An ELISA kit with two detection modes for the diagnosis of lymphatic filariasis.

The aim of this study was to develop a low-cost antifilarial immunoglobulin (Ig) G4 detection kit for the diagnosis of lymphatic filariasis. The kit was designed to be used by minimally trained personnel without the constraints of expensive laboratory equipment. We provide a description of the development and validation of a single-serum-dilution based enzyme-linked immunosorbent assay (ELISA) kit with ready-to-use reagents for measuring antifilarial IgG4 antibodies. The kit was tested on residents in Brugia malayi-endemic areas in southern Thailand. Detection was performed by naked-eye observation of the resultant colour of the immunological reactivity. The coefficient of variation (CV) was used to assess the reproducibility of the results. Long-term stability was measured over a 6-month period. Sensitivity of the test kit was 97% when compared with microfilariae detection in thick blood smears. Specificity was 98.7% based on the sera of 57 patients living outside the endemic areas who were infected with other parasites and 100 parasite-free subjects. All positive CVs were < 10%. The test kit was remarkably stable over 6 months. Field validation was performed by the detection of antifilarial IgG4 in 4365 serum samples collected from residents of brugian filariasis-endemic areas and compared with outcome colours of the test samples by the naked eye. Subsequent ELISA evaluation of these results using an ELISA reader indicated high agreement by the kappa statistic. These results demonstrate that the test kit is efficient and useful for public health laboratories as an alternative tool for the diagnosis of lymphatic filarial infection.