We're actually having a worse situation re/ animals than our ancestors. We nowadays cram farm animals in stables so tightly that without antibiotics and medical treatment the animals would almost immediately perish. Our farms and our animal "care" practices have been the breeding ground for all recent global pandemics (swine flu, bird flu, SARS/MERS/SARS2). Not to mention the conditions that farm and slaughterhouse workers have to work and live in (as evidenced by massive COVID outbreaks).

The chance of any infectious agent "jumping the species" due to cramped conditions or because of exposure of workers to contaminated animal parts in unclean slaughterhouses is immense - the current SARS-CoV-2 pandemic in my opinion is a warning signal of something much worse to come, and no matter what kind of agent it will be, we're pretty much screwed. Half the population or more of the world doesn't believe in vaccination, a quarter or more don't have access to vaccines or any kind of modern medicine at all, we are already running out on reserve antibiotics...