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.
Every 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 stress.
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 disease.
"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 mycobacteria."
So far, Kirsebom says the spores have not been detected in mycobacterium tuberculosis, which causes most cases of human TB.
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.
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