Testes sorológicos específicos para MYCOBACTERIUM LEPRAE: implicações para a vigilância epidemiológica de casos de hanseníase e contatos domiciliares.

Abstract

The development of effective applications such as rapid tests for early detection of Mycobacterium leprae infection, prediction of leprosy progress and identification of the disease in the early stages has been considered a research priority and may contribute to prior diagnosis and timely treatment. The objective of the study was to analyze a response to specific serological tests for Mycobacterium leprae - Natural Disodium-Binding Linked to Human Serum Albumin by means of an Octyl (NDOHSA), Leprosy Diagnostic-1 Disease Research Institute (LID-1) and Natural Disaccharide Octyl - Research Institute for Infectious Diseases of Leprosy Diagnosis-1 (NDOLID) - in a longitudinal follow-up leprosy cases and household contacts and their implications for epidemiological surveillance. The studied population consisted of leprosy diagnosed between 2010 and 2015 and household contacts. The Enzyme-Linked Immunosorbent Assay (ELISA) was used to analyse the reactivity of antibodies against NDOHSA, LID-1 and NDOLID. Samples and controls are tested in duplicate and antibody titer is expressed as an ELISA index. The data collection was performed by home visits in two moments (2014 and 2015) with application of questionnaire, collection of biological samples and evaluation of all household contacts. The cases under treatment presented higher indexes ELISA and proportions of seropositivity for the three antigens. There was also a greater reduction in ELISA index values as the time elapsed from the start of treatment increased. The seropositivity to the three antigens was also higher in the group of multibacillary cases than in the paucibacillary cases. The clinical characteristics that showed a significant association with the anti-NDOHSA and LID-1 deltas were operational classification, clinical form of Madrid and bacilloscopy. For the NDOLID delta, no significant associations were observed with those clinical characteristics evaluated. The seropositivity in the group of household contacts was lower than in group of leprosy cases. The anti NDOHSA and NDOLID seropositivity were higher between contacts of paucibacillary cases and the anti LID-1 seropositivity showed similar values between contacts of paucibacillary and multibacillary cases. Regarding factors that may influence seropositivity it was observed a significant association between age and schooling and anti LID-1 seropositivity and between sex and anti-NDOHSA and NDOLID seropositivity. Of the clinical characteristics of the index case evaluated, only clinical form of Madri and number of cutaneous lesions were significantly associated with an anti NDOLID seropositivity of the household contacts. The percentage of anti NDOLID reactivity did not reflect the anti NDOHSA and LID-1 reactivity alone as expected. However, a positive correlation was observed between the three serological tests. The characteristics of indoor exposure and the clinical characteristics of leprosy index cases had less influence on the seropositivity of household contacts than expected. These results suggest the influence of exposure to undiagnosed cases outside the home environment, mainly in endemic regions, and emphasize the importance of surveillance of social contacts. The evaluation of more than one antigen and its results in a combined manner may enhance the determination of the operational classification and the treatment follow-up of leprosy case and the monitoring of household contacts. However, it can be configured as a limitation for the implementation of the tests as a tool for epidemiological surveillance in routine health services. It is suggested that studies be developed in geographically distinct populations and in sites with different epidemiological characteristics to increase the understanding of the influence of these factors on the behavior of serological tests.