Lycanthropy

Lycanthropy is a magical disease that causes the victim to transform into a were-creature. This disease has a number of ways it can spread. The most common is that of a bite or scratch from a pre-existing were-creature, though quite a few are also the result of being sired by parents who themselves are lycanthropes. The odd time its caused by being cursed by magical means, a Fey, or deity. In very rare cases the victim uses some other means to transform periodically but becomes trapped in being able to do so without the need to use the means. Also this can be caused by an item that carries the disease in some other form.
The most common form is the werewolf, at least in Europe. In many cases it depends on the strain, and the region, as well as regional beliefs, as to what that strain is.
Some try to fight the disease and seek a cure, while others wholeheartedly embrace it. Many can change at will going between their original shape, an animal form and a mix between the two. They all have to change at nights of the full moon, and feel a pull to do so.
The majority show a weakness to silver and in a few may have weaknesses to other substances.

Transmission & Vectors

The disease is usually transmitted through a scratch or bite from a lycanthrope. Curses by powerful beings or magic, cursed items or incorrectly performed rituals can cause it to be transmitted too. Also passed down through families too.
If the recipient isn't tough enough they will immediately become infected.

Causes

The disease has not been isolated but believed to be magical in nature and tied to some type of extra-dimensional plane or god.

Symptoms

The first full moon after being infected brings on a lust for blood, and the transformation into either a half-beast or full beast form. From then on, the this happens every month at the same time. Some can control it at other times and can shape shift into any form. Others end up showing symptoms at the sight / smell of blood. In rare cases it is brought on by puberty.

Treatment

The only way to cure the average lycanthrope is by magical or divine cures. Most of these involve silver.
The lycanthrope can be rarely cured by an exact dose of silver but it is extremely difficult to work out the amount.
Killing the lycanthrope with silver weapons are the only sure way to stop this disease.

Prognosis

There is no known symptoms until the start of the first full moon.

Hosts & Carriers

Lycanthropy seems to only affect sentient bipeds.

Prevention

Very rarely there is magical means (certain magical items or spells) that protect the wearer from this disease.

Epidemiology

Lycanthropy moves very slowly through a population and never reaches epidemic or higher proportions as the infected are driven out, leave of their own recognisance, killed on sight or forcibly cured.

History

Many many myths exist as to how lycanthropy started, even in the one culture. Usually there are stories of people shapeshifting using the skins of animals, or having an innate ability to do so. It seems that some disease vector picked up the traits for this after infecting a shapeshifter and spread that way. In near every culture it seems that there was some divine curse or evil being using shapeshifting for nefarious purposes.

Cultural Reception

In the majority of cultures they are reviled and either driven out or killed. A few are healed if they haven't done any real damage and are repentant.
In a few cultures, like the Norse and some of their Berserkers, they are revered as being blessed by the gods themselves.

Type

Magical

Origin

Magical

Cycle

Chronic, Acquired & Congenital

Rarity

Extremely Rare