A recent study conducted by researchers from Harvard Medical School analysed the migration patterns of various Tuberculosis (TB) strains across diverse populations in cosmopolitan cities.
The findings indicated that the likelihood of an exposed individual contracting TB varies based on whether the person and the bacterium share the same geographic origin.
This research provided compelling evidence that the interaction between the pathogen, location, and human host uniquely influences infection risk and susceptibility.
Understanding the Transmission of Tuberculosis
Tuberculosis (TB) is an infectious disease primarily caused by the bacterium Mycobacterium tuberculosis. It most commonly affects the lungs but can also impact other parts of the body.
Modes of Transmission
- Airborne Transmission: TB is mainly spread through the air when an infected person coughs, sneezes or speaks. Tiny droplets containing the bacteria are released into the air and can be inhaled by others nearby.
- Close Contact: People who spend a lot of time in close proximity to someone with active TB, especially in poorly ventilated spaces, are at a higher risk of infection.
- Environmental Factors: Crowded living conditions, inadequate ventilation, and poor sanitation can increase the risk of TB transmission. This is often a concern in urban settings and areas with high population density.
Factors Influencing Transmission
– Infectiousness of the Source: Individuals with active pulmonary TB are the most contagious, particularly those with a high bacterial load in their sputum.
– Duration and Frequency of Exposure: Prolonged and repeated exposure to an infectious person increases the risk of contracting TB.
– Host Susceptibility: People with weakened immune systems, such as those with HIV, malnutrition, or other medical conditions, are more susceptible to TB infection.
Pathogen-Host Affinity in Tuberculosis Transmission
Researchers from Harvard Medical School conducted an in-depth study by creating a custom cohort using case files from TB patients. The analysis revealed significant insights into how TB transmission is influenced by the geographic lineage of the bacteria and the background of the infected individuals.
1. Household Transmission Rates: Close household contacts of individuals diagnosed with TB strains from geographically restricted lineages had a 14% lower infection rate and a 45% lower rate of developing active TB compared to those exposed to widespread lineages.
2. Geographic Affinity: Strains of TB with narrow geographic ranges were significantly more likely to infect individuals whose roots matched the bacteria’s native region. The odds of infection decreased by 38% when a person was exposed to a geographically restricted TB strain from a region different from their own background, compared to exposure to a strain from their home region.
3. Pathogen-Host Compatibility: The study highlighted a unique pathogen-host affinity, suggesting a shared evolution between humans and microbes. Certain biological features in both hosts and pathogens seem to render them more compatible, increasing the risk of infection.
Key Insights
This new study revealed that for geographically restricted strains of Tuberculosis (TB), a person’s ancestral background is a more significant predictor of infection risk than the bacterial load in their sputum. Specifically, individuals with ancestors from regions where the TB strain is prevalent face a higher infection risk.
1. Ancestral Influence: The study demonstrated that the risk associated with common ancestry surpassed the risk posed by diabetes and other chronic diseases, which are traditionally known to increase susceptibility to TB.
2. Lineage-Specific Interactions: The findings emphasized the critical importance of recognizing the considerable variation between different TB lineages and understanding how these lineages interact with diverse host populations.
“The size of the effect is surprisingly large. That’s a good indicator that the impact on public health is substantial. These findings emphasize how important it is to understand what makes different strains of TB behave so differently from one another, and why some strains have such a close affinity for specific, related groups of people,” stated the study authors.
