The very long run for SARS Covid 2
Many of the worst pandemics that afflict us are from pathogens that don't normally prey on humans. Probably the most famous pandemic in history was the Black Death. On the steppe it lives in marmots which it has reached an equilibrium with. But sometimes a flea transmits it to a rat. The rat gives the disease to its other fleas and then dies. Those fleas go to other rats and spread the disease. When all the rats are dead the fleas find their way to humans instead. The disease isn't quite as lethal in humans as it is in rats but it still killed a large fraction of the people who got it before the rise of antibiotics. That's pretty typical of zoonotic diseases, or diseases that spread from one species to another. Most of the time they're just ineffective and can't survive or are mopped up easily by our automatic immune system without us noticing. But if they succeed they're often the most dangerous diseases that can afflict us because we're not in