A multicenter evaluation of the Filariasis IgG4 Rapid Test for detection of lymphatic filariasis.

Most endemic regions for lymphatic filariasis (LF), caused by Brugia malayi and Wuchereria bancrofti, are well-defined and rapid tests for each species are available. However, in co-endemic areas and situations, such as screening foreign workers from various endemic regions, a single rapid test that detects both species is needed. The Filariasis IgG4 Rapid Test (Reszon Diagnostics International, Selangor, Malaysia) is an improved version of the previous PanLF Rapid, which detects IgG4 antibodies against both LF species. The 'new' test may also be helpful for post-validation surveillance in W. bancrofti areas. The test features two test lines with BmR1 and BmSXP recombinant antigens, alongside a control line. A 20 μL sample is added to the sample well, followed by two drops of buffer. The result is read visually after 15 minutes. We conducted a multicentre laboratory evaluation of the rapid test across centres in three countries (Malaysia, Thailand, and Indonesia), using 296 serum/plasma samples. These included samples from individuals infected with B. malayi (n = 55), W. bancrofti (n = 25), other parasitic infections (n = 184), healthy individuals (n = 30), and two cases of hyper-IgE syndrome. The rapid test demonstrated an overall sensitivity of 98.7% (100% for B. malayi, 96% for W. bancrofti) and 100% specificity. However, a limitation of the test is non-suitability for areas co-endemic with non-lymphatic filaria due to potential cross-reactivity. These results suggest that it is a promising point-of-care test for LF surveillance, particularly for the aforementioned use cases, and merit further laboratory and field validation studies.