i think it depends on the movie. like any other not real stuff, like in some movies ghosts can go trough walls,fly,go transperent and in some they cant
The thing is that with time, even supernatural creatures have been made to be more realistic and "natural". Remember that originally, zombies where extremely slow walking, stupid, brain eating, dead bodies. That being extremely unrealistic (as if now it isn't) they've modified the imagine of a zombie almost entirely.
Now you get a disease which totally changes your DNA, turning you into a running, white eyed, kinda intelligent creature, that chooses either to eat you (any part of the body will do now) or infect you. In "I Am Legend" the most recent movie about zombies I can remember of, they made them inhumanely powerful and even more intelligent adding a social hierarchy and changing the disease story into a mutation one. Now they're bald, and instead of moaning, they talk by screaming, other then that they look like your normal, every day people..well kinda.
The point being that it depends on what era we are talking about. I see your movie was made in 2008 so I guess they might have and contract diseases since it is more natural.
If you consider other blood sucking beasties like mosquitos, they just act as a vector for diseases such as malaria. As far as I know, they do not actually catch the disease, but carry it and pass it on.
Vampires generally are given lifetimes of hundreds of years, if they caught human diseases then I imagine their life expectancy would be a lot less.
I agree with you but then again, you should try to see what cultural legacy the vampire in this movie has. If it's based on the classical vampire, the undead one, it is naturally impossible for it to contract a disease but maybe it can be the carrier of one or not (much like a dead corpse). The new vampire which is more a physical state (given by a vampire bat as a disease trough a bite) should logically be able to contract diseases.
My god! I've just noticed that we're speaking of vampires as if we are speaking of physics (something that is real and can actually be proven). This is just so nerdy, fan boy-ist and useless
Well Edward in Twilight had no diseases so I'd guess so... besides Vampires probably have a much stronger defence system and are more resistant to diseases anyway!