> But viral load from viruses that spread from human-to-human and live exclusively in humans has increased because there are more humans and they spread the diseases around the world more effectively than before.
This seems like pure conjecture to me, and without any actual evidence to support it, I'm disinclined to believe it. My guess is that the number of people any one individual interacts with has gone down considerably since the beginning of the century, and earlier. Before the advent of the car, shared forms of travel were much more common. People do much less forms of basic shopping than they used to given the rise of the Internet. Air travel, while much faster, is much less crowded that the ship travel of earlier generations.
> Before the advent of the car, shared forms of travel were much more common. Air travel, while much faster, is much less crowded that the ship travel of earlier generations.
Maybe in the US. Definitely not in most of the world. For my grandparent 70 years or so ago, the way to travel long distances was riding a donkey. Now travel by bus, train, subway, etc. is really common and something that most people experience often. 100 years ago of course there were trains, stagecoaches, boats, etc. but they were for a tiny minority of society or for special occasions (like to migrate a different continent to not return in decades, etc.). I'm also pretty sure air travel has a much higher penetration than ship travel would have 100 years ago.
As further anec-data points, there are much more massive gatherings now (concerts, sports, etc. - church used to be the major gathering, but churches tend to be ample and ventilated). And every parent knows that daycare and kindergarten are a major vector for pathogens. I used to get like a cold a year with 2 days mild congestion, and since my kid started kindergarten (he didn't go to daycare) we all started getting sick like monthly or so, for a couple of years. Putting dozens of kids in a closed space for hours is something that just wasn't a thing in previous generations either.
So personally, yes, I would bet that chances for pathogen spread have increased greatly.
There are significantly fewer humans living in close contact with livestock in which a zoonotic virus could be transmitted. I'm skeptical that there has been a net increase. It's possible but I haven't seen any reliable evidence one way or the other.
But there are significantly more amounts of livestock in contact with those fewer humans.
Think of it this way: more total numbers = more opportunities for viruses to grow or mutate = more chances for runaway or novel infections. Runaway infections are dealt with fairly well by government entities. Novel infections... might be harder to discover because they're, well, novel.
This seems like pure conjecture to me, and without any actual evidence to support it, I'm disinclined to believe it. My guess is that the number of people any one individual interacts with has gone down considerably since the beginning of the century, and earlier. Before the advent of the car, shared forms of travel were much more common. People do much less forms of basic shopping than they used to given the rise of the Internet. Air travel, while much faster, is much less crowded that the ship travel of earlier generations.