*Note: "Monstrous" refers to the protagonist's personality change, not appearance.
This story was featured in a short story collection about vampires. I read it in a library in early 2001 (in Germany, but the book was in English), but the book itself was older. I'm guessing 80s or 90s, but I'm not sure at all.
What I remember: The main character was a middle-aged, married man who got turned into a vampire. I don't remember how he was bitten/turned, but the transformation wasn't immediate. Rather, it was a process that took at least a day or three. He didn't realize what was happening at first (I think he thought he had just been attacked by a madman), I don't remember if he realized it before the transformation was completed.
The story also featured a side character who was a vampire hunter. He would locate a vampire's grave and prevent them from leaving the area by encircling it with crosses and iron wire (I think). Something about that metal was repulsive to vampires.
There was also a plot point that the vampire had to return to its initial grave. I think the vampire hunter got turned in the end, because I remember either him or another newly turned vampire lamenting the fact that his grave was in a ditch by the side of the road and that he would likely be easily discovered.
What impressed me about this story and made it stick to my mind for all these years was how the thought process of the main character changed during his slow transformation. Since so much of the story was told from his point of view, witnessing his change from average Joe to barely-sentient monster was really eerie.
The vampires in this setting looked human but had a more animalistic intelligence. Maybe that's not the correct way to state it; I mean, they could form complex thoughts, but their thought process was focused on a very limited number of things, like finding prey and avoiding danger and supernatural constraints (like iron and crosses). I remember the main character, after his transformation was completed, looking at his house from a distance. He saw his wife in the doorway, and I think he reacted to her as if he would to a stranger.