Can cloud saves be infected by viruses?

maybe, but I like to think that they scan the files that you upload

Basically any file can be infected, if you don't take some level of precaution. :P

Anything can happen, but it's highly unlikely. It's probably something else.

It is theoretically possible yes but everything involved makes it that so that if you are one of the one in a million that for necessity or paranoia took all the higher priority precautions you would have never installed Steam due to them in the first place so pointless to worry about cloud.

If your PC gets virus, and the virus infects save file, infected file will get uploaded to cloud.

Saves don't contain executable code, just data. So no, a virus can't infect a save. The most a virus can do is corrupt a save. Unless a specific game has a specific bug that would allow a virus to run code from the save using buffer overrun. But this means such virus would target a specific game. The developers could then patch the game to fix the bug and the virus would no longer work.

Uplay cloud sync eats games saves- maybe a virus

I doubt clouds today can get infected. If you put a virus on the cloud, you will probably either infect the Cloud (which is unacceptable today) or get the file deleted. Worst case scenario, you get some kind of cloud save ban.

in practice: no

see answer of "oginer" above for details-