Longitudinal assessment of anti-PGL-I serology in contacts of leprosy patients in Bangladesh

Abstract

Background: Despite elimination efforts, the number of Mycobacterium leprae (M. leprae) infected individuals who develop leprosy, is still substantial. Solid evidence exists that individuals living in close proximity to patients are at increased risk to develop leprosy. Early diagnosis of leprosy in endemic areas requires field-friendly tests that identify individuals at risk of developing the disease before clinical manifestation. Such assays will simultaneously contribute to reduction of current diagnostic delay as well as transmission. Antibody (Ab) levels directed against the M.leprae-specific phenolic glycolipid I (PGL-I) represents a surrogate marker for bacterial load. However, it is insufficiently defined whether anti-PGL-I antibodies can be utilized as prognostic biomarkers for disease in contacts. Particularly, in Bangladesh, where paucibacillary (PB) patients form the majority of leprosy cases, anti-PGL-I serology is an inadequate method for leprosy screening in contacts as a directive for prophylactic treatment.

Methods: Between 2002 and 2009, fingerstick blood from leprosy patients' contacts without clinical signs of disease from a field-trial in Bangladesh was collected on filter paper at three time points covering six years of follow-up per person. Analysis of anti-PGL-I Ab levels for 25 contacts who developed leprosy during follow-up and 199 contacts who were not diagnosed with leprosy, was performed by ELISA after elution of bloodspots from filter paper.

Results: Anti-PGL-I Ab levels at intake did not significantly differ between contacts who developed leprosy during the study and those who remained free of disease. Moreover, anti-PGL-I serology was not prognostic in this population as no significant correlation was identified between anti-PGL-I Ab levels at intake and the onset of leprosy.

Conclusion: In this highly endemic population in Bangladesh, no association was observed between anti-PGL-I Ab levels and onset of disease, urging the need for an extended, more specific biomarker signature for early detection of leprosy in this area.

Trial registration: ClinicalTrials.gov ISRCTN61223447.

Fig 1. Cross-sectional analysis of anti-PGL-I Ig antibody levels at intake.

Anti-PGL-I antibodies at intake for contacts of leprosy patients who developed leprosy during the study (black circle; n = 25) and contacts who remained free of leprosy disease (white box; n = 198) were detected by ELISA using natural disaccharide of PGL-I linked to HSA (ND-O-HSA). Optical density readings were performed at 450nm (OD₄₅₀) and corrected for background levels. Median values per group are indicated by horizontal lines. The cut-off for positivity is indicated by the dashed horizontal line.

Fig 2. Longitudinal analysis of anti-PGL-I Ig antibody levels.

Anti-PGL-I antibodies for all contacts of leprosy patients who developed leprosy during the study (A; n = 25) and contacts who remained free of leprosy disease (B; n = 199) and 4 contacts who developed MB leprosy (C; n = 4) were determined by ELISA using natural disaccharide of PGL-I linked to HSA (ND-O-HSA). Sera were tested at three follow-up time points; FU1: 2 years after intake, FU2: 4 years after intake, FU3: 6 years after intake. Optical density readings were performed at 450nm (OD₄₅₀) and corrected for background levels. Anti-PGL-I Ab levels at the time point of leprosy diagnosis are indicated with black circles (A and C). The cut-off for positivity is indicated by the dashed horizontal lines.