The "Hansen-anergic fringe"

The Hansen-Anergic Fringe ("HAF") of the population is the minority genetically incapable of developing that variety of specific immunity to Myco. hansenii which leads to the positivity of the Mitsuda reaction. In spite of the fact that the HAF was identified as early as 1937, its real proportion in the human species is still not exactly known. Considering that Myco. tuberculosis has been proved to induce Mitsuda-positivity in the genetically capable majority, studies with the tuberculin reactions and cross-stimulation with BCG should be instrumental for the determination of the width of the HAF in various races and different endemic and non-endemic areas. In Brazil it stands around 20-25%, but more accurate studies are necessary. Between the HAF and the Mitsuda-positive or potentially positive majority there is a zone of "intermediate reactivity" which also needs quantification. The specific HAF reacts normergically to all other tests so far investigated and has not yet been associated with any other kind of immuno-deficiency. Also, it has not been associated with any of the known genetical markers, although HLA studies seem promising. If its postulated genetical nature is confirmed, the possibility of effective vaccination will be doubtful.