It is also stirring community participation. It promotes a culture of partnership between all these parties concerned, that is national governments, international organizations, non-governmental organizations, as well as the constituency of the persons affected by the disease, referred today as the stake-holders. In addition, for a large part due to the success of MDT, the stigmatization of the persons affected with leprosy has considerably diminished. These encouraging signs would have been unthinkable of even twenty years ago.
In many countries, however, as reported at the Congress, in spite of the dramatic fall in prevalence, the number of newly detected cases reported each year does not show a marked decline. A number of operational reasons could be invoked to explain this apparent epidemiological paradox. All the same, it suggests that transmission might possibly be maintained at a level higher than expected. Would it be that the untreated or relapsing clinical patients do not constitute the sole source of transmission of the disease? To what extent could people with subclinical infection serve as a source of transmission? Would an extra-human reservoir of M. leprae exist, and in that case what, where, and how does it operate?
These are questions that have resisted elucidation for ages. They nevertheless have important implications. Will transmission be maintained in some countries at a low level with no hope for further progress, at least for a while? Should we learn to live with leprosy as a rare disease, and concentrate on the prevention of disability in order to render it, as a way of speaking, "but a minimal skin inconvenience"? Should we be worried that, if large-scale MDT is stopped, incidence will resume? If so, what other strategy should already be envisaged and worked out to counteract this possible backlash?
It is too early to say. The next five years will provide a crucial test to vindicate the basic assumptions regarding transmission. Nevertheless, it is not too early to prepare for unpleasant surprises, however unlikely they may seem.
New investigative tools are being developed which may help to solve these issues. By comparing the gene sequences of M. leprae and M.tuberculosis, synthetic peptide skin tests can be designed that would identify individuals infected with, or exposed to M. leprae. Actual protein and products of genes have also been obtained from armadillos and tested for their immunogenicity. The prevalence of PGL-1 antibodies has been correlated with the prevalence of clinical cases in endemic areas. Regarding the possible existence of an extra-human reservoir, using the polymerase chain reaction (PCR) , DNA of M. leprae has been found in the water supply of rural communities that have a high prevalence of leprosy.
PCR is opening the door to the study of the epidemiology of leprosy infection. Hypotheses regarding an animal and/or environmental reservoir are becoming testable. In a large international cooperative research project conducted in a number of endemic countries, PCR is used to study the prevalence of subclinical infection, the risks associated with exposure to positive PCR individuals, the infection rates, the cell mediated immunity in the nasal mucosa, and the role of the nose as primary site and portal of entry for the bacillus.
