Apparently, he has decided to give $900 million dollars US for research into tuberculosis. Although many in the developed world would probably scratch their heads in wonder, tuberculosis is actually a massive killer in the developing world. Aside from infecting roughly 1/3 people in the world, it forms an 'axis of death' with two other microbes, namely HIV and malaria. Additionally, tuberculosis is also a problem with farmed animals, such as cattle and deer. There, Mycobacterium bovis, which is a close relative of the human form of tuberculosis (Mycobacterium tuberculosis) can thin herds and make animals very sick. Additionally, M. bovis is having a devastating effect on lion populations as it spreads from wild buffalo.
Tuberculosis is serious buisness and it's good to see that Bill Gates is making such a gesture.