BOOK REVIEW / Millions of Draculas tapping at the window: 'The Hot Zone' - Richard Preston: Doubleday, 14.99 pounds

OF ALL the things that go bump in our nightmares, the scariest are those that make no sound. Perhaps it is because we have supped full of the obvious horrors - sharks, snakes and so on - that we feel a special susceptibility on the subject of viruses. Perhaps our vulnerabilities have been tuned by Aids to react with dread to the news of every fresh outbreak; an all-conquering mystery illness in Gloucester, a plague in India. Or perhaps it is simply a question of technology, which through miracles of magnification brings us pictures of the fatal threads and loops that can invade and destroy our bodies with such rapacious indifference and zeal.

Richard Preston's new book is about four particular viruses: Marburg, Reston and two types of Ebola. They are very rare, and very scary. Several times in recent years they have sneaked out of the rainforests of Africa, but so far they have not ignited and caught fire in the human population. Nevertheless, The Hot Zone is here to tell us that we're not safe, that before going to bed tonight we'd better hose each other down with Clorox bleach and don inflatable orange suits, wearing three or four pairs of rubber gloves and with sticky tape wrapped round our ankles and elbows.

These new viruses are so tiny that 10 million or so can feed and writhe on a piece of flesh the size of a full stop. They race through colonies of monkeys like fire. And they can - no one knows how - jump into humans as well. At the moment there have been few fatalities: a handful. But Preston wants us to believe that this is just freak luck, that the viruses are sniffing around looking for a way in, like Dracula tapping at the window.

The effects of the creatures in question are so horrifying they almost qualify as a marvel. Richard Preston narrates the progress of the symptoms with frosty relish, talking about the ferocity of his bugs with awe, almost with pride. Ebola, for instance, attacks connective tissue and pulverises it, turning a body into mush. Here is Preston on what happens next:

'The skin bubbles up into a sea of tiny white blisters mixed with red spots known as maculopapular rash. This rash has been likened to tapioca pudding. Spontaneous rips appear in the skin, and haemorrhagic blood pours from the tips. The red spots on the skin grow and spread and merge to become huge, spontaneous bruises, and the skin goes soft and pulpy, and can tear off if it is touched with any kind of pressure. Your mouth bleeds, and you bleed around your teeth, and you may have haemorrhages from the salivary glands - literally every opening in the body bleeds, no matter how small. The surface of the tongue turns brilliant red and then sloughs off, and is swallowed or spat out. It is said to be extraordinarily painful to lose the surface of one's tongue.'

Nice, eh? Much of the book describes an outbreak of this virus in a monkey colony outside Washington, and very frightening it is too, the idea that a couple of the little devils could waft through a bit of porous plasterwork and wipe out America. And large parts of the book are superbly informative and exciting. In one scene a woman called Nancy, dissecting an Ebola-infested monkey, rips her rubber gloves. She knows that the least contact with this blood will almost certainly kill her in an unimaginably horrid way. She starts tearing off her layers of glove, to see how far the nick has gone through. Three have been breached. She fills the last one with water, looking for the telltale squirt of water, and. . . and. . . and. . .

Preston works hard to make it as exciting as possible, and in the main he succeeds. But at the end the virus just sort of packs its bags and fades away, and so, to a certain extent, does the story. All that brilliant fright-mongering dissolves in a series of false alarms. The technicians kill the monkeys and wait to see whether the terrible putrefying process will leap into human beings, and . . . nothing happens. They all survive. Panic over.

As the book comes out of the hot zone and finds itself free of infection, it becomes a little desperate to impress us. Several times it suggests that the fact the virus sloped off without killing anyone makes it even more dastardly, as if it were teasing us. 'Something very strange was going on here,' he writes. 'Just at the moment when Nature was closing in on us for a kill, she suddenly turned her face away and smiled. It was a Mona Lisa smile, the meaning of which no one could figure out.'

Hang on a minute - a Mona Lisa smile? Have we seriously been led through all these maculopapular rashes and blood clots only to be told that Nature with a capital N was just kidding? It seems an odd and disappointing conclusion, though perhaps it is useful to know that if your skin starts going soft and pulpy, you should get over to the Louvre at once to look at the Leonardo da Vincis.

In truth, though, it is hard to blame Preston for indulging the horrifying possibilities thrown up by these viruses, because that is exactly what they are. One of the most extraordinary aspects of the book - indeed, one that gives rise to some uneasiness - is this: it seems amazing that if all this is true, it is not more widely known. A world willing to quarantine India after an outbreak of a curable virus ought to be able to make a real fuss about these incurable ones. The details in the book are wonderful - there is a certain deadly bacteria that smells of grape juice; the bug-scientists like to munch on termites when they are on field duty in Africa - and the descriptions of the viruses themselves are exquisite. Preston also has an attractive, if unscientific, tendency towards proverbial cadences. 'When you begin probing into the origins of Aids and Marburg,' he writes, 'the light fails and things go dark.' Later, he adds: 'All monsters and beasts have their benign moments.'

But there is a fair bit of the-nightmare-continues stuff as well. 'Every case is one more case,' Preston intones. 'Every death is another kill, and the end of one human life is like a dream foretelling a catastrophe for the human species.' This is a tone calculated to make exact medical types fidget. But we can all be unsettled a touch by the book's unequivocal desire to give us goose pimples.

As it happens, this is a full-blown version of a story that first broke in the New Yorker a couple of years ago, in a superb feature article by the same author that zapped the blood of everyone who looked at it. For a while it lay low, but now it has emerged again in this bigger, gentler mutation. Soon it will be a grisly big-budget film. So the story continues to grow and replicate, searching for new hosts it can invade and destroy. Who knows, perhaps one day it'll be a Broadway smash.