A new study analyzed how different types of Tuberculosis By migrating among mixed populations in metropolitan cities, an infected person’s chances of getting infected increases. TB This depends on whether humans and bacteria live in the same city. The study was led by researchers at Harvard Medical School. The study provides evidence that bacteria, location, and human hosts interact in unique ways that affect the risk and susceptibility to infection.

The findings of this study could also help in the development of prevention and new treatment methods for TB, which affects more than 10 million people worldwide and causes over one million deaths, according to the World Health Organisation (WHO).

For the study, the researchers created a study group by combining case files of TB patients in New York City, Amsterdam and Hamburg. This gave them enough data to strengthen their model.

The analysis found that close family contacts of people infected with a type of TB from a geographically restricted lineage had a 14 percent lower rate of infection and a 45 percent lower rate of developing active TB disease compared with close family contacts of people infected with a type of TB from a widespread lineage.

The study also found that bacteria with a narrow geographic range were more likely to infect people living in their original geographic area than those outside the region.

The researchers found that when a person was exposed to a restricted germ from a geographic region that did not match the person’s background, his or her risk of becoming infected was reduced by 38 percent, whereas when a person was exposed to a geographically restricted germ from a region that matched his or her home country, the risk of infection was reduced by 50 percent.

This microbe-host affinity points to a shared evolution between humans and microorganisms, with certain biological features that make both more adaptable and increase the risk of infection, the researchers said.

“The effect size is surprisingly large. It’s a good indicator that the impact on public health is quite large,” said Maha Farhat, the Gilbert S. Oomen, MD ’65, PhD Associate Professor of Biomedical Informatics in the Blavatnik Institute at HMS.

The new study highlights that for geographically restricted strains, whether a person’s ancestors lived in a place where the strain is common was even more predictive of infection risk than the bacterial load in sputum. In the cases analysed in the study, this risk of common ancestry was even greater than the risk from diabetes and other chronic diseases that previously made people more vulnerable to infection.

These findings are among the growing evidence of the importance of paying attention to the wide variation among different tuberculosis species, and to how different tuberculosis species interact with different host populations.

“These findings emphasize how important it is to understand why different TB strains behave so differently from one another, and why certain types have such close associations with specific, related groups of people,” said Matthias Gröschel, research fellow in biomedical informatics in Farhat’s lab at HMS, a resident physician at Charité, a university hospital in Berlin, and first author of the study.

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