Give recent events, some people have called for the 'wet markets' in China to be shut down, (for many reasons) but largely because it is likely the source of the recent plague outbreak, due to the close human-animal contact there.
(I am not here to debate if the markets should or should not be closed down. That is something for another question.)
However looking at the (very short and incomplete) history of the smallpox vaccine: Someone noticed that milk maids didn't have the ugly smallpox scars those who had survived a smallpox infection had. They conjectured the maids had caught the mild cow pox off their cows, and had gained an immunity to smallpox as a bonus. Cowpox was then developed in to a vaccine, fast-forward a few years and now smallpox has been eradicated. The 'natural' cow pox was basically an attenuated live vaccine for smallpox.
Now today we have supermarkets and mechanized agriculture and so have far less contact with animals (e.g. back in the day many households would have their own cow and chickens, we rode horses for transport, etc.) Therefore we have less of a chance to develop immunity to 'naturally attenuated' diseases, which they can immediately fend off if the disease does mutate/break the species barrier into a plague worthy foe.
I am not suggesting we should go back to milking our own cow before breakfast, however:
Does our lack of contact with domesticated animals mean we have less 'naturally attenuated' disease exposure and therefore we are at a higher risk of plagues?
