Specific antigen serologic tests in leprosy: implications for epidemiological surveillance of leprosy cases and household contacts

Abstract

BACKGROUND There is a lack of straightforward tests for field application and known biomarkers for predicting leprosy progression in infected individuals.OBJECTIVE The aim was to analyse the response to infection by Mycobacterium leprae based on the reactivity of specific antigens: natural disaccharide linked to human serum albumin via an octyl (NDOHSA), a semisynthetic phenolic glycolipid-I (PGL-I); Leprosy Infectious Disease Research Institute Diagnostic-1 (LID-1) and natural disaccharide octyl - Leprosy Infectious Disease Research Institute Diagnostic-1 (NDOLID).METHODS The study population consisted of 130 leprosy cases diagnosed between 2010 and 2015 and 277 household contacts. An enzyme-linked immunosorbent assay (ELISA) was used to analyse the reactivity of antibodies against NDOHSA, LID-1 and NDOLID. The samples and controls were tested in duplicate, and the antibody titer was expressed as an ELISA index. Data collection was made by home visits with application of questionnaire and dermatological evaluation of all household contacts to identify signs and symptoms of leprosy.FINDINGS Significant differences in the median ELISA results were observed among leprosy cases in treatment, leprosy cases that had completed treatment and household contacts. Higher proportions of seropositivity were observed in leprosy cases in treatment. Seropositivity was also higher in multibacillary in relation to paucibacillary, with the difference reaching statistical significance. Lower titers were observed among cases with a longer treatment time or discharge. For household contacts, the differences according to the clinical characteristics of the leprosy index case were less pronounced than expected. Other factors, such as the endemicity of leprosy, exposure outside the residence and genetic characteristics, appeared to have a greater influence on the seropositivity.MAIN CONCLUSIONS Serologic tests could be used as auxiliary tools for determining the operational classification, in addition to identifying infected individuals and as a strategy for surveillance of household contacts.

Serum IgA Antibodies Specific to M. leprae Antigens as Biomarkers for Leprosy Detection and Household Contact Tracking

“…The antigens NDO-HSA, LID-1 and NDO-LID have been also used in surveillance studies targeting household contacts ( 36 , 37 ). Leprosy household contacts represent a group at high risk of developing the disease, thus, tracking new cases among this population contributes for early detection and better control of the disease ( 38 , 39 ).…”

Prevalence and spatial distribution of Mycobacterium leprae infection in a medium endemicity municipality

“…Studies in different regions of Brazil and South America have found similar situations, which confirm that the serology varies according to the degree of endemic of the geographic region, genetic predisposition of the population and level of proximity to the leprosy patient, in the case of household and social contacts (5,10) . The results of the research revealed that the health services performed late and inopportune diagnoses, due to the presence of changes in foot strength after treatment.…”

“…The profile of household contacts with positive serology -men over 60 years and spouses of the index case -also suggests that the length of time and exposure to the focus of the infection puts them at risk of acquiring the disease (5,15) , corroborating the affirmation that a set of factors greatly influence the transmission of Mycobacterium leprae, in addition to the clinical features of the index case (10) .…”

“…The time between the diagnosis of the cases and the carrying out of this investigation was considered a limitation of this study, which may have generated memory bias and reduced the serological level between the groups, especially among the home contacts. However, there are explanations in the literature for these findings, since there is a possibility of reduction in the titre of anti-PGL-1 IgM antibodies, due to the decrease in the bacillary load after the end of the poly chemotherapy (10)(11)(12) of the interviewed cases.…”

“…The reading was in a spectrophotometer at 492 nm of absorbance (6) . The ELISA was repeated for samples displaying ELISA index values, classified as positive in a single well of the duplicate, and samples whose values exhibited 25.0% or more of variation between the duplicate (10) .…”