It seems unlikely that ALL of the world's supercentenarians somehow managed to avoid all of the common "germs" that are passed from person to person over the course of a lifetime, and thus that is why they have lived so long.
Common infectious pathogens which persist long-term in the body do not always cause the diseases they are associated with in every individual who harbors those pathogens. A given pathogen may only cause its associated disease(s) in, for example, 0.2% of the population who carry that pathogen. We now know that Epstein-Barr virus (EBV) causes more than one type of cancer (such as nasopharyngeal carcinoma); but most people do not get those cancers, in spite of the fact that EBV is found in 90% of adults.
(EBV hides in a latent state in the B-cells in the blood; that's the main reason it is not eliminated by the immune system; new antivirals that tackle this latent B-cell infection may in future allow us to fully eliminate this virus from the body).
So unlike HIV, which will cause AIDS in nearly 100% of the people it infects (if antiviral are not used), in the case of many infectious pathogens in common circulation, they only cause the diseases they are associated with in a small percentage of the population.
Indeed, this is what makes it harder to ascribe causality. Prof Paul Ewald points out that historically, science was quick to identity the infectious micro-organisms which when caught led to disease quickly and consistently every time — because in these cases, the cause-effect relationship is easy to observe. But when it takes 2 decades before a pathogen triggers the disease, and when it only triggers the disease in 0.2% of the population, that makes causality a lot harder to ascribe. This is the issue facing scientists who research into these pathogen-disease connections.
So in the case of supercentenarians, their longevity might be partly because they managed to avoid some of the nastier pathogens in circulation; party a bit of luck that the pathogens they did catch did not trigger disease in their case; and no doubt partly to do with avoidance of the non-infectious factors that are also linked to diseases and ill health, such as environmental toxins, stress and bad diet.
"Germs", ever since they have been discovered, are frequently blamed for pretty much everything that ails the individual human.
It has often been the other way around, with people ridiculed for suggesting that an infectious pathogen may cause a disease or illness.
One famous example is Ignaz Semmelweis, the Hungarian obstetrician who observed in 1847 that there was a higher chance mothers would die of a fever just after a childbirth which had been assisted by doctors. Semmelweis hypothesized the existence of invisible microbes on the hands of the doctors that were getting into the female reproductive tract, and postulated these microbes caused the fever, and ordered that all doctors should wash their hands thoroughly before assisting with childbirth. This led to a dramatic lowering of maternal mortality in his obstetric ward.
However, most of his contemporaries did not believe in his theory of "invisible germs," and eventually after a few years, these doctors abandoned the hand-washing practice, which then resulted in the mortality rate going back up.
Nothing has changed much today. I was recently in contact with a research group who are investigating the connection between herpes simplex virus (HSV) and Alzheimer's. Although there is good preliminary evidence for HSV causing Alzheimer's (in people with a certain genetic susceptibility in the APOE gene), this research group cannot get any funding, because the leading experts in Alzheimer's research think the idea that HSV might cause it is ridiculous, and so refuse all their research grant applications. Thus they can only proceed very slowly, and on a shoestring budget, due to the incredulity of the rest of the Alzheimer's research community.
Edited by Hip, 29 December 2018 - 04:31 PM.