Vampires, demons and whispering nasties populate the novels of Darren O'Shaughnessy like characters in a ghoulish soap opera. O'Shaughnessy's Saga of Darren Shan, a sprawling series of teen vampire novels, has assumed near permanent residency in the best-seller lists of the United States, Britain and Japan.

With sales approaching eight million, the books have achieved the status of a cult phenomenon, second perhaps only to Harry Potter in the loyalty of their readership.

These juvenile shockers inhabit a lavishly grotesque territory between Hammer Horror and bedtime yarn, a place where pantomime yuckiness shares stage time with breathless storytelling.

“Kids love to be scared,” says O'Shaughnessy, who has recently published the first three Darren Shan books in collected form. “We all love it. There's a difference between something that's horrific in real life - a car crash for example - and something that is horrifying in a book.

“Children get a kick from being terrified when they know the danger isn't real.”

Despite his stature internationally, the Limerick-based writer remains practically unknown in Ireland, an anonymous anomaly scuffing away at the fringes of the literary mainstream.

This, surely, is because he is an exponent of genres - horror and children's literature - viewed with disdain by the indigenous writing establishment.

That his novels cleave to one of our nation's proudest authorial traditions, the baroque fatalistic fantasy of Bram Stoker and Sheridan Le Fanu, is overlooked.

If O'Shaughnessy, who uses the name of his hero Darren Shan as a pseudonym, feels perturbed by the lack of profile here, the bitterness is well hidden. You almost suspect that he rather enjoys the novelty of being an unknown. Perhaps O'Shaughnessy has realised that the unlikely conjunction of success and anonymity cannot last.

Late last year, Universal Studios won a bidding war for the film rights to his Darren Shan novels. With writer-director Brian Helgeland (whose credits include LA Confidential and A Knight's Tale) rumoured to be casting an eye over the project, O'Shaughnessy is undoubtedly preparing himself for the coming firestorm of celebrity.

For now though, it is his new project that weighs heaviest. He's working on a series “about demons'‘ that will mark his first departure from the Shan franchise.

The novelist's fan base is extraordinarily devoted, even by the standards of cult fiction, but there is still a sense that in stepping away from Darren Shan, he is striking out for uncharted vistas.

The irony is that the Shan novels are in many ways the children of happenstance. Six years ago, O'Shaughnessy, then in his early 20s, was coming to terms with failure as an adult novelist. His two ‘grown up' works had garnered kind reviews - he was variously compared to Clive Barker and JG Ballard - but suffered pitiful sales.

To occupy himself between ‘proper' projects he bashed out Cirque Du Freak, a brief, spooky kid's novel about a boy, Darren Shan, who is adopted by a vampire named Crepsley when he goes poking around a travelling freak-show. The tale, relayed in unfussy, occasionally unsettling prose, visited a welcome cliché upon O'Shaughnessy: he became an overnight success.

Yet he wasn't surprised that Cirque Du Freak, and its 11 sequels, were embraced worldwide. Darren Shan gives his fans something that teen literature, even that with pretensions towards horror, seldom delivers: genuine shivers.

He believes his talent for empathising with young readers stems from his own childhood passion for horror.

“When I was about five I used to have a big poster of Dracula on my bedroom wall,” he says. “I remember waking up and seeing Drac leering down at me. I loved being scared as a child, loved that creepy feeling. In real life, you have worries, but in fantasy you have scares. I really enjoy that.”

The Shan sequence chronicles the eponymous hero's struggle to reconcile himself to his identity as a vampire. While the books are marinaded in blood-drinker lore, the author doesn't regard himself as a part of the contemporary vampire movement.

Buffy the Vampire Slayer, for example, was never a favourite. In fact, he feels generally detached from the vampire ‘mainstream', as exemplified by American writers such as Anne Rice and Poppy Z Brite (whose output often tip into fully-fledged erotica).

“My vampires are a little bit different. I have fun with the rules. They're not afraid of garlic, they don't have fangs. I try to make things a little different. Ultimately though, everyone who is writing about vampires owes it all to one man. We're all the children of [Dracula author] Bram Stoker.”

What truly distinguishes O'Shaughnessy's work from other vampire novels is its unflinching humanity. For all the functionality of his prose, O'Shaughnessy is an eloquent and sensitive storyteller.

The Shan books investigate soberly the central theme of vampire mythology: that the children of the night are forever tormented by their twilight existence, trapped perpetually between mortal and monstrous conditions.

Early in the saga, Darren is forced to confront how it feels to be both more and less than human. On being transformed into a blood-drinker, the boy is wrenched away from family and friends. When he attempts to reconnect with them, he causes accidental hurt (vampires are many times stronger than humans).The solitude of the hunter is made chillingly palpable to readers.

O'Shaughnessy is notoriously prolific, once boasting of writing six books a year. Recently the pace has eased.

Now he spends up to 18 months on a novel.

“I work quickly on the first draft; I can put it out in three to four weeks.

“But then I let it sit and move on to something else. I will spend a few years editing the book. I think time gives you an important distance from your writing. You see it with neutral eyes,” he says.

Those who achieve wealth and acclaim ritually insist that success hasn't changed them. In the case of O'Shaughnessy this turns out to be true. He still lives in the Limerick village where he grew up (his family relocated from London when he was six, and his accent retains an Estuary burr).

Writing aside, movies are his chief passion, and his DVD collection runs into the thousands. There are more author tours today than there once were. Otherwise, his routine has hardly altered since he gave up his job with cable company Chorus for full-time writing in the late 1990s.

Teen novels are infamously formulaic, with authors often churning out endless retreads of the same basic plot (the explicit policy of Edward Stratemeyer, creator of Nancy Drew and the Hardy Boys).

For O'Shaughnessy, however, stepping on to the conveyor-belt would be ruinous. He says he lacks the capacity to re-tool an unchanging storyline time after time.

“I need to write novels that are interesting to me. If I were forced to churn the same thing out again and again, I'd get bored very quickly. I have to keep it interesting - for myself above all.”

Despite selling millions of books, O'Shaughnessy differs from other popular children's writers in a significant respect. His novels are generally not read by adults.

“You do get a few of them reading the books, but mostly it's the 10 to 14 age group. Those are the core readership.”

It doesn't perturb him that his work is sometimes dismissed as frippery for excitable youngsters. Children's writing, he says, is seldom treated with the seriousness it merits.

“That's the thing about children's books. You aren't often acknowledged or taken seriously by critics and the like. To be honest, though, that isn't really something that I think about very often. Those aren't the people I'm writing for.”

Vampire Blood: Books 1, 2 and 3 of The Saga of Darren Shan, is published by HarperCollins. A new novel, Lord Loss, follows in June.