Swedish researchers say they may have figured out how
tuberculosis hibernates in humans, becoming active only long after the original
infection. The latent form of TB is carried by an estimated one-third of the
world's population, and most people never get sick. It appears TB may form
inactive spores which suddenly spring to life in some individuals.
year, 10 million new cases of tuberculosis are diagnosed around the world and 2
to 3 million people die of the lung disease. Many of them have been infected
with a latent form of the tuberculosis bacteria that can become active and cause
the illness. But many others are infected without ever getting sick. Scientists
have been trying to figure out why.
In new research, scientists at
Sweden's Uppsala University found evidence that a relative of the tuberculosis
bacteria (called mycobacterium marinum) that causes tuberculosis in fish forms
hibernating spores when scientists cultured the microorganism in the laboratory.
Another similar bacterium, which causes tuberculosis in cows but can also infect
humans, also forms spores.
Lead investigator Leif Kirsebom says
scientists don't understand the molecular mechanism that causes the TB
mycobacterium to remain silent in human cells - for decades, in some cases - and
then spring to life. But the scientists' work suggests the microorganism goes
into hiding by forming spores when it is under environmental
Kirsebom says discovery of the spores may open a new chapter in
the study of mycobacteria, including an aggressive microbe (mycobacterium
ulcerans} that causes disfiguring skin lesions called Buruli ulcer
"It might, it might, I say might, shed light on perhaps spread
of disease - for example mycobacterium Buruli ulcerans which causes Buruli ulcer
in Africa - and the transmission of those bacteria," said Leif Kirsebom. "Also,
it [may] open new avenues of latent infection caused by
So far, Kirsebom says the spores have not been detected
in mycobacterium tuberculosis, which causes most cases of human
Kirsebom says if it turns out the microorganism does not form spores
that would also give scientists valuable information about the behavior of
latent TB in humans.
Kirsebom says discovery of the spores in marine and
cow versions of the bacteria could eventually pave the way for treatments to
stop latent tuberculosis from becoming active in humans.
"It opens.. a
new biology to study and understand [mycobacteria]," he said. "And if you
understand there might be new targets, there might be new ways, for example,
[to] understand how the mycobacteria grows."
Experts say breakthroughs in
the field of tuberculosis research are needed now more than ever to battle
increasingly common drug-resistant strains of TB which threaten the lives of
millions of people the world over.
The study by Uppsala researchers is
published this week in the Proceedings of the National Academy of Sciences.