I'm sorry, but I don't see the connection between type 1 diabetes and the current discussion here.
Why, because you are just focusing on the diseases of ageing? Well you find that type 2 diabetes is also linked to various pathogens:
https://pubmed.ncbi....h.gov/16108236/
https://pubmed.ncbi....h.gov/19266182/
https://pubmed.ncbi....h.gov/19780970/
Regarding atherosclerosis, I think it's important to have a clear theory about how a virus can cause it before we consider these papers as evidence. Since macrophages are involved in the development of atherosclerosis, I expect many types of pathogens to be present in the plaque.
The way in which viruses and bacteria can induce cellular, tissue and organ dysfunction are many and varied. We may not yet know the particular mechanism for a given disease, because it takes a lot of work to figure out the mechanism; but finding pathogens in the diseased tissue is a red flag which promotes further investigation, to see if these pathogens might play a causal role in the disease.
Pathogens can trigger disease because of harmful proteins and toxins they synthesise while living in the host. They can cause disease because of the collateral damage done by the immune system as it constantly tries to eradicate the pathogen. The can cause disease indirectly, by triggering autoimmunity (in this case, the location of the pathogen in the body may be different to the location of the disease, as autoimmunity once triggered can attack anywhere in the body).
Once classic example of an autoimmune disease triggered by a pathogen is Streptococcus sore throat triggered OCD or PANDAS. You get a sore throat from this bacterium, and because proteins on the bacterium are similar to proteins in the brain, the immune system mistakes these brain proteins for the bacterium, and attacks the brain. This constant immune attack of the brain leads to OCD. I believe about 25% of OCD cases have this Streptococcus origin.
If pathogens really played a major role in age-related diseases, we would see these diseases much more often in young individuals. I mean, if all it really takes to catch a virus to get a heart attack, infants with untrained immune systems probably would be at high risk. I find this theory highly implausible.
This is a good point to bring up, but I think we easily explain why pathogen-associated chronic diseases tend to appear later in life. For one thing, the immune system of children is stronger and more robust. Children generally have milder versions of a viral infection, compared to when adults catch the same infection. For example, chickenpox in kids is mild, but can cause serious issues in adults.
So children may be able to wipe out or control an infection before it gets a chance to disseminate into critical organs. For example, certain neurological diseases like Parkinson's are linked an enterovirus infection of brain cells. Now, in order to infect those brain cells, the virus first has to break into the brain. But if during the acute infection the virus is rapidly brought under control by a robust immune response, then that may prevent the virus ever reaching the brain. So a healthy immune response during the acute infection may help protect against chronic disease.
This may also explain why chronic stress has been linked to some diseases, as such stress is known to weaken Th1 antiviral immunity (though chronic stress actually boosts Th2 antibacterial immunity). If you were unlucky enough to catch a viral infection during a period of chronic stress, that virus would tend to run riot in your body, because of your weak immunity. This may then give the virus a chance to insinuate itself into critical organs like the brain, heart, etc, which may later precipitate a chronic disease.
The other thing is that it is important to appreciate is that chronic diseases manifest slowly. Multiple sclerosis is strongly linked to EBV, and most people catch EBV in their teens or 20s, often from kissing. By 25 years old, about 90% of adults will have caught EBV. But you may only get MS when you are 40. So it may have taken a decade or two of having this virus in your body for it to precipitate the disease.
So there can be decades of time lag between catching the pathogen, and the appearance of the disease. You can think of pathogen-caused chronic diseases as a very slow infectious disease, taken decades to manifest. This is another reason why chronic diseases will tend to appear later in life.
Edited by Hip, 12 June 2023 - 09:00 PM.