Leprosy transmission and mucosal immunity: towards eradication?

Area of Science:

• Infectious Diseases
• Microbiology
• Immunology

Background:

• Leprosy prevalence is declining, but incidence remains high, indicating ongoing Mycobacterium leprae transmission.
• Multidrug therapy (MDT) has not halted transmission, despite its widespread use in control programs.
• Most individuals in endemic areas show immunological evidence of M. leprae exposure, yet few develop clinical disease.

Purpose of the Study:

• To investigate the paradox of declining leprosy prevalence versus persistent incidence.
• To explore the role of sub-clinical Mycobacterium leprae infections in disease transmission.
• To evaluate the potential for targeting transmission clusters for leprosy control.

Main Methods:

• Review of epidemiological data on leprosy prevalence and incidence.
• Analysis of immunological evidence of M. leprae exposure in endemic populations.
• Examination of evidence from nasal PCR studies on sub-clinical M. leprae transmission.
• Assessment of factors influencing transmission, such as close contact and duration.

Main Results:

• Sub-clinical M. leprae infections are proposed as a mechanism for persistent transmission.
• These transient, non-disease-developing infections may facilitate spread within communities.
• Evidence suggests sub-clinical infections occur in clusters and require prolonged close contact for transmission.
• Mucosal immune responses may develop during the resolution of initial, sub-clinical infections.

Conclusions:

• Sub-clinical M. leprae infections likely contribute significantly to leprosy transmission.
• Targeting individuals within identified infection clusters may be an effective control strategy.
• This approach could facilitate progress towards the ultimate eradication of leprosy.