Leprosy is an
infectious disease caused by Mycobacterium leprae with tropism for skin and peripheral nerves. Incessant transmission in endemic areas is still impeding elimination of
leprosy. Although detection of M. leprae
infection remains a challenge in asymptomatic individuals, the presence of
antibodies specific for phenolglycolipid-I (PGL-I) correlate with bacterial load. Therefore, serosurveillance utilizing field-friendly tests detecting anti-PGL-I
antibodies, can be applied to identify those who may transmit bacteria and to study (reduction of) M. leprae transmission. However, serology based on antibody detection cannot discriminate between past and present M. leprae
infection in humans, nor can it detect individuals carrying low bacillary loads. In humans, anti-PGL-I
IgM levels are long-lasting and usually detected in more individuals than anti-PGL-I
IgG levels. Inherent to the characteristically long incubation time of
leprosy,
IgM/
IgG relations (antibody kinetics) in
leprosy patients and infected individuals are not completely clear. To investigate the antibody response directly after
infection, we have measured antibody levels by ELISA, in longitudinal samples of experimentally M. leprae infected, susceptible nine-banded armadillos (Dasypus novemcinctus). In addition, we assessed the user- and field-friendly, low-cost lateral flow assay (LFA) utilizing upconverting reporter particles (UCP), developed for quantitative detection of human anti-PGL-I
IgM (UCP-LFA), to detect treatment- or vaccination-induced changes in viable bacterial load. Our results show that serum levels of anti-PGL-I
IgM, and to a lesser extent
IgG, significantly increase soon after experimental M. leprae
infection in armadillos. In view of
leprosy phenotypes in armadillos, this animal model can provide useful insight into antibody kinetics in early
infection in the various spectral forms of human
leprosy. The UCP-LFA for quantitative detection of anti-PGL-I
IgM allows monitoring the efficacy of vaccination and
rifampin-treatment in the armadillo
leprosy model, thereby providing a convenient tool to evaluate the effects of drugs and
vaccines and new diagnostics.