Bancroftian filariasis-differential reactivity of anti-sheath antibodies in microfilariae carriers

Anti-sheath antibodies have been detected using an immunofluorescent assay (IFAT) in the sera of microfilariae carriers (AS cases) residing in areas endemic for Bancroftian filariasis. Microfilariae (mf) of Wuchereria bancrofti purified from five different mf carriers were used separately as antigen to identify anti-sheath antibodies. The reactivity of sera from AS cases to mf sheath was found to be variable to the five different mf preparations. While as high as 25% of the sera reacted with mf purified from one individual, none of them reacted with mf purified from two other individuals. Such a differential reactivity to the sheath was found to be a feature of antibodies in AS cases only. Sera of seven amicrofilaraemic patients with elephantiasis reacted uniformly with all five mf preparations. The possible existence of polymorphic antigen (s) on the sheath of W. bancrofti mf has been proposed.     

The Impact of Two Semiannual Treatments with Albendazole Alone on Lymphatic Filariasis and Soil-Transmitted Helminth Infections: A Community-Based Study in the Republic of Congo

Implementation of mass drug administration (MDA) with ivermectin plus albendazole (ALB) for lymphatic filariasis (LF) has been delayed in central Africa because of the risk of serious adverse events in subjects with high Loa loa microfilaremia. We conducted a community trial to assess the impact of semiannual MDA with ALB (400 mg) alone on LF and soil-transmitted helminth (STH) infections in the Republic of Congo. Evaluation at 12 months showed that ALB MDA had not significantly reduced Wuchereria bancrofti antigenemia or microfilaria (mf) rates in the community (from 17.3% to 16.6% and from 5.3% to 4.2%, respectively). However, the geometric mean mf count in mf-positive subjects was reduced from 202.2 to 80.9 mf/mL (60% reduction, P = 0.01). The effect of ALB was impressive in 38 subjects who were mf-positive at baseline and retested at 12 months: 37% had total mf clearance, and individual mf densities were reduced by 73.0%. MDA also dramatically reduced the hookworm infection rate in the community from 6.5% to 0.6% (91% reduction), with less impressive effects on Ascaris and Trichuris. These preliminary results suggest that semiannual community MDA with ALB is a promising strategy for controlling LF and STH in areas with coendemic loiasis.     

Assessment of microfilaria prevalence in Karimnagar and Chittoor Districts of Andhra Pradesh,India

ObjectiveTo assess the prevalence of disease and microfilaraemia in villages of Karimnagar and Chittoor districts.MethodsData on age and sex of all the respondents were collected and compared with the microfilaria rate (mf) and density (20 μL of peripheral blood by using finger prick method) to examines the relationship between the dynamics of Wuchereria bancrofti among the population.ResultsMicrofilaraemia prevalence was found among all the age groups and its occurrence was more prevalent especially above 30 years age groups. Similarly, the microfilaraemia and disease rates were found significantly higher in males compared to females.ConclusionsUsing these baseline data would be useful in planning for the elimination of lymphatic filariasis in Andhra Pradesh as per the WHO goal to eliminate lymphatic filariasis by 2020.     

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 mm³of 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.     

Studies on the periodicity and intravascular distribution of Wuchereria bancrofti microfilariae in paired samples of capillary and venous blood from Recife, Brazil

We examined the periodicity and intravascular distribution of Wuchereria bancrofti microfilariae (mf) and determined the effect of these parasite properties on the accuracy of blood filming and filtration methods for diagnosis of bancroftian filariasis in the endemic area of Recife, Brazil. Microfilariae in both venous and capillary blood exhibited a nocturnal periodicity pattern with a relatively high amplitude. Overall, capillary blood contained ? 1.25 times the number of mf present at the same time in the same volume of venous blood. However, the ratio of mf present in capillary and venous blood varied over a 24-hour period, so that the fewest mf were present in the capillary bed of the skin at the time when biting activity of the local Culex vector is the lowest. Twenty or 60 μl blood films did not reliably detect carriers with fewer than 100 or 60 mf/ml venous blood, respectively, and were thus inadequate for the identification of low density mf carriers. In contrast, all carriers with > I mf/20 or 60 μl blood smear at night could be identified during daytime hours by filtration of I ml venous blood     

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.     

Lymphatic filariasis in East District, Sikkim

East district of Sikkim has been considered as non-endemic for lymphatic filariasis (LF). However, a LF survey conducted during 2008 revealed microfilaria rate (mf rate) of 1.2%. The LF survey was carried out in 15 randomly selected villages and urban localities of East Sikkim. Out of 3,428 night blood smears collected and examined, 42 were found positive for Wuchereria bancrofti. Microfilaria (mf) carriers were detected from 5 surveyed villages and 5 urban localities of Singtam and Rangpoo with mf rate ranging from 0.5% to 4.2%. The mean mf density was 5.4 per 20cmm3 blood. All mf carriers were residents of east district, Sikkim except two persons who were from Bihar. The detection of microfilaria in young children who had never moved from the area indicates probable indigenous transmission. Out of 15 surveyed areas LF disease was found in 11 areas with prevalence ranging from 0.4% to 7.0%.(Disease rate was 1.6%) (1.7% for Males & 1.4% for females). One local individual was found with lymphoedema and also mf positive. Vector density ranged from 70 to 435 per ten-man-hours, sufficient for transmission of LF. 712 female Cx. quinquefasciatus were dissected to detect the filarial infection and none was found positive. The present survey findings indicate endemicity of filariasis in East district of Sikkim.     

Filamentation temperature-sensitive protein Z (FtsZ) of Wolbachia, endosymbiont of Wuchereria bancrofti: A potential target for anti-filarial chemotherapy

Lymphatic filariasis (LF) is a leading cause of morbidity in the tropical world. It is caused by the filarial parasites Wuchereria bancrofti, Brugia malayi and Brugia timori and transmitted by vector mosquitoes. Currently a programme for the elimination of LF, Global programme for Elimination of Lymphatic Filariasis (GPELF), is underway with the strategy of mass administration of single dose of diethylcarbamazine or ivermectin, in combination with an anthelmintic drug, albendazole. However, antifilarial drugs used in the programme are only microfilaricidal but not or only partially macrofilaricidal. Hence, there is a need to identify new targets for developing antifilarial drugs. Filarial parasites harbor rickettsial endosymbionts, Wolbachia sp., which play an important role in their biology and hence are considered as potential targets for antifilarial chemotherapy development. In this study, one of the cell division proteins of Wolbachia of the major lymphatic filarial parasite, W. bancrofti, viz., filamentation temperature-sensitive protein Z (FtsZ), was explored as a drug target. The gene coding for FtsZ protein was amplified from the genomic DNA of W. bancrofti, cloned and sequenced. The derived amino acid sequence of the gene revealed that FtsZ protein is 396 amino acids long and contained the tubulin motif (GGGTGTG) involved in GTP binding and the GTP hydrolyzing motif (NLDFAD). The FtsZ gene of endosymbiont showed limited sequence homology, but exhibited functional homology with β-tubulin of its host, W. bancrofti, as it had both the functional motifs and conserved amino acids that are critical for enzymatic activity. β-tubulin is the target for the anti-helminthic activity of albendazole and since FtsZ shares functional homology with, β-tubulin it may also be sensitive to albendazole. Therefore, the effect of albendazole was tested against Wolbachia occurring in mosquitoes instead of filarial parasites as the drug has lethal effect on the latter. Third instar larvae of Culex quinquefasciatus were treated with 0.25 mg/ml of albendazole (test) or tetracycline (positive control) in the rearing medium for different intervals and tested for the presence of Wolbachia by FtsZ PCR. All the treated larvae were negative for the presence of the FtsZ band, whereas all the control larvae were positive. The findings of the study, thus indicated that FtsZ is sensitive to albendazole. In view of this albendazole appears to have dual targets; FtsZ in Wolbachia and β-tubulin in W. bancrofti. Further, the functional domain of the gene was assessed for polymorphism among recombinant clones representing 120 W. bancrofti parasites, prevalent across wide geographic areas of India and found to be highly conserved among them. Since it is highly conserved and plays an important role in Wolbachia cell division it appears to be a potential target for anti-filarial chemotherapy development.     

Assessment of family and neighbors of an individual infected with Wuchereria bancrofti from a non-endemic area in the city of Maceió, Brazil

The family and neighbors of a patient infected with W. bancrofti microfilariae were assessed aiming to evaluate the occurrence of cases of lymphatic filariasis in a non-endemic area in the city of Maceió, in the Brazilian state of Alagoas. The patient had previously lived in an endemic focus; however, he has been living in an area where the parasite has never been detected for the past ten years. Female ingurgitated Culex quinquefasciatus mosquitoes captured in the houses of the microfilaremic individual and of his neighbors in the non-endemic region were also examined by polymerase chain reaction (PCR) technique. The thick blood smear examination, blood membrane filtration, and rapid immunochromatography (antigen search) revealed no infected individuals in the family of the microfilaremic individual. All 334 neighbors undergoing the thick blood smear examination were negative for W. bancrofti microfilariae. In 478 ingurgitated C. quinquefasciatus mosquitoes examined by PCR, no W. bancrofti DNA was detected. The microfilaremic individual had a microfilaremia considered very low according to WHO standards (4 microfilariae/mL of blood). As the vectorial infection depends on microfilaremia, the patient's low parasite load did not determine the contamination of other individuals in the area. Our data have shown that the long-term residence of the microfilaremic individual in the non-endemic region was not sufficient to start a new transmission focus of lymphatic filariasis in Maceió.     

Ongoing Surveillance for Lymphatic Filariasis in Togo: Assessment of Alternatives and Nationwide Reassessment of Transmission Status

Tremendous progress has been made towards the goal of global elimination of lymphatic filariasis (LF) transmission by 2020. The number of endemic countries reducing LF transmission through mass drug administration continues to increase, and therefore, the need for effective post-intervention surveillance also continues to increase. Togo is the first sub-Saharan African country to implement LF surveillance, and it has 6 years of experience with this passive surveillance system. We herein report the results of a recent evaluation of the Togolese LF surveillance system, including an evaluation of blood donors as a surveillance population, and provide updated results of ongoing surveillance, including expansion in remote areas. Since implementation of LF surveillance in 2006, only three cases of positive Wuchereria bancrofti filaremia have been detected, suggesting that interruption of transmission has been sustained. Given the impracticality of validating the surveillance system in the absence of ongoing transmission, we confirmed the lack of transmission through a nationwide reassessment survey.     

The significance of low density microfilaraemia in the transmission of lymphatic filarial parasites.

Low density microfilaraemia (mf) is a density of circulating mf which is often undetected by standard survey techniques; it occurs naturally, after anti-filarial drug administration and after vector control. Its occurrence in human populations is closely related to the observed mf frequency distributions in them, and it is an important cause of underestimation of mf prevalence rates in epidemiological surveys. In the present paper it is defined quantitatively as a count of less than 4 mf 20 microliters-1 of capillary blood or less than 30 mf ml-1 of venous blood. Detection of low intensity transmission of parasites is difficult; detection by clinical, entomological or immunological methods may be more sensitive than the usually employed parasitological techniques, due to the extreme inefficiency of the transmission process. Mosquito vectors of filariasis ingest and develop low density mf readily; since they exhibit limitation or proportionality, Aedes, Culex and Mansonia spp. vectors do this more efficiently than Anopheles spp. which exhibit facilitation. Field studies indicate that low level microfilaraemia can initiate a resumption of transmission after very efficient control programmes where Aedes spp. are vectors, whereas eradication has been achieved in areas of Anopheles transmission by levels of vector control which fall far short of eradicating malaria. The situation in the extensive endemic areas where Culex spp. are vectors is less clear, and should be a research priority.     

Filarial Antigenemia and Loa loa Night Blood Microfilaremia in an Area Without Bancroftian Filariasis in the Democratic Republic of Congo

Implementation of mass drug administration for lymphatic filariasis (LF) has been delayed in central Africa because of incomplete mapping and coendemic loiasis. We mapped two regions in eastern Democratic Republic of Congo that were suspected to have LF. Night blood samples were collected from 2,724 subjects in 30 villages. Filarial antigenemia rates by card test exceeded 1% in 28 villages (range = 0–14%). Prevalence rates for large sheathed microfilariae (Mf) ranged from 4% to 40%; Mansonella perstans rates ranged from 22% to 98%. Large Mf were exclusively Loa loa by microscopy, and only 1 of 337 samples tested by quantitative polymerase chain reaction (qPCR) was positive for Wuchereria bancrofti DNA. Filarial antigen positivity was strongly associated with high L. loa Mf counts. Periodicity studies revealed atypical patterns, with no significant diurnal periodicity in some individuals. Thus, methods routinely used for LF mapping may not be reliable in areas in central Africa that are highly endemic for loiasis.     

Cats with single Brugia pahangi infections: relationship between parasitological status and humoral responses to somatic and surface parasite antigens

Cats given a single inoculation of Brugia pahangi infective larvae (L3) were retrospectively allocated into three groups according to parasitological outcome of infection. Recognition of somatic and surface antigens of B. pahangi by sera from each group was compared by ELISA, immunoelectroblotting, and immunoprecipitation techniques. In cats that never became microfilaraemic mean serum IgG antibody levels against somatic extracts from adult male worms, L3, and microfilariae (mf) were higher than levels in cats that initially became microfilaraemic (mf + ve) then spontaneously became nonmicrofilaraemic (mf - ve). The lowest levels of antibody against each stage were found in cats that remained persistently mf + ve. Antigenic components of 18 kD and 22 kD in somatic extracts of adult worms and L3 were recognized by sera from cats that never became mf + ve and by spontaneously mf - ve cats, but not by sera of persistently mf + ve cats. When radioiodinated surface antigens of mixed adult worms and microfilariae were immunoprecipitated by sera from cats in the three groups, no correlation was observed between recognition of individual antigen components and parasitological outcome of infection.     

Lymphatic filariasis in rural areas of Patna District, Bihar. A challenge ahead

Patna district was endemic for lymphatic filariasis (LF). During November 2004, a lymphatic filariasis survey was carried out in seven randomly selected villages from four PHCs of Patna district. Of 1878 night blood smears (NBS) examined, 117 were found positive for W. bancrofti infection (mf rate 6.2%). Microfilaria carriers were detected from all surveyed villages. In all areas prevalence of microfilaria generally increased with age to maximum 15-34 years and then decline within most age-groups. More males (6.4%) were affected than the females (5.8%). All microfilaria (mf) carriers were residents of Patna district. Over all disease rate was 9.1%. Out of 171 diseased individuals, 121 persons were having hydrocele (6.4%). Disease rate was higher in males (12.0%) than females (4.1%). The mean mf density was 11.7. There was no significant difference of mean mf density in males and females. Vector density ranged from 205 to 780 per ten man hours. The survey indicates that the filariasis situation remained unchanged since last fifty years and still is one of the major public health problem in surveyed areas.     

Need for a differential criteria to stop mass drug administration,based on an epidemiological perspective of lymphatic filariasis in Thiruvananthapuram,Kerala, India

ObjectiveTo determine the prevalence of any of the clinical manifestations of lymphatic filariasis, parasitological and entomological indices in Thiruvananthapuram district, Kerala, India, prior to launching mass drug administration (MDA) in the district in 2005.MethodsA cross sectional survey was conducted in 7 endemic wards of the district, in a sample of 2 472 individuals above the age of one year. The study consisted of data collection using questionnaire, night blood smear examination and mosquito collection followed by identification and dissection.ResultsThe prevalence of any of the clinical manifestations of filariasis in this endemic area was 3% (73/2 472) (95% CI between 2.3% to 3.7%). The microfilaria rate was found to be 0.38%. Culex quinquefasciatus formed the predominant mosquito species. The vector infection rate was 1.4% and infectivity rate was 0.47%. Half of the population had satisfactory knowledge regarding the disease. In almost an equal number, the knowledge was poor and only about 10% had good knowledge. Most of the people had not heard about the MDA program.ConclusionsThe prevalence of filariasis even in an area considered to be endemic in Kerala, was low. Microfilaraemia was much lower than the clinical manifestations. However, the potential risk of transmission of disease continues. For such areas which had a pre-MDA mf rate less than 1%, there needs to be more stringent criteria for evaluating the effectiveness of the programme, doing transmission assessment surveys and stopping MDA.     

Cost and cost effectiveness of mass diethylcarbamazine chemotherapy for the control of bancroftian filariasis: comparison of four strategies in Tanzania

This study examines the costs and cost effectiveness of four different mass diethylcarbamazine (DEC) chemotherapy regimens—standard dose, semi‐annual single dose, low monthly dose and DEC‐medicated salt—in reducing microfilarial (mf) prevalence at the community level. Costs were estimated for each intervention in relation to both ingredient and activity, by the derivation and use of detailed itemized cost menus. The most expensive and most effective strategy in reducing community mf prevalence over 2 years was DEC salt intervention, followed in order of costs by the standard, low monthly and semi‐annual DEC strategies. The most cost effective strategy was the low monthly DEC treatment. Cost and sensitivity analyses, however, suggest that the optimal choice of mass DEC strategy for reducing mf is very sensitive to programme design parameters. In particular, the results demonstrate that if the salt delivery structure is simplified, DEC salt has the potential to be the dominant intervention for filariasis control. The results suggest that economies of scale considerations might militate against the adoption of this intervention for large‐scale applications, unless perhaps offset by its potential for cost recovery by direct patient purchase. Further analyses require a more realistic evaluation of filariasis intervention effectiveness by addressing changes in infection intensity and by accounting for the population dynamics of parasite transmission and control.     

Semi-Quantitative Scoring of an Immunochromatographic Test for Circulating Filarial Antigen

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.The current methods of choice for diagnosis of active infections with Wuchereria bancrofti, the main agent of lymphatic filariasis (LF), are based on detection of microfilaria (mf) or circulating filarial antigens (CFA) in blood. Although antigenemia can be detected by enzyme-linked immunosorbent assay (ELISA), field studies and filariasis elimination programs generally use a point-of-care immunochromatographic card test (ICT) (Binax Now Filariasis ICT test, Alere, Portland, ME).¹Several publications have addressed the issue of the choice of diagnostic tools for use in different phases of LF control programs.^2–4 Before the initiation of mass drug administration (MDA), the simplest method for assessing LF endemicity in an area is to measure the proportion of individuals with CFA, using the ICT test. Night blood testing of persons with positive ICT tests can be used to estimate the mf rate in the population. After MDA has been initiated, antigen testing can also be used to assess the impact of MDA.⁴ However, as the primary objective of the control programs is to remove mf (required for transmission of the parasite), and as filarial antigen rates decrease more slowly than the microfilaria rates,⁵ it is also useful to follow mf rates during MDA programs.⁶Another key factor determining the duration of the control programs is the impact of MDA on the lifespan of adult W. bancrofti.^7,8 Two methods have been used to evaluate this, namely ultrasonography, which permits visualization of motile adult worms (the “filarial dance sign”) in some infected individuals, and quantitative CFA testing.^9–13 However, ultrasonography for LF is not sensitive for diagnosis of filarial infections and it requires expensive equipment and highly trained personnel. Quantitative CFA testing also requires highly trained personnel and significant laboratory infrastructure. Thus, these techniques are not feasible for routine use in LF control programs. Therefore, this study was designed to explore the value of using a scoring system for ICT tests as a semi-quantitative method for assessing W. bancrofti adult worm loads in individuals and in populations.An LF survey was conducted in October 2012 in the village of Séké Pembé, located in the Bouenza division of the Republic of Congo. Séké Pembé had not received MDA for LF, but some village residents had received treatment with mebendazole for intestinal worm infections. A detailed census of the population had been performed 1 month before the LF survey, and all persons 5 years of age and above were invited to be tested for W. bancrofti infection. Blood was collected by finger prick, and ICT tests were performed according to the manufacturer''s instructions. The ICT tests were read in 10 minutes by a single trained operator (author MB). Intensity of the test (“T”) line was scored as follows: (0) indicating no visible “T” lines; (0.5) for questionable “T” lines or very faint shadows requiring the opinion of a second examiner; (1) for clearly visible “T” lines but weaker than the control line; (2) for “T” lines that were approximately as dark as the control line; and (3) for cards with a “T” line darker than the control line.Subjects with ICT scores > 0 were called back for a second blood sampling (thick smear for detection of mf) between the hours of 10:00 PM and 1:00 AM. Blood was collected using a capillary tube, and two blood smears (volume 70 μL) were prepared for each subject. On the next day, the blood smears were dehemoglobinized, stained with Giemsa, and read by two experienced microscopists (authors JB and MB). As loiasis and Mansonella perstans filariasis are also endemic in the area, special attention was paid to identify the species of each mf present in the thick smears, and counts were recorded separately for each species. The mf density was defined as the highest count of the two slides and expressed as mf per 70 microliters of blood (mf/70 μL). The maximum ratio between the higher and lower mf count from two slides from individuals was 2.9 (22 and 64 mf/70 μL). The median ratio was 1.5 (interquartile range [IQR]: 1.2–1.7). When not specified, all results presented below will refer only to W. bancrofti mf.The distribution of the ICT scores was compared between microfilaremic and amicrofilaremic subjects using the Wilcoxon test. Mean microfilarial densities were compared between ICT score groups using the Cuzick''s test for trend¹⁴; the correlation between ICT scores and mf density was assessed using the Spearman''s rank correlation coefficient. All analyses were performed using STATA 12.1 (StataCorp, College Station, TX).This study was approved by the ethical committee of the Republic of Congo (Ministry of Public Health). Written informed consent was obtained from all adults participating in the study and from parents or legal guardians of minors.The ICT tests were performed on 774 of the 876 individuals ≥ 5 years of age and recorded during the preliminary census. A total of 145 individuals had an ICT score > 0; 11 had scores of 0.5 (1.4% of the population tested), 85 had scores of 1 (11%), 35 had scores of 2 (4.5%), and 14 had scores of 3 (1.8%).All but one of the individuals with ICT scores > 0 had night blood collected for mf testing. Only 3 and 2 patients had Loa loa or M. perstans mf in the blood smears, respectively. Wuchereria bancrofti microfilaremia was detected in 41 individuals. This number represented 5.3% (41 of 773) of the population tested, 28.5% (41 of 144) of those ICT scores > 0, and 30.8% (41 of 133) of those with ICT scores > 0.5. None of the individuals with ICT of 0.5 was microfilaremic. The proportions of people with microfilaremia were 10.7%, 57.1%, and 85.7% in people with ICT scores of 1, 2, and 3, respectively. The distribution of the ICT scores among the microfilaremic and amicrofilaremic ICT positive subjects is presented in Figure 1; the median score was significantly higher in microfilaremics than in individuals with no mf (Wilcoxon test; P < 0.001).Open in a separate windowFigure 1.Frequency distributions of the immunochromatographic card test (ICT) scores in microfilaremic (striped boxes) and amicrofilaremic (white boxes) subjects with positive ICT test results.The arithmetic mean mf density in those who were microfilaremic was 44.1 mf/70 μL. Figure 2 shows the distributions of the microfilarial densities for each ICT score group. The overall (i.e., including amicrofilaremic individuals) mean mf densities in score groups 1, 2, and 3 were 1.6 (SD: 5.2), 22.2 (SD: 41.7), and 64.6 mf/70 μL (SD: 87.2), respectively (Figure 2, right side). The mean mf densities among microfilaremic individuals were 14.1 (SD: 8.1) in group 1, 38.8 (SD: 49.3) in group 2, and 75.4 mf/70 μL (SD: 90.0) in group 3 (Figure 2, left side). Cuzick''s test showed a highly significant trend for higher microfilarial densities in groups with higher ICT scores (P < 0.001 for the entire study population and P = 0.021 in those who were microfilaremic). The correlation, at the individual level, between ICT scores (for those with scores ≥ 1) and mf density was positive and significant (ρ = 0.61, P < 0.001 for all subjects with scores ≥ 1; and ρ = 0.37, P = 0.0187 for subjects with microfilaremia).Open in a separate windowFigure 2.Distribution of Wuchereria bancrofti microfilarial densities by immunochromatographic card test (ICT) score for microfilaremic subjects (left panel) and for all ICT positive subjects (right panel). Horizontal lines represent arithmetic means and 95% confidence intervals.Circulating filarial antigen levels are believed to be correlated with adult worm counts in humans with bancroftian filariasis.^1,9 Though it is impossible to accurately determine the number of macrofilariae in vivo, this assertion is supported by studies that have shown a relationship between antigen levels and microfilarial densities in mf-positive individuals before treatment,^1,15–22 and a relationship between antigen levels and microfilarial densities with the frequency of detection of worm nests by ultrasonography.^{10–12,16,23}The original AD12 ELISA and the Og4C3-based TropBio ELISA tests are useful for quantitating filarial antigenemia.^1,9,24 However, these tests require highly trained personnel and significant laboratory infrastructure, and they are usually not practical for use by national LF elimination programs.¹³ The fact that the ICT test can provide a semi-quantitative assessment of antigen levels (and perhaps relative adult worm burdens) may be helpful to LF elimination programs as an indicator of infection intensity in populations. Similarly, changes in mean ICT scores could provide an indication of the impact of MDA on adult worms in endemic communities. Decreases in mean ICT scores among those with positive antigen tests after the first rounds of MDA might provide a more accurate indication of the success of MDA than changes in antigen prevalence rates.Our study also provided new data on the issue of equivocal ICT card test results. Because all 11 of the people with ICT scores of 0.5 (very faint shadow lines) were amicrofilaremic, our study suggests that cards with very faint shadow lines should be considered to be negative for filarial antigenemia.The ICT filarial antigen tests are widely performed before, during, and after MDA programs. Our results suggest that it is useful to score these tests and that test scores can be used together with antigen prevalence data. A recently published study used a similar scoring system to evaluate the Alere Filariasis Test Strip that is expected to replace the ICT test in the near future.²⁵ Although the Test Strip was more sensitive than the ICT test in that study, antigen scores for blood samples that were positive by either test were highly correlated. Note that there is no additional cost associated with scoring filarial antigen tests, and scores can be written directly on the cards. Antigen test score data from other endemic areas with different infection rates and treatment histories will help to confirm the practical value of antigen test scoring for LF elimination programs.     

A field survey on the role of low-density microfilaraemia cases in the transmission of filariasis

In former filariasis endemic areas, where the disease has been basically controlled, a few cases of low-density microfilaraemia remain. A survey was carried out in Deqing County, Zhejiang Province, from September 1981 to 1986 in order to determine whether such cases play a role in the continuation of transmission. The results of parasitological and entomological investigations for two consecutive years revealed that after the implementation of intervention measures, the mean microfilaraemia rate in the population fell to about 0.5% and the mean microfilaria density to about 4.2 mf/60 microliter of blood in previously endemic areas of malayan filariasis. Although there were considerable numbers of An. sinensis biting humans, infective larvae could be found in only two positive mosquitoes out of 5,484 dissected, and no new microfilaraemic cases were detected in the 1983 and 1986 follow-up blood examinations, indicating that transmission had already been interrupted. Two volunteers with a microfilaraemia of 3-5 mf/60 microliter of blood were exposed to two batches of An. sinesis in August 1981. The engorged mosquitoes were dissected eight days later. Even though the infection rate of An. sinensis having fed on low-density microfilaraemic cases was as high as 16.8%, the intensity of infection was extremely low, being 1.1 mf/mosquito. From the transmission dynamics point of view, infected mosquitoes carrying very few infective larvae have no practical significance in the transmission of filariasis. It is suggested that the treatment of persons with low-density microfilaraemia (with 5 mf/60 microliters of blood) in areas with low microfilaria rates (less than 1%) need not to be considered as essential.     

The effect of compliance on the impact of mass drug administration for elimination of lymphatic filariasis in Egypt

We studied effects of compliance on the impact of mass drug administration (MDA) with diethylcarbamazine and albendazole for lymphatic filariasis (LF) in an Egyptian village. Baseline microfilaremia (mf) and filarial antigenemia rates were 11.5% and 19.0%, respectively. The MDA compliance rates were excellent (> 85%). However, individual compliance was highly variable; 7.4% of those surveyed after five rounds of MDA denied having ever taken the medications and 52.4% reported that they had taken all five doses. The mf and antigenemia rates were 0.2% and 2.7% in those who reported five doses of MDA and 8.3% and 13.8% in those who reported zero doses. There was no significant difference in residual infection rates among those who had taken two or more doses. These results underscore the importance of compliance for LF elimination programs based on MDA and suggest that two ingested doses of MDA are as effective as five doses for reducing filariasis infection rates.     

A double-blind controlled field trial of doxycycline and albendazole in combination for the treatment of bancroftian filariasis in India

In a placebo controlled field trial, the effects of doxycycline (200 mg/day) for 23 days followed by doxycycline (200 mg/day) in combination with albendazole (ABZ) (400 mg/day) for 7 days on depletion of Wolbachia endobacteria from Wuchereria bancrofti and microfilaricidal activity were studied in 68 patients (34 males and 34 females) from West Bengal, India. The drugs in combination (i.e., doxycycline + ABZ) provided the best efficacy by totally eliminating the circulating microfilaria (mf) (in 42% cases) on day 365 with (99.8%, P < 0.05) suppression even on day 365 post-treatment compared to both exclusive doxycycline (69%, P < 0.05) and ABZ (89%, P < 0.05) groups. Thus, our results have established that a 30-day course of doxycycline in combination with a 7-day course of ABZ is sufficient to ensure long-term reduction in mf level by depleting Wolbachia from worm tissues. Doxycycline combined with ABZ led to a greater reduction in mf density in blood at 4 months (post-treatment) in comparison to doxycycline or ABZ alone. There were significant differences between the three treatments after 12 months (post-treatment). Further, the impact of a 7-day regimen of ABZ was surprisingly good in reducing mf compared to doxycycline-alone group. Adverse reactions were mild. A 30-day course of doxycycline and ABZ in combination is a safe and well-tolerated treatment for lymphatic filariasis with significant activity against microfilaremia.