South-East Asia Regional Conference on Epidemiology

<strong>South</strong>-<strong>East</strong> <strong>Asia</strong> <strong>Regional</strong> <strong>Conference</strong> on Epidemiology | 349
to endemic leprosy, many develop subclinical and some develop more serious forms of the disease.
The moment BCG vaccination is given, there is a shift in immunity to a more Th-1 type of response.
What happens then is a more subclinical and more indeterminate type of leprosy among the vaccinated
and that does not matter. The impact is in terms of a reduced incidence of serious forms of leprosy
and consequent disabilities.
In an ecological study, it was realized that if the BCG vaccination rate is maintained for a long time,
the leprosy incidence seems to fall. In 40 clusters of villages, the BCG scar rate was measured among
the 20-year-olds (which was an indicator of BCG coverage 20 years ago) and current prevalence of
leprosy. There was a significant negative correlation (Fig.2).
Leprosy
prevalence
Fig. 2: Ecological evidence
0 10 20 30 40 50 60 70 80
% BCG scar+among 20-year-olds
By 2000, leprosy was supposed to have been eliminated from India. The elimination of leprosy
means prevalence of one case per 10 000 population. India has over one billion people, and if there
are less than 100 000 cases on the leprosy register, the disease would then be considered to have been
eliminated. The aim was to eliminate leprosy by 31st December 2000. Did it happen? No, India did
not achieve the target. Myanmar, Bangladesh and many other countries were able to eliminate leprosy.
Then the target date for leprosy elimination was reset for 2005. What happened between 2000 and
2005? In the top 16 leprosy-prevalent countries in the world, there has hardly been any fall in the
new case detection rate since 1993. In fact, some countries like Indonesia showed an increase. It is
fascinating to note that during 2000-2005, new case detection has crashed in India (Fig. 3). This is a
miracle. Should not there be research to find out how India succeeded in bringing down the incidence
of new cases of leprosy so rapidly which no other country could achieve? One needs to explain why
leprosy incidence declined in India.