I found an interesting quote from a high level Qi Gong Master (Mr Li Hongzhi ) that talks about the manifestation of illness:
“I’ve told you that, regardless of whether it’s Jesus, St. Mary, Yahweh (whose ability exceeds that of even the previous two), or the Buddhas in Eastern religions, with a wave of the hand there wouldn’t be one single sick person on this tiny Earth. Why aren’t they being compassionate and doing that for people? Because people themselves are doing bad things. Of course, this isn’t to punish people—it’s the principle of the universe evaluating all beings. Since humans have done bad things, they have to pay for them themselves. Suppose you killed someone, and a Buddha eliminated the karma for you.
Then, would it mean that you’re allowed to kill people as you please? How could it be acceptable for a Buddha to eliminate your diseases as soon as you had killed people and generated karma? When people do bad things they have to pay for it and bear the responsibility. But when people have done bad things, the most obvious manifestation of it in the human body is sickness, which is used to punish people. I’m not the only one saying this—Jesus also said that people have sins. Why do people have sins? It’s exactly because people have karma in their bodies. Western culture doesn’t have the word “karma”—there’s no such word in Western culture. So Jesus used the word “sin” to illustrate the general point. In fact, isn’t having karma the same as having sins? Without sins, how could there be karma? It’s the same idea.”