zombies

I did not quite get the whole zombies thing.
Why were people becoming zombies?
Why did the male lead turn back to a human. what did the zombies do to Bela?
Dont get me wrong I love the idea of Zombies in a Bela movies but it made no sense.
At the end the cops were just like "eh the professor is out of the pictures now" unfazed by zombies that were attacking him. They also did not seem like flesh eating ones so not sure what exactly they did to him.
Some how at the end the male lead is a human again...made no sense.