What disease / parasite / fungi has affected the mango in the picture?
If you zoom in on your picture, you will see that the small orange blobs have legs. These are red spider mites (Tetranychus urticae), which is a very common pest species of plants world-wide. They are called spider mites as they may spin webs on the plants they are feeding off. You have quite the infestation in the picture. It will take quite a bit of pest control to get this under control. I suggest spraying with Neem oil.
The mites feed by puncturing the cells of the plant they are feeding off and sucking the cytoplasm out. This puncturing results in damage to the plant, which might cause invasion from a bacterium or fungus. In your case I would guess a fungus, probably a sooty mold. Sooty molds grow on sugary excretions from parasitic animals (like spider mites) or on secretions from the fruit itself.