Well yeah, if you look at it that way. But everything about vampirism is treated as if it's a disease, down to the way the player is informed that they have 'contracted' it. Nothing in the UESP Wiki that I see disputes this.

Of course it would be silly, but lore-wise it seems possible.

Perhaps the initial "start" is a disease, Porphyric Hemophilia, but if the after-effects are truly a disease, then why does it require Daedric intervention to remove it (Morrowind) or the intervention of the Witches of Glenmoril (Oblivion)?

I can see your reasoning with this. But I will work on an excuse for this lol.

In the Norwegian folklore we have bearmen, people(usually just men) who transform into bears(we also got werewolves, stories all since the viking age and up to 1900), uncontrollably and turns violent.
Though, i would be happy enough with werewolves, werelions seems a bit strange.

For the same reason that the game world is filled with magical healers, and not surgeons. One of the fascinating aspects of TES is that magic is treated as a mundane, commonplace thing (I really hope that Keyes' novel taps into this). In the TES world, scientific endeavour seems pointless - the Gods are real, and the powers of magic far outstrip anything that scientists can hope to currently achieve.

So why is magic/supernatural intervention needed to cure vampirism? Because scientific progress is slow if even nonexistent, and most likely always will be.

yea true, the lack of atheism slows the scientific progress.

Part of the problem is how relatable it is to a disease is that it's never been explained in detail in the first place, and tends to vary from game to game (further confused by there being many vampire breeds). In Daggerfall, it was pretty clearly undeath. After getting vampirism you woke up in a tomb, because your heart stopped and you died, and people buried you. In Morrowind and Oblivion there was no such obvious indicator, and as far as I know Turn Undead spells don't work on vampires (never tried, myself). If vampires are considered undead, it would be more than "just" a disease, considering the supernatural portion, and beyond just about any scientific progress to reverse. Modern medicine can do a lot, but we still can't revive the long-dead.

I do tend to think of it as undeath, though, and that's one of the reasons it would seem incompatible with lycanthropy to me. The werewolf virus seems to require a living host; I have never seen or heard of a zombified werecreature. Considering that it can physically cripple those who fail to nourish themselves while transformed, I'd argue it requires a fairly strong and healthy body, thanks to the severe bodily change that you still wake up from alive.

You are confusing many points here. Diseases may have magickal roots, but they are just that - diseases. Can they be cured by magickal means? Of course. However, they can also be cured by conventional means that do exist within Tamriel. Do game mechanics present this? No, just the same as game mechanics don't present linen bandages or wound cauterization. Should we argue, then, that since game mechanics don't present these things, they don't exist? http://search.freefind.com/find.html?oq=cauterize&id=72791987&pageid=r&_charset_=UTF-8&bcd=%C3%B7&scs=1&query=bandage&Find=Search&mode=ALL&search=all That would be silly. Therefore, traditional methodology of curing diseases (i.e. prepping oneself as best as possible for the immune system to fight it off, eating herbal concoctions to ease the symptoms or the source, etc) still exists, because in lore (as opposed to game-mechanics), mages are much rarer, and hardly anyone has the money to pay healers. And yet they aren't all shriveling up and dying en masse of the level to be expected from no other alternatives other than magickal intervention. Therefore, they must be using non-magickal means to treat their victims.

The point to note here is not that all diseases can be cured by magic and therefore, by virtue of being cured by magickal means, vampirism and lycanthropy mix in with diseases. No.
The point(s) to note are as follows:
1. Though diseases may be cured by magickal restorative healing spells/potions, those traditional restorative methods simply do not work on vampirism and lycanthropy. Because of this, the only solutions (very rare solutions, I might add) to vampirism and lycanthropy involve Daedric princes (specifically, Hircine, Molag Bal, and Vaermina) undoing said curses via their immense power, or the Witches of Glenmoril (who are often associated with Daedra trafficking and the like, are ridiculously powerful themselves, and therefore are influenced by Oblivion and are beyond the scope of "normal magic") mixing up a rare concoction to undo said curses. Therefore, vampirism and lycanthropy are outside the range of traditional "diseases."
2. More importantly, what you don't seem to be grasping overall, is that lycanthropy and vampirism aren't just diseases that popped out of unknown origins, like the rest of the random afflictions in Tamriel. Lycanthropy was created and set upon the world by Hircine; it is HIS curse/blessing. Vampirism was created and set upon the world by either Molag Bal or Vaermina, or a combination of both, depending on which source you cite; it is THEIR curse/blessing. The only reason that the Glenmoril Witches are even capable of curing such things is because they themselves are way more versed than even powerful mages about such Daedric curses, and they can mimic Hircine's/Molag Bal's/Vaermina's methods of undoing said curse/blessing.

Now, to get back to the origin of this, since these afflictions arise from Daedric sources, not mundane sources, the odds of mixing and matching are ridiculously low, because Hircine is not going to want to tie someone down to his sphere who is already tied to Vaermina's/Molag Bal's sphere, and Vaermina/Molag Bal is not going to want to tie someone down to his/her sphere who is already tied to Hircine's sphere.

that is extremley true.

However, I do agree that we need more Were-creatures. Were-wolf (speed, agility) Were Boar (In between Wold and bear) were Bear (In between wolf and croc) Were Croc Strength and edurence.

Then there would be like were-shark that transports you to the nearest body of water. you would both be strong and exceedingly quick.

There would also be (dependin on where the game take place) a were-crow. you would take off into flight but be very weak.

In Skyrim, it is noted that werebears were the most common lycanthrope in the region. The boars seem to make their home in the Iliac Bay. As for werecrocs, they seem to be in Black Marsh. However Mere-Glim thinks they're nothing but a tale.