Abstract
Early detection of leprosy is key to reduce the ongoing transmission. Antibodies directed against M. leprae PGL-I represent a useful biomarker for detecting multibacillary (MB) patients. Since efficient leprosy diagnosis requires field-friendly test conditions, we evaluated two rapid lateral flow assays (LFA) for detection of Mycobacterium leprae-specific antibodies: the visual immunogold OnSite Leprosy Ab Rapid test [Gold-LFA] and the quantitative, luminescent up-converting phosphor anti-PGL-I test [UCP-LFA]. Test performance was assessed in independent cohorts originating from three endemic areas. In the Philippine cohort comprising patients with high bacillary indices (BI; average:4,9), 94%(n = 161) of MB patients were identified by UCP-LFA and 78%(n = 133) by Gold-LFA. In the Bangladeshi cohort, including mainly MB patients with low BI (average:1), 41%(n = 14) and 44%(n = 15) were detected by UCP-LFA and Gold-LFA, respectively. In the third cohort of schoolchildren from a leprosy hyperendemic region in Brazil, both tests detected 28%(n = 17) seropositivity. Both rapid tests corresponded well with BI(p < 0.0001), with a fairly higher sensitivity obtained with the UCP-LFA assay. However, due to the spectral character of leprosy, additional, cellular biomarkers are required to detect patients with low BIs. Therefore, the UCP-LFA platform, which allows multiplexing with differential biomarkers, offers more cutting-edge potential for diagnosis across the whole leprosy spectrum.
Highlights
Leprosy, an infectious disease caused by Mycobacterium leprae (M. leprae), still poses a major health threat in developing countries
All 5 nonendemic controls (NEC) included as negative controls were confirmed negative in both Gold-lateral flow assays (LFA) and up-converting phosphor (UCP)-LFA
Test performance of UCP-LFA and Gold-LFA in a Bangladeshi cohort. Since both LFAs performed well in cohort 1, which was selected to include polar types of leprosy, we evaluated test performance in an unbiased population characterized by representation of less polar forms of leprosy and MB patients with low bacillary indices (BI), consisting of leprosy patients, healthy household contacts (HHC) and endemic controls (EC) from Bangladesh (Cohort 2)
Summary
An infectious disease caused by Mycobacterium leprae (M. leprae), still poses a major health threat in developing countries. Mis- or delayed diagnosis frequently occurs as leprosy diagnosis still relies on clinical symptoms[1]. As the majority of people have sufficient natural immunity to (myco)bacterial infection and will not progress to disease[3], a small proportion (1–5%) of M. leprae infected individuals will develop clinical symptoms. The OnSite Leprosy Ab Rapid test is an immunochromatographic LFA, detecting IgM antibodies against PGL-I and IgG antibodies to LID-1. The latter fusion protein, encoded by the genes for ML0405 and ML2331, has been shown to be a useful diagnostic marker for MB leprosy[13, 14]
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