High frequency of M. leprae DNA detection in asymptomatic household contacts

Abstract

Background: Characterization of the Mycobacterium leprae genome has made possible the development of Polymerase Chain Reaction (PCR) systems that can amplify different genomic regions. Increased reliability and technical efficiency of quantitative PCR (qPCR) makes it a promising tool for early diagnosis of leprosy. Index cases that are multibacillary spread the bacillus silently, even before they are clinically diagnosed. Early detection and treatment could prevent transmission in endemic areas.

Methods: In this study, the qPCR technique is used to detect DNA of M. leprae in samples of slit skin smears (SSS) of the ear lobe and blood of leprosy patients and their asymptomatic household contacts residing in Governador Valadares, MG, Brazil, a hyperendemic area for leprosy. A total of 164 subjects participated in the study: 43 index cases, 113 household contacts, and, as negative controls, 8 individuals who reported no contact with patients nor history of leprosy in the family. The qPCR was performed to amplify 16S rRNA fragments and was specifically designed for M. leprae.

Results: Of asymptomatic household contacts, 23.89% showed bacillary DNA by qPCR in samples of SSS and blood. Also, 48.84% of patients diagnosed with leprosy were positive for qPCR while the bacillary load was positive in only 30.23% of patients. It is important to note that most patients were already receiving treatment when the collection of biological material for qPCR was performed. The level of bacillary DNA from household contacts was similar to the DNA levels detected in the group of paucibacillary patients.

Conclusion: Considering that household contacts comprise a recognizable group of individuals with a high risk of disease, as they live in close proximity to a source of infection, qPCR can be used to estimate the risk of progress towards leprosy among household contacts and as a routine screening method for a chemoprophylactic protocol.

Keywords: Household contacts; Leprosy; qPCR.

Fig. 1

Spearman correlation between genome numbers and bacillary load for MB patients with positive bacilloscopy. (N = 12*; p = 0.3894; r = 0.3571) * Only individuals with bacillary DNA in SSS and positive bacilloscopy were selected

Fig. 2

Comparison of M. leprae genome numbers between the groups of index cases. NC = Negative control (n = 8); PB = Paucibacillary (n = 5); MB = Multibacillary (n = 16). Each point represents the individual value of a genome number. The median is represented by the horizontal line. Mann-Whitney test was applied

Fig. 3

Comparison of M. leprae genome number among household contacts groups. NC = Negative control (n = 8); HHC-PB = Contact of paucibacillary (n = 10); HHC-MB = Contact of multibacillary (n = 17). Each point represents the individual value of a genome number. The median is represented by the horizontal line. Mann-Whitney test

Fig. 4

Comparison of the M. leprae genome number of all household contacts and index cases PB and MB. Household contacts (HHC) (n = 27); PB = paucibacillary (n = 5); and MB = multibacillary (n = 16). Each point represents the individual value of 1/Ct. The median is represented by the horizontal line. Kruskal-Wallis statistic and Dunn’s Multiple Comparison Test were applied