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2 strains of bacteria cause nearly all TB cases in China
Just two strains of Mycobacterium tuberculosis account for almost all cases of tuberculosis in China, according to study findings published in Nature Ecology & Evolution.
“Mycobacterium tuberculosis complex (MTBC), which causes tuberculosis (TB), has circulated among human populations for thousands of years,” Caitlin S. Pepperell, MD, associate professor of medical microbiology at University of Wisconsin-Madison, and colleagues wrote.
According to the researchers, there are more than 10 million cases of TB globally each year — caused by seven major lineages — resulting in 1.7 million deaths. With about 1 million cases a year, China has the third-highest TB burden in the world, they noted. Literature indicates the disease may have been circulating in the country as far back as 5,700 years ago, and DNA testing shows it has been there for at least 2,000 years.
“In this study, we aimed to investigate historical migration events and bacterial population history underlying the current TB epidemic in China,” Pepperell and colleagues wrote.
To do this, they collected samples from patients with TB in 32 provinces across China and genetically scanned them to determine strain diversity. They detected little genetic diversity, reporting that one strain estimated to have arisen in Southeast Asia accounted for 80.8% of China’s current cases and another strain thought to have been introduced hundreds of years ago by ships engaged in the silk trade accounted for another 17%.
In fact, according to Pepperell and colleagues, 99.4% of the M. tuberculosis bacteria analyzed belonged to just four strains from two lineages, indicating that the TB epidemic in China was shaped by the historical expansion of these four strains.
Pepperell said she was “surprised” by the lack of diversity uncovered in the study, which she explained is likely the result of historical dynastic policies that kept China secluded, according to a news release.
“The hypothesis my colleagues and I use to explain the surprising lack of diversity is that at the time when the current TB epidemic was taking hold in China, there was less contact with other regions compared to contemporaneous societies elsewhere, but there was a lot of movement within China,” Pepperell said in the release. – by Marley Ghizzone
Disclosures: The authors report no relevant financial disclosures.