Tuberculosis is not solely caused by the bacterium but a combination of the bacterium and the environment!
Study by Edward Trudeau in late 1800’s:
a. Five M. tuberculosis infected rabbits kept in a crowded, dark cage → 4 dead, 1 severely ill
b. Five M. tuberculosis infected rabbits kept on a small, outdoor island → 4 alive and well, 1 dead
Conclusion: TB not caused by bacterium alone; bacterium + environmental conditions induce illness. The poor rabbits in the cage were all breathing in each other’s TB infested coughs. They were sick and cramped. Conversely, the rabbits on the island were free to roam as they pleased. They may have had the bacterium, but the disease had yet to manifest.
So…
It started out with a cough
How did it end up like this
It was only a cough
It was only a cough
http://www.angelfire.com/sd/pma/Tb.html
When a TB infected person coughs, they release tiny TB infected droplets in the air which are inhaled by someone else.
These droplets travel down the trachea and enter the alveolar sacs of the lungs.
In the lungs, macrophages surround the bacterium and form a granuloma to keep the TB contained.
As long as the granuloma stays intact, the person will not experience any symptoms of the disease. At this point, the disease is latent.
BUT, if the granuloma breaks, it releases the TB infected macrophages. This is when the person starts experiencing symptoms and can infect others.
https://www.sciencedirect.com/science/article/pii/S1931312808001546
Here’s a cool video by the CDC to help you better visualize this process:
https://www.youtube.com/watch?v=9112brXCOVc