card test (ICT card test) in a survey performed in Northeastern Brazil. 625 people were examined by the thick blood film (TBF) and ICT card test. Residents of a non-endemic area were also tested by the whole blood card test and Og4C3. The sensitivity of the ICT card test was 94.7% overall, but lower in females than males, based on the reasonable assumption that TBF is 100% specific. However, since TBF and other methods have unknown sensitivity, the true specificity of the card test is unknown. Nevertheless, it is possible to estimate upper and lower limits for the specificity, and relate it to the prevalence of the disease. In the endemic area, the possible range of the specificity was from 72.4% to 100%. 29.6% of the card tests performed in the non-endemic area exhibited faint lines that were interpreted as positives. Characteristics of the method including high sensitivity, promptness and simplicity justify its use for screening of filariasis. However, detailed information about the correct interpretation in case of extremely faint lines is essential. Further studies designed to consider problems arising from imperfect standards are necessary, as is a sounder diagnostic definition for the card test.

Animated documentation of the filaria dance sign (FDS) in bancroftian filariasis

BACKGROUND: Ultrasonography is able to detect adult Wuchereria bancrofti worms in scrotal lymphatic vessels of infected men on account of the characteristic pattern of adult worm movements, known as the filarial dance sign. Furthermore, the technique is able to delineate associated pathology, such as hydrocoele and lymphoedema, which can be diagnosed in early stages. Ultrasonography is also useful in the assessment of macrofilaricidal effects of antifilarial medication.The purpose of this study was to evaluate the usefulness of scrotal ultrasonography, in combination with a new method of digital documentation, in men infected with Wuchereria bancrofti. METHODS: Ultrasonography of the scrotal areas was carried out in 33 male patients from an endemic area in Ghana using a hand-carried ultrasound system and a linear array transducer at 7.5 MHz. Wuchereria bancrofti infection was also assessed by quantification of night blood microfilaraemia and semi-quantitative detection of circulating filarial antigen. Ultrasound findings were documented by print outs and by Digital Video sequences directly exported from the ultrasound machine which were edited in Final Cut Pro 3ledR; and exported, using QuickTimecircledR; Pro, as MPEG-1 video. RESULTS: Worm nests, i.e. dilated lymphatic vessels with the characteristic movement patterns of worms, were found in all patients, and typical examples of larger as well as smaller nests are presented through MPEG-1 video in b- and m-modes as well as Colour Doppler and Pulse Wave Doppler images. CONCLUSION: In this study, the filarial dance sign is being made available on the Internet to readers through MPEG-1 video. This method allows for demonstration of movement patterns rather than static images. In addition, the pathologic ultrasonographic signs of filariasis can be rapidly relayed over great distances and may be helpful to other investigators or clinicians in the diagnosis of patients infected with Wuchereria bancrofti.

Diagnosis of human filariases (except onchocerciasis)

The traditional method of diagnosing filarial infections is to examine blood or skin samples for microfilariae and for many this is still the standard procedure. However, since the present global campaign to eliminate lymphatic filariasis new diagnostic tools have emerged like PCR, antigen detection using finger-prick blood taken during the day and ultrasound to visualize adult worms. The last two can be applied in endemic countries with limited resources and enable the detection of early infections. As well as their value in control schemes, the latter is particularly important for the individual since recent research has shown that damage is usually caused long before symptoms appear. The usefulness in different situations and the advantages and disadvantages of the various new tools for diagnosis of lymphatic filariasis are discussed. For loiasis, immunodiagnostic methods have not been very successful but repetitive DNA sequences in the Loa genome have been found to be species specific. Techniques based on them are particularly useful for diagnosing cases of occult infection without microfilaraemia. There have been no advances in the diagnosis of Mansonella perstans but both immunodiagnostic and PCR tests show promise in differentiating M. streptocerca, and the latter in differentiating M.ozzardi, from Onchocerca. In addition to the human filariae, the dog parasites Dirofilaria immitis and D. repens can also occur in humans but do not produce microfilariae in them. ELISAs and PCR probes have been devised and can usefully differentiate between pulmonary dirofilariasis and lung cancer.

Filaria dance sign and subclinical hydrocoele in two east African communities with bancroftian filariasis

During population-wide cross-sectional surveys for Wuchereria bancrofti microfilaremia, circulating antigenaemia, and clinical disease in a high and a low endemicity community in East Africa in 1998, a portable ultrasound scanner was used simultaneously to examine the scrotal tissue of the male populations (n = 422 and 328, respectively) for signs of adult worms. The overall microfilaria (mf) and circulating filarial antigen (CFA) prevalences in the scanned males were 30.8% and 53.6% in the high and 4.3% and 19.8% in the low endemicity community, respectively. During ultrasound examination, the filaria dance sign (FDS)--indicating the presence of live adult W. bancrofti worms--was observed in 16.1% and 6.7% of the males in these communities, respectively. This examination also revealed that subclinical hydrocoele (fluid accumulation in the scrotal sac, not detected during physical examination for clinical hydrocoele) was very common, affecting 25.3% and 15.5% of the examined males in the high and low endemicity community, respectively. Both of these ultrasonographic signs started to appear around the age of puberty and were most common in adults. In the high endemicity community, the prevalence and mean intensity of mf and CFA were considerably higher in FDS-positive than in FDS-negative adult males, whereas no obvious difference in these parameters was noted between adult males with and without subclinical or the combination of clinical and subclinical hydrocoele. Associations were less clear in the low endemicity community, probably because of the low number of infected individuals. The application of ultrasonography as a tool in bancroftian filariasis epidemiological field studies thus indicated that scrotal pathology may be much more common in endemic areas than hitherto reported.

Lymphatic filariasis: new insights into an old disease

Lymphatic filariasis has afflicted people in the tropical areas of the world for thousands of years but even up to comparatively recent times it has been poorly understood and its importance under recognised. In the last 2 decades or so there has been a flurry of activity in filariasis research, which has provided new insights into the global problem of filariasis, the pathogenesis of filarial disease, diagnosis and control.

Serum ferritin, alpha-tocopherol, beta-carotene and retinol levels in lymphatic filariasis

Based on a cross-sectional study conducted among 100 adults in 1993 in Tanga, Tanzania, the relationship between Wuchereria bancrofti infection and markers of iron, vitamin A and vitamin E status was assessed. Potential predictors assessed were elephantiasis, hydrocoele, W. bancrofti microfilaria intensity and antigen concentration, and intensity of Schistosoma haematobium, hookworm, Trichuris trichiura and Ascaris lumbricoides infection, while controlling for age, sex and elevated serum alpha-1 antichymotrypsin. Of the 100 adults, 62 had W. bancrofti antigenaemia and 43 microfilaraemia, and 21 had elephantiasis. Of the 64 males, 31 had hydrocoele. W. bancrofti microfilaria intensity was a positive predictor of serum ferritin and a negative predictor of serum alpha-tocopherol. In contrast, negative relationships observed between W. bancrofti microfilaria intensity and serum beta-carotene and retinol were not significant. Neither antigen concentration nor clinical manifestations were predictors of micronutrient status. Intensity of hookworm infection was associated with lower serum ferritin. S. haematobium egg output was not a significant predictor of serum ferritin, but was a positive predictor of serum beta-carotene. In conclusion, W. bancrofti microfilaria intensity was associated with higher serum ferritin, but lower serum alpha-tocopherol. The associations probably reflect increased oxidative stress due to microfilariaehost interactions, which could play a role in the pathogenesis.

Evaluation of the ICT whole-blood antigen card test to detect infection due to Wuchereria bancrofti in Sri Lanka

The sensitivity, specificity and cost effectiveness of an immunochromatographic card test (ICT, AMRAD) for the diagnosis of bancroftian filariasis were estimated against 2 standard parasitological techniques: thick blood film (TBF) and Nuclepore membrane filtration (NMF). Individuals were selected from endemic localities in the Western Province (n = 213) and from the non-endemic Central Province (n = 29) of Sri Lanka. Blood was collected between 21:00 and midnight. Sixty microlitre of non-heparinized blood, and 1 mL and 100 microL of heparinized blood were used in TBF, NMF and ICT, respectively. NMF was positive in 31.5% (67/213) of the endemic group, with a mean microfilaria (mf) count of 343/mL (range 8-1782, SD 422). All 67 were positive by ICT (sensitivity 100%), but only 63 by TBF (sensitivity 94%). Among the endemic population there were 12 who were mf negative but antigen positive by ICT. There were, however, no false positives among the non-endemic controls, indicating the possibility that the ICT may in fact be more sensitive and 100% specific. Thus, ICT filariasis test appears to be more effective (both sensitive and specific) than TBF or NMF in diagnosing infection in lymphatic filariasis. The direct unit recurrent costs of the 2 survey tools, TBF and ICT, were US$ 0.30 (Rs. 27/=) and US$ 2.75 (Rs. 248/=), respectively. The high cost of the ICT may be offset by other factors that are difficult to cost.

Resurgence in filarial transmission after withdrawal of mass drug administration and the relationship between antigenaemia and microfilaraemia--a longitudinal study

Seven village units endemic for filariasis were assigned randomly into three arms with different intervention strategies in the years 1995 and 1996. Villages in Group A received two annual mass drug administrations (MDAs) of diethylcarbamazine (DEC) plus ivermectin (IVR). Group B received the same MDAs in combination with vector control; in Group C only placebo was administered. Post-treatment evaluation in 1997 revealed marked reductions in microfilaraemia prevalences (MFP) and geometric mean intensities (GMI). Subsequently, vector control in Group B was continued by the community. Groups A and B received no MDAs between 1997 and 1999 and were re-evaluated in 1999. During this evaluation, antigenaemia prevalence (AGP) was estimated along with MFP, using immunochromatographic test (ICT) kits. The gains of the MDAs were sustained in Group B, while resurgences occurred in Group A, where annual transmission potential (ATP) rose from 21 to 631.6 and MFP doubled. Group C continued to have high ATPs (1057-1617), while Group B had very low ATPs (0-63). After Mulla's corrections, the reductions in MFP were 62.7 and 83.5% and for GMI 72.1 and 91.4% in Group A and B, respectively, compared with Group C. Vector control preserved the gains of MDAs and accounted for 55.8% and 67.1% reductions in MFP and GMI in Group B compared with Group A. The reductions in AGP were 29.4% in Group A and 39.2% in Group B against Group C. The differences between MFP and AGP were nearly uniform across all villages and there was a significant correlation (r=0.98) between the two variables. A similar significant relationship was observed between MFP and AGP values across age groups (r=0.95). Prediction of AGP values from MFP values was proposed with regression equations. We conclude that vector control would be useful as an adjuvant to chemotherapy to prevent resurgences.

Evaluation of ICT filariasis card test using whole capillary blood: comparison with Knott's concentration and counting chamber methods

An immunochromatographic card test (ICT) that uses fingerprick whole blood instead of serum for diagnosis of bancroftian filariasis has recently been developed. The card test was validated in the field in Kenya by comparing its sensitivity to the combined sensitivity of Knott's concentration and counting chamber methods. A total of 102 (14.6%) and 117 (16.7%) persons was found to be microfilaremic by Knott's concentration and counting chamber methods, respectively. The geometric mean intensities (GMI) were 74.6 microfilariae (mf)/ml and 256.5 mf/ml by Knott's concentration and counting chamber methods, respectively. All infected individuals detected by both Knott's concentration and counting chamber methods were also antigen positive by the ICT filariasis card test (100% sensitivity). Further, of 97 parasitologically amicrofilaremic persons, 24 (24.7%) were antigen positive by the ICT. The overall prevalence of antigenemia was 37.3%. Of 100 nonendemic area control persons, none was found to be filarial antigen positive (100% specificity). The results show that the new version of the ICT filariasis card test is a simple, sensitive, specific, and rapid test that is convenient in field settings.

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

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

Genetic polymorphisms in molecules of innate immunity and susceptibility to infection with Wuchereria bancrofti in South India

A pilot study was conducted to determine if host genetic factors influence susceptibility and outcomes in human filariasis. Using the candidate gene approach, a well-characterized population in South India was studied using common polymorphisms in six genes (CHIT1, MPO, NRAMP, CYBA, NCF2, and MBL2). A total of 216 individuals from South India were genotyped; 67 normal (N), 63 asymptomatic microfilaria positive (MF+), 50 with chronic lymphatic dysfunction/elephantiasis (CP), and 36 tropical pulmonary eosinophilia (TPE). An association was observed between the HH variant CHIT1 genotype, which correlates with decreased activity and levels of chitotriosidase and susceptibility to filarial infection (MF+ and CP; P = 0.013). The heterozygosity of CHIT1 gene was over-represented in the normal individuals (P = 0.034). The XX genotype of the promoter region in MBL2 was associated with susceptibility to filariasis (P = 0.0093). Since analysis for MBL-sufficient vs insufficient haplotypes was not informative, it is possible the MBL2 promoter association results from linkage disequilibrium with neighboring loci. We have identified two polymorphisms, CHIT1 and MBL2 that are associated with susceptibility to human filarial infection, findings that merit further follow-up in a larger study.

Assessment of morbidity in Schistosoma haematobium infection: current methods and future tools

Recently, new potential tools for assessment of Schistosoma haematobium related morbidity have emerged. The tools are based on detection of S. haematobium egg antigens in urine or detection of eosinophil cationic protein (ECP) in urine, which may reflect the inflammatory response in the urinary tract. So far two markers have been assessed in long-term post treatment follow-up studies, allowing for an evaluation both before treatment and during regression and reappearance of infection and urinary tract morbidity. The results from these studies and the usefulness of the markers as morbidity assessment tools are discussed.

Lymphatic filariasis in the Philippines

Lymphatic filariasis caused by Wuchereria bancrofti and Brugia malayi is endemic throughout most of the southern half of the Philippine archipelago. Economic and manpower shortages prior to 1996 made it difficult to acquire new prevalence data and vector control data concurrently from all provinces. Nevertheless, analysis of cumulative prevalence data on filariasis indicates the persistence of filariasis in each of the three major island groups - Luzon, Visayas and Mindanao - including 45 out of 77 provinces. Here, Michael Kron and colleagues summarize the prevalence data, and review host, parasite and vector characteristics relevant to the design and implementation of disease control initiatives in the Philippines planned for the year 2000.

Single-dose treatment of Wuchereria bancrofti infections with ivermectin and albendazole alone or in combination: evaluation of the potential for control at 12 months after treatment

The effect of single-dose ivermectin (150-200 micrograms/kg) and albendazole (400 mg) treatment alone and in combination on Wuchereria bancrofti microfilaraemia, antigenaemia and clinical manifestations was compared 12 months after treatment in a double-blind placebo-controlled field trial carried out in Ghana in 1996-98, to evaluate the potential of these treatments for control. Both ivermectin and combination treatments resulted in pronounced reductions in microfilaraemia among individuals who were microfilaria positive before treatment. Among individuals who were positive for circulating filarial antigen before treatment, antigen levels increased considerably over the 1-year period after treatment in the placebo group, whereas they decreased in the ivermectin and combination groups. However, the post-treatment difference reached statistical significance in neither microfilaraemia nor antigenaemia between the ivermectin and the combination groups. Albendazole treatment alone showed only a minor effect on microfilaraemia and antigenaemia. No effect of the treatments on the incidence of new cases of microfilaraemia or antigenaemia, or on clinical manifestations, was observed. Both ivermectin and combination treatment thus appeared effective for control of W. bancrofti infections, but the difference in efficacy between the 2 treatments after 12 months appeared to be minimal.

The control of the human filariases

There is a growing momentum for the global control and elimination of the major human filariases as public health problems worldwide. The renewed optimism for undertaking this objective reflects the development of simple and potentially cost-effective strategies for mass drug delivery in onchocerciasis and the availability of new extremely effective drug combinations to treat infection, and new methods of morbidity control in lymphatic filariasis. It also reflects the development and current availability of very effective diagnostic, surveillance and control modeling tools for both parasites. Control programming will also be aided by our greater understanding of the biology of transmission, host immunity and disease pathogenesis.

A study on the provocative day test effect of ivermectin and albendazole on nocturnal periodic Wuchereria bancrofti microfilaraemia

We conducted a randomized double-blind placebo-controlled study, in the Ahanta West District of Ghana, on the provocative day test effect of ivermectin and albendazole alone and in combination on nocturnal periodic Wuchereria bancrofti microfilaraemia. Sixty-three individuals with high night-time microfilaria (mf) intensities were identified in 1997 or 1998 and randomized into 4 groups. Blood samples for mf were then collected from the same individuals in the daytime (between 09:00 and 15:00) immediately before and 30-50 min after treatment. Groups 1-4 were treated with ivermectin alone (150-200 micrograms/kg), albendazole alone (400 mg), the combination of ivermectin and albendazole, and placebo, respectively. Intensities of mf in daytime samples were considerably lower than in night-time samples. Neither ivermectin or albendazole alone nor their combination provoked significant liberation of W. bancrofti mf into the peripheral circulation after the daytime treatment.