Witzend
midgey
I don’t think you are quite right there Growstuff, I became immune to TB because my mother did the shopping for people in the TB hospital when I grew up.
I was found to be immune to TB too - after the BCG test at school. A grandfather and an aunt who we’d been in contact with had contracted it.
Only about 10% of people who contract TB go on to become ill. There are research papers about it because it's a bit of a mystery. It's true that some people have had TB without knowing it, but it's also true that some people have some kind of genetic resistance.
This is the conclusion from one paper:
"The involvement of a human genetic component in susceptibility to infection with M. tuberculosis and progression to active disease is incontestable. Findings from clinical genetics, genetic epidemiology, population and functional genetics have all contributed to identify TB susceptibility genes. More intriguing is the other side of the phenotypic coin—that of resistance to either initial infection or, after infection, resistance to progression to disease. Although the phenomenon is now recognized, the exact genetic variants and mechanisms that contribute still require elucidation. The most successful approaches in resistance/susceptibility investigation have focused on specific infection and disease phenotypes and the resister phenotype may hold the key to the discovery of actionable genetic variants in TB infection and disease."
www.ncbi.nlm.nih.gov/pmc/articles/PMC6170664/
The cause of TB is a bacterium - it's different from a virus. People with otherwise robust immune systems can fight off the bacterium before it does serious damage. That's why TB is (or was) rife in poorer areas, where people tended to be malnourished. Continued exposure to TB won't create immunity any more than covering open wounds in germs every day will stop them becoming infected.