Hmm, rather a wilfully eye-catching title, I thought, but catch my eye it did, and I am very glad. Elizabeth Pisani is an epidemiologist, but when she's asked what she does for a living she says "sex and drugs". Specifically, going all over the world (but mainly in Asia) taking blood samples from prostitutes, their clients, gay men, intravenous drug users and anyone else at risk from HIV. She then collates all the data and tries to get governments to give her money to stop people from getting Aids.

This might not, on the face of it, seem like a sound basis on which to write an enthralling book. However, enthralling it is; also wise, witty, humane and intelligent. And, I would venture, rather important. For one thing, it will open your eyes to the incredible stupidity of much American and British policy. Try this for size: "Unlike the prison service in Iran, the Kyrgyz republic and 10 European countries, the UK's prison system can't quite bring itself to allow inmates to swap used needles for clean ones." You can imagine what the result of such a stance might be. But you will also relish, en passant, the sly, exasperated sarcasm of "can't quite bring itself to".

In fact, Pisani seems like not only an extremely dedicated and knowledgeable person, but the kind of person you'd like to go for a drink with. There is a lot of her own character in the book - which is just as well, not only because without it we would be looking at a lot of statistics, but also because her character is consistently entertaining. Let me give you a couple of examples.

At one point, she listens to a speaker at a conference explain that poverty, wide inequality gaps and gender imbalances (both in terms of numbers and differing levels of literacy) explain the spread of HIV. "All the epi-nerds" - and what a glorious term for epidemiologists that is - "in the room had one question. I stuck up my hand and asked it. 'Mead, where's the hard-on in your formula?'" Or, to put it another way, "The World Bank believes poverty and gender inequality spread Aids. I believe sex and drug injection spread Aids." Do not begrudge her the odd conference, by the way. "It beats trying to keep the rats out of the rural hospitals or taking anal swabs in the slums, or whatever it is that we're doing most of our working life."

The other example that sprang to mind is much sillier, but it still makes a point: she tells us that her father, in retirement, now works at the Partnership for a Drug Free America. Its most famous slogan was a picture of a fried egg in a pan, accompanied by the words "this is your brain on drugs". In a footnote, Pisani tells us "I later gave my father a T-shirt with a picture of a slap-up fried breakfast and the slogan 'This is your brain on drugs with bacon and a side order of toast', but he never wore it." In other words, she is a cant-free zone; and one of the most encouraging aspects of her personality is that she's prepared to tell us when she's been wrong.

You imagine it's not that often. I noticed that "Vatican", "Catholic church's attitude to condoms" and so on were not in the index, though "Islam, opposition to condom use" is; but we do get to hear the toxic flapdoodle peddled by Cardinal Alfonso López Trujillo, that the Aids virus can pass through the membrane of a condom, so condoms are useless. The message is: ideology, inflexibly dogmatic religion and prudery are all the enemy of Aids-reduction programmes, and so, if you want to look at it this way, enemies of life.

I was recently dismayed by a book written by a professional comedian exposing the evils of a well-known multinational; dismayed because the jokes in it simply weren't funny. For all its good intent, I couldn't recommend it to you. No such problem here. Pisani is smart and funny. You will also learn that there is a weekly volleyball match in Jakarta between the local police and the ladyboys (or waria, as they are known there). If that's not worth the price of the book I don't know what is.

 To order The Wisdom of Whores for £8.99 with free UK p&p call Guardian book service on 0330 333 6846 or go to guardian.co.uk/bookshop