Don't understand why deer turned into a zombie.

I thought that the truck that hit it was coming from wherever the contamination was, and noticed that whoever sprayed the truck at the checkpoint did a very sloppy job. Don't think the right side of the truck was sprayed, which was where it hit the deer. Voila, zombie Bambi.

That's my guess, anyway!

Or maybe it's like in The Walking Dead. Everybody is infected but only turn into a zombie when they die.

Except these weren't really zombies, they were infected with a virus or something. They were rabid.

I think the explanation that the truck had some goo on it that didn't get washed off and it got in the deer is the best explanation I've heard. It certainly makes the most sense, because if the deer was rabid before the truck hit it it would've just stood right up and started to attack, not wait for a minute or so then stand up all white-eyed.

The deer was in the quarantine zone. The driver of the truck was going into it and even asked about his hogs having to be put down again.

Later the father was at work looking online at the news article that showed dead fish wash in up in a reservoir. The reservoir was in the same quarentine zone. The fathers company was also responsible for releasing it because they worked for a biotek facility that was designing the virus. Hope this helps clear this up. Was an awesome movie.