How might Mycobacterium leprae enter the body?

Abstract

While it is known that LL patients disseminate large numbers of viable M. leprae from the nose and mouth, and possibly also in faeces, the route, or routes of entry of the organism into the human body remain unclear. The inability to infect nude mice either through intact or abraded skin fails to support the traditional view of skin-to-skin transmission, whilst the experiments suggest that the nasal mucosa is, on balance, most likely to be the predominant entry site. However, the evidence is still inconclusive. It must be remembered that investigators working with nude mice are using a highly artificial model of human leprosy even highly bacilliferous nude mice cannot transmit M. leprae infection to uninfected nude mice kept in the same cage. However, this discovery may indirectly support the hypothesis of entry through damaged or diseased nasal mucosa since infective rhinitis is unlikely in pathogen-free mice and injury improbable because of the extremely small nasal apperture. Indeed, it may be that rhinitis not only contributes to the dissemination of M. leprae into the environment but also facilitates entry of the bacillus into the body. Leprosy bacilli could be introduced into the nose in an aerosol or in nose-blow material carried by hand-to-hand and hand-to-nose contact. It is generally accepted that, whatever the portal of entry into the body, it is necessary in human leprosy for there to be a predisposing immunological defect.