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

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

Binding sites of mosquitocidal toxins of Pseudomonas fluorescens and Bacillus subtilis on pupae and larvae of Culex quinquefasciatus

Two of the potential bacterial isolates, viz., Pseudomonas fluorescens (VCRC B-426) and Bacillus subtilis (VCRC B-471) whose toxins kill the mosquito pupae/larvae have been identified at our center. As the mode of action of these bacteria are not known, an attempt was made to find out the binding sites of the toxic proteins through immunological methods. Antibodies were raised in BALB/c mice and egg yolk system of chicken layers against the mosquitocidal proteins. The antibodies showed specific binding on to the cephalic and thoracic cuticle of the pupae as well as the paddles of the larvae, indicating the binding of the mosquitocidal proteins.

Effect of a single dose of diethylcarbamazine, albendazole or both on the clearance of Wuchereria bancrofti microfilariae and antigenaemia among microfilaria carriers: a randomized trial

BACKGROUND

Lymphatic filariasis is a major vector-borne parasitic disease. The global programme to eliminate lymphatic filariasis was launched in 1997 and currently over 570 million people are covered under it in 48 countries. Mass annual single-dose drug administration of diethylcarbamazine (DEC), co-administrated with albendazole for 5-6 years and mass distribution of diethylcarbamazine-fortified salt are the two strategies for elimination of filariasis.

METHODS

Asymptomatic volunteers residing in Puducherry, India were screened for microfilaria (mf) by examining nocturnal thick blood smears. Those testing positive were randomly assigned to receive a single dose of DEC (6 mg/kg body weight) or albendazole 400 mg or both. Participants were hospitalized for 5 days. Membrane filtration count was used to assess microfilaraemia and ELISA (Og4C3) assay to measure circulating filarial antigens (CFA). Measurements were done before treatment and at 1, 2 and 3 years post-treatment. Viability of the adult worms was assessed by looking for the filarial dance sign (FDS) using ultrasound examination of the scrotum in men with hydrocele.

RESULTS

Fifty-four microfilaraemic Individuals were studied. The mf prevalence started decreasing only by day 180 posttreatment in the DEC group but much earlier in the other two groups (day 30 in the albendazole and day 90 in the DEC with albendazole group). The decrease in mfwas marginal (17.6%, 26.3% and 27.8%, respectively) by the end of year 1 posttreatment, but significant (96.7%, 78.6% and 93.3%, respectively) by the end of year 2 post-treatment (p < 0.05). By the end of year 3, the level decreased to 80% in the DEC, 90% in the albendazole and to 100% in the DEC and albendazole groups. However, the mf intensity decreased significantly (by 39%; p < 0.05) by day 7 post-treatment in both the DEC and DEC with albendazole groups, but only by day 30 in the albendazole group. In all the drug groups, the prevalence as well as intensity of CFA returned to pretreatment levels by the end of year 3 post-treatment.

CONCLUSION

Annual single-dose administration of all the 3 drug regimens significantly reduced antigenaemia levels. There were no significant differences in the efficacy and overall pattern of CFA clearance between the 3 drug regimens.

A method for detecting microfilaraemia, filarial specific antigens and antibodies and typing of parasites for drug resistance and genotypes using finger prick blood sample

Monitoring and evaluation of programme to eliminate lymphatic filariasis (LF) depends on epidemiological assessment using appropriate indicators. Minimum efforts using reliable tests are necessary to guide the programme managers in decision-making. Impact of Mass Drug Administration (MDA) towards filariasis elimination can be assessed by the detection of microfilariae (mf) or parasite DNA (infective), filarial antigens (infected) and antibodies (exposure). It is also important to monitor drug resistance and variation in genetic structure of parasite populations using molecular markers. We developed a method to carry out parasitological, molecular, immunological and genetic analysis from a minimum volume of blood sample (about 150 microl) drawn from finger tip of an individual residing in LF endemic area. The method involves separation of sera for immunological assays and isolation of mf of Wuchereria bancrofti from the blood clots for counting, which were then used for W. bancrofti specific PCR, screening for albendazole sensitivity/resistance alleles by AS-PCR, RAPD profiling and ITS 2 PCR for genotyping. A protocol is also suggested for the separation of sera for assays to detect antigen and antibodies and isolation of mf from clots for genetic analysis. The protocol developed has shown potential application in monitoring several immunological, parasitological and molecular parameters from a limited amount of blood sample collected by finger prick, in large-scale operations.

Monoclonal antibodies generated against excretory/secretory antigens of mammalian stage larvae of the lymphatic filarial parasite Wuchereria bancrofti

Monoclonal antibodies (Mabs) against excretory/secretary (e/s) antigens of fourth stage (L4) larvae of Wuchereria bancrofti were raised and screened for their specificity and sensitivity and evaluated for their potential in detecting homologous e/s antigens in human blood samples. Five Mabs were obtained and, among them, Mab A7 showed high reactivity against e/s antigens of L4 and crude somatic antigens of microfilariae (mf) of W. bancrofti, and infective stage (L3) and adult stage larvae of Brugia malayi. It reacted strongly with sera of Mastomys coucha harbouring L4 stage of B. malayi moderately against sera of the animal having later stages of the parasite. But, it exhibited a low and negligible reactivity against the crude antigens of Setaria cervi and Ascaris lumbricoides, respectively. Another Mab, A6, showed very high reactivity against mf antigens of W. bancrofti and B. malayi and a moderate reactivity against antigens of S. cervi and A. lumbricoides. The two Mabs were tested for their reactivity against filarial antigens in human sera, whose microfilaraemic status was determined by membrane filtration of 1 mL blood sample collected during night. When Mab A7 was tested, 7 out of 22 serum samples (32.0%) from amicrofilaraemic normal individuals from filariasis endemic areas showed positive reactions for filarial antigens, indicating the presence of early stage (L4) of the parasite in them. It also reacted with 84% (n=19) mf positive samples and 11% of non endemic normal serum samples (n=17). Mab A6 showed high reactivity with 86% (n=26) of mf positive serum samples, but did not react with non-endemic normal serum samples (n=17). The results, thus, indicate that the Mab A7 has potential in the detection of e/s antigens of L4 stage larvae of filarial parasites in humans, enabling early diagnosis of filariasis. Mab A6 could be used in the diagnosis of patent infection with microfilaraemia. Western blotting with Mab A7 reacted with the 29.0 kDa protein band of L4 e/s antigens of W. bancrofti.

Localization of Brugia malayi (sub-periodic) adults in different organs of Mastomys coucha and its influence on microfilaraemia and host antibody response

Lymphatic filariasis caused by nematode parasites Wuchereria bancrofti or Brugia malayi is a spectral disease and produces wide range of immune responses and varying levels of microfilaraemia in infected individuals. The relationship between the immune response of host and the developmental stage of the parasite as well as the microfilariae (mf) density and specific location of the adult worms is yet to be understood. As an experimental model, B. malayi adapted in the experimental animal Mastomys coucha has been used widely for various studies in filariasis. The present study was to assess microfilaraemia as well as the humoral immune response of M. coucha during various stages of B. malayi development and their localization in different organs. The result showed that the density of mf in the circulating blood of the experimental animal depended upon the number of female worms as well as the location and co-existence of male and female worms. The mf density in the blood increased with the increase in the number of females. The clearance of inoculated infective stage (L3) or single sex infection or segregation of male and female to different organs of infected host resulted in a microfilaraemic condition. With respect to antibody response, those animals cleared L3 after inoculation and those with adult worm as well as mf showed low antibody levels. But those with developmental fourth stage and/or adult worms without mf showed significantly higher antibody levels.

Suppression of Brugia malayi (sub-periodic) larval development in Aedes aegypti (Liverpool strain) fed on blood of animals immunized with microfilariae

Preliminary studies were carried out to investigate the role of filarial specific antibodies, raised in an animal model against the filarial parasite, Brugia malayi (sub-periodic), in blocking their early development in an experimental mosquito host, Aedes aegypti (Liverpool strain). In order to generate filarial specific antibodies, Mongolian gerbils, Meriones unguiculatus, were immunized either with live microfilariae (mf) of B. malayi or their homogenate. Mf were harvested from the peritoneal cavity of Mongolian gerbils with patent infection of B. malayi and fed to A. aegypti along with the blood from immunized animals. Development of the parasite in infected mosquitoes was monitored until they reached infective stage larvae (L3). Fewer number of parasites developed to first stage (L1) and subsequently to L2 and L3 in mosquitoes fed with blood of immunized animals, when compared to those fed with blood of control animals. The results thus indicated that filarial parasite specific antibodies present in the blood of the immunized animals resulted in the reduction of number of larvae of B. malayi developing in the mosquito host.

Enhanced recovery of fourth stage larvae of Wuchereria bancrofti from mongolian gerbil, Meriones unguiculatus & their in vitro maintenance

Earlier attempts to produce different stages of W. bancrofti, such as fourth stage larvae (L4), in small animal models have yielded very low recovery rates. In order to enhance the recovery of L4, two routes of inoculating a small animal, M. unguiculatus, with infective larvae (L3) viz., intraperitoneal and intrathoracic routes, were compared. On day 17 post-inoculation, higher percentage (23-25%) of L4 were recovered from animals inoculated intrathoracically compared to that from animals inoculated intraperitoneally (2-8%). Also, comparatively higher proportion of worms (75-92%) remained within the intrathoracic region, unlike in the intraperitoneal region (50-80%). A few worms (1-4%) could be recovered even on 31 days post-inoculation from animals inoculated intrathoracically. When the L4 produced in animals were cultured in modified Frank's medium, all of them survived for 15 days and 50 per cent survived till the 25th day. The higher yield and ease of recovery from the thoracic cavity makes this route of inoculation a suitable method for production of L4. In vitro maintenance of L4 for prolonged period is significant with respect to excretory/secretory products or for drug screening.

In vitro cultivation of third stage larvae of Wuchereria bancrofti to fourth stage: influence of some physico-chemical factors

It has been reported that third stage larvae (L3) of Wuchereria bancrofti strain from Jakarta, molted to the fourth stage (L4) in vitro, in a simple culture medium supplemented with 10% human serum. In the present study, this culture medium has been used to examine the effects of some physico-chemical parameters on larval growth, development and molting of Wuchereria bancrofti from India. Lymph at 10% concentration enhanced the in vitro survival time of larvae. Molting of larvae from L3 to L4 stage has been obtained using human fetal lung cells in cellular co-culture and as a source of conditioned medium. Given these improvements in the medium supplementation, it has been observed that the age of L3s (duration of L3s maintenance within the mosquitos) is one of the most important parameters for the development of L3s in vitro. No molting was observed when one day L3s were used whereas, molting occurred with one or two weeks old L3s. On the contrary, when more than 3 weeks old L3s were used molting failed to occur even though duration of survival of L3s was improved and in this case, most of the larvae were degenerated.