The best evolutionary path from virus point of view is to reduce lethality so the host can spread it longer. I thought I read that HIV did something similar and used to be more deadly - even without modern treatment.

Problem with Ebola is that its transmission among humans is via the same thing that kills humans.

It depends on the environment. Mortality of cholera is high (~ 60 % if untreated), but by spreading abundantly the bacterium finds a supply of new victims.

I seem to remember a study from ages ago where they compared strains of HIV from South Africa and Japan. Condom usage in South Africa is low, so the virus evolved to develop a high viral load quickly. In Japan the opposite was true, condom usage was high, the strains that caused the victim to die early became extinct.