We humans are protected by the fact that most bacteria and viruses cannot jump species to species. If your cat sneezes right in your face, you do not get a Cold, since the virus giving kitty a cold had no effect on people.
Note that we said most viruses and bacteria. The problem is that in real life, the few diseases that have jumped from animals to people have turned out to be the most deadly of all.
In 1918, a Kansas farm boy caught a flu virus from the pigs. This inter-species germ jump became The Great Influenza which spread world-wide and ended up killing more people than World War I.
The virus that causes AIDS originally came from monkeys and was transmitted by people butchering monkeys for food.
Let’s not forget the king of all Bacteria – Yersinia Pestis, better know as the Black Death. In the Middle Ages it killed as many as half of all the people in Europe. It spread from rats and mice to people. Ironically the religious superstitions of those days made things worse. Cats were thought to be in league with the Devil, so most cats were killed. If the Europeans had not done this, the cats would have controlled the mice & rat population, considerably slowing the spread of the Black Death.
Fairy tales like Sleeping Beauty come from the days of the Black Death. In some areas, entire towns, villages and even kingdoms no longer had any people. Decades later travelers would come through a forest and suddenly find an huge castle completely empty. That’s where the stories of an evil witch putting everyone to sleep started and became Sleeping Beauty.
Remember that all these diseases still exist in the world. They are still capable of killing millions. One day, they may mutate into something even more powerful and kill billions. Something to think about the next time your pet dog, cat or hamster isn’t feeling well and you give it a great big hug.