The tuberculosis epidemic in China stems from the expansion of four strains of bacteria a thousand years ago

The tuberculosis epidemic in China stems from the expansion of four strains of bacteria a thousand years ago https://i0.wp.com/www.eresviral.com/wp-content/uploads/2018/11/La-epidemia-de-tuberculosis-en-China-se-deriva-de-la-expansión-de-cuatro-cepas-de-bacterias-hace-mil-años.jpg?fit=260%2C132&ssl=1

The tuberculosis epidemic in China stems from the expansion of four strains of bacteria a thousand years ago





The tuberculosis epidemic in China stems from the expansion of four strains of bacteria a thousand years ago


99% of the TB strains currently circulating in China are actually descendants of four previous strains that were introduced into China about 1,000 years ago, probably through the Maritime Silk Road, and which have gone through several expansions since the twelfth century, according to a study by the University of Shanghai with the participation of researchers from the Institute of Biomedicine of Valencia (IBV), of the Higher Council for Scientific Research (CSIC) (Spain).



The study, which reconstructs the genomic history of the tuberculosis epidemic in China and is published in the journal Nature Ecology & Evolution, shows that the incidence of tuberculosis in China is due more to a historical legacy that originated hundreds of years ago. a resurgence associated with social factors such as population growth, mobility and increased urbanization.



Tuberculosis is an infectious disease caused by the bacterium Mycobacterium tuberculosis that has affected humans for at least 6,000 years. To date, tuberculosis ranks first among infectious diseases with an incidence of 10.4 million cases per year.



The researcher of the CSIC in the IBV Iñaki Comas, who has participated in the work, explains that "tuberculosis does not affect the population of the countries in a uniform way. For example, 30 countries that account for only 9% of the total support 87% of those affected by tuberculosis. This raises the question of how did the tuberculosis epidemic originate in those countries? China is the third country with the most cases of tuberculosis. There are historical records of cases of tuberculosis in places like Laobing or Shizhu, but there are no outbreaks of tuberculosis. So, when did TB spread to China and when did the mass epidemic begin? "







Mycobacterium tuberculosis. (Image: CSIC)



Researchers have genotyped and sequenced a total of 4,578 strains of tuberculosis collected in 76 sites in 31 provinces in China, and analyzed them by comparing them with 15,591 strains of tuberculosis from other parts of the world. Thus they have discovered that 99% of the strains of tuberculosis currently circulating in China are actually descendants of four previous strains that were introduced into China about 1,000 years ago, probably through the Maritime Silk Road, and that they have passed. by several expansions since the 12th century.



Subsequently, some of these genotypes were dispersed to other parts of the world. For example, one spread to the province of Xinjiang, in the northwest of China, probably through the Route of the Terrestrial Silk, and from there to Europe in the XIV and XVII centuries, from where it returned to expand. These expansions reached the epidemic peak in China in the late eighteenth century and have suffered an abrupt decline since the mid-twentieth century due to the use of antibiotics.



"When was the tuberculosis epidemic in China? The different genotypes of tuberculosis strains may differ in their ability to transmit or cause disease. The strains with higher transmissibility can outperform the others and sweep a larger proportion of the population. This study shows how a Chinese TB genotype called L2.3 was separated at the beginning of the 16th century from one of the original four and has undergone overwhelming expansions to reach 60% of the Chinese population, and is still very active today. " explains Comas.



"We have also observed at least a dozen other tuberculosis strain genotypes that have been introduced later in China, but have not achieved a successful population expansion, suggesting that indigenous genotypes could better adapt to the local human population than the new genotypes ", clarifies the researcher Comas.



This work shows that the incidence of tuberculosis in China is due more to a historical legacy that originated hundreds of years ago than to a resurgence associated with social factors such as population growth, mobility and increased urbanization. The four strains that were introduced into China hundreds of years ago expanded in parallel, presumably in response to the common ecological factors of epidemic tuberculosis. The results of this study could serve to improve the epidemiological surveillance of tuberculosis based on the dynamics of expansion of its different strains. (Source: CSIC / DICYT)

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