Which event from Bram Stoker's life likely influenced him to write novels with the Gothic themes of death and isolation?

There are some factors that could have influenced Bram Stoker's writing style

Explanation:

One of those factors and maybe the mos important one is his childhood in Ireland, because the vampire legends made part of the folclore in Europe.

Other thing that could have influenced him was that fact of had been a really sick boy, some people believed in bleeding to heal sick people and he could have gotten that treatment.

Finally, his mother played an important role because she used to tell him a lot stories and tales, those stories were usually about destructive effects on the human being which had as a consequence skeletal people walking around.