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.

Human antibody responses to Wuchereria bancrofti infective larvae

Human IgG antibody responses to Wuchereria bancrofti third stage infective larvae (L3) surface and somatic antigens were studied by indirect immunofluorescence (IFA) and immunoblot with endemic Egyptian sera (n = 115) with the aim of identifying targets of protective immunity. Human sera variably recognized 14 major bands in L3 by immunoblot. The statistical significance of group differences in antibody prevalence was assessed by the chi-squared test. Children and young adults (aged 10-20 years) tended to have antibodies to more L3 somatic antigens than older adults, with significant differences for bands at 66, 60 and 5 kDa. Infected subjects had more consistent antibody responses to antigens at 55, 50 and 6 kDa than endemic normal subjects with negative serum filarial antigen tests, who are presumed to be uninfected. A 5 kDa antigen was preferentially recognized by the latter group. Antibodies to L3 surface antigens were equally prevalent in uninfected children (75%) and adults (90%) but less prevalent in people with microfilaremia (38%) than in amicrofilaremic subjects with or without filarial antigenemia (81%) (P < 0.001). IFA-positive sera showed significantly enhanced recognition of antigens at 66, 40 and 14 kDa in immunoblots relative to IFA-negative sera. Additional studies are needed to further characterize antigens identified in this study and to establish whether they are indeed targets of protective immunity in humans.

Detection of DNA of nocturnally periodic Brugia malayi in night and day blood samples by a polymerase chain reaction-ELISA-based method using an internal control DNA

An internal control was used in a polymerase chain reaction (PCR)-ELISA-based technique to detect the Hha I repeat of the filarial parasite Brugia malayi. A single microfilaria added to 200 microl of blood was reliably detected. The assay was evaluated on field samples from persons living in an area endemic for Anopheles-transmitted, nocturnally periodic B. malayi in central Sulawesi, Indonesia. Examination of night blood of 138 individuals for the presence of microfilariae by filtration revealed 44 microfilaria carriers. All microfilaria carriers were also positive in the PCR-ELISA and, in addition, 14 more samples were proven to contain parasite DNA. The sensitivity of both methods was compared on night and on day blood samples collected from 113 persons. Whereas 37 microfilaria carriers were identified by filtration of night blood, no microfilariae were observed in the corresponding day blood samples. The PCR-ELISA result was positive in all 37 night blood samples of microfilaria carriers and in an additional 13 night blood samples without microfilariae. Parasite DNA was detected in 31 day blood samples of microfilaria carriers and in 3 day blood samples of amicrofilaremic persons. Assuming a sensitivity of the PCR-ELISA on night blood of 100%, the sensitivity of night blood filtration is 74% and that of the PCR-ELISA on day blood is 68%. These data suggest that the described PCR-ELISA method is capable of detecting infections with nocturnally periodic B. malayi in day blood samples. Therefore, this method may facilitate both the identification of endemic areas and the monitoring of control programs.

Field evaluation of a rapid-format kit for the diagnosis of bancroftian filariasis in Egypt

The AMRAD-ICT Filariasis Test (ICT-Fil) is a new, rapid-format card test for the detection of bancroftian antigenaemia in human blood. We evaluated the performance of the test under field conditions in Egypt by comparing 1813 endemic and 102 nonendemic participants. Endemic participants were tested for microfilaraemia (thick smear and membrane filtration) and serum antigenaemia (ELISA). The infection rates detected were 2.8% by thick smear, 3.5% by membrane filtration, 8.8% by ELISA and 9.0% by ICT-Fil. The card test detected antigenaemia in 98.0% and 95.3% of microfilaraemia carriers testing positive by thick smear and blood filtration respectively. Nonendemic participants were ICT-Fil negative. Identical results were obtained for 173 out of 184 (94%) endemic participants tested by the serum and whole blood ICT-Fil versions.

The effect of pregnancy on Wuchereria bancrofti microfilarial load in humans

As part of a drug trial against bancroftian filariasis in the East Sepik Province of Papua New Guinea we measured the pre-treatment microfilarial densities of 2219 individuals. Mean levels generally increased with age in both sexes, with a tendency to plateau at the highest ages. However, there was a reduction among women of approximately reproductive age. Allowing for the tendency for aggregation to decrease with age, this reduction was statistically significant. However, a comparison of pregnant women and controls showed no evidence that the reduction is specifically related to pregnancy. Moreover, a simple differential equation model of microfilarial acquisition and loss suggests that age-specific patterns of exposure are also unlikely to be solely responsible. Therefore, we suggest that the observed reduction in microfilarial intensity may result from hormonal changes associated with female reproduction, possibly in combination with other factors.

Wuchereria bancrofti antigenaemia in Sri Lanka

The prevalence of Wuchereria bancrofti antigenaemia determined in 353 subjects in Matara, Sri Lanka by Og4C3 ELISA was 20.7%. Positive rates obtained with the same subjects by 1 ml Nuclepore filtration and 60 microl thick blood smear were 11.3% and 7.9%, respectively. Antigen levels were positively associated with microfilaria counts. Two-thirds of antigen-positive and microfilaria-negative (Ag+/Mf-) individuals were > 25-year-old, but younger age groups (< or = 25-year-old) tended to have proportionally more Ag+/Mf- cases. Possible origins of the Ag+/Mf- status are discussed.

ICT filariasis test: a new screening test for Bancroftian filariasis

Bancroftian filariasis can be detected by using the ICT Filariasis test kit which is composed of specific polyclonal and monoclonal antibodies to Wuchereria bancrofti antigen. Chromatographic reaction with serum or plasma shows a result within 5 minutes. When compared with 454 thick blood films (standard smear method) within the same study, the ICT Filariasis test had sensitivity = 100%, specificity = 96.37%, efficiency = 96.70%, predictive value positive (PVP) = 70.70%, predictive value negative (PVN) = 100%. Compared with 454 membrane filtration technic (MFT), the MFT had sensitivity = 95.10%, specificity = 99.50%, efficiency = 99.12%, PVP = 95.10%, PVN = 99.50%. When we compared capillary tube technic (CAP) with TBF, CAP showed sensitivity = 85.40%, specificity = 100%, efficiency = 98.68%, PVP = 100%, PVN = 98.60%. With the convenience, high sensitivity-efficiency, lack of cross-reactions, no night blood collection, single reagent and rapidity of the test, the ICT Filariasis test can be recommended for screening of Bancroftian filariasis, and is suitable for the confirmation of suspected cases in the field where microscopic diagnosis is not available.

Bancroftian filariasis in an irrigation project community in southern Ghana

An epidemiological study to document the endemicity and transmission characteristics of bancroftian filariasis was conducted in an irrigation project community in southern Ghana. In a 50% random sample of the population, the prevalence of microfilaraemia was 26.4% and the geometric mean microfilarial intensity among positives was 819 microfilariae/ml of blood. Hydrocoele was found in 13.8% of the males aged > or =18 years, and 1.4% of the residents examined, all females, had tymphoedema/elephantiasis. Detailed monitoring of the microfilarial intensity in 8 individuals over a 24-h period confirmed its nocturnal periodicity with a peak at approximately 0100 hours. The most important vector was Anopheles gambiae s.l., followed by An. funestus. The abundance of these mosquitoes and their relative importance as vectors varied considerably between the wet and the dry season. Opening of the irrigation canals late in the dry season resulted in a remarkable increase in the population of An. gambiae (8.3% of which carried infective filarial larvae) to levels comparable to those seen during the wet season, suggesting that the irrigation project is responsible for increased transmission of lymphatic filariasis in the community.

Short report: total serum levels of the nitric oxide derivatives nitrite/nitrate during microfilarial clearance in human filarial disease

Nitric oxide (NO) has recently been shown to be cytotoxic to both microfilariae and adult Brugia malayi in vitro and in a murine model, as well against Onchocerca lienalis microfilariae in vitro. We studied the kinetics of nitrite/nitrate, both stable end products of NO, by high-pressure liquid chromatography during microfilaricidal chemotherapy in four filariasis (three Loa loa, and one Onchocerca volvulus) patients. High serum levels of nitrite/nitrate were released during microfilarial clearance and sustained elevated levels were observed six months after chemotherapy, suggesting a role of NO in the elimination of microfilariae in human filariasis.

Antigen-stimulated IL-4, IL-13 and IFN-gamma production by human T cells at a single-cell level

To understand the intricate balance and the coordinate expression of the Th1 and Th2 cytokines following a natural mode of T cell triggering, antigen-stimulated IL-4, IL-13 and IFN-gamma production was studied in primary peripheral blood mononuclear cell cultures at a single-cell level. Cells from filariasis patients who respond to parasite antigen by producing not only IFN-gamma but also IL-4 and IL-13 were stimulated with Brugia malayi adult worm antigen and analyzed for co-expression of cytokines by intracellular staining. IL-4 and IL-13 were frequently co-expressed (54% of IL-4+ cells stained for IL-13 and 29% of IL-13+ cells expressed IL-4 at all time points), whereas IFN-gamma expression was totally segregated from both IL-4 and IL-13. These data indicate that in human peripheral T cells the co-expression of the dominant Th1 and Th2 cytokines within a single cell is a rare event and that IL-13 is clearly more frequently associated with a Th2 than a Th1 type response in primary T cell cultures.

Microfilarial periodicity of Wuchereria bancrofti and man landing periodicity of the vector Culex quinquefasciatus say in Matara, Sri Lanka

OBJECTIVE

To compare the microfilarial periodicity of Wuchereria bancrofti, with the man landing periodicity of the vector Culex quinquefasciatus in Matara, Sri Lanka.

DESIGN

Periodicity was estimated using a statistical method. 60 microliters finger prick (FP) blood was smeared from a single subject every 2 hours for 24 hours of the day to make 12 samples. Smears were stained with Giemsa and the microfilariae (mff) counted. Man landing catches of mosquitoes were made inside a bedroom of a house in the same area on a sleeping volunteer during the night, between 18.00 and 06.00 hours. Each hourly catch was placed in separate paper cups. Hourly C. quinquefasciatus taken were counted.

SUBJECTS

10 asymptomatic microfilaria (mf) carriers.

RESULTS

The individual mf peaks in the 10 carriers varied from 22.00 to 04.00 hours. Using the statistical method the parameter k showing the mf peak hour was 1.19 estimating the peak mf density at 01.11 hours. The influence of different times of blood collection on false negatives among the very low density carriers was estimated by the periodicity curve. It would be desirable to collect blood during the estimated time interval when the mf count was 80% of the peak count, between 21.55 and 04.27 hours in Matara. The results of 25 all-night mosquito landing catches gave a peak activity hours of k as 7.78, corresponding to 01.47 hours.

CONCLUSION

The close agreement in the peak hours of mf density and vector activity suggests a perfect adaptation between parasite and vector for optimum transmission.

Diagnosis of Wuchereria bancrofti infection by the polymerase chain reaction using urine and day blood samples from amicrofilaraemic patients

A sensitive and specific polymerase chain reaction (PCR) based on a highly repeated deoxyribonucleic acid (DNA) sequence (188 bp; SspI repeat) was tested for the detection of Wuchereria bancrofti DNA in blood and urine samples collected during the day from individuals in Coque, Recife, Brazil, an endemic area for W. bancrofti. All microfilaraemic individuals were also positive by PCR, irrespective of the samples used. The PCR system was capable of detecting W. bancrofti DNA in amicrofilaraemic individuals: c. 93% were positive by PCR when day blood samples were used and 59.7% when urine samples collected at 07:00 were used. Thus, nocturnally periodic W. bancrofti infection can be detected in blood samples collected during the day, which is convenient for large-scale screening. In addition, non-invasive urine collection provided suitable samples for PCR, which is clearly advantageous for preliminary mass diagnosis.

Bancroftian filariasis in Maceio, state of Alagoas, Brazil: Observations on Culex quinquefasciatus after blood feeding on individuals with different densities of microfilariae in the peripheral blood stream

Females of laboratory-reared Culex quinquefasciatus were allowed to take blood meals on individuals with low (1-100 microfilariae/ml of peripheral blood), moderate (101-500 microfilariae/ml), and high (> 500 microfilariae/ml) microfilaremia. The mosquitoes ingested 1.39-3.80 microl of blood and infective third-stage (L3) larvae were first recorded 13-14 days after the infecting blood meal. The number of microfilariae ingested by mosquitoes was proportional to the density of microfilariae in the peripheral blood of the human subjects, but with a concentration factor of up to 6.5 times the expected number. Survival of mosquitoes was not influenced by the density of microfilariae in the peripheral blood of infected individuals. Infectivity indices were proportional to microfilaremia in human subjects. The number of L3 larvae/female (intensity of infection) was not influenced by individual microfilaremia. The highest vector efficiency and the best experimental infection index were recorded in mosquitoes that blood fed on individuals with moderate microfilaremia. The results are discussed in relation to the transmission on Bancroftian filariasis in the study area.

Evaluation of quantitative buffy coat analysis in the detection of canine Dirofilaria immitis infection: a model to determine its effectiveness in the diagnosis of human filariasis

Quantitative buffy coat (QBC) analysis has been reported to have a high degree of methodical sensitivity in the detection of human filariasis. This study was conducted to evaluate its usefulness in the diagnosis of filariasis using a Dirofilaria immitis/dog model. By necropsy of 244 stray dogs, 40.6% of the animals were found to harbor 1-58 worms of D. immitis (mean 6.5 +/- 8.4 worms/infected dog). The QBC analysis and thick blood smear (TBS) method detected microfilaremia in 31.6% and 21.3% of these dogs, respectively. The results of these two methods were highly correlated with the presence of bisexual worms in the dogs. The QBC analysis was more sensitive (55% versus 39%) and efficient (79% versus 72%) than the conventional TBS method. However, accurate speciation of the microfilariae was impossible using the QBC analysis. Although this technique is more sensitive, simpler, and less time-consuming and does not require as much skill or experience in comparison with the conventional TBS method, the failure in speciation of the parasites may limit its usefulness.

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.

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.

Detection of microfilarial antigen in circulating immune complex from sera of Wuchereria bancrofti-infected individuals

Polyethylene glycol-precipitated circulating immune complexes (CICs) from the sera of patients with Bancroftian filariasis were examined for parasite antigen content by an ELISA. Of the 227 patients, 214 were asymptomatic microfilariae carriers with microfilaremias ranging between six and 14,000/ml blood, and 13 were symptomatic patients with chronic filariasis without microfilaremia. In addition, the sera of 10 of the patients treated with diethyl carbamazine were also examined. These assays were devised using mouse monoclonal antibody raised against microfilariae of Wuchereria bancrofti. Using an acid-phase covalent-bound plate for the ELISA makes it possible to assay the antigen contents simply. Microfilarial antigens were detected from 92 (43.0%) of microfilaria (mf)-positive individuals. Furthermore, the level of antigen in CIC was correlated with mf counts from night blood Nuclepore filtration results. Antigen was not detected in CIC from patients with a variety of nonfilarial helminth infections. These findings indicate that microfilariae play an important role of CIC formation in lymphatic filariasis.

Circulating connective tissue metabolites in patients with bancroftian filariasis

Sera from adults from an area of Tanzania with high endemicity for Wuchereria bancrofti infection were examined for 4 serological markers of extracellular matrix activity, namely the amino-terminal propeptide of type III procollagen (PIIINP), the carboxy-terminal propeptide of type I procollagen (PICP), the carboxy-terminal telopeptide of type I collagen (ICTP), and hyaluronan. Sera from individuals with non-filarial elephantiasis and from healthy Danes were included as controls. No association was observed between the mean serum concentration of PIIINP or PICP and the clinical, microfilarial or circulating filarial antigen status of the individuals. The mean concentration of ICTP was significantly higher (P < 0.01) in sera from individuals with filarial and non-filarial elephantiasis than in sera from individuals living in filariasis endemic areas but without elephantiasis or in the Danish control sera. Among individuals from the filariasis endemic area, the mean serum concentration of hyaluronan was significantly higher (P < 0.01) in microfilaraemic than in amicrofilaraemic individuals, and significantly higher (P < 0.01) in individuals who had circulating filarial antigens than in those who did not, but there was no relation to the clinical status. The significance of the findings are discussed in relation to the pathological processes taking place in bancroftian filariasis.

Diethylcarbamazine: effect on lysosomal enzymes and acetylcholine in Wuchereria bancrofti infection

We measured the levels of lysosomal enzymes and acetylcholine in Wuchereria bancrofti-infected asymptomatic microfilaraemic human serum, and found a significant decrease in the activity of beta-glucuronidase and acid phosphatase compared to normal serum. Acetylcholine levels were also decreased during infection. However, after giving diethylcarbamazine (6 mg/kg body wt/day) the level of lysosomal enzymes and acetylcholine increased and reached a normal value after two weeks of therapy. It is proposed that parasites secrete acetylcholinesterase in the circulation which degrades acetylcholine. Since acetylcholine stimulates the release of lysosomal enzymes and phagocytosis, the immune response of the host is suppressed during infection. During diethylcarbamazine (DEC) therapy the parasitic enzyme is inhibited by the drug and the normal level of acetylcholine is resumed, which again stimulates the release of lysosomal enzyme and the process of phagocytosis.

A polymerase chain reaction-based assay for detection of Wuchereria bancrofti in human blood and Culex pipiens

Human blood samples and indoor-resting Culex pipiens were collected in 33 randomly selected houses from different sectors of a village in the Nile Delta of Egypt which was endemic for Wuchereria bancrofti. Blood was also collected from subjects with no history of living in filarial endemic areas. Human blood samples were divided and assessed by both membrane filtration and polymerase chain reaction (PCR). Similarly, mosquito samples were assessed by both dissection and PCR. Blood pools representing each household were tested by PCR. If a pool gave a positive result, then individual blood specimens were also tested by PCR. Of the 33 houses tested, both membrane filtration and blood pools assayed by PCR identified 14 (42.4%) 'infected houses'. PCR detected parasite deoxyribonucleic acid (DNA) in blood pools from an additional 3 households that gave negative results by membrane filtration. Of 178 endemic blood samples tested by membrane filtration, 22 (12.3%) had microfilariae and all were individually positive by PCR. Although microfilaria counts were lower in blood collected during the day than in night-collected blood, the PCR results were consistent, regardless of time of collection. All non-endemic blood samples were negative by PCR. Among the 33 houses rested, mosquito pools assayed by PCR identified 17 (51.5%) as 'infected households'. Of these, 8 houses (47%) contained at least one microfilaraemic resident. One 'infected household' was identified by mosquito dissection. We concluded that PCR is a powerful epidemiological tool for screening villages for the prevalence of W. bancrofti. PCR detection of W. bancrofti DNA in blood-fed mosquitoes could be used initially to locate endemic areas with transmission of bancroftian filariasis. PCR detection of W. bancrofti DNA in blood collected during the day could then be used to assess W. bancrofti infection rates.

Evaluation of the Og4C3 ELISA in Wuchereria bancrofti infection: infected persons with undetectable or ultra-low microfilarial densities

The recently developed Og4C3 ELISA, which detects circulating Wuchereria bancrofti antigen, appears promising for use in epidemiological surveys, but its sensitivity is unknown in persons with ultra-low microfilarial densities. We used the Og4C3 to test the sera of 282 persons who were microfilaria-positive in 1-16 ml of blood, 18 persons who were microfilaria-negative but who had ultrasonographic or biopsy evidence of adult W. bancrofti infection, and 63 lifelong residents of a non-endemic area of Brazil. A total of 276 (97.9%) persons with detectable microfilaraemia tested positive (optical density > 0.033). At microfilarial densities of < 1, 1-30, and > 30 microfilariae per ml of blood, the sensitivity of the Og4C3 was 72.2, 97.6 and 100%, respectively (chi 2-test for trend, P < 10(-6)). The assay was positive in 66.7% of amicrofilaraemic persons with evidence of adult worm infection and in one (1.6%) of 63 residents of the non-endemic area (specificity, 98.4%). Our findings support the increasingly widespread use of the Og4C3 for field investigations and epidemiological assessments. However, the sensitivity of the assay may be low in persons who are microfilaria-negative or with densities of < 1 microfilaria per ml.

The sheath of the microfilaria of Brugia malayi from human infections has IgG on its surface

Microfilariae (mf) of Brugia malayi from microfilaraemic people had human IgG on their sheath. Fluorescent antibody studies showed that the predominant IgG isotype was IgG3, with IgG4 and IgG1 being present in lower quantities. Human albumin could not be detected. The sera of patients with chronic disease contained high levels of an IgG2 antibody that reacted with the sheath of mf taken from other people.

A survey of bancroftian filariasis among South-East Asian expatriate workers in Saudi Arabia

In a survey of bancroftian filariasis among expatriate workers from five South-East Asian countries (India, Bangladesh, Sri Lanka, Thailand and the Philippines) where human filariasis is endemic, 762 individuals were examined in the Abha area (Asir) of south-western Saudi Arabia. A prevalence of microfilaraemia of 3.5% and a mean mf density of 6.0/20 mm3 of blood was found among 259 Indian males only. In three out of 9 microfilaraemic cases, clinical signs suggestive of filariasis were observed. The only species identified was Wuchereria bancrofti showing strict nocturnal periodicity. Preliminary laboratory studies on the susceptibility of local mosquitoes to infection with W. bancrofti in which laboratory-bred Culex (C.) pipiens was fed directly on a microfilaraemic volunteer from Madras, South India, revealed that this species was highly susceptible to the Madras strain of the parasite with an average infection rate of 57 (range 41-75)% and a worm burden of 3.5 L3/infective mosquito. This is the first report that local Cx. pipiens mosquitoes may act as a potential vector of introduced bancroftian filariasis in Saudi Arabia. The potential danger of bancroftian filariasis importation and, more importantly, the establishment of new self-sustained foci of the disease is likely to depend upon the abundance of mf carriers and density of vector mosquitoes feeding on carriers.