Leprosy

Well, I'm no expert but I would have to say that it has something to do with the brain's blood-brain barrier. Thanks to this most diseases with big enough carriers can't pass through and thus the brain is very well protected. What d you mean about the most probable port of bacilli? Its mode of transmission? Well that actually depends if you have normal or abnormal T-lymphocyte response to the organism. If you have a normal response then chances are you have a tuberculoid leprosy and its transmitted by respiratory droplets. On the other hand an abnormal response will give you a lepromatous leprosy which is transmitted via contact of the skin lesion and the blood of the recipient (e.g. cuts on the skin).