Massachusetts [US], August 1 (HBTV): According to a recent study evaluating how various strains migrate across mixed populations in cosmopolitan cities, the chances of an exposed person becoming infected with TB vary depending on whether the human and the bacterium share a hometown. 

The study, led by Harvard Medical School scientists provides evidence that pathogen, place, and human host interact in a unique way that affects infection risk and susceptibility.

The study strengthens the case for a long-standing hypothesis in the field that specific bacteria and their human hosts likely coevolved over hundreds or thousands of years, the researchers said. 

The findings may also help inform new prevention and treatment approaches for tuberculosis, a wily pathogen that, each year, sickens more than 10 million people and causes more than a million deaths worldwide, according to the World Health Organization. 

In the current analysis, believed to be the first controlled comparison of TB strains' infectivity in populations of mixed geographic origins, the researchers custom-built a study cohort by combining case files from patients with TB in New York City, Amsterdam, and Hamburg. Doing so gave them enough data to power their models. 

The analysis showed that close household contacts of people diagnosed with a strain of TB from a geographically restricted lineage had a 14 per cent lower rate of infection and a 45 per cent lower rate of developing active TB disease compared with those exposed to a strain belonging to a widespread lineage. 

The study also showed that strains with narrow geographic ranges are much more likely to infect people with roots in the bacteria's native geographic region than people from outside the region. 

The researchers found that the odds of infection dropped by 38 per cent when a contact is exposed to a restricted pathogen from a geographic region that doesn't match the person's background, compared with when a person is exposed to a geographically restricted microbe from a region that does match their home country. This was true for people who had lived in the region themselves and for people whose two parents could each trace their heritage to the region. 

This pathogen-host affinity points to a shared evolution between humans and microbes with certain biological features rendering both more compatible and fueling the risk for infection, the researchers said. 

"The size of the effect is surprisingly large," said Maha Farhat, Gilbert S. Omenn, MD '65, PhD Associate Professor of Biomedical Informatics in the Blavatnik Institute at HMS. "That's a good indicator that the impact on public health is substantial." 

Thanks to the growing use of genetic sequencing, researchers have observed not all circulating strains are created equal. Some lineages are widespread and responsible for much of the TB around the world, while others are prevalent only in a few restricted areas. Given the complex nature of TB transmission in high-incidence settings where people often have multiple exposures to different lineages, researchers have not been able to compare strains under similar conditions and have been left to speculate about possible explanations for the differences between strains. 

(ANI)