Take any movie that contains Zombies nowadays and the most common source is a virus. Mythical viruses or parasites that make the host crave flesh and therefore spreading the virus further by biting its victims.
In real life, what makes you look horrible and feel sick isn't the virus, it's your immune system reacting to the virus.
Viruses are as old as life itself and have time after time found ways to alter their existence, and in the process perhaps altering ours. They do so by hiding, adapting and tricking our bodies. Our immune system is not only a defense mechanism, but also a way to tell the others in our population that "this specimen is contagious, thus stay away". Making our very phenotype change in comparison to those healthy around us. So, why would a Zombie exhibit these extreme phenotypical changes, that far from benefit it.
Now imagine a zombie movie with another approach. The virus makes you more "beautiful"! Makes you smarter, more charming and socially adaptable, thus infecting more people before your immune system ultimately shows your true intentions, turning you in to a rotting zombie. Wouldn't that be scary. Is the girl you're dating a beautiful socialite, or the death of you?