Try to take a foreign western disease to an isolated island in the east and see how that balances out.
That's why you need vaccinations to visit Asia from America, because your immune systems doesn't know wth those diseases are, and can't build a natural resistance against it when you haven't been born and raised there, so you don't get any kind of exposure. This applies to the animal kingdom as well.
Like http://www.animalcontrol.com.au/foxes.htm
No, nature cannot just balance things like this.