Disease is karma. If you get it, you have to endure it. If you don't want it, you should practice the precepts and change the karma you deserve. But all this depends on yourself, and your efforts and the wishes of Buddha and Bodhisattva complement each other to be effective. Buddhists and bodhisattvas are just helpers. If you don't practice, no matter which bodhisattva you ask for, the result will still come.
The Diamond Sutra says: If you see me with color and beg me with voice, the world will do evil and can't see the Tathagata.