Both Vampires and Werewolves (PvE) will spawn in high-level areas, and their attacks have some chance of infecting you with the relevant disease. Once infected, you will have a new quest that you must complete to either become the monster you wish to be, or be cured of the disease.
You can not be infected by the Vampire disease if you are currently infected with the Werewolf one, and vice versa.
Vampirism Effects (more details)
You'll unlock a new skill line you can make use of, you'll also start to have these effects at various stages, until you feed on a human opponent (PC or NPC), which will reset it to "stage 0".
- Up to 30 mins:
- 30 to 60 mins:
- -25% Health Regeneration
- +50% Fire Damage Weakness
- -20% Health Cost to Vampirism Skills
- 60 to 90 mins:
- -50% Health Regeneration
- +50% Fire Damage Weakness
- -40% Health Cost to Vampirism Skills
- More than 90 mins:
- -75% Health Regeneration
- +50% Fire Damage Weakness
- -60% Health Cost to Vampirism Skills
Werewolf Effects (more details)
You gain access to a skill, Werewolf Transformation that does pretty much what it says on the tin. While transformed, you'll have access to a new line of skills to unleash your inner puppy, and there are some ill effects of course -- such as a passive ability that increases damage taken from abilities in Fighters Guild skill line, +50% to all poison damage.
PvP Infection
Players can also infect other players with their condition.
For Werewolves, the skill Bloodmoon can be used once every seven days, acting as a rate-limit. For Vampires, the equivalent skill is called Blood Ritual. You have to use these skills at the ritual sites, so it's unlikely you could be turned against your will. Both require level 6 in the respective skill trees.
Correct. Right now, both servers are located in the US, so you won't notice any significant ping/lag/latency difference. However - as you said - the EU server will be moved to Europe (I think Frankfurt, but don't quote me on that).
That being said, it's hard to say how/if latency will change for you. If you don't have any issues so far, I wouldn't worry too much about lag alone. It can't get worse, it may only improve.
Geographically, I'd assume the European server would be the better choice for you, since it's quite a bit closer to you. This also means that your prime time won't be that far off compared to other players playing there.
Overall, you should try to see where your friends are playing, assuming you already know people you'd like to stick with for this game.
What you definitely should keep in mind are server downtimes, which will follow different schedule for NA/EU as stated here (you might have to try to open that link twice for it to show the proper article for whatever reason):
Tuesday (Patches)
00:01 am EDT (06:01 CEST) - EU
08:00 am EDT (14:00 CEST) - NA
Friday (Reboot/Hotfixes)
00:01 am EDT (06:01 CEST) - EU
08:00 am EDT (14:00 CEST) - NA
North American Megaserver
Tuesdays at 8:00 am EDT (14:00 CEST)
Fridays at 8:00 am EDT (14:00 CEST)
European Megaserver
Tuesdays at 00:01 am EDT (6:00 am CEST)
Fridays at 00:01 am EDT (6:00 am CEST)
After all, you most likely don't want downtimes to happen during your playing time all the time.
Best Answer
Yes, it does exist in a side quest. Other than that, it is not available for general consumption. You will have to go with some other catnip brand instead.
Here is a video about this side quest:
Contains spoilers, obviously.