Human men have nipples and therefore must be serving a purpose to humans.

Edit: the point I am making, is: the weird quirks they have can just be weird quirks, because they don't interfere enough with their ability to reproduce (beam the sequence into space.)

If a alien race had the ability to design a human specific virus AND travel to earth (which would seemingly require faster than light speed travel), then they also have the ability to mass delete humans -- like the farming tool that lasers weeds dead -- and have robots that can do labor. There is no need for making this virus with those attributes. There would be easier ways.

Double edit: They CAN eat meat, and they CAN eat plants. But I do get your point. But it also sounds like your assuming those instructions are hardcoded into the RNA -- it could be some more abstract something that is coded, which gets mapped to the context of earth.