Abstract
The development of antibody testing for the diagnosis of lymphatic filariasis (LF) is intended to enhance the monitoring and evaluation activities of the Global Program for the Elimination of LF. This is due to the fact that antibody tests are expected to be the most sensitive at detecting exposure to LF compared to antigen that takes longer to develop. To this end a new antibody-based enzyme linked immunosorbent assay (ELISA) to Wuchereria bancrofti antigen Wb123 has been developed and further designed into a point of care rapid diagnostic test, under evaluation. In pre-treatment surveys, individuals were tested for antigen using the immuno-chromatographic test (ICT) card, and night blood microfilariae, after which all positives were treated using Ivermectin and Albendazole. The Wb123 ELISA was tested in antigen positive individuals, three months after they were treated. Samples were also tested for ICT and night blood microfilariae. The results revealed a reduction in microfilariae and ICT prevalence after treatment. Antigen and antibody prevalence increased with age. However, there was no correlation with the antibody responses observed. The mean WB123 antibody titers were higher among ICT positives, but not significantly different from ICT negative persons. While the Wb123 is targeted for use in untreated populations, further evaluations and guidelines will be required to define its use in populations that have undergone treatment for the control of LF.
Highlights
Lymphatic filariasis (LF) is a neglected tropical disease (NTD) caused by infection with the parasitic worms Wuchereria bancrofti, Brugia malayi and B. timori [1]
Wb123 assay picked up 53% of the immuno-chromatographic test (ICT) positive results, whereas ICT picked up 56% of the Wb123 positive results
Negative test concordance revealed that 59% of ICT negatives were negative for Wb123, while 56% of Wb123 negatives were negative for ICT Table 1
Summary
Lymphatic filariasis (LF) is a neglected tropical disease (NTD) caused by infection with the parasitic worms Wuchereria bancrofti, Brugia malayi and B. timori [1]. There are challenges to the program, one of which is a reliable tool to determine when it is appropriate to stop MDA and proceed with post-intervention surveillance [4] This is especially due to the significant reduction in microfilaremia and antigenemia in endemic communities under treatment. The WHO recommends Transmission Assessment Surveys (TAS) for post-MDA surveillance [5] based on detecting circulating filarial antigen This has a limitation of detecting infections only after the development of adult parasites. Various antibody based assays to recombinant filarial antigens have been developed, with challenges of cross-reactivity to other filarial parasites [6, 7] These problems of specificity have been addressed through the development of a new antibody based assay to Wuchereria bancrofti antigen Wb123 [8, 9]. While this assay is still under evaluation, we tested it in two communities with at least 12 rounds of yearly MDA
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