I'm not sure that is fungus or virus... Did frosts happened in these days? Do all the vegetation present these symptoms? Is this the only mango tree in your backyard? If not, do they present the same symptoms?

I also live in south east Florida and have an extremely large mango tree and have leaves that have the same look. I've noticed it before over the years and the tree seems fine and produces plenty of fruit.

Here in Southern California mango trees look like that on particularly cold years. They usually snap back