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Aerosol transmission, asymptomatic carriage aid persistence of M. leprae
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Aerosol transmission between close asymptomatic contacts appears to be a key route of transmission for Mycobacterium leprae, and it likely contributes to its persistence within many affected countries, according to recently published data.
“Leprosy is one of the oldest infectious diseases to affect mankind and nowadays continues to be a public health problem, particularly in Brazil,” Isabela Maria Bernardes Goulart, MD, PhD, researcher at the National Reference Center for Sanitary Dermatology and Leprosy at the Federal University of Uberlandia, Brazil, and colleagues wrote.
“Untreated leprosy patients (ULPs) are generally considered the main source of transmission. However, this contrasts with more than 30 years of an effective and globally available treatment and the occurrence of new cases among people with no previous contact with ULPs, indicating that there must be other undisclosed sources of infection.”
Goulart and colleagues examined nose vestibule, nose turbinate mucosa and peripheral blood samples collected from 133 ULPs and 104 household contacts (HHCs) from 2003 to 2015. They tested these samples for M. leprae DNA using qualitative PCR and identified any relevant antibodies in sera using an enzyme-linked immunosorbent assay (ELISA). Along with measuring the presence of M. leprae among these sample sites, the researchers used follow-up data to conduct correspondence analyses to identify the risk for leprosy for HHCs.
Among ULPs, the researchers detected M. leprae DNA in 66.4% of nasal swabs, 71.7% of nasal turbinate biopsies and 19.5% of blood samples, as well as antibodies among 62.8% of serum samples. Detection was generally lower among HHCs, with Goulart and colleagues reporting DNA in 49% of nasal swabs, 53.8% of nasal biopsies and 6.7% of blood samples; 18.3% had serum antibodies. ULPs were more often multibacillary than paucibacillary, with analyses of sample sites revealing congruent associations between every pair of dichotomous variables (P ≤ .003). Analysis of the HHCs found associations between nasal swab and turbinate biopsy positivity (OR = 2.3; 95% CI, 1-5.1), as well as between nasal turbinate and serology (OR = 4.2; 95% CI, 1.2-14.8).
Follow-up of 104 HHCs revealed seven new cases of leprosy within 5 to 7 years, according to the researchers, with the chance of developing leprosy being greater among those with positive blood samples and ELISA tests.
These data indicate the potential for nasal M. leprae exposure to infect nasal mucosa, elicit immune responses and disseminate through the blood stream, the researchers explained. Further, the prevalence of M. leprae in the nasal swab samples of HHCs provides “indirect evidence of the role of asymptomatic carriers as a neglected mode of dispersal,” they wrote. – by Dave Muoio
Disclosure: The researchers report no relevant financial disclosures.
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