Detection of day blood filarial antigens by Og4C3 ELISA test using filter paper samples.

BACKGROUND: The launching of the global filariasis elimination programme has necessitated the use of highly sensitive and specific diagnostic tests. The Og4C3 monoclonal antibody-based ELISA test has been found to be highly specific and sensitive for the diagnosis of filariasis using night blood samples. However, it requires a serum sample which poses problems of transport and storage. Collection of blood samples on filter paper the will greatly circumvent these problems. Therefore, we evaluated the utility of the Og4C3 assay on filter paper samples collected during daytime. METHODS: Blood samples were collected from 63 microfilariae (mf) carriers during different time periods in a day on filter paper discs as well as venous blood for sera. The mf carriers and chronic (hydrocele n = 20; lymphoedema n = 120) and acute filariasis (adenolymphangitis n = 39) patients were from the endemic areas and the non-endemic normals were from Uthagamandalam district of Tamil Nadu, India. The filarial antigens in the samples were determined using the Og4C3 filarial antigen assay as per the manufacturer's instructions (JCU TrapBio, Australia). The sensitivity of the assay on sera and filter paper samples collected during night and also on filter paper samples collected during different time intervals of the day were compared with those of the membrane filtration technique, which was used as a gold standard. RESULTS: The geometric mean titre of the sera samples collected during night was 11 units/ml for non-endemic normals and 601.2 units/ml for mf carriers. The specificity of the assay on sera samples collected during night was 100% and the sensitivity 96.8% and the positive and negative values were 100% and 95.2%, respectively. The antigen positivity of the filter paper samples collected during morning hours was 93.3% while it was 76.6% and 86.7% for afternoon and evening hours. A significant association was observed between antigenaemia levels and mf density in the blood samples collected during the night. CONCLUSION: The samples collected on filter paper during the day can be used as an alternative to sera samples for detection of filarial antigens employing Og4C3 ELISA. Also, samples collected during morning hours yield a higher positivity. The assay when applied to serum samples will be useful especially when quantitative results are required.

Response of gravid Phlebotmus papatasi females to an oviposition attractant/stimulant associated with conspecific eggs.

Oviposition response of gravid P. papatasi females to conspecific eggs was studied in laboratory colonized sandflies. It was observed that significantly higher number of eggs were laid in the vicinity of conspecific eggs. However, a certain minimum number of eggs were required to be placed on the substratum to influence the rate of oviposition. The fecundity of females (mean = 56.5 +/- 4.9 eggs) exposed to conspecific eggs was significantly higher (P < 0.05) than that of blank control group. Perhaps, the chemical substances/pheromone of egg origin stimulated the oviposition rate. In an attempt to isolate the active ingredient, solvent washing of the conspecific eggs were tested. No increase in the rate of oviposition was noticed when the test site was treated with distilled water extract, whereas, significantly larger number of eggs were laid at the site treated with di-ethyl ether extract. This indicated that the oviposition attractant associated with the eggs dissolved in the organic solvent, but not in water. The possible application of this attractant for wild sandflies in nature and for regulating the site of oviposition on the substratum in the laboratory colonized sandflies needs to be explored.