[afro-nets] Tuberculosis fight needs regional vaccines

[Claudio Schuftan <claudio@hcmc.netnam.vn>]

Tuberculosis fight 'needs regional vaccines'
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http://www.scidev.net/News/index.cfm?fuseaction=readNews&itemid=2658&language=1

The study suggests that multiple drugs and vaccines might be
needed to fight regional forms of TB

by Sophie Hebden

The bacterium that causes tuberculosis (TB) is so genetically
distinct in different parts of the world that tackling the dis-
ease could require separate vaccines for each region, say re-
searchers.

In a study published yesterday (13 February) in Proceedings of
the National Academy of Sciences, the researchers say the bacte-
rium has evolved into six distinct lineages.

Each of these was mostly found in a different human population
around the world, prompting the researchers to classify them as
the East-African-Indian, East-Asian, Euro-American, Indo-
Oceanic, and two West-African lineages.

"This study shows that TB is not just TB: people developing vac-
cines should work with different strains for different parts of
the world," says lead author Sebastien Gagneux of Stanford Uni-
versity Medical Centre, United States.

Tuberculosis kills about two million people a year. About two
billion people, one-third of the world's population, carry the
bacterium, but it is active only in about ten per cent of these
people.

The current TB vaccine varies in effectiveness depending on
where it is used. Scientists have suggested this is due to envi-
ronmental factors or using different bacterial strains to create
the vaccine, but Gagneux's study suggests that the TB bacte-
rium's genetic variability could be to blame.

The researchers analysed genes from 875 samples of the bacterium
that came from 80 countries. Their findings suggest that dis-
tinct bacterial strains have adapted over time to specific human
populations.

Joanne Flynn of the University of Pittsburgh School of Medicine,
United States says this is important as different strains might
use slightly different mechanisms to cause disease "and this may
be specific to the population it is most likely to encounter".

"A vaccine that is effective against one strain might not be ef-
fective against another strain," she told SciDev.Net.

Understanding the differences between strains could explain why
some are more dangerous than others, and identify possible vac-
cine or drug targets, she added.

Link to full paper in Proceedings of the National Academy of
Sciences http://www.pnas.org/cgi/content/abstract/0511240103v1

Reference:
Proceedings of the National Academy of Sciences 103, 2869 (2006)