One of the most obvious ways to become a werewolf is to get attacked by a werewolf. It seems the most common in films and literature. A person who survives being attacked by a werewolf becomes infected by the same curse. A werewolf is mostly treated like a contagious disease and also a condition. The whole concept is very similar to how viruses behave, but mostly it's part of modern werewolf lore. It almost parallels the idea of getting bitten by a vampire that will turn someone. Yet the bite from a werewolf isn't just that alone, it can also be from the saliva or a scratch from a werewolf. The origins may come from reality and the most horrible of all diseases passed from animal to human, which is rabies.
There was an article in the Brooklyn Daily Eagle, written in 1855, about a young woman in France who was mauled to death by her husband on their wedding night. The groom died soon afterwards. It was mentioned that sometime before the wedding, the man was bitten by a "strange dog" who passed on the infection. This was a tragic case of a man with rabies, who caught the disease after being attacked by an infected animal. There are many stories about people infected by rabies, which wasn't fully understood in times passed, so there was once the supernatural attached to it.
The historian Eugen Weber has said that the French peasantry feared "wolves, fire and mad dogs". The latter meaning dogs with rabies. For those living in the countryside it would've been one of the most terrifying things to encounter. Some scholars believe that the myth of werewolves was inspired by frightening true events about rabies because of its behaviour. The disease itself is fatal. Once a person has been infected with rabies, they go through various incubation phases, before declining in health and losing all sense of humanity, drooling, fevers, breathing problems, hallucinations and violent outbursts. Its as though a person loses a part of themselves. When rabies is too progressed, the victim won't be responsive to medicine. Its as though the rabid person became a werewolf.
Wolf Girl Night