Transmission of leprosy
Viability of M.leprae outside the human host
The possiblity of discharge of M.leprae from the nasal mucosa raises the question of survival of the discharged organisms outside the human host. Davey & Rees (1974) have reported that M.leprae from the nasal secretions can survive up to 36 hours or more. Desikan (1977) has reported on the survival of M.leprae in nasal secretions under tropical conditions for up to nine days. Such survival of the organisms suggests the possibility of contaminated clothing and other fomites acting as sources of infection.
Portal of entry of M.leprae
The portal of entry of M.leprae into the human body is not definitely known. However, the two portals of entry seriously considered are the skin and the upper respiratory tract. With regard to the respiratory route of entry of M.leprae, the evidence in its favour is on the increase in spite of the long-held belief that the skin was the exclusive portal of entry. Rees & McDougall (1977) have succeeded in the experimental transmission of leprosy through aerosols containing M.leprae in immune-suppressed mice, suggesting a similar possibility in humans. Successful results have also been reported on experiments with nude mice when M.leprae were introduced into the nasal cavity through topical application (Chehl et al, 1985). In summary, although no firm conclusions can be reached with regard to the portal of entry, entry through the respiratory route appears most probable, although other routes, particularly broken skin, cannot be ruled out.