Mf Density Research Articles

Bancroftian filariasis: a 13-year follow-up study of asymptomatic microfilariae carriers and endemic normals in Orissa, India

The natural history of human filarial infections leading to development of disease has been a subject of intense debate. The models proposed so far have largely been based on cross-sectional data on microfilariae (Mf) and disease prevalence in filariasis endemic areas. In an attempt to study the parasitological and clinical consequences of filarial infection in Beldal (Orissa, India), an area endemic for Bancroftian filariasis, cohorts of 59 asymptomatic Mf carriers (AS) and 187 asymptomatic and amicrofilaraemic subjects or 'endemic normals' ('EN'), were followed-up and a fraction (73% and 46% respectively) re-examined after 13 years to monitor (a) Mf prevalence, (b) Mf density, (c) circulating filarial antigen (CFA) and (d) chronic disease manifestations. The Mf prevalence and density were also monitored in Mf carriers after 1 and 4 years. Both Mf prevalence and density decreased progressively in the cohort of Mf carriers over a period of 13 years in Beldal. Only 37% of them continued to be microfilaraemic and the Mf density in these subjects was only 10% of the original level. However, loss of circulating Mf in this cohort did not result in loss of CFA and 95% remained CFA positive regardless of Mf status. About 23% of males in the 'EN' cohort developed hydrocoele while only 5.7% of male Mf carriers, who were not treated with DEC, had developed hydrocoele after 13 years. A cohort of Mf carriers in another area, Jatni, was also examined after 10 years to study the parasitological and clinical outcome. In this area, about 59% of the Mf carriers continued to be microfilaraemic after 10 years. These results reveal that in Mf carriers adult filarial worms persist for several years and that loss of circulating Mf with or without chemotherapy with DEC (single 12-day course) does not influence adult worm survival. The findings have been discussed in the context of 'static' and 'dynamic' models describing the relationship between infection and disease in human filariasis.

Amazonian onchocerciasis: parasitological profiles by host-age, sex, and endemicity in southern Venezuela.

This paper describes, for the human onchocerciasis focus of southern Venezuela, the age profiles of Onchocerca volvulus microfilarial (mf) and nodule prevalence, mf intensity, and mf aggregation for the whole examined population (836 Yanomami people) living in 20 villages, and for these communities classified according to endemicity levels (hypoendemic: < or = 20 %; mesoendemic: 21-59 %; hyperendemic: < or = 60 % infected). Mf prevalence and intensity increased with age, particularly in the hyperendemic areas, and there were no marked differences between the sexes. The prevalence of nodules followed the same age pattern. Fifty percent mf prevalence was reached in the 15-19 year age-class when the population was taken as a whole; nearly in the 10 to 14-year-olds for the hyperendemic level, in those aged 20-29 years in mesoendemic areas, and not reached at all in hypoendemic villages. The degree of mf aggregation was measured by the k value of the negative binomial distribution and by the variance to mean ratio (VMR). The relationship between the standard deviation (S.D.) of mf counts and the mean mf density was also explored. These 3 indices (k, VMR, and S.D.) showed a tendency to increase with both mean mf load and host age. Since infection intensity and host age were themselves positively related, it was not possible to draw definite conclusions about age-specific changes of parasite aggregation. There was not a significant decrease of mf intensity after an earlier peak neither was there a shift towards younger ages of the maximum no. of mf/mg reached as the endemicity level increased. These results are discussed in relation to detection of density dependence in the human host, selection of an indicator age-group for rapid epidemiological assessment (REA) methods, and strategies of ivermectin distribution in the Amazonian focus. It is recommended that, for the Amazonian onchocerciasis focus, the indicator group for REA consists of all those aged 15 years and over.

Development of Wuchereria bancrofti in Culex quinquefasciatus that survived the exposure of sub-lethal dose of Bacillus sphaericus as larvae

Development of Wuchereria bancrofti in Culex quinquefasciatus emerged from the larvae that survived the exposure of sub-lethal dose of Bacillus sphaericus was examined in the laboratory. Third instar larvae of Cx. quinquefasciatus were treated with B. sphaericus at a sub-lethal dose of 11.35 μg/250 ml. The female mosquitoes that emerged from the survived larvae were fed on microfilaraemic human blood and parasite development was monitored in the fed mosquitoes. Both treated and untreated mosquitoes could ingest microfilaria (mF) equally as there was no significant difference in mF density between them. But, density of developmental stages of the parasite in treated group was significantly lower. Since, there was no mortality of mosquitoes, the lower density of the developmental stages could be attributed to the loss of parasites in the treated mosquitoes. Consequently, the proportion of mosquitoes with infective larvae (L3) and number of L3 were also significantly lower in treated females. Delay in parasite development was also noticed in treated mosquitoes. The present study indicates that B. sphaericus, when applied at sub-lethal dose kills larvae, and in addition, inhibits development of the filarial parasite and consequently reduces L3 yield in adult mosquitoes that emerged from the survived larvae.

Efficacy of ivermectin in the treatment of Wuchereria bancrofti infection: a model-based analysis of trial results.

Ivermectin is a promising drug for the treatment of lymphatic filariasis. A meta-analysis of trials investigating the effects of a single treatment suggested a dose-dependent effect on the production of microfilariae (mf) by adult Wuchereria bancrofti parasites. A mathematical model that describes the parasite dynamics in the human host and the impact of ivermectin treatment is presented and its outputs compared with these trials. The calculated trend in mf density after treatment appears to be particularly sensitive to the assumption about the mean life-span of mf. Adopting 0.5-2 years as a range of plausible values for this mf life-span, the model is used to estimate the impact of treatment on the parasite. It is found that irrespective of dosage, ivermectin eliminates 100% of the blood mf from a patient. Furthermore, at a dosage level of 400 micrograms/kg a single treatment irreversibly reduces the mf production of the adult parasites by at least 65%. For a dosage of 200 micrograms/kg this reduction is at least 35%. No such effect can be concluded from the results of trials using lower dosages.

Bloodmeal microfilariae density and the uptake and establishment of Wuchereria bancrofti infections in Culex quinquefasciatus and Aedes aegypti.

The relationship between ingestion of microfilariae (mf), production of infective larvae (L3) and mf density in human blood has been suggested as an important determinant in the transmission dynamics of lymphatic filariasis. Here we assess the role of these factors in determining the competence of a natural vector Culex quinquefasciatus and a non vector Aedes aegypti to transmit Wuchereria bancrofti. Mosquitoes were infected via a membrane feeding procedure. Both mosquito species ingested more than the expected number of microfilariae (concentrating factor was 1.28 and 1.81 for Cx. quinquefasciatus and Ae. aegypti, respectively) but Cx. quinquefasciatus ingested around twice as many mf as Ae. aegypti because its larger blood meal size. Ae. aegypti showed a faster mf migration capacity compared to Cx. quinquefasciatus but did not allow parasite maturation under our experimental conditions. Similar proportions of melanized parasites were observed in Ae. aegypti (2. 4%) and Cx. quinquefasciatus (2.1%). However, no relationship between rate of infection and melanization was observed. We conclude that in these conditions physiological factors governing parasite development in the thorax may be more important in limiting vectorial competence than the density of mf ingested.

Diminished Production of T Helper 1 Cytokines and Lack of Induction of IL-2R+T Cells Correlate with T-Cell Unresponsiveness in Rhesus Monkeys Chronically Infected withBrugia malayi

Giambartolomei, G. H., Lasater, B. L., Villinger, F., and Dennis, V. A. 1998. Diminished production of T helper 1 cytokines and lack of induction of IL-2R+T cells correlate with T-cell unresponsiveness in rhesus monkeys chronically infected withBrugia malayi. Experimental Parasitology90, 77–85. The relationship between antigen-specific responsiveness, parasitic burden, and lymphatic pathology was investigated in nine rhesus monkeys with chronicBrugia malayiinfections. Specifically,in vitroproliferation, cytokine gene expression and production, IL-2R expression on T cells, microfilaria (mf) densities, and lymphedema were evaluated. PBMC from three animals (two mf− one mf+) proliferated in response to filarial antigen (responder monkeys, RM) and cells from six animals (5 mf+; one mf−) did not (nonresponder monkeys, NRM). All RM showed lymphedema and none of the NRM did. Antigen-specific IL-2 and IFN-γ (mRNA and protein) were induced in PBMC from all RM whereas PBMC from only one of six NRM responded with IL-2 and IFN-γ expression. IL-4 transcripts were induced in PBMC from two of three RM and in cells from all six NRM. IL-10 mRNA expression and protein production were induced in PBMC from two of three RM and in cells from five of six NRM. A marked increase in the frequency of IL-2R+T cells was observed in antigen-stimulated PBMC cultures of RM but not in those of NRM. The data show that diminished production of Th1 cytokines and lack of induction of IL-2R+T cells may contribute to the unresponsiveness of PBMC from NRM to filarial antigen. They also show that the polarization of immune responses and lymphatic pathology observed in rhesus monkeys is similar to that generally described in human lymphatic filariasis patients.

The relationship between microfilarial load in the human host and uptake and development of Wuchereria bancrofti microfilariae by Culex quinquefasciatus: a study under natural conditions.

The uptake of Wuchereria bancrofti microfilariae (Mf) by Culex quinquefasciatus and their development in relation to human Mf density were quantified by allowing a total of 1096 wild mosquitoes to feed on 13 volunteers sleeping under partially open bed-nets. For each volunteer, each hour between 18.00 and 06.00 h the Mf density in finger-prick blood was determined and engorged mosquitoes collected. Each hourly collection of mosquitoes was kept separately. Half of them was dissected within 18 h post-feeding for the presence of ingested Mf, the other half was reared for 12 days to allow for the development of L3 larvae. About 20% of the latter mosquitoes died during these 12 days and these harboured significantly more larvae than the surviving ones, which could be an indication of excess-mortality among heavily infected mosquitoes. Assuming that variability in Mf uptake and in the number of developed L3 larvae can be described by a negative binomial distribution, a maximum-likelihood procedure was applied to estimate the relationship between human Mf density and both the arithmetic mean Mf uptake and L3 development. Both were adequately described by a saturating hyperbolic function that significantly differed from linearity. The saturation level for Mf was estimated at 29 (CI: 20-54) and for L3 larvae at 6.6 (CI: 4.3-17.0). Next, the L3 yield was related to Mf uptake indicating that the W. bancrofti-C. quinquefasciatus complex shows 'limitation', i.e. a decreasing yield for an increasing uptake. Both the number of Mf ingested and the number of L3 larvae developing per mosquito were found to be highly aggregated, with the level of aggregation decreasing in a non-linear way with human Mf density.

Antifilarial Effect of a Combination of Botanicals from Acacia auriculiformis and Centella asiatica on Canine Dirofilariasis

A mixture (1:1) of the ethanol extracts from the leaves of Centella asiatica and the funicles of Acacia auriculiformis was administered orally to pariah dogs naturally infected with Dirofilaria immitis at 0.04 mg/g body weight/d for 45 days. Two triterpenoid saponins, acaciaside A and B, isolated from the funicles of A. auriculiformis were combined with the leaf ethanol extract from C. asiatica (1:1) and tested at 0.04 mg/g body weight/d for 45 days on microfilaraemic dogs. There was an initial fluctuation in the microfilarial (mf) count in the blood following treatment with the mixture of crude extracts, and then the mf density decreased up to 99%. This suppression lasted for 120 days. When treated with the saponins mixed with the C. asiatica ethanol extract, there was an 86% reduction in mf density 30 days after the last date of treatment, and 68% reduction was maintained 120 days after the treatment.

Wuchereria bancrofti in Tanzania: microfilarial periodicity and effect of blood sampling time on microfilarial intensities.

The circadian periodicity of Wuchereria bancrofti microfilarial (mf) intensities in peripheral blood was analysed in a group of infected individuals from an endemic community in north-eastern Tanzania. The mf density was quantified at two-hourly intervals for 24 hours. A clear nocturnal periodic pattern was observed. Mathematical analysis of the data indicated a peak at 0152 h and a periodicity index of 117.5. A periodicity equation was developed describing the average relation between mf intensity and hour of the day for the study area. Based on the observed periodicity pattern, the effect of blood sampling before peak time is discussed, and the importance of taking sampling time into consideration when analysing data from epidemiological studies is emphasized. A simple method is devised which can be used to adjust for the influence of time on mf intensities, in studies where accurate information on mf intensities is necessary, and where it is impossible to obtain all samples at peak time.

Treatment of human Mansonella streptocerca infection with ivermectin.

We studied the short-term effects of a single dose of 150 micrograms/kg body weight ivermectin on Mansonella streptocerca in an area endemic for streptocerciasis, but not for onchocerciasis, in western Uganda. Six and 12 days after treatment no microfilaria (mf) were found in the skin of 53 out of 96 mf carriers living in 3 villages, and the geometric means of the mf densities of remaining mf carriers were only 33-40% of pretreatment levels. This reduction of mf density was highly significant (P < 0.0001). Immunohistological examination of skin biopsies showed degenerated and disintegrating mf surrounded by activated eosinophils (positive for activated cationic protein), macrophages, and neutrophils (positive for myeloperoxidase and defensin) on day 6 after treatment. Remarkable was the invasion of young, L1 protein-positive macrophages and the release of neutrophil defensin as signs of acute inflammation. We conclude that ivermectin has a strong microfilaricidal activity against M. streptocerca. Common adverse effects were increased pruritus and acute papular dermatitis in 45% of 86 mf carriers on day 6 after treatment. No serious adverse side-effects were noticed in about 700 treated persons.

Occurrence and diagnosis of Mansonella streptocerca in Uganda

During filaria surveys Mansonella streptocerca was found for the first time in Uganda, in 12 widely scattered villages in the Bundibugyo district between the Ruwenzori mountains and the Ituri forest, an area not endemic for Onchocerca volvulus. The crude prevalence in 806 examined adult persons ranged from 5 to 89% with an average of 61%. In 148 children the prevalence was 36%. The geometric mean of microfilaria (mf) densities in adult mf carriers was 1.7 mf/mg skin and the community microfilarial loads ranged from 1.0 to 13.7 mf/skin snip. In 476 persons skin snips from the shoulder contained mf in 58% and those from the buttocks in 48%. Skin snips from 68 persons digested with collagenase showed that only 30–37% of the mf emerged during 24 h incubation at 30°C in isotonic salt solution. An itching acute or more often chronic papular dermatitis, predominantly on the upper parts of the body, was the typical skin lesion observed in 24% of 177 M. streptocerca mf carriers.

Setaria digitata microfilaraemia in Mastomys coucha: an animal model for chemotherapeutic and immunobiological studies.

Intraperitoneal implantation of adult gravid females of the bovine filarial parasite, Setaria digitata in Mastomys coucha was found to induce microfilaraemia lasting for about 125 days. The microfilariae (mf) could be detected as early as 4 days post-implantation (p.i.) and peak levels of about 30 mf in 20 microliters of blood were observed by 21 days. A significant positive correlation was found between mf density and the body weight of recipients pre-implantation. The implanted adult worms were generally viable only for less than 1 week. Implantation resulted in a significant decrease in total leucocytes and erythrocytes, induction of eosinophilia, splenomegaly and anti-erythrocyte autoantibodies. The microfilariae in circulation developed into 3rd-stage infective larvae (L3) when fed onto Aedes aegypti (refm, Liverpool strain). The mf in circulation were found to be eliminated by oral administration of diethylcarbamazine citrate, indicating the usefulness of this model for screening potential anti-microfilarial drugs. During the microfilaraemic phase, priming with tetanus toxoid (TT) resulted in significantly decreased production of anti-toxin levels indicating a state of generalized immunosuppression. Induction of antibodies to various fractionated antigenic components of adult parasites could be demonstrated by enzyme immunoassay (EIA) in M. coucha implanted with live or cold-stunned adult worms. The S. digitata-M. coucha model thus is found amenable to perform chemotherapeutic and immunobiological investigations in experimental filariasis.

Control of lymphatic filariasis by annual single-dose diethylcarbamazine treatments

It has long been stressed that diethylcarbamazine citrate must be given at a total dosage of 72 mg per kilogram of body weight in 12 divided doses of 6 mg kg −1 to obtain maximum effect against Wuchereria bancrofti. However, recent studies revealed that only a single dose at 6 mg kg −1 could reduce microfilaria (Mf) counts by 90%, and that the effect would persist for 12–18 months. The annual repeat of the single-dose mass treatment was shown to be effective in reducing Mf prevalence and density in large-scale, long-term field trials. The scheme is simple and economic, and could be sustainable in many endemic areas, where health manpower and resources are often not sufficient. Annual single-dose mass treatments can be an effective weapon against human lymphatic filariasis, as discussed here by Eisaku Kimura and Jona Mataika.

Sensitivity of a polymerase chain reaction-based assay to detect Onchocerca volvulus DNA in skin biopsies.

A polymerase chain reaction (PCR) of a 150-bp tandem repeat of Onchocerca volvulus (O-150) combined with Southern-blot hybridization to species-specific DNA probes was employed for DNA detection. O-150 was amplified from parasites originating from Uganda, Benin, Cameroon, Liberia, Ghana, Burkina Faso, Mali, and Zaire and was successfully hybridized to digoxigenin-labeled oligonucleotides. To investigate the sensitivity of the PCR, 2 skin biopsies were taken from each of 227 persons from Uganda with proven O. volvulus infections but with low microfilaria (mf) densities due to ivermectin treatment. One biopsy was tested by PCR and the other was digested using collagenase to assess the total number of mf. The PCR revealed 76.2% of the samples to be positive, and the collagenase method showed that 78.9% were positive, indicating similar sensitivity for the two methods. It is probable that for both techniques the biopsy must contain at least one live mf or fragments of a dead mf. In this study, no free or circulating O. volvulus DNA could be detected in skin biopsies by PCR.

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.

Bancroftian filariasis in two urban areas of Recife, Brazil: pre-control observations on infection and disease

Bancroftian filariasis is a major public health problem in the city of Recife in north-eastern Brazil. In some of its urban areas microfilaraemia prevalence reaches 14%. This study describes epidemiological characteristics, infection and disease, in 2 urban areas, Coque and Mustardinha, before control measures were applied. The parasitological survey was performed by a ‘door-to-door’ census covering 5563 subjects, aged between 5 and 65 years. Microfilaraemia was detected by the thick drop technique, using 45 μL of peripheral blood collected between 20:00 and 24:00. In both areas the prevalence of microfilaraemia was 10%, and males had higher prevalences of infection and disease than females. The prevalence of microfilaraemia was higher in the 15–24 and 25–34 years age groups in both sexes. Most microfilaria (mf) carriers (72·1% in Coque and 79·7% in Mustadrinha) had mf densities < 100 60 μL of blood. Females of reproductive age had significantly lower mf densities than males. The overall disease prevalence in both areas was 6·3%. Amongst the subjects who presented with chronic disease 15·7% were microfilaraemic. Chronic disease prevalence increased from 1·4% in the 5–14 years age group to 11·3% in the oldest age group. The most frequent clinical manifestation was hydrocele (5·4%), followed by lymphoedema (1·8%). The epidemiological pattern of filariasis in the populations studied was marked by high prevalence of microfilaraemia, low mf density, and relatively low prevalence of filarial disease considering the level of endemicity.

Variation in the vector competence of Aedes polynesiensis for Wuchereria bancrofti

The vector competences of 6 geographic strains of Aedes polynesiensis for Wuchereria bancrofti were studied using two types of experimental infections. Experimental infection of laboratory-bred mosquitoes fed on the carriers' forearms with different levels of microfilaraemia showed that microfilariae (mf) uptake was directly proportional to the carrier's mf density and, as mf densities decreased, concentration capacity of Ae. polynesiensis increased. It was also shown that infection has an important effect on mosquito mortality, and that the mortality rate differed among mosquito strains. In infections using artificial feeders, the mf uptake was closely regulated, thus showing differences in the vectorial efficiency of Ae. polynesiensis related to the geographic origin of the mosquito strain. The mosquitoes from the Society archipelago were more efficient intermediate hosts than geographically distant strains when infected with W. bancrofti from an island within the archipelago (Tahiti). Mosquito strains from the Society archipelago developed the highest proportion of infective-stage larvae and exhibited the lowest mortality rate when infected with sympatric Tahitian W. bancrofti.

Double-blind controlled trial of a single dose of the combination ivermectin 400 μg/kg plus diethylcarbamazine 6 mg/kg for the treatment of bancroftian filariasis: results at six months

In 1993, a three-arm double-blind controlled trial was implemented in French Polynesia to compare the tolerance and efficacy of a single dose of the combination ivermectin (IVR) 400 μg/kg plus diethylcarbamazine (DEC) 6 mg/kg vs. IVR 400 μg/kg alone vs. DEC 6 mg/kg alone, for treatment of Wuchereria bancrofti carriers. Of the 57 treated male patients in whom microfilaria (mf) densities ranged from 22 to 4709 mg/mL, 3 groups of 19 were randomly selected and allocated to one of the 3 treatments. Side effects were experienced by 34 patients (60%), but none suffered a severe reaction. Grade of reaction did not differ between treatment group, but was significantly correlated with the pretreatment mf density. Six months after treatment, 26%, 32% and 53% of patients were amicrofilaraemic in the DEC, IVR and IVR + DEC groups, respectively. Mf levels were 6·3 %, and 3·1% and 1·0% of the pretreatment level, respectively, significantly lower in the IVR + DEC group than in both the IVR and DEC comparison groups. The combination IVR + DEC showed promise in term of sustained mf decrease, and could be an effective alternative for lymphatic filariasis control programmes.

Turnover of microfilariae in small mammals 2. Disintegration of microfilariae (Acanthocheilonema viteae) (Filarioidea: Nematoda) after intravenous injection into the jird, Meriones unguiculatus.

After i.v. injection of 305 x 10(3) microfilariae (mf) per animal (50 g) into naive jirds, 50.8% of them could be recovered at autopsy 15 min later. Of these, 65.8% were calculated to be in the peripheral circulating blood (PCB) and were completely intact; 18.6% were recovered by perfusion of the lungs and 13.6% from the liver. In both organs about half the mf were associated with adherent lymphocytes and neutrophils but a few were partly disintegrated. Only 2.6% were recovered from the kidneys and the spleen. In long-term injection experiments using the same inoculum size the autopsy was done 15 min and 1, 3 and 6 weeks post-injection (p.i.) of mf into naive jirds. Throughout the experimental period the density of mf remained more or less constant in the PCB, but 3 weeks p.i. the density in the lungs increased up to 14 times to that in the PCB, whereas in the liver it decreased at the same time to a density similar to that in the PCB. In patent animals with adult worms delivering mf these were distributed as follows: 34.7% were calculated to be in the PCB; 24.4% were obtained by perfusion from the lungs and 22.0% from the liver; the rest were found in the kidneys (16.6%) and spleen (2.3%). In the lungs and the liver about 5/6 were associated with adherent cells, partly disintegrated or as fragments. In view of the fact that very few mf become disintegrated immediately after i.v. injection and also from their extremely long sojourn in the PCB, a low turnover rate of mf is presumed.(ABSTRACT TRUNCATED AT 250 WORDS)

Og4C3 circulating antigen: a marker of infection and adult worm burden in Wuchereria bancrofti filariasis.

Og4C3 circulating filarial antigen was detected in the sera of 94.5% (259/274) of microfilaremic patients, 32% (239/751) of persons with presumption of filariasis, and 23% (11/48) of chronic filariasis patients. The antigen level was correlated with the microfilariae (Mf) density and patient age (P < .01). It remained stable in patients treated with microfilaricidal drugs. Og4C3 antigen, undetectable in Mf culture media, was demonstrated to be a rare somatic Mf antigen. It appears to be an excreted or secreted antigen from adult filaria. It could be used as a marker of infection and an indicator of adult worm burden.