How environmental mycobacteria may predetermine the protective efficacy of BCG.

A proposal is made that there are 2 mechanisms of cell mediated response to mycobacteria, both of which produce positive tuberculin tests and that one of them is more protective against mycobacterial infection than is the other. These are referred to respectively as the Listeria-type and the Koch-type of responses. Contact with environmental mycobacteria will induce one or other of these types of response and BCG vaccination will enhance it. Thus in those places where the environmental species prime for the Listeria-type of response subsequent BCG vaccination will afford good protection from both tuberculosis and leprosy. Where the Koch-type of response frequently results from environmental contact BCG will be ineffective. Evidence if presented that a large contact with Mycobacterium scrofulaceum is prejudicial to at least one marker of BCG efficacy in Burma.