Tribals in India, Why are diseases spreading?

This is a sincere doubt so please do not take any sarcastic meanings out of it, i want to know and if possible to make a difference.

There has been recent news of tribals and their ill health. We understand that they are far from medical help or any such facility, and i would perfectly understand if they had a slightly lesser life expectancy than normal urban citizens, considering that though they are away from medical attention, they are also away from many things that cause the need for medical attention. They live in unpolluted environs for one.But what is more worrying is the fact that they are not slightly unwell, but highly malnourished and suffering from many communicable diseases. Yes, it is true that they might be living in conditions less hygienic than us, but weren't their ancestors too living the same way? why is it now that people have suddenly started contracting these diseases? haven't they been living like that since time immemorial?I'd be grateful if someone could shed some light..

This question gains more significance now, because it is only when these people are happy and satisfied that we will be able to really help the wild animals too, if the local tribal people are unhappy and ill, they might bow down to financial pressures and wrongly use the forests resources and also kill wild animals ..