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The microbiological confirmation of leprosy patients with tongue swabs exhibits a lower sensitivity compared to nasal swabs

L Krausser(1,2,3) A Said(4,5) N Attoumane(4,5) S H Grillone(4,5) M Van Dyck-Lippens(2) A Baco(4,5) W Abdou(4,5) A Mzembaba(4,5) E Hasker(2) Y Asoumani(4,5) B C de Jong(2) S M Braet(1,2,3)

1:University of Antwerp, Belgium; 2:Institute of Tropical Medicine, Antwerp, Belgium; 3:Research Foundation Flanders (FWO), Brussels, Belgium; 4:Damien Foundation, Brussels, Belgium; 5:National Tuberculosis and Leprosy Control Program, Moroni, Comoros

Skin biopsies remain the most reliable source for Mycobacterium leprae bacilli to microbiologically confirm leprosy patients. In an effort to find less invasive sampling techniques, we compared nasal swabs and tongue swabs obtained from clinically confirmed leprosy patients enrolled in the PEOPLE study in the Comoros.

Twenty-three patients were requested to provide a swab sample from the anterior two-thirds of the tongue dorsum, along with a nasal swab and a biopsy from the margin of a skin lesion. DNA extracted from these concurrent samples was quantified with the M.  leprae specific RLEP qPCR assay. In addition, all swab-derived DNA extracts were checked for human mitochondrial DNA to confirm adequate sampling. 

M. leprae DNA was detected on 8/23 (34,8 %) tongue swabs, 12/23 (52,2 %) nasal swabs and in 16/23 (69,6 %) skin biopsies. Although the Cq values from the various sampling sites correlated, the tongue swab extracts had an average delay of nine cycles compared to the corresponding nasal swabs, suggesting that the burden of M. leprae on the tongue is lower than in the nasal cavity. Only multibacillary patients tested positive for M. leprae on tongue swabs.

This is the first study to detect M. leprae on the tongue dorsum in a third of leprosy patients, although DNA yield is considerably lower than for nasal swabs and skin biopsies. We will continue to optimise the tongue swab sampling to increase the confirmation rate of clinically diagnosed leprosy patients. 

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