杏吧原创

THE leprosy bacterium has fewer genes in its genome than that of any other
pathogen sequenced so far. The sequence, announced this week, should lead to
better diagnosis and treatment of one of humanity鈥檚 most dreaded diseases.

Leprosy infects some 700,000 people a year, mainly in Asia and South America.
It is caused by Mycobacterium leprae, which lives inside white blood
cells and nerve cells. The resulting nerve damage and loss of feeling means that
people can wound themselves without noticing it. Antibiotics can cure the
disease, although any damage to hands or feet is permanent.

A team led by Stewart Cole of the Pasteur Institute in Paris has now
sequenced M. leprae鈥檚 genome. They found it has only half as many
working genes as its close relative M. tuberculosis, which causes
TB.

鈥淚t is amazing it can still cause such a horrendous disease after losing half
its genome,鈥� says Cole. The greatest loss previously known in a pathogen is in
the Rickettsia bacterium that causes typhus, which has only 76 per cent
as many genes as its relatives. The lost genes mean M. leprae can
consume only a few compounds, mostly fats, and must absorb many nutrients that
it cannot make for itself. This may explain why all efforts to culture it
outside a live host have failed, says Cole.

The researchers have not yet found which M. leprae genes cause
disease. 鈥淚n such a small haystack, the needle should be more obvious,鈥� says
Cole. But there will be practical benefits even without knowing this. The gene
sequence will reveal antigens that are unique to M. leprae, Cole says,
and this will lead to a diagnostic test. The sooner leprosy is recognised the
less chance it has to spread, but early diagnosis of the disease can be
difficult using today鈥檚 techniques.

Pharmaceuticals companies are unlikely to develop a vaccine for an uncommon
disease that can be treated with drugs, says Cole. But diagnostic kits could be
sponsored by charities.