Here are some key points from a couple of reviews.   Because these reviews are a bit dated I checked the points below against the articles in Up to Date and Dynamed Plus.
What is the classification?
Discrete categorization is difficult. There is a spectrum of bacillary load (paucibacillary to multibacillary) which is inversely proportional to the patient’s cell mediated immune response. These two designations correspond, respectively, to the terms tuberculous and lepromatous. Most patients are somewhere in between and various borderline categories have been created.
What are leprosy reactions?
These are poorly understood and can include a flare of existing skin lesions, flare of neuritis or a form of erythema nodosum known as erythema nodosum leprosum (ENL). These are inflammatory responses.
What is the treatment?
Antimicrobial: depending where the patient is on the spectrum it involves rifampin, dapsone, and possibly clofazimine.
Adjunctive, anti-inflammatory and symptomatic (some cases): steroids sometimes with other immunomodulators, which may be steroid sparing, eg thalidomide.
What about transmission?
This is poorly understood. It is not highly contagious. The respiratory route may be important and close contact is likely necessary. Nine banded Armadillo exposure is a risk factor in the Southern US.
What are some factors in the host response?
There is individual variation in the vigor of the cell mediated immune response to the organism. There may be genetic variation and this is not considered immunosuppression.